Structural and Mechanistic Insights into a Cu-Adenine MOF for Selective Fluorescence Sensing of Antibiotics: Experimental and TDDFT Approaches

Structural and Mechanistic Insights into a Cu-Adenine MOF for Selective Fluorescence Sensing of Antibiotics: Experimental and TDDFT Approaches | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Structural and Mechanistic Insights into a Cu-Adenine MOF for Selective Fluorescence Sensing of Antibiotics: Experimental and TDDFT Approaches Tanin Nanok, Tontrakarn Pongpai, Kittinan Ketsrisung, Jiraporn Singhophon, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6562459/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 07 Jul, 2025 Read the published version in Journal of Inorganic and Organometallic Polymers and Materials → Version 1 posted 11 You are reading this latest preprint version Abstract An adenine–succinate-based metal–organic framework, [Cu(adenine)(succinate)]ₙ (CuAS), was synthesized via a solvothermal method and structurally characterized by single-crystal X-ray diffraction, PXRD, IR, TGA, and elemental analysis. CuAS forms a three-dimensional framework featuring two directional channels along the a - and b -axes, with amino groups oriented toward the cavities. The material exhibits solid-state fluorescence at 440 nm (λₑₓ = 330 nm) and, when dispersed in methanol, emits at 430 nm (λₑₓ = 350 nm), consistent with intraligand transitions of adenine. CuAS was employed as a fluorescent sensor for antibiotics, showing high selectivity toward nitrofurantoin (NFT) and nitrofurazone (NFZ), with strong fluorescence quenching driven mainly by photoinduced electron transfer (PET). Stern–Volmer analysis revealed K sv values of 5.98 × 10⁴ M⁻¹ (NFZ) and 5.88 × 10⁴ M⁻¹ (NFT), with detection limits of 0.136 ppm and 0.110 ppm, respectively. DFT and TDDFT calculations support the PET mechanism, indicating that π-stacked interactions between adenine and NFZ/NFT facilitate electron transfer upon excitation. In contrast, bulky antibiotics show minimal quenching due to steric hindrance. These findings provide molecular-level insights into fluorescence sensing mechanisms and establish CuAS as a promising selective sensor for nitrofuran antibiotics. Adenine-based MOF Fluorescence quenching Photoinduced electron transfer (PET) Antibiotic sensing TDDFT calculations Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 1. Introduction Technological advancements have significantly improved modern life, yet they often bring unintended consequences for human health and the environment. In response, there is growing interest in developing advanced sensing materials that can detect environmental pollutants and pharmaceutical residues with high sensitivity and selectivity. Among these, metal–organic frameworks (MOFs), highly crystalline materials composed of metal ions or clusters coordinated to organic ligands, have emerged as versatile platforms. Their modular architecture, combined with a high surface area, adjustable pore dimensions, and robust thermal and chemical stability enable a wide range of applications including catalysis [1,2], gas storage [3], drug delivery [4], chemical sensing [5,6], water purification [7], and environmental remediation [8]. A particularly promising subclass of these materials is luminescent MOFs (LMOFs), which exhibit fluorescence properties that can be harnessed for chemical sensing. By judiciously selecting metal centers and π-conjugated organic linkers, researchers can fine-tune the luminescence behavior of LMOFs [9–15]. Emission in LMOFs may originate from linker-centered fluorescence, metal-centered transitions, charge transfer, or interactions with guest molecules [16]. The strategic design of LMOFs enables sensitive detection of target analytes through mechanisms such as fluorescence enhancement or quenching. Copper-based luminescent MOFs (LMOFs) have attracted considerable attention as sensitive fluorescence-based sensors due to their rich coordination chemistry, tunable luminescent properties, and, in many cases, favorable biocompatibility and low toxicity [17–20]. Functionalization with ligands bearing electron-rich and hydrogen-bond-donating groups further enhances their sensing capabilities. These frameworks are particularly effective for detecting electron-deficient analytes such as nitrofuran antibiotics, including nitrofurazone (NFZ) and nitrofurantoin (NFT), which are frequently used in veterinary medicine [21–23] but pose environmental and food safety risks if not properly monitored. In this study, we report the synthesis of a Cu-based luminescent MOF (CuAS) constructed from succinic acid and adenine. Succinic acid provides structural flexibility, while adenine contributes π-electron density and functional groups that facilitate strong interactions with antibiotic analytes [24–30]. The resulting framework exhibits pronounced fluorescence quenching upon exposure to nitrofuran antibiotics. To elucidate the underlying sensing mechanism, we investigated two key quenching pathways: Förster resonance energy transfer (FRET) [31] and photoinduced electron transfer (PET) [32]. Spectral overlap analysis suggested limited contribution from FRET, while electronic structure calculations via time-dependent density functional theory (TDDFT) indicated that PET, facilitated by LUMO level alignment between the MOF and antibiotic molecules, is the dominant mechanism. Furthermore, molecular orbital mixing and internal conversion effects were considered to explain variations in oscillator strengths observed in π-stacked complexes. By combining experimental fluorescence data with theoretical calculations, this study provides detailed insight into the fluorescence quenching mechanisms of Cu-adenine MOFs. Our findings contribute to the rational design of MOF-based sensors for selective antibiotic detection, with potential applications in environmental and food safety monitoring. 2. Experimental 2.1 Materials and methods All chemicals were purchased from commercial suppliers and used without further purification. Powder X-ray diffraction (PXRD) data were collected using a Bruker D8 Advance diffractometer with Cu-Kα radiation (λ = 1.54060 Å). The FT-IR spectrum was recorded on a Bruker Vertex 70 spectrophotometer in the range of 400–4000 cm⁻¹ using attenuated total reflectance (ATR) mode. Thermogravimetric analysis (TGA) was performed on a PerkinElmer TGA7 with a heating rate of 10 °C per minute under a nitrogen atmosphere. UV-Vis absorption spectra were measured in the range of 190–700 nm using a Shimadzu UV-2600 spectrophotometer for solid samples, and a PerkinElmer Lambda 365 for solid dispersions in methanol. Fluorescence emission spectra were recorded using a Horiba Scientific FluoroMax-4P and a PerkinElmer FL 8500 fluorescence spectrophotometer. Elemental analyses (C, H, and N) were performed using a LECO CHNS-932 elemental analyzer. 2.2 X-ray Crystallography Crystallographic data were collected on a Bruker D8 QUEST CMOS PHOTON II diffractometer using graphite-monochromated Mo-Kα radiation. Absorption corrections were applied using a multi-scan method with SADABS 2016/2 [33]. The structure was solved using OLEX2 1.3 [34] and refined with the XL refinement package [35] via Gauss-Newton minimization. Non-hydrogen atoms were refined anisotropically. Hydrogen atoms were treated using a combination of independent and constrained refinements. All atoms of the adenine molecule were found to be disordered and were refined with two occupancy states in the asymmetric unit. Crystallographic data are summarized in Table 1. Selected bond lengths and angles are provided in Tables S1and S2. Table 1. Crystallographic data for [Cu(Ade)(succinate)]ₙ Formula Empirical formula Formula weight Temperature (K) Crystal system Space group a (Å) b (Å) c (Å) α (º) β (º) γ (º) Volume (Å 3 ) Z Dc (g cm -3 ) F(000) Crystal size (mm 3 ) Radiation source Wavelength 2ϴ range for data collection ( o ) Index ranges No. of reflections collected Δρ max , Δρ min (e Å 3 ) R1a/wR2b [I > 2σ(I)] R1a/wR2b (all) Goodness-of-fit on F 2 [Cu(Ade)(succinate)] n C 7 H 6 CuN 5 O 2 255.71 283-303 I 41/a (88) tetragonal 15.7506(4) 15.7506(4) 22.4819(10) 90 90 90 5577.34 16 1.218 2048 0.22 x0.20 x 018 Mo Kα 0.71073 5.17 to 54.25 -19 ≤ h ≤ 20, -20 ≤ k ≤ 20, -28 ≤ l ≤ 28 57263 0.536, -0.38 0.0404/0.1080 0.0508/0.1139 1.053 2.3 Synthesis of [Cu(Ade)(succinate)]ₙ (CuAS) The new Cu-MOF was synthesized via a hydrothermal method. Briefly, copper(II) nitrate (0.2 mmol, 0.0483 g), adenine (0.2 mmol, 0.0237 g), and succinic acid (0.2 mmol, 0.0236 g) were dissolved in a DMF:H₂O mixture (1:1, 10 mL) and stirred for 5 minutes. Subsequently, 1 mL of 1 M nitric acid was added. Once the solution became homogeneous, it was transferred to a Teflon-lined autoclave and heated at 130 °C for 24 hours. After slow cooling to room temperature, blue crystals were obtained. The crystals were collected, washed three times with 3 mL of DMF, and dried under ambient conditions. Anal.(%) calcd for C 7 H 6 CuN 5 O.2(H 2 O): C, 30.9%; H, 3.43%; N, 20.03%; found: C, 32.00%; H, 4.03%; N, 20.61%. IR (ATR, cm -1 ): 3332(m), 3194(m), 2937(w), 1651(s), 1577(s), 1541(m), 1453(m), 1394(s), 1295(m), 1270(m), 1201(s), 1138(s), 1093(s), 982(m), 889(m), 790(s), 741(s), 633(s), 578(s). 2.4 Fluorescence Properties he fluorescence properties of CuAS were investigated both in the solid state and as a dispersion in MeOH at ambient temperature. Solid-state fluorescence spectra were recorded using a Horiba Scientific FluoroMax-4P spectrophotometer, while measurements of CuAS dispersed in MeOH were performed using a PerkinElmer FL 8500 fluorescence spectrophotometer. 2.5 Antibiotic Sensing Study 2.5.1 Selectivity: To evaluate the potential of CuAS as a sensor for antibiotics, 5 mg of the MOF powder was dispersed in 2.5 mL of MeOH and sonicated for 30 minutes. Then, 0.5 mL of a 0.5 mM MeOH solution of each antibiotic, namely nitrofurazone (NFZ), nitrofurantoin (NFT), 1,2-dimethyl-5-nitroimidazole (DTZ), penicillin (PCL), chloramphenicol (CAP), metronidazole (MDZ), and sulfadiazine (SDZ), was added to the suspension. The fluorescence emission intensity of each mixture was measured. To visually demonstrate selectivity under UV light, 5 mg of CuAS powder was dispersed in 3.0 mL of 0.5 mM MeOH solutions of the individual antibiotics and incubated for 30 minutes. The fluorescence under UV irradiation was then observed. After that, 3.0 mL of 0.5 mM NFZ solution was added to each dispersion and the mixtures were sonicated for 30 minutes. The fluorescence under UV light was observed again to assess any changes. 2.5.2 Sensitivity: To investigate the sensitivity of CuAS toward antibiotic detection, fluorescence titration experiments were conducted. A 5 mg portion of CuAS was dispersed in 3 mL of MeOH via sonication for 30 minutes. Increasing amounts of a 0.5 mM solution of NFZ (or NFT) were gradually added to the CuAS dispersion. After each addition, the mixture was sonicated to ensure proper mixing, and the fluorescence intensity was measured to monitor the response. 2.6 DFT/TDDFT calculations To investigate the mechanism of fluorescence quenching in CuAS by antibiotic molecules, time-dependent density functional theory (TDDFT) calculations [36] were performed using the Gaussian09 program [37]. Adenine was chosen to represent the fluorescent moiety of CuAS, as its fluorescence mainly arises from intraligand electronic transitions. Ground-state geometries of adenine, the antibiotics, and their corresponding adenine–antibiotic complexes in methanol were optimized at the B3LYP/6-31G(d,p) level of theory [38–41], including Grimme’s D3 dispersion correction with Becke–Johnson damping (D3BJ) [42,43]. Solvent effects were modeled using the polarizable continuum model (PCM) [44]. Ten vertical excitations were computed via TDDFT, and the frontier molecular orbitals involved in excitation and emission processes were analyzed based on the optimized geometries. These calculations provided insight into the electronic interactions responsible for fluorescence quenching in the CuAS–antibiotic complexes. 3. Results and discussion 3.1 Crystal Structure Descriptions The asymmetric unit of CuAS consists of one adenine molecule and half of a succinate ligand (Fig. 1a). The succinate ligand is centered on a C₂ axis, and a center of symmetry is located between two Cu(II) ions. Upon applying these symmetry operations, the full 3D framework structure is generated (Fig. 1b). Each Cu(II) ion adopts a distorted square pyramidal geometry, coordinated by two nitrogen atoms from two adenine ligands and two oxygen atoms from two succinate ligands in the equatorial plane, with one nitrogen atom from adenine occupying the axial position. Two adjacent Cu(II) ions are bridged by both succinate and adenine ligands, forming dinuclear nodes (Fig. 1c). Each dinuclear node is further connected through one bridging succinate and two bridging adenine ligands. The succinate ligand adopts a μ₄-κ¹:κ¹:κ¹:κ¹ coordination mode and exhibits an anti–anti conformation with a torsion angle of 135.12°. The adenine ligands coordinate through a μ₃-κ¹:κ¹:κ¹ mode in two alternating styles: (1) terminal bridging to monodentate and (2) monodentate to terminal bridging. This alternating coordination leads to a perpendicular arrangement of adjacent adenine rings. As a result, the network extends along two diagonal directions defined by the ac and bc planes, while the succinate ligands propagate along the a - and b -axes (Fig. 2a, 2b). The combination of these linkages generates a three-dimensional framework with channels oriented along the a - and b -axes. The pore dimensions are approximately 8.77 × 11.82 Å, with free amino groups from the adenine ligands pointing into the cavities. Viewed along the c -axis, no significant channels are observed (Fig. 2c). 3.2 Powder XRD Patterns and Thermogravimetric Analysis The phase purity of the synthesized CuAS was confirmed by powder X-ray diffraction (PXRD). The experimental PXRD pattern matches closely with the simulated pattern derived from single-crystal data (Fig. 3), indicating that the bulk material is phase-pure. Thermogravimetric analysis (TGA) was used to investigate the thermal stability of CuAS (Fig. 4). The TGA curve shows an initial weight loss of 9.0% (calculated 10.3%) from room temperature to 170 °C, attributed to the removal of adsorbed moisture. A subsequent mass loss of 32.0% (calculated 33.19%) occurs between 180–420 °C, corresponding to the decomposition of the succinate ligand. A final mass loss of 38.0% (calculated 38.66%) between 420–700 °C is associated with the decomposition of the adenine ligands, leaving CuO as the final residue. 3.3 UV-Visible Spectroscopy The UV–visible spectra of CuAS were measured both in the solid state and as a powder dispersed in methanol (MeOH). In the solid state, CuAS exhibits a broad absorption band centered around 350 nm (Fig. 5a). In contrast, when dispersed in MeOH, CuAS shows an absorption maximum (l max ) at approximately 260 nm (Fig. 5b), similar to that of free adenine. These results suggest that the optical absorption of CuAS in MeOH is primarily derived from the adenine ligand. 3.4 Fluorescence Properties of CuAS The solid-state fluorescence properties of succinic acid, adenine, and CuAS MOF were systematically investigated, as presented in Fig. 6a. Upon excitation at 330 nm, succinic acid and CuAS exhibit emission maxima at 395 nm and 440 nm, respectively. In contrast, solid-state adenine displays emission bands centered at 380 nm and 435 nm when excited at 250 nm. To further elucidate the photophysical behavior, the emission spectra of adenine in MeOH solution and CuAS MOF dispersed in MeOH were recorded at room temperature (Fig. 6b). Both adenine and CuAS exhibit comparable emission features with maxima at 405 nm and 430–425 nm under excitation at 350 nm, indicating similar excited-state properties in the dispersed phase. These findings strongly suggest that the fluorescence of CuAS MOF predominantly arises from intraligand transitions associated with the adenine linker. The slight red-shifts observed relative to the solid-state spectra can be ascribed to solvent effects and excitation-wavelength-dependent relaxation processes. 3.5 Detection of Antibiotics: Selectivity and Sensitivity 3.5.1 Selectivity As shown in Fig. 7a, the photoluminescence emission of CuAS exhibited different intensities at two emission bands (405 nm and 425 nm), depending on the specific antibiotic present in the methanol (MeOH) solution. Notably, the fluorescence intensity of CuAS decreased significantly in the presence of nitrofurazone (NFZ) and nitrofurantoin (NFT), with quenching efficiencies of approximately 98% for both antibiotics (Fig. 7b). This indicates that NFZ and NFT induce the most significant quenching effect among the tested antibiotics. Furthermore, the fluorescence responses of CuAS suspensions under 365 nm UV irradiation were visually observed (Fig. 8a), again confirming the substantial quenching effect caused by NFZ and NFT. To further evaluate selectivity, additional nitrofurazone was introduced into solutions already containing other antibiotics. After NFZ addition, the emission intensity of all suspensions decreased markedly (Fig. 8b), demonstrating that CuAS exhibits a selective fluorescence response towards nitrofurazone. 3.5.2 Sensitivity To investigate the sensitivity of CuAS towards NFZ and NFT, the emission intensity at 405 nm was measured in the presence of varying concentrations of these antibiotics. As shown in Fig. 9a and 9c, the fluorescence intensity of CuAS gradually decreased with increasing concentrations of NFZ and NFT, respectively. The quenching behavior was further analyzed using the Stern–Volmer (S–V) equation. The resulting S–V plots (Fig. 9b and 9d) exhibited a good linear relationship. The Stern–Volmer quenching constants (K sv ) were calculated to be 5.98 × 10⁴ M⁻¹ for NFZ and 5.88 × 10⁴ M⁻¹ for NFT. The limits of detection (LOD) were determined to be 0.1357 ppm for NFZ and 0.1099 ppm for NFT. A comparison of the K sv values with previously reported MOF-based sensors is provided in Table 2. The results highlight that CuAS exhibits competitive, if not superior, sensitivity for detecting NFZ and NFT relative to other reported complexes Table 2. Comparison of Stern–Volmer quenching constants (Ksv) for NFZ and NFT detection by different MOF-based fluorescent sensors. Sensor K SV (M -1 ) for NFZ K SV (M -1 ) for NFT Reference {[Zn 2 (bcob)(OH)(H 2 O)]•DMA} n 2.50 × 10 4 2.26 × 10 4 [45] [Zn(DCPP)(H 2 O)]•(DMF) 4.73 × 10 4 6.42 × 10 4 [46] Cu 0.1 /{[Zn(L)]•CH3CN} n 4.85 × 10 4 5.27 × 10 4 [47] [Zn(TTDPa)(bodca)]·H 2 O 6.76 × 10 4 5.94 × 10 4 [48] [Zn 4 (ad) 3 (BPTC)(H 2 O) 4 ]•0.75ad •0.25NO 3 •2.5DMF•2.5H 2 O Film 4.35 × 10 4 3.14 × 10 4 [49] CuAS MOF 5.98 × 10 4 5.88 × 10 4 This work 3.6 Mechanism of Sensing The fluorescence quenching of CuAS toward antibiotics is attributed to two possible mechanisms: Förster resonance energy transfer (FRET) and photoinduced electron transfer (PET). 3.6.1 Förster Resonance Energy Transfer (FRET) To investigate the possibility of FRET, the UV–Vis absorption spectra of the antibiotics were compared with the fluorescence emission spectrum of CuAS (Fig. 10a). Only NFZ and NFT exhibit partial spectral overlap with the emission of CuAS, while negligible overlap is observed for the other antibiotics. Although this suggests that energy transfer from CuAS to NFZ and NFT may contribute to the quenching, the limited extent of overlap indicates that FRET is not the dominant quenching mechanism. 3.6.2 Photoinduced Electron Transfer (PET) Alternatively, fluorescence quenching could arise from photoinduced electron transfer. The energy levels of the frontier orbitals were analyzed to assess the feasibility of this process (Fig. 10b). The LUMO energy of the adenine ligand in CuAS is higher than those of the antibiotics, with the exception of PCL and SDZ which are fairly close to it. This alignment enables electron transfer from the excited state of CuAS to the LUMO levels of the antibiotics. Notably, NFZ and NFT possess the lowest LUMO energies among the tested antibiotics, facilitating more efficient electron transfer. This observation is consistent with the fluorescence quenching results, where NFZ and NFT exhibited the highest quenching efficiencies. Based on the above analysis, PET is proposed as the primary mechanism responsible for the fluorescence quenching observed in CuAS suspensions, while FRET likely plays a minor role. Based on the above discussion, fluorescence emission is attributed to intraligand transitions within adenine, while fluorescence quenching primarily arises from photoinduced electron transfer (PET) processes. To gain deeper insights into these mechanisms, density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were performed at the B3LYP/6-31G(d,p) level of theory. All calculations employed the Polarizable Continuum Model (PCM) to account for solvent effects, enhancing the reliability of the computed excitation properties. Fig. 11 presents the computed Jablonski diagram for adenine excitation. The calculated oscillator strength (¦) of 0.2197 strongly supports that the primary excitation corresponds to a transition from the ground singlet state (S₀) to the first excited singlet state (S₁), which governs fluorescence emission. This transition is predominantly characterized by excitation from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), indicative of a π–π* transition, with a calculated excitation wavelength of 244 nm. Although this value deviates from the experimentally observed absorption maximum at 262 nm [50], the difference is within an acceptable range considering the approximations inherent in the PCM model and DFT methods [51]. To elucidate the fluorescence quenching mechanism in CuAS upon interaction with antibiotic molecules, we examined the stacked complexes formed between adenine and various antibiotics. π–Stacked interactions are known to facilitate molecular orbital mixing and fluorescence quenching, as demonstrated for 2-aminopurine complexes with purine and pyrimidine bases [52,53]. Given the coordination of adenine to Cu centers within the MOF, antibiotic molecules are expected to interact primarily with the exposed purine ring of adenine through π–stacking, although steric constraints imposed by the MOF may limit these interactions, particularly for bulkier antibiotics. The key electronic features of the adenine–NFZ dimer are summarized in Fig. 11. The vertical transition from S₀ to the second excited singlet state (S₂) exhibits a strong oscillator strength (¦ = 0.5905), primarily originating from a HOMO–1 → LUMO excitation. In this transition, the HOMO–1 is delocalized over both adenine and NFZ, while the LUMO is localized mainly on NFZ. Importantly, a lower-lying S₁ state is present, where the S₀ → S₁ transition is weakly allowed, with a low oscillator strength (¦ = 0.0325), involving predominantly a HOMO (localized on adenine) → LUMO transition. This spatial separation of HOMO and LUMO orbitals across adenine and NFZ is a hallmark of photoinduced electron transfer (PET) processes. Upon photoexcitation, an electron can migrate from adenine (donor) to NFZ (acceptor), facilitating nonradiative deactivation. According to Kasha’s rule [54], rapid internal conversion from S₂ to the dark S₁ state is expected, and the low oscillator strength of S₁ indicates that radiative decay (fluorescence) is inefficient. Thus, the TDDFT results not only explain fluorescence quenching but strongly support PET as the underlying mechanism. A similar PET-driven quenching mechanism is predicted for the adenine–NFT complex (Fig. 12), where NFT differs from NFZ by substitution of an amide group with a furan ring, introducing additional delocalization. Although minor differences in transition energies and oscillator strengths are observed, the trend toward rapid internal conversion and fluorescence suppression remains consistent. In contrast, π–stacked conformations between adenine and DTZ or MDZ induce significant molecular orbital mixing, altering electronic transition properties (Figs. 13 and 14). Electron density redistribution across the stacked molecules leads to modified energy levels and transition dipole moments. As a result, oscillator strengths for both the S₀ → S₁ (0.0013 for adenine–DTZ and 0.0089 for adenine–MDZ) and S₀ → S₂ (0.0026 for adenine–DTZ and 0.0097 for adenine–MDZ) transitions are substantially decreased compared to isolated adenine. This suppression of oscillator strengths inhibits radiative decay pathways and enhances nonradiative relaxation via internal conversion and vibrational dissipation. In these cases, the interaction resembles static quenching through ground-state complex formation [52] rather than dynamic PET processes. In complexes with CAP, SDZ, and PCL (Figs. 15–17), the oscillator strengths for the S₀ → S₁ transitions remain relatively stronger (0.0232, 0.0148, and 0.0239, respectively) compared to the S₀ → S₂ transitions. Although these values are reduced relative to free adenine, they indicate that molecular orbital mixing does not substantially disrupt radiative decay pathways. As a result, fluorescence quenching is minimal, and adenine largely retains its fluorescent properties upon complexation with CAP, SDZ, and PCL. Steric hindrance from the MOF framework further influences these interactions. Small, planar antibiotics such as NFZ, NFT, DTZ, and MDZ can engage in π–stacking within the MOF pores, promoting PET and/or orbital mixing-induced quenching. In contrast, bulkier antibiotics such as CAP, SDZ, and PCL face steric constraints that prevent close approach to the purine ring, thereby preserving fluorescence. Although explicit binding energy calculations were not performed, the trends in oscillator strengths, combined with orbital analyses, strongly support PET-driven quenching in small, planar complexes and negligible quenching in bulkier systems. Overall, the TDDFT (PCM) results align closely with experimental observations, providing molecular-level evidence for PET-mediated fluorescence quenching and highlighting the critical role of π–stacking interactions in these systems. 4. Conclusion In this work, adenine-based metal-organic framework (MOF) materials with fluorescent properties were synthesized: CuAS MOF (A = adenine, S = succinic acid). The crystal structure of CuAS reveals a three-dimensional framework with two directional channels along the a and b axes, with amino groups oriented toward the cavities. CuAS exhibits solid-state fluorescence emission at 440 nm (λ ex = 330 nm), and when dispersed in methanol, shows emission at 430 nm (λ ex = 350 nm), consistent with intraligand transitions of adenine. This material was designed for antibiotic detection via fluorescence quenching. The sensor demonstrated high specificity toward nitrofuran antibiotics, particularly Nitrofurantoin (NFT) and Nitrofurazone (NFZ), which produced the highest percentage of fluorescence quenching. The quenching process is primarily governed by photoinduced electron transfer (PET), as supported by DFT/TDDFT calculations, with a possible minor contribution from fluorescence resonance energy transfer (FRET). DFT/TDDFT calculations elucidate the quenching mechanisms: antibiotics such as NFZ, NFT, DTZ, and MDZ can form π-stacked interactions with adenine within the MOF, promoting molecular orbital (MO) mixing. In the NFZ and NFT systems, the primary S₀ → S₂ transitions involve electron density that is initially delocalized across both adenine and NFZ/NFT, becoming localized on NFZ/NFT upon excitation, thereby facilitating PET. This promotes rapid internal conversion to a nonradiative S₁ state, leading to fluorescence quenching. In DTZ and MDZ systems, fluorescence quenching predominantly occurs through static quenching mechanisms, where ground-state complex formation with adenine leads to reduced oscillator strengths and enhanced nonradiative relaxation. In contrast, CAP, SDZ, and PCL, due to their bulky structures, experience steric hindrance that limits π–π stacking interactions within the MOF framework. As a result, adenine retains its fluorescence with minimal quenching. Overall, the experimental and theoretical results together provide detailed molecular-level insights into fluorescence quenching mechanisms and establish CuAS MOF as a selective fluorescent sensor for nitrofuran antibiotics. Declarations 5. Acknowledgements This research was supported by the Department of Chemistry, Faculty of Science, Kasetsart University; the Center of Excellence for Innovation in Chemistry (PERCH-CIC); and the Kasetsart University Research and Development Institute under Grant No. FF(KU-SRIU) 11.67. Author Contributions Tanin Nanok: Software, Calculation Validation, Writing- original draft, Writing- review & editing; Tontrakarn Pongpai: Formal analysis, Data curation; Kittinan Ketsrisung: Formal analysis, Visualization; Jiraporn Singhophon: Formal analysis, Investigation; Kittipong Chainok: Investigation, Resources, Software. Tanwawan Duangthongyou: Validation, Resources, Supervision, Writing- original draft, Writing- review & editing, Project administration. Funding Not applicable Data Availability No datasets were generated or analysed during the current study Ethical Approval Not applicable Competing Interests The authors declares no competing interests References Y. Zhong, P. Liao, J. Kang, Q. Liu, S. Wang, S. Li, X. Liu, G. Li, Locking Effect in Metal@MOF with Superior Stability for Highly Chemoselective Catalysis. J. Am. Chem. Soc. 145 , 4659-4666 (2023) V. Pascanu, G. González Miera, A.K. Inge, B. Martín-Matute, Metal–Organic Frameworks as Catalysts for Organic Synthesis: A Critical Perspective. J. Am. Chem. Soc. 141 , 7223-7234 (2019) H. Chu, D. Sun, P. Cui, Highly Water-Stable Zn5 Cluster-Based Metal–Organic Framework for Efficient Gas Storage and Organic Dye Adsorption. Inorg. Chem. 61 , 19642-19648 (2022) S. Rojas, F.J. Carmona, C.R. Maldonado, P. Horcajada, T. Hidalgo, C. Serre, J.A.R. Navarro, E. Barea, Nanoscaled Zinc Pyrazolate Metal–Organic Frameworks as Drug-Delivery Systems. Inorg. Chem. 55 , 2650-2663 (2016) A. Gheorghe, O. Lugier, B. Ye, S. Tanase, Metal–organic framework based systems for CO 2 sensing. Journal of Materials Chemistry C, 9 (2021) 16132-16142. P. Qin, B.A. Day, S. Okur, C. Li, A. Chandresh, C.E. Wilmer, L. Heinke, VOC mixture sensing with a MOF film sensor array: detection and discrimination of xylene isomers and their ternary blends. ACS Sens. 7 , 1666-1675 (2022) H. Qu, X. Xiao, Z. Han, M. Hu, S. Shen, L. Yang, F. Jia, T. Wang, Z. Ye, W. Sun, Y. Wang, L. Huang, Z. Zhu, P. Servati, J. Tang, J. Chen, Graphene Oxide Nanofiltration Membrane Based on Three-Dimensional Size-Controllable Metal–Organic Frameworks for Water Treatment. ACS Appl. Nano Mater. 5 , 5196-5207 (2022) R. Taghavi, S. Rostamnia, M. Farajzadeh, H. Karimi-Maleh, J. Wang, D. Kim, H.W. Jang, R. Luque, R.S. Varma, M. Shokouhimehr, Magnetite Metal–Organic Frameworks: Applications in Environmental Remediation of Heavy Metals, Organic Contaminants, and Other Pollutants. Inorg. Chem. 61 , 15747-15783 (2022) T. Islamoglu, Z. Chen, M. C. Wasson, C. T. Buru, K. O. Kirlikovali, U. Afrin, M. R. Mian, O. K. Farha, Metal-Organic Frameworks against Toxic Chemicals. Chem. Rev. 120 , 8130− 8160 (2020) W. Guan, W. Zhou, J. Lu, C. Lu, Luminescent Films for Chemo- and Biosensing. Chem. Soc. Rev. 44 , 6981−7009 (2015) Li, H. Y.; Zhao, S. N.; Zang, S. Q.; Li, J. Functional MetalOrganic Frameworks as Effective Sensors of Gases and Volatile Compounds. Chem. Soc. Rev. 49 , 6364−6401 (2020) Y. Zhang, X. Qu, B. Yan, A Visual Logic Alarm Sensor for Diabetic Patients Towards Diabetic Polyneuropathy Based on a Metal-Organic Framework Functionalized by Dual-Cation Exchange. J. Mater. Chem. C. 9 , 3440−3446 (2021) X. D. Ying, J. X. Chen, D. Y. Tu, Y. C. Zhuang, D. Wu, L. Shen, Tetraphenylpyrazine-Based Luminescent Metal-Organic Framework for Chemical Sensing of Carcinoids Biomarkers. ACS Appl. Mater. Interfaces. 13 , 6421−6429 (2021) X. Wang, M. Lei, T. Zhang, Q. Zhang, R. Zhang, M. Yang, A Water-Stable Multi-Responsive Luminescent Zn-MOF Sensor for Detecting TNP, NZF and Cr 2 O 7 2‑ in Aqueous Media. Dalt. Trans. 50 , 3816−3824 (2021) M. A. Andres, M. T. Vijjapu, S. G. Surya, O. Shekhah, K. N. Salama, C. Serre, M. Eddaoudi, O. Roubeau, I. Gascon, Methanol and Humidity Capacitive Sensors Based on Thin Films of MOF Nanoparticles. ACS. Appl. Mater. Interfaces. 12 , 4155− 4162 (2020) J.-X. Wang, J. Yin, O. Shekhah, O. M. Bakr, M. Eddaoudi, O. F. Mohammed, Energy Transfer in Metal–Organic Frameworks for Fluorescence Sensing. ACS Appl. Mater. Interfaces. 14 (8), 9970–9986 (2022) C. E. Kivi, D. Song, A luminescent cationic metal–organic framework featuring [Cu–pyrazolate] 3 units for volatile organic compound sensing. Dalton Trans. 45, 17087-17090 ( 2016) S. Hui, P. C. Saha, S. Guha, P. Mahata, Two-Dimensional Cu-Based MOF for Selective Staining of the Cellular Nucleus through Fluorescence Imaging and Selective Sorption of Dye Molecules in Aqueous Medium. Inorg. Chem. 63 (29), 13439–13449 (2024) E. Moradi, R. Rahimi, Vahid Safarifard, Ultrasound-assisted preparation nanostructures of Cu2(BDC)2(BPY)-MOF: Highly selective and sensitive luminescent sensing of THF small molecule and Cu 2+ and Pb 2+ ions. J. Solid State Chem. 288 , 121397 (2020) J. Yang, J. Che, X. Jiang, Y. Fan, D. Gao, J. Bi, Z. Ning, A Novel Turn-On Fluorescence Probe Based on Cu(II) Functionalized Metal–Organic Frameworks for Visual Detection of Uric Acid. Molecules 27 , 4803 ( 2022) J. Jia, H. Zhang, J. Qu, Y. Wang, N. Xu, Immunosensor of Nitrofuran Antibiotics and Their Metabolites in Animal-Derived Foods: A Review. Front. Chem. 10 , 813666 (2022) J. Points, D. Thorburn Burns, M.J. Walker, Forensic issues in the analysis of trace nitrofuran veterinary residues in food of animal origin. Food Control. 50 , 92-103 (2015) L. Molognoni, H. Daguer, R.B. Hoff, Chapter 12 - Analysis of nitrofurans residues in foods of animal origin, in: C.M. Galanakis (Ed.) Food Toxicology and Forensics. Academic Press. 379-419 (2021) J. Buasakun, P. Srilaoong, K. Chainok, C. Raksakoon, R. Rattanakram, T. Duangthongyou, Novel zinc(II) coordination polymers (CPs) based on flexible aliphatic carboxylic acids and an N-donor ligand for fluorescence sensors. Inorg. Chim. Acta. 511 , 119839 (2020) J. Buasakun, P. Srilaoong, K. Chainok, C. Raksakoon, R. Rattanakram, T. Duangthongyou, Dual luminescent coordination polymers based on flexible aliphatic carboxylate ligands supplemented by rigid bipyridyl ligands for 2,4-dinitrophenol (DNP) and iron(III) ion detection. Polyhedron. 204 , 115265 (2021). M. Brezovan, V. Kuchtanin, J. Moncol, J. Pavlik, Ľ. Dlháň, P. Segľa, Four novel cobalt(II) succinate coordination polymers with N -heterocyclic ligands: crystal structures, spectral properties, magnetism and computational study. Chem. Pap. 74 3741–3753 (2020) M. Brezovan, J. Juráková, J. Moncol, Ľ. Dlháň, M. Korabik, I. Šalitroš, J. Pavlik, P. Segľa, The Role of the Bridge in Single-Ion Magnet Behaviour: Reinvestigation of Cobalt(II) Succinate and Fumarate Coordination Polymers with Nicotinamide. Inorganics. 10 , 128 (2022). X. Wu, X. Xiong, J.L. Li, D. Luo, K. Wu, Y.B. Wei, X.Y. Liu, W. Lu, D. Li, J. He, An Adenine‐Based Biological Metal‐Organic Framework as an Efficient Luminescent Sensor for Tetracycline Detection. Eur. J. Inorg. Chem. 23 , e202200278 (2022) A. Eskemech, D. Gambhir, H. Kaur, A. Karmakar, R. R. Koner , Amino decorated adenine based metal–organic framework for multi-faceted applications. Dalton Trans. 52, 8275-8283. ( 2023) D. Jonckheere, E. Coutino-Gonzalez, W. Baekelant, B. Bueken, H. Reinsch, I. Stassen, O. Fenwick, F. Richard, P. Samorì, R. Ameloot, J. Hofkens, M. B. J. Roeffaers, D. E. De Vos, Silver-induced reconstruction of an adeninate-based metal–organic framework for encapsulation of luminescent adenine-stabilized silver clusters. J. Mater. Chem. C 4 , 4259-4268 (2016) S. S. Nagarkar, B. Joarder, A. K. Chaudhari, S. Mukherjee, S. K. Ghosh, Highly selective detection of nitro explosives by a luminescent metal-organic framework. Angew. Chem. Int. Ed. 52 (10), 2881-2885 (2013) R. Goswami, S. C. Mandal, B. Pathak, S. Neogi, Guest-Induced Ultrasensitive Detection of Multiple Toxic Organics and Fe 3+ Ions in a Strategically Designed and Regenerative Smart Fluorescent Metal–Organic Framework. ACS Appl. Mater. Interfaces, 11 (9), 9042-9053 (2019) SAINT and SADABS; Bruker AXS Inc.: Madison, WI, USA, 2003. O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschman, LESS: A New GUI Implementation of the Least-Squares Refinement Program for Crystal Structure Analysis. J. Appl. Cryst. 42 , 339 – 341 (2009) G.M. Sheldrick, A Short History of SHELX. Acta Cryst. A64 , 112 – 122 (2008) Runge, Erich; E. K. U. Gross, Density-Functional Theory for Time-Dependent Systems. Phys. Rev. Lett. 52 (12), 997–1000 (1984) M. J. Frisch et al., Gaussian 09, Revision D.01, Gaussian, Inc., Wallingford CT, 2009. A.D. Becke, Density-functional thermochemistry. III. The role of exact exchange. J.Chem.Phys. 98 , 5648-5652 (1993) C. Lee, W. Yang, R.G. Parr, Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 37 , 785-789 (1988) S.H. Vosko, L. Wilk, M. Nusair, Accurate spin-dependent electron liquid correlation energies for local spin density calculations: a critical analysis. Can. J. Phys. 58 , 1200-1211 (1980) P.J. Stephens, F.J. Devlin, C.F. Chabalowski, M.J. Frisch, Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. J. Phys. Chem. 98 , 11623-11627 (1994) S. Grimme, J. Antony, S. Ehrlich, and S. Krieg, A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 132 , 154104 (2010). S. Grimme, S. Ehrlich, and L. Goerigk, Effect of the damping function in dispersion corrected density functional theory. J. Comput. Chem. 32 , 1456 (2011). J. Tomasi, B. Mennucci, R. Cammi, Quantum Mechanical Continuum Solvation Models. Chem. Rev. 105 (8), 2999-3094 (2005) S. Gai, J. Zhang, R. Fan, K. Xing, W. Chen, K. Zhu, X. Zheng, P. Wang, X. Fang, Y. Yang, Highly Stable Zinc-Based Metal-Organic Frameworks and Corresponding Flexible Composites for Removal and Detection of Antibiotics in Water. ACS Appl Mater Interfaces, 12 (7) 8650-8662 (2020) S.-L. Sun, X.-Y. Sun, Q. Sun, E.-Q. Gao, Highly efficient fluorescent chemosensor for nitro antibiotic detection based on luminescent coordination polymers with 2, 6-di(4-carboxyphenyl)pyrazine. CrystEngComm. 23 (17), 3167-3174 (2021) R.-Q. Jia, G. Tan, Y.-J. Chen, L.-Y. Zuo, B. Li, L.-Y. Wang, Cu II Ion Doping Enhances the Water Stability of Luminescent Metal–Organic Framework, Realizing the Detection of Fe 3+ and Antibiotics in Aqueous Solutions. Front. Chem. 10 , 860232 (2022) Z.-L. Mu, Y.-Q. Ma, Y. Zhu, Z. Chen, H.-P. Xiao, X. Li, H.-Y. Wang, J.-Y. Ge, Two Stable Bifunctional Zinc Metal–Organic Frameworks with Luminescence Detection of Antibiotics and Proton Conduction. Inorg. Chem. 62 (49) 20314-20324 (2023) P. Srilaoong, P. Puengtham, J. Buasakun, C. Raksakoon, S. Suramitr, K. Chainok, P. Harding, D. J. Harding, T. Duangthongyou, Zn-metal organic framework containing electron rich linkers and film preparation for applications in antibiotic detection. Inorg. Chim. Acta 559 , 121780 (2024) H. H.Hammud, K. H. Bouhadir, M. S. Masoud, A. M. Ghannoum, S.A. Assi, Solvent Effect on the Absorption and Fluorescence Emission Spectra of Some Purine Derivatives: Spectrofluorometric Quantitative Studies. J. Solution Chem. 37 (7), 895–917 (2008) Z. Zara, J. Iqbal, K. Ayub, M. Irfan, A. Mahmood, R. A. Khera, B. Eliasson, A comparative study of DFT calculated and experimental UV/Visible spectra for thirty carboline and carbazole based compounds. J. Mol. Struct. 1149 , 282–298 (2017) J. M. Jean, 2-Aminopurine fluorescence quenching and lifetimes: Role of base stacking. Proceedings of the National Academy of Sciences. 98 (1), 37–41(2000). doi:10.1073/pnas.011442198 J. Liang, S. Matsika, Pathways for Fluorescence Quenching in 2-Aminopurine π-Stacked with Pyrimidine Nucleobases. J. Am. Chem. Soc. 133 (17), 6799–6808 (2011) M. Kasha, Characterization of electronic transitions in complex molecules. Discuss. Faraday Soc. 9 , 14-19 (1950) Additional Declarations No competing interests reported. Supplementary Files Table1.docx Table2.docx Supplementarydata.docx Cite Share Download PDF Status: Published Journal Publication published 07 Jul, 2025 Read the published version in Journal of Inorganic and Organometallic Polymers and Materials → Version 1 posted Editorial decision: Revision requested 13 May, 2025 Reviews received at journal 11 May, 2025 Reviews received at journal 11 May, 2025 Reviews received at journal 10 May, 2025 Reviewers agreed at journal 03 May, 2025 Reviewers agreed at journal 02 May, 2025 Reviewers agreed at journal 01 May, 2025 Reviewers invited by journal 30 Apr, 2025 Editor assigned by journal 30 Apr, 2025 Submission checks completed at journal 30 Apr, 2025 First submitted to journal 30 Apr, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6562459","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":451369857,"identity":"431a30e8-a08c-4fd2-b2c6-bc0da84f67bf","order_by":0,"name":"Tanin Nanok","email":"","orcid":"","institution":"Kasetsart University","correspondingAuthor":false,"prefix":"","firstName":"Tanin","middleName":"","lastName":"Nanok","suffix":""},{"id":451369858,"identity":"4232ecbd-4e08-4337-ac23-5daa62545be7","order_by":1,"name":"Tontrakarn Pongpai","email":"","orcid":"","institution":"Kasetsart University","correspondingAuthor":false,"prefix":"","firstName":"Tontrakarn","middleName":"","lastName":"Pongpai","suffix":""},{"id":451369860,"identity":"fcd9d09e-cc30-4409-9619-4b18407a393b","order_by":2,"name":"Kittinan Ketsrisung","email":"","orcid":"","institution":"Kasetsart University","correspondingAuthor":false,"prefix":"","firstName":"Kittinan","middleName":"","lastName":"Ketsrisung","suffix":""},{"id":451369861,"identity":"c22956e0-8066-4823-a1dd-1802955ca2bf","order_by":3,"name":"Jiraporn Singhophon","email":"","orcid":"","institution":"Kasetsart University","correspondingAuthor":false,"prefix":"","firstName":"Jiraporn","middleName":"","lastName":"Singhophon","suffix":""},{"id":451369862,"identity":"5b635586-59e7-481b-a745-957a2ad72eed","order_by":4,"name":"Kittipong Chainok","email":"","orcid":"","institution":"Thammasat University","correspondingAuthor":false,"prefix":"","firstName":"Kittipong","middleName":"","lastName":"Chainok","suffix":""},{"id":451369863,"identity":"a2fc50b7-f1dc-4aa3-9d81-0e4579adfcc8","order_by":5,"name":"Tanwawan Duangthongyou","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAvUlEQVRIiWNgGAWjYBAC9gYGhgMMDMxyElCBBIJaeIDqDxxgYDaGajEgTgvQGubEGcRr4T/88PDHNuv0mTMSGD/8YPiTR1iLRJrBgYNt6bmzJRKYJXsYDIoJarGX4GE4cHDb4dx5EgkM0kCHJTYQdtgZsJZ0OaAtv4nTwpAD1pIgLZHARqQtIL+c/ZduOLPnYZtlj4ExMQ47/PhDxRlreYnjyYdv/KiQI6wFCTACFRuQoH4UjIJRMApGAW4AAPjhPOMl9daeAAAAAElFTkSuQmCC","orcid":"","institution":"Kasetsart University","correspondingAuthor":true,"prefix":"","firstName":"Tanwawan","middleName":"","lastName":"Duangthongyou","suffix":""}],"badges":[],"createdAt":"2025-04-30 07:53:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6562459/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6562459/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10904-025-03928-9","type":"published","date":"2025-07-07T15:57:18+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":82299286,"identity":"3d4bc084-0f97-49c8-8cfb-15738fbd7b2e","added_by":"auto","created_at":"2025-05-08 20:33:25","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":219777,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Asymmetric unit of CuAS; (b) Coordination environment around Cu(II) ions; (c) Dinuclear node of Cu(II) ions.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/68af4384f243b5422c506cb1.png"},{"id":82300205,"identity":"77e7ebb0-5218-4bbc-8c25-e28f4c54d4e6","added_by":"auto","created_at":"2025-05-08 20:41:25","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1082348,"visible":true,"origin":"","legend":"\u003cp\u003ePacking view of the CuAS crystal structure: (a) along a-axis, (b) along b-axis, (c) along c-axis.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/fdaa14b783d24d03afac7595.png"},{"id":82299285,"identity":"1601bd0d-e269-4c9a-a9de-7c65e25c4729","added_by":"auto","created_at":"2025-05-08 20:33:25","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":52264,"visible":true,"origin":"","legend":"\u003cp\u003ePowder XRD pattern of CuAS.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/213348613e353616f19f2f30.png"},{"id":82299292,"identity":"770ac5c0-b001-49c9-bf66-1dc7df162acf","added_by":"auto","created_at":"2025-05-08 20:33:25","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":394879,"visible":true,"origin":"","legend":"\u003cp\u003eTGA curve of CuAS.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/aae2b513638f5e4320c235cc.png"},{"id":82299291,"identity":"087b6813-6516-4db3-a9ea-b88d2c2f380f","added_by":"auto","created_at":"2025-05-08 20:33:25","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":893963,"visible":true,"origin":"","legend":"\u003cp\u003eUV-Vis spectra of the CuAS (a) in the solid state (b) solid dispersion in the MeOH\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/09c8d17841819d7604f872bd.png"},{"id":82300682,"identity":"f7c1bd84-b837-4c95-8fa4-5984114cc57b","added_by":"auto","created_at":"2025-05-08 20:49:25","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":236025,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Solid state fluorescence spectra of CuAS, adenine and succinic acid ligands. (b) Spectra of solid CuAS disperse in MeOH and adenine in MeOH solution.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/b5af77820dfbdba54979b575.png"},{"id":82301408,"identity":"f88e987e-308f-49f9-951e-d88159a3bbc0","added_by":"auto","created_at":"2025-05-08 20:57:25","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":305516,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Fluorescence emission spectra of CuAS in 0.5 mM MeOH solutions containing different antibiotics. (b) Relative fluorescence quenching percentages of CuAS in the presence of various antibiotics.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/b7f7f3864838a5ba5b8d115a.png"},{"id":82299294,"identity":"ff42c756-a039-4697-a625-562e22489110","added_by":"auto","created_at":"2025-05-08 20:33:25","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":517923,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Photographs showing fluorescence of CuAS suspensions under 365 nm UV irradiation in MeOH solutions with different antibiotics. (b) Emission intensity changes after addition of nitrofurazone (NFZ) to the antibiotic-containing CuAS suspensions, indicating selectivity toward NFZ.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/bd1eff6a2e5960e3796ae4b2.png"},{"id":82300210,"identity":"04090f8a-553a-4d0d-99d7-f287e1b71540","added_by":"auto","created_at":"2025-05-08 20:41:25","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":503457,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Fluorescence response spectra of CuAS with varying concentrations of NFZ in MeOH. (b) Stern–Volmer plot for fluorescence quenching of CuAS by NFZ. (c) Fluorescence response spectra of CuAS with varying concentrations of NFT in MeOH.\u003c/p\u003e\n\u003cp\u003e(d) Stern–Volmer plot for fluorescence quenching of CuAS by NFT.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/0ca1e012c6b27450189da5e7.png"},{"id":82301532,"identity":"31476b88-64a6-4c62-8445-c6a14270eea2","added_by":"auto","created_at":"2025-05-08 21:05:25","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":220493,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Spectral overlap between the UV–Vis absorption spectra of various antibiotics and the fluorescence emission spectrum of CuAS in methanol. (b) HOMO and LUMO energy levels of the succinic acid ligand and selected antibiotics.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/1a0150c551fda186c01fc490.png"},{"id":82300212,"identity":"eb1992fb-d866-4b46-bc1d-19f42afc05a2","added_by":"auto","created_at":"2025-05-08 20:41:25","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":327112,"visible":true,"origin":"","legend":"\u003cp\u003eJablonski diagrams of adenine, NFZ, and the adenine-NFZ complex obtained from TDDFT [B3LYP/6-31G(d,p)]. Oscillator strengths (in parentheses) and dominant one-electron orbital contributions are provided, along with key orbital amplitudes.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/008f2fe98f4f369148eb6f83.png"},{"id":82300213,"identity":"c9a25d3b-6b87-424d-803b-66be366f3227","added_by":"auto","created_at":"2025-05-08 20:41:25","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":314259,"visible":true,"origin":"","legend":"\u003cp\u003eJablonski diagrams of adenine, NFT, and the adenine-NFT complex obtained from TDDFT [B3LYP/6-31G(d,p)]. Oscillator strengths (in parentheses) and dominant one-electron orbital contributions are provided, along with key orbital amplitudes.\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/5381c5d2188f361bbdb52eb0.png"},{"id":82299304,"identity":"6334fba8-be22-4921-8638-bc138028f822","added_by":"auto","created_at":"2025-05-08 20:33:25","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":298289,"visible":true,"origin":"","legend":"\u003cp\u003eJablonski diagrams of adenine, DTZ, and the adenine-DTZ complex obtained from TDDFT [B3LYP/6-31G(d,p)]. Oscillator strengths (in parentheses) and dominant one-electron orbital contributions are provided, along with key orbital amplitudes.\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/4de0efede77f624a8fa5b9a3.png"},{"id":82299303,"identity":"23660684-09f8-4794-873a-ca4393f1a56a","added_by":"auto","created_at":"2025-05-08 20:33:25","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":310247,"visible":true,"origin":"","legend":"\u003cp\u003eJablonski diagrams of adenine, MDZ, and the adenine-MDZ complex obtained from TDDFT [B3LYP/6-31G(d,p)]. Oscillator strengths (in parentheses) and dominant one-electron orbital contributions are provided, along with key orbital amplitudes.\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/cd420faa64319af19d6438da.png"},{"id":82299305,"identity":"ef344bda-4543-4d3b-9899-4cb4219d6b0f","added_by":"auto","created_at":"2025-05-08 20:33:25","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":294150,"visible":true,"origin":"","legend":"\u003cp\u003eJablonski diagrams of adenine, CAP, and the adenine-CAP complex obtained from TDDFT [B3LYP/6-31G(d,p)]. Oscillator strengths (in parentheses) and dominant one-electron orbital contributions are provided, along with key orbital amplitudes.\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/e7694a24999ea2fed1fef5c6.png"},{"id":82299302,"identity":"3fda4287-1983-4f0e-a79e-e011f42f3bc0","added_by":"auto","created_at":"2025-05-08 20:33:25","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":306357,"visible":true,"origin":"","legend":"\u003cp\u003eJablonski diagrams of adenine, SDZ, and the adenine-SDZ complex obtained from TDDFT [B3LYP/6-31G(d,p)]. Oscillator strengths (in parentheses) and dominant one-electron orbital contributions are provided, along with key orbital amplitudes.\u003c/p\u003e","description":"","filename":"16.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/b16ade5bd09e78483de20c96.png"},{"id":82299299,"identity":"9ae4f109-24cb-48ac-8292-7e07155ebf43","added_by":"auto","created_at":"2025-05-08 20:33:25","extension":"png","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":348039,"visible":true,"origin":"","legend":"\u003cp\u003eJablonski diagrams of adenine, PCL, and the adenine-PCL complex obtained from TDDFT [B3LYP/6-31G(d,p)]. Oscillator strengths (in parentheses) and dominant one-electron orbital contributions are provided, along with key orbital amplitudes.\u003c/p\u003e","description":"","filename":"17.png","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/20952b92b460b66233db252a.png"},{"id":86699353,"identity":"afa7748a-7ac9-4e9e-a507-19c03c0cb496","added_by":"auto","created_at":"2025-07-14 16:08:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6265268,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/06679c10-2bb8-4092-a179-813d80cffbd7.pdf"},{"id":82299293,"identity":"0cda686a-7a8d-4eab-b807-55f5e3d50b6e","added_by":"auto","created_at":"2025-05-08 20:33:25","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":12855,"visible":true,"origin":"","legend":"","description":"","filename":"Table1.docx","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/f35958eab4ccd0923a8eef98.docx"},{"id":82300681,"identity":"c0054ea1-1ccf-4ebf-9fb9-0577be7122f4","added_by":"auto","created_at":"2025-05-08 20:49:25","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":13069,"visible":true,"origin":"","legend":"","description":"","filename":"Table2.docx","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/972e5a4d80eea7d1e85e0fe3.docx"},{"id":82300207,"identity":"a546c139-1b76-4719-8973-15c4e93160a5","added_by":"auto","created_at":"2025-05-08 20:41:25","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":14235,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarydata.docx","url":"https://assets-eu.researchsquare.com/files/rs-6562459/v1/4de1089d56ab296281f10216.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Structural and Mechanistic Insights into a Cu-Adenine MOF for Selective Fluorescence Sensing of Antibiotics: Experimental and TDDFT Approaches","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eTechnological advancements have significantly improved modern life, yet they often bring unintended consequences for human health and the environment. In response, there is growing interest in developing advanced sensing materials that can detect environmental pollutants and pharmaceutical residues with high sensitivity and selectivity. Among these, metal–organic frameworks (MOFs), highly crystalline materials composed of metal ions or clusters coordinated to organic ligands, have emerged as versatile platforms. Their modular architecture, combined with a high surface area, adjustable pore dimensions, and robust thermal and chemical stability enable a wide range of applications including catalysis [1,2], gas storage [3], drug delivery [4], chemical sensing [5,6], water purification [7], and environmental remediation [8].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA particularly promising subclass of these materials is luminescent MOFs (LMOFs), which exhibit fluorescence properties that can be harnessed for chemical sensing. By judiciously selecting metal centers and π-conjugated organic linkers, researchers can fine-tune the luminescence behavior of LMOFs [9–15]. Emission in LMOFs may originate from linker-centered fluorescence, metal-centered transitions, charge transfer, or interactions with guest molecules [16]. The strategic design of LMOFs enables sensitive detection of target analytes through mechanisms such as fluorescence enhancement or quenching.\u003c/p\u003e\n\u003cp\u003eCopper-based luminescent MOFs (LMOFs) have attracted considerable attention as sensitive fluorescence-based sensors due to their rich coordination chemistry, tunable luminescent properties, and, in many cases, favorable biocompatibility and low toxicity [17–20]. Functionalization with ligands bearing electron-rich and hydrogen-bond-donating groups further enhances their sensing capabilities. These frameworks are particularly effective for detecting electron-deficient analytes such as nitrofuran antibiotics, including nitrofurazone (NFZ) and nitrofurantoin (NFT), which are frequently used in veterinary medicine [21–23] but pose environmental and food safety risks if not properly monitored.\u003c/p\u003e\n\u003cp\u003eIn this study, we report the synthesis of a Cu-based luminescent MOF (CuAS) constructed from succinic acid and adenine. Succinic acid provides structural flexibility, while adenine contributes π-electron density and functional groups that facilitate strong interactions with antibiotic analytes [24–30]. The resulting framework exhibits pronounced fluorescence quenching upon exposure to nitrofuran antibiotics. To elucidate the underlying sensing mechanism, we investigated two key quenching pathways: Förster resonance energy transfer (FRET)\u0026nbsp;[31] and photoinduced electron transfer (PET) [32]. Spectral overlap analysis suggested limited contribution from FRET, while electronic structure calculations via time-dependent density functional theory (TDDFT) indicated that PET, facilitated by LUMO level alignment between the MOF and antibiotic molecules, is the dominant mechanism. Furthermore, molecular orbital mixing and internal conversion effects were considered to explain variations in oscillator strengths observed in π-stacked complexes.\u003c/p\u003e\n\u003cp\u003eBy combining experimental fluorescence data with theoretical calculations, this study provides detailed insight into the fluorescence quenching mechanisms of Cu-adenine MOFs. Our findings contribute to the rational design of MOF-based sensors for selective antibiotic detection, with potential applications in environmental and food safety monitoring.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cp\u003e2.1 Materials and methods\u003c/p\u003e\n\u003cp\u003eAll chemicals were purchased from commercial suppliers and used without further purification. Powder X-ray diffraction (PXRD) data were collected using a Bruker D8 Advance diffractometer with Cu-Kα radiation (λ = 1.54060 Å). The FT-IR spectrum was recorded on a Bruker Vertex 70 spectrophotometer in the range of 400–4000 cm⁻¹ using attenuated total reflectance (ATR) mode. Thermogravimetric analysis (TGA) was performed on a PerkinElmer TGA7 with a heating rate of 10 °C per minute under a nitrogen atmosphere. UV-Vis absorption spectra were measured in the range of 190–700 nm using a Shimadzu UV-2600 spectrophotometer for solid samples, and a PerkinElmer Lambda 365 for solid dispersions in methanol. Fluorescence emission spectra were recorded using a Horiba Scientific FluoroMax-4P and a PerkinElmer FL 8500 fluorescence spectrophotometer. Elemental analyses (C, H, and N) were performed using a LECO CHNS-932 elemental analyzer.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e2.2 X-ray Crystallography\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e Crystallographic data were collected on a Bruker D8 QUEST CMOS PHOTON II diffractometer using graphite-monochromated Mo-Kα radiation. Absorption corrections were applied using a multi-scan method with SADABS 2016/2 [33]. The structure was solved using OLEX2 1.3 [34] and refined with the XL refinement package [35] via Gauss-Newton minimization. Non-hydrogen atoms were refined anisotropically. Hydrogen atoms were treated using a combination of independent and constrained refinements. All atoms of the adenine molecule were found to be disordered and were refined with two occupancy states in the asymmetric unit. Crystallographic data are summarized in Table 1. \u0026nbsp;Selected bond lengths and angles are provided in Tables S1and S2.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e Crystallographic data for [Cu(Ade)(succinate)]ₙ\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"555\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eFormula\u003c/p\u003e\n \u003cp\u003eEmpirical formula\u003c/p\u003e\n \u003cp\u003eFormula weight\u003c/p\u003e\n \u003cp\u003eTemperature (K)\u003c/p\u003e\n \u003cp\u003eCrystal system\u003c/p\u003e\n \u003cp\u003eSpace group\u003c/p\u003e\n \u003cp\u003ea (Å)\u003c/p\u003e\n \u003cp\u003eb (Å)\u003c/p\u003e\n \u003cp\u003ec (Å)\u003c/p\u003e\n \u003cp\u003eα (º)\u003c/p\u003e\n \u003cp\u003eβ (º)\u003c/p\u003e\n \u003cp\u003eγ (º)\u003c/p\u003e\n \u003cp\u003eVolume (Å\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\n \u003cp\u003eZ\u003c/p\u003e\n \u003cp\u003eDc (g cm\u003csup\u003e-3\u003c/sup\u003e)\u003c/p\u003e\n \u003cp\u003eF(000)\u003c/p\u003e\n \u003cp\u003eCrystal size (mm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\n \u003cp\u003eRadiation source\u003c/p\u003e\n \u003cp\u003eWavelength\u003c/p\u003e\n \u003cp\u003e2ϴ range for data collection (\u003csup\u003eo\u003c/sup\u003e)\u003c/p\u003e\n \u003cp\u003eIndex ranges\u003c/p\u003e\n \u003cp\u003eNo. of reflections collected\u003c/p\u003e\n \u003cp\u003eΔρ\u003csub\u003emax\u003c/sub\u003e, Δρ\u003csub\u003emin\u003c/sub\u003e (e Å\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\n \u003cp\u003eR1a/wR2b [I \u0026gt; 2σ(I)]\u003c/p\u003e\n \u003cp\u003eR1a/wR2b (all)\u003c/p\u003e\n \u003cp\u003eGoodness-of-fit on F\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e[Cu(Ade)(succinate)]\u003csub\u003en\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003eC\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eCuN\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e255.71\u003c/p\u003e\n \u003cp\u003e283-303\u003c/p\u003e\n \u003cp\u003eI 41/a (88)\u003c/p\u003e\n \u003cp\u003etetragonal\u003c/p\u003e\n \u003cp\u003e15.7506(4)\u003c/p\u003e\n \u003cp\u003e15.7506(4)\u003c/p\u003e\n \u003cp\u003e22.4819(10)\u003c/p\u003e\n \u003cp\u003e90\u003c/p\u003e\n \u003cp\u003e90\u003c/p\u003e\n \u003cp\u003e90\u003c/p\u003e\n \u003cp\u003e5577.34\u003c/p\u003e\n \u003cp\u003e16\u003c/p\u003e\n \u003cp\u003e1.218\u003c/p\u003e\n \u003cp\u003e2048\u003c/p\u003e\n \u003cp\u003e0.22 x0.20 x 018\u003c/p\u003e\n \u003cp\u003eMo Kα\u003c/p\u003e\n \u003cp\u003e0.71073\u003c/p\u003e\n \u003cp\u003e5.17 to 54.25\u003c/p\u003e\n \u003cp\u003e-19 ≤ h ≤ 20, -20 ≤ k ≤ 20, -28 ≤ l ≤ 28\u003c/p\u003e\n \u003cp\u003e57263\u003c/p\u003e\n \u003cp\u003e0.536, -0.38\u003c/p\u003e\n \u003cp\u003e0.0404/0.1080\u003c/p\u003e\n \u003cp\u003e0.0508/0.1139\u003c/p\u003e\n \u003cp\u003e1.053\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e2.3 Synthesis of [Cu(Ade)(succinate)]ₙ (CuAS)\u003c/p\u003e\n\u003cp\u003e The new Cu-MOF was synthesized via a hydrothermal method. Briefly, copper(II) nitrate (0.2 mmol, 0.0483 g), adenine (0.2 mmol, 0.0237 g), and succinic acid (0.2 mmol, 0.0236 g) were dissolved in a DMF:H₂O mixture (1:1, 10 mL) and stirred for 5 minutes. Subsequently, 1 mL of 1 M nitric acid was added. Once the solution became homogeneous, it was transferred to a Teflon-lined autoclave and heated at 130 °C for 24 hours. After slow cooling to room temperature, blue crystals were obtained. The crystals were collected, washed three times with 3 mL of DMF, and dried under ambient conditions. Anal.(%) calcd for C\u003csub\u003e7\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eCuN\u003csub\u003e5\u003c/sub\u003eO.2(H\u003csub\u003e2\u003c/sub\u003eO): C, 30.9%; H, 3.43%; N, 20.03%; found: C, 32.00%; H, 4.03%; N, 20.61%. IR (ATR, cm\u003csup\u003e-1\u003c/sup\u003e): 3332(m), 3194(m), 2937(w), 1651(s), 1577(s), 1541(m), 1453(m), 1394(s), 1295(m), 1270(m), 1201(s), 1138(s), 1093(s), 982(m), 889(m), 790(s), 741(s), 633(s), 578(s). \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e2.4 Fluorescence Properties\u003c/p\u003e\n\u003cp\u003e he fluorescence properties of CuAS were investigated both in the solid state and as a dispersion in MeOH at ambient temperature. Solid-state fluorescence spectra were recorded using a Horiba Scientific FluoroMax-4P spectrophotometer, while measurements of CuAS dispersed in MeOH were performed using a PerkinElmer FL 8500 fluorescence spectrophotometer.\u003c/p\u003e\n\u003cp\u003e2.5 Antibiotic Sensing Study\u003c/p\u003e\n\u003cp\u003e 2.5.1 \u003cem\u003eSelectivity:\u003c/em\u003e To evaluate the potential of CuAS as a sensor for antibiotics, 5 mg of the MOF powder was dispersed in 2.5 mL of MeOH and sonicated for 30 minutes. Then, 0.5 mL of a 0.5 mM MeOH solution of each antibiotic, namely nitrofurazone (NFZ), nitrofurantoin (NFT), 1,2-dimethyl-5-nitroimidazole (DTZ), penicillin (PCL), chloramphenicol (CAP), metronidazole (MDZ), and sulfadiazine (SDZ), was added to the suspension. The fluorescence emission intensity of each mixture was measured. To visually demonstrate selectivity under UV light, 5 mg of CuAS powder was dispersed in 3.0 mL of 0.5 mM MeOH solutions of the individual antibiotics and incubated for 30 minutes. The fluorescence under UV irradiation was then observed. After that, 3.0 mL of 0.5 mM NFZ solution was added to each dispersion and the mixtures were sonicated for 30 minutes. The fluorescence under UV light was observed again to assess any changes.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e \u0026nbsp;2.5.2 \u003cem\u003eSensitivity:\u003c/em\u003e To investigate the sensitivity of CuAS toward antibiotic detection, fluorescence titration experiments were conducted. A 5 mg portion of CuAS was dispersed in 3 mL of MeOH via sonication for 30 minutes. Increasing amounts of a 0.5 mM solution of NFZ (or NFT) were gradually added to the CuAS dispersion. After each addition, the mixture was sonicated to ensure proper mixing, and the fluorescence intensity was measured to monitor the response.\u003c/p\u003e\n\u003cp\u003e2.6 DFT/TDDFT calculations\u003c/p\u003e\n\u003cp\u003eTo investigate the mechanism of fluorescence quenching in CuAS by antibiotic molecules, time-dependent density functional theory (TDDFT) calculations [36] were performed using the Gaussian09 program [37]. Adenine was chosen to represent the fluorescent moiety of CuAS, as its fluorescence mainly arises from intraligand electronic transitions. Ground-state geometries of adenine, the antibiotics, and their corresponding adenine–antibiotic complexes in methanol were optimized at the B3LYP/6-31G(d,p) level of theory [38–41], including Grimme’s D3 dispersion correction with Becke–Johnson damping (D3BJ) [42,43]. Solvent effects were modeled using the polarizable continuum model (PCM) [44]. Ten vertical excitations were computed via TDDFT, and the frontier molecular orbitals involved in excitation and emission processes were analyzed based on the optimized geometries. These calculations provided insight into the electronic interactions responsible for fluorescence quenching in the CuAS–antibiotic complexes.\u003c/p\u003e"},{"header":"3. Results and discussion","content":"\u003cp\u003e3.1 Crystal Structure Descriptions\u003c/p\u003e\n\u003cp\u003eThe asymmetric unit of CuAS consists of one adenine molecule and half of a succinate ligand (Fig. 1a). The succinate ligand is centered on a C₂ axis, and a center of symmetry is located between two Cu(II) ions. Upon applying these symmetry operations, the full 3D framework structure is generated (Fig. 1b). Each Cu(II) ion adopts a distorted square pyramidal geometry, coordinated by two nitrogen atoms from two adenine ligands and two oxygen atoms from two succinate ligands in the equatorial plane, with one nitrogen atom from adenine occupying the axial position. Two adjacent Cu(II) ions are bridged by both succinate and adenine ligands, forming dinuclear nodes (Fig. 1c).\u003c/p\u003e\n\u003cp\u003eEach dinuclear node is further connected through one bridging succinate and two bridging adenine ligands. The succinate ligand adopts a \u0026mu;₄-\u0026kappa;\u0026sup1;:\u0026kappa;\u0026sup1;:\u0026kappa;\u0026sup1;:\u0026kappa;\u0026sup1; coordination mode and exhibits an anti\u0026ndash;anti conformation with a torsion angle of 135.12\u0026deg;. The adenine ligands coordinate through a \u0026mu;₃-\u0026kappa;\u0026sup1;:\u0026kappa;\u0026sup1;:\u0026kappa;\u0026sup1; mode in two alternating styles: (1) terminal bridging to monodentate and (2) monodentate to terminal bridging. This alternating coordination leads to a perpendicular arrangement of adjacent adenine rings. As a result, the network extends along two diagonal directions defined by the \u003cem\u003eac\u003c/em\u003e and \u003cem\u003ebc\u003c/em\u003e planes, while the succinate ligands propagate along the \u003cem\u003ea\u003c/em\u003e- and \u003cem\u003eb\u003c/em\u003e-axes (Fig. 2a, 2b). The combination of these linkages generates a three-dimensional framework with channels oriented along the \u003cem\u003ea\u003c/em\u003e- and \u003cem\u003eb\u003c/em\u003e-axes. The pore dimensions are approximately 8.77 \u0026times; 11.82 \u0026Aring;, with free amino groups from the adenine ligands pointing into the cavities. Viewed along the \u003cem\u003ec\u003c/em\u003e-axis, no significant channels are observed (Fig. 2c).\u003c/p\u003e\n\u003cp\u003e3.2 Powder XRD Patterns and Thermogravimetric Analysis\u003c/p\u003e\n\u003cp\u003eThe phase purity of the synthesized CuAS was confirmed by powder X-ray diffraction (PXRD). The experimental PXRD pattern matches closely with the simulated pattern derived from single-crystal data (Fig. 3), indicating that the bulk material is phase-pure. Thermogravimetric analysis (TGA) was used to investigate the thermal stability of CuAS (Fig. 4). The TGA curve shows an initial weight loss of 9.0% (calculated 10.3%) from room temperature to 170 \u0026deg;C, attributed to the removal of adsorbed moisture. A subsequent mass loss of 32.0% (calculated 33.19%) occurs between 180\u0026ndash;420 \u0026deg;C, corresponding to the decomposition of the succinate ligand. A final mass loss of 38.0% (calculated 38.66%) between 420\u0026ndash;700 \u0026deg;C is associated with the decomposition of the adenine ligands, leaving CuO as the final residue.\u003c/p\u003e\n\u003cp\u003e3.3 UV-Visible Spectroscopy\u003c/p\u003e\n\u003cp\u003eThe UV\u0026ndash;visible spectra of CuAS were measured both in the solid state and as a powder dispersed in methanol (MeOH). In the solid state, CuAS exhibits a broad absorption band centered around 350 nm (Fig. 5a). In contrast, when dispersed in MeOH, CuAS shows an absorption maximum (l\u003csub\u003emax\u003c/sub\u003e) at approximately 260 nm (Fig. 5b), similar to that of free adenine. These results suggest that the optical absorption of CuAS in MeOH is primarily derived from the adenine ligand.\u003c/p\u003e\n\u003cp\u003e3.4 Fluorescence Properties of CuAS\u003c/p\u003e\n\u003cp\u003eThe solid-state fluorescence properties of succinic acid, adenine, and CuAS MOF were systematically investigated, as presented in Fig. 6a. Upon excitation at 330 nm, succinic acid and CuAS exhibit emission maxima at 395 nm and 440 nm, respectively. In contrast, solid-state adenine displays emission bands centered at 380 nm and 435 nm when excited at 250 nm.\u003c/p\u003e\n\u003cp\u003eTo further elucidate the photophysical behavior, the emission spectra of adenine in MeOH solution and CuAS MOF dispersed in MeOH were recorded at room temperature (Fig. 6b). Both adenine and CuAS exhibit comparable emission features with maxima at 405 nm and 430\u0026ndash;425 nm under excitation at 350 nm, indicating similar excited-state properties in the dispersed phase.\u003c/p\u003e\n\u003cp\u003eThese findings strongly suggest that the fluorescence of CuAS MOF predominantly arises from intraligand transitions associated with the adenine linker. The slight red-shifts observed relative to the solid-state spectra can be ascribed to solvent effects and excitation-wavelength-dependent relaxation processes.\u003c/p\u003e\n\u003cp\u003e3.5 Detection of Antibiotics: Selectivity and Sensitivity\u003c/p\u003e\n\u003cp\u003e3.5.1 Selectivity\u003c/p\u003e\n\u003cp\u003eAs shown in Fig. 7a, the photoluminescence emission of CuAS exhibited different intensities at two emission bands (405 nm and 425 nm), depending on the specific antibiotic present in the methanol (MeOH) solution. Notably, the fluorescence intensity of CuAS decreased significantly in the presence of nitrofurazone (NFZ) and nitrofurantoin (NFT), with quenching efficiencies of approximately 98% for both antibiotics (Fig. 7b). This indicates that NFZ and NFT induce the most significant quenching effect among the tested antibiotics.\u003c/p\u003e\n\u003cp\u003eFurthermore, the fluorescence responses of CuAS suspensions under 365 nm UV irradiation were visually observed (Fig. 8a), again confirming the substantial quenching effect caused by NFZ and NFT. To further evaluate selectivity, additional nitrofurazone was introduced into solutions already containing other antibiotics. After NFZ addition, the emission intensity of all suspensions decreased markedly (Fig. 8b), demonstrating that CuAS exhibits a selective fluorescence response towards nitrofurazone.\u003c/p\u003e\n\u003cp\u003e3.5.2 Sensitivity\u003c/p\u003e\n\u003cp\u003eTo investigate the sensitivity of CuAS towards NFZ and NFT, the emission intensity at 405 nm was measured in the presence of varying concentrations of these antibiotics. As shown in Fig. 9a and 9c, the fluorescence intensity of CuAS gradually decreased with increasing concentrations of NFZ and NFT, respectively. The quenching behavior was further analyzed using the Stern\u0026ndash;Volmer (S\u0026ndash;V) equation. The resulting S\u0026ndash;V plots (Fig. 9b and 9d) exhibited a good linear relationship. The Stern\u0026ndash;Volmer quenching constants (K\u003csub\u003esv\u003c/sub\u003e) were calculated to be 5.98 \u0026times; 10⁴ M⁻\u0026sup1; for NFZ and 5.88 \u0026times; 10⁴ M⁻\u0026sup1; for NFT. The limits of detection (LOD) were determined to be 0.1357 ppm for NFZ and 0.1099 ppm for NFT. A comparison of the K\u003csub\u003esv\u0026nbsp;\u003c/sub\u003evalues with previously reported MOF-based sensors is provided in Table 2. The results highlight that CuAS exhibits competitive, if not superior, sensitivity for detecting NFZ and NFT relative to other reported complexes\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2.\u003c/strong\u003e Comparison of Stern\u0026ndash;Volmer quenching constants (Ksv) for NFZ and NFT detection by different MOF-based fluorescent sensors.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 45.5696%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSensor\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 19.5298%;\"\u003e\n \u003cp\u003eK\u003csub\u003eSV\u003c/sub\u003e (M\u003csup\u003e-1\u003c/sup\u003e) for NFZ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16.2749%;\"\u003e\n \u003cp\u003eK\u003csub\u003eSV\u003c/sub\u003e (M\u003csup\u003e-1\u003c/sup\u003e) for NFT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18.6257%;\"\u003e\n \u003cp\u003eReference\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 45.5696%;\"\u003e\n \u003cp\u003e{[Zn\u003csub\u003e2\u003c/sub\u003e(bcob)(OH)(H\u003csub\u003e2\u003c/sub\u003eO)]\u0026bull;DMA}\u003csub\u003en\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.5298%;\"\u003e\n \u003cp\u003e2.50 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.2749%;\"\u003e\n \u003cp\u003e2.26 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18.6257%;\"\u003e\n \u003cp\u003e[45]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 45.5696%;\"\u003e\n \u003cp\u003e[Zn(DCPP)(H\u003csub\u003e2\u003c/sub\u003eO)]\u0026bull;(DMF)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.5298%;\"\u003e\n \u003cp\u003e4.73 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.2749%;\"\u003e\n \u003cp\u003e6.42 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18.6257%;\"\u003e\n \u003cp\u003e[46]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 45.5696%;\"\u003e\n \u003cp\u003eCu\u003csub\u003e0.1\u003c/sub\u003e/{[Zn(L)]\u0026bull;CH3CN}\u003csub\u003en\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.5298%;\"\u003e\n \u003cp\u003e4.85 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.2749%;\"\u003e\n \u003cp\u003e5.27 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18.6257%;\"\u003e\n \u003cp\u003e[47]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 45.5696%;\"\u003e\n \u003cp\u003e[Zn(TTDPa)(bodca)]\u0026middot;H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.5298%;\"\u003e\n \u003cp\u003e6.76 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.2749%;\"\u003e\n \u003cp\u003e5.94 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18.6257%;\"\u003e\n \u003cp\u003e[48]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 45.5696%;\"\u003e\n \u003cp\u003e[Zn\u003csub\u003e4\u003c/sub\u003e(ad)\u003csub\u003e3\u003c/sub\u003e(BPTC)(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e]\u0026bull;0.75ad\u003cbr\u003e\u0026bull;0.25NO\u003csub\u003e3\u003c/sub\u003e\u0026bull;2.5DMF\u0026bull;2.5H\u003csub\u003e2\u003c/sub\u003eO Film\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.5298%;\"\u003e\n \u003cp\u003e4.35 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.2749%;\"\u003e\n \u003cp\u003e3.14 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18.6257%;\"\u003e\n \u003cp\u003e[49]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 45.5696%;\"\u003e\n \u003cp\u003eCuAS MOF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.5298%;\"\u003e\n \u003cp\u003e5.98 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.2749%;\"\u003e\n \u003cp\u003e5.88 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.6257%;\"\u003e\n \u003cp\u003eThis work\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e3.6 Mechanism of Sensing\u003c/p\u003e\n\u003cp\u003eThe fluorescence quenching of CuAS toward antibiotics is attributed to two possible mechanisms: F\u0026ouml;rster resonance energy transfer (FRET) and photoinduced electron transfer (PET).\u003c/p\u003e\n\u003cp\u003e3.6.1 F\u0026ouml;rster Resonance Energy Transfer (FRET)\u003c/p\u003e\n\u003cp\u003eTo investigate the possibility of FRET, the UV\u0026ndash;Vis absorption spectra of the antibiotics were compared with the fluorescence emission spectrum of CuAS (Fig. 10a). Only NFZ and NFT exhibit partial spectral overlap with the emission of CuAS, while negligible overlap is observed for the other antibiotics. Although this suggests that energy transfer from CuAS to NFZ and NFT may contribute to the quenching, the limited extent of overlap indicates that FRET is not the dominant quenching mechanism.\u003c/p\u003e\n\u003cp\u003e3.6.2 Photoinduced Electron Transfer (PET)\u003c/p\u003e\n\u003cp\u003eAlternatively, fluorescence quenching could arise from photoinduced electron transfer. The energy levels of the frontier orbitals were analyzed to assess the feasibility of this process (Fig. 10b). The LUMO energy of the adenine ligand in CuAS is higher than those of the antibiotics, with the exception of PCL and SDZ which are fairly close to it. This alignment enables electron transfer from the excited state of CuAS to the LUMO levels of the antibiotics. Notably, NFZ and NFT possess the lowest LUMO energies among the tested antibiotics, facilitating more efficient electron transfer. This observation is consistent with the fluorescence quenching results, where NFZ and NFT exhibited the highest quenching efficiencies.\u003c/p\u003e\n\u003cp\u003eBased on the above analysis, PET is proposed as the primary mechanism responsible for the fluorescence quenching observed in CuAS suspensions, while FRET likely plays a minor role.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBased on the above discussion, fluorescence emission is attributed to intraligand transitions within adenine, while fluorescence quenching primarily arises from photoinduced electron transfer (PET) processes. To gain deeper insights into these mechanisms, density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were performed at the B3LYP/6-31G(d,p) level of theory. All calculations employed the Polarizable Continuum Model (PCM) to account for solvent effects, enhancing the reliability of the computed excitation properties.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFig. 11 presents the computed Jablonski diagram for adenine excitation. The calculated oscillator strength (\u0026brvbar;) of 0.2197 strongly supports that the primary excitation corresponds to a transition from the ground singlet state (S₀) to the first excited singlet state (S₁), which governs fluorescence emission. This transition is predominantly characterized by excitation from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), indicative of a \u0026pi;\u0026ndash;\u0026pi;* transition, with a calculated excitation wavelength of 244 nm. Although this value deviates from the experimentally observed absorption maximum at 262 nm [50], the difference is within an acceptable range considering the approximations inherent in the PCM model and DFT methods [51].\u003c/p\u003e\n\u003cp\u003eTo elucidate the fluorescence quenching mechanism in CuAS upon interaction with antibiotic molecules, we examined the stacked complexes formed between adenine and various antibiotics. \u0026pi;\u0026ndash;Stacked interactions are known to facilitate molecular orbital mixing and fluorescence quenching, as demonstrated for 2-aminopurine complexes with purine and pyrimidine bases [52,53]. Given the coordination of adenine to Cu centers within the MOF, antibiotic molecules are expected to interact primarily with the exposed purine ring of adenine through \u0026pi;\u0026ndash;stacking, although steric constraints imposed by the MOF may limit these interactions, particularly for bulkier antibiotics.\u003c/p\u003e\n\u003cp\u003eThe key electronic features of the adenine\u0026ndash;NFZ dimer are summarized in Fig. 11. The vertical transition from S₀ to the second excited singlet state (S₂) exhibits a strong oscillator strength (\u0026brvbar; = 0.5905), primarily originating from a HOMO\u0026ndash;1 \u0026rarr; LUMO excitation. In this transition, the HOMO\u0026ndash;1 is delocalized over both adenine and NFZ, while the LUMO is localized mainly on NFZ. Importantly, a lower-lying S₁ state is present, where the S₀ \u0026rarr; S₁ transition is weakly allowed, with a low oscillator strength (\u0026brvbar; = 0.0325), involving predominantly a HOMO (localized on adenine) \u0026rarr; LUMO transition. This spatial separation of HOMO and LUMO orbitals across adenine and NFZ is a hallmark of photoinduced electron transfer (PET) processes. Upon photoexcitation, an electron can migrate from adenine (donor) to NFZ (acceptor), facilitating nonradiative deactivation. According to Kasha\u0026rsquo;s rule [54], rapid internal conversion from S₂ to the dark S₁ state is expected, and the low oscillator strength of S₁ indicates that radiative decay (fluorescence) is inefficient. Thus, the TDDFT results not only explain fluorescence quenching but strongly support PET as the underlying mechanism.\u003c/p\u003e\n\u003cp\u003eA similar PET-driven quenching mechanism is predicted for the adenine\u0026ndash;NFT complex (Fig. 12), where NFT differs from NFZ by substitution of an amide group with a furan ring, introducing additional delocalization. Although minor differences in transition energies and oscillator strengths are observed, the trend toward rapid internal conversion and fluorescence suppression remains consistent.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn contrast, \u0026pi;\u0026ndash;stacked conformations between adenine and DTZ or MDZ induce significant molecular orbital mixing, altering electronic transition properties (Figs. 13 and 14). Electron density redistribution across the stacked molecules leads to modified energy levels and transition dipole moments. As a result, oscillator strengths for both the S₀ \u0026rarr; S₁ (0.0013 for adenine\u0026ndash;DTZ and 0.0089 for adenine\u0026ndash;MDZ) and S₀ \u0026rarr; S₂ (0.0026 for adenine\u0026ndash;DTZ and 0.0097 for adenine\u0026ndash;MDZ) transitions are substantially decreased compared to isolated adenine. This suppression of oscillator strengths inhibits radiative decay pathways and enhances nonradiative relaxation via internal conversion and vibrational dissipation. In these cases, the interaction resembles static quenching through ground-state complex formation [52] rather than dynamic PET processes.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn complexes with CAP, SDZ, and PCL (Figs. 15\u0026ndash;17), the oscillator strengths for the S₀ \u0026rarr; S₁ transitions remain relatively stronger (0.0232, 0.0148, and 0.0239, respectively) compared to the S₀ \u0026rarr; S₂ transitions. Although these values are reduced relative to free adenine, they indicate that molecular orbital mixing does not substantially disrupt radiative decay pathways. As a result, fluorescence quenching is minimal, and adenine largely retains its fluorescent properties upon complexation with CAP, SDZ, and PCL.\u003c/p\u003e\n\u003cp\u003eSteric hindrance from the MOF framework further influences these interactions. Small, planar antibiotics such as NFZ, NFT, DTZ, and MDZ can engage in \u0026pi;\u0026ndash;stacking within the MOF pores, promoting PET and/or orbital mixing-induced quenching. In contrast, bulkier antibiotics such as CAP, SDZ, and PCL face steric constraints that prevent close approach to the purine ring, thereby preserving fluorescence. Although explicit binding energy calculations were not performed, the trends in oscillator strengths, combined with orbital analyses, strongly support PET-driven quenching in small, planar complexes and negligible quenching in bulkier systems.\u003c/p\u003e\n\u003cp\u003eOverall, the TDDFT (PCM) results align closely with experimental observations, providing molecular-level evidence for PET-mediated fluorescence quenching and highlighting the critical role of \u0026pi;\u0026ndash;stacking interactions in these systems.\u003c/p\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this work, adenine-based metal-organic framework (MOF) materials with fluorescent properties were synthesized: CuAS MOF (A = adenine, S = succinic acid). The crystal structure of CuAS reveals a three-dimensional framework with two directional channels along the a and b axes, with amino groups oriented toward the cavities. CuAS exhibits solid-state fluorescence emission at 440 nm (λ\u003csub\u003eex\u003c/sub\u003e = 330 nm), and when dispersed in methanol, shows emission at 430 nm (λ\u003csub\u003eex\u003c/sub\u003e = 350 nm), consistent with intraligand transitions of adenine. This material was designed for antibiotic detection via fluorescence quenching. The sensor demonstrated high specificity toward nitrofuran antibiotics, particularly Nitrofurantoin (NFT) and Nitrofurazone (NFZ), which produced the highest percentage of fluorescence quenching. The quenching process is primarily governed by photoinduced electron transfer (PET), as supported by DFT/TDDFT calculations, with a possible minor contribution from fluorescence resonance energy transfer (FRET).\u003c/p\u003e\n\u003cp\u003eDFT/TDDFT calculations elucidate the quenching mechanisms: antibiotics such as NFZ, NFT, DTZ, and MDZ can form π-stacked interactions with adenine within the MOF, promoting molecular orbital (MO) mixing. In the NFZ and NFT systems, the primary S₀ → S₂ transitions involve electron density that is initially delocalized across both adenine and NFZ/NFT, becoming localized on NFZ/NFT upon excitation, thereby facilitating PET. This promotes rapid internal conversion to a nonradiative S₁ state, leading to fluorescence quenching. In DTZ and MDZ systems, fluorescence quenching predominantly occurs through static quenching mechanisms, where ground-state complex formation with adenine leads to reduced oscillator strengths and enhanced nonradiative relaxation. In contrast, CAP, SDZ, and PCL, due to their bulky structures, experience steric hindrance that limits π–π stacking interactions within the MOF framework. As a result, adenine retains its fluorescence with minimal quenching.\u003c/p\u003e\n\u003cp\u003eOverall, the experimental and theoretical results together provide detailed molecular-level insights into fluorescence quenching mechanisms and establish CuAS MOF as a selective fluorescent sensor for nitrofuran antibiotics.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003e5. Acknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the Department of Chemistry, Faculty of Science, Kasetsart University; the Center of Excellence for Innovation in Chemistry (PERCH-CIC); and the Kasetsart University Research and Development Institute under Grant No. FF(KU-SRIU) 11.67.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u0026nbsp;\u003c/strong\u003eTanin Nanok: Software, Calculation Validation, Writing- original draft, Writing- review \u0026amp; editing; Tontrakarn \u0026nbsp;Pongpai: \u0026nbsp;Formal analysis, \u0026nbsp;Data curation; Kittinan \u0026nbsp; Ketsrisung: Formal analysis, Visualization; Jiraporn Singhophon: Formal analysis, Investigation; Kittipong Chainok: Investigation, Resources, Software. Tanwawan Duangthongyou: Validation, Resources, Supervision, Writing- original draft, Writing- review \u0026amp; editing, Project administration.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u0026nbsp;\u003c/strong\u003eNo datasets were generated or analysed during the current study\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u0026nbsp;\u003c/strong\u003eThe authors declares no competing interests\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eY. Zhong, P. Liao, J. Kang, Q. Liu, S. Wang, S. Li, X. Liu, G. Li, Locking Effect in Metal@MOF with Superior Stability for Highly Chemoselective Catalysis. J. Am. Chem. Soc. \u003cstrong\u003e145\u003c/strong\u003e, 4659-4666 (2023)\u003c/li\u003e\n \u003cli\u003eV. Pascanu, G. Gonz\u0026aacute;lez Miera, A.K. Inge, B. Mart\u0026iacute;n-Matute, Metal\u0026ndash;Organic Frameworks as Catalysts for Organic Synthesis: A Critical Perspective. J. Am. Chem. Soc. \u003cstrong\u003e141\u003c/strong\u003e, 7223-7234 (2019)\u003c/li\u003e\n \u003cli\u003eH. Chu, D. Sun, P. Cui, Highly Water-Stable Zn5 Cluster-Based Metal\u0026ndash;Organic Framework for Efficient Gas Storage and Organic Dye Adsorption. Inorg. Chem. \u003cstrong\u003e61\u003c/strong\u003e, 19642-19648 (2022)\u003c/li\u003e\n \u003cli\u003eS. Rojas, F.J. Carmona, C.R. Maldonado, P. Horcajada, T. Hidalgo, C. Serre, J.A.R. Navarro, E. Barea, Nanoscaled Zinc Pyrazolate Metal\u0026ndash;Organic Frameworks as Drug-Delivery Systems. Inorg. Chem. \u003cstrong\u003e55\u003c/strong\u003e, 2650-2663 (2016)\u003c/li\u003e\n \u003cli\u003eA. Gheorghe, O. Lugier, B. Ye, S. Tanase, Metal\u0026ndash;organic framework based systems for CO 2 sensing. Journal of Materials Chemistry C, \u003cstrong\u003e9\u003c/strong\u003e (2021) 16132-16142.\u003c/li\u003e\n \u003cli\u003eP. Qin, B.A. Day, S. Okur, C. Li, A. Chandresh, C.E. Wilmer, L. Heinke, VOC mixture sensing with a MOF film sensor array: detection and discrimination of xylene isomers and their ternary blends. ACS Sens. \u003cstrong\u003e7\u003c/strong\u003e, 1666-1675 (2022)\u003c/li\u003e\n \u003cli\u003eH. Qu, X. Xiao, Z. Han, M. Hu, S. Shen, L. Yang, F. Jia, T. Wang, Z. Ye, W. Sun, Y. Wang, L. Huang, Z. Zhu, P. Servati, J. Tang, J. Chen, Graphene Oxide Nanofiltration Membrane Based on Three-Dimensional Size-Controllable Metal\u0026ndash;Organic Frameworks for Water Treatment. ACS Appl. Nano Mater. \u003cstrong\u003e5\u003c/strong\u003e, 5196-5207 (2022)\u003c/li\u003e\n \u003cli\u003eR. Taghavi, S. Rostamnia, M. Farajzadeh, H. Karimi-Maleh, J. Wang, D. Kim, H.W. Jang, R. Luque, R.S. Varma, M. Shokouhimehr, Magnetite Metal\u0026ndash;Organic Frameworks: Applications in Environmental Remediation of Heavy Metals, Organic Contaminants, and Other Pollutants. Inorg. Chem. \u003cstrong\u003e61\u003c/strong\u003e, 15747-15783 (2022)\u003c/li\u003e\n \u003cli\u003eT. Islamoglu, Z. Chen, M. C. Wasson, C. T. Buru, K. O. Kirlikovali, U. Afrin, M. R. Mian, O. K. Farha, Metal-Organic Frameworks against Toxic Chemicals. Chem. Rev. \u003cstrong\u003e120\u003c/strong\u003e, 8130\u0026minus; 8160 (2020)\u003c/li\u003e\n \u003cli\u003eW. Guan, W. Zhou, J. Lu, C. Lu, Luminescent Films for Chemo- and Biosensing. Chem. Soc. Rev. \u003cstrong\u003e44\u003c/strong\u003e, 6981\u0026minus;7009 (2015)\u003c/li\u003e\n \u003cli\u003eLi, H. Y.; Zhao, S. N.; Zang, S. Q.; Li, J. Functional MetalOrganic Frameworks as Effective Sensors of Gases and Volatile Compounds. Chem. Soc. Rev. \u003cstrong\u003e49\u003c/strong\u003e, 6364\u0026minus;6401 (2020)\u003c/li\u003e\n \u003cli\u003eY. Zhang, X. Qu, B. Yan, A Visual Logic Alarm Sensor for Diabetic Patients Towards Diabetic Polyneuropathy Based on a Metal-Organic Framework Functionalized by Dual-Cation Exchange. J. Mater. Chem. C. \u003cstrong\u003e9\u003c/strong\u003e, 3440\u0026minus;3446 (2021)\u003c/li\u003e\n \u003cli\u003eX. D. Ying, J. X. Chen, D. Y. Tu, Y. C. Zhuang, D. Wu, L. Shen, Tetraphenylpyrazine-Based Luminescent Metal-Organic Framework for Chemical Sensing of Carcinoids Biomarkers. ACS Appl. Mater. Interfaces. \u003cstrong\u003e13\u003c/strong\u003e, 6421\u0026minus;6429 (2021)\u003c/li\u003e\n \u003cli\u003eX. Wang, M. Lei, T. Zhang, Q. Zhang, R. Zhang, M. Yang, A Water-Stable Multi-Responsive Luminescent Zn-MOF Sensor for Detecting TNP, NZF and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e2‑\u003c/sup\u003e in Aqueous Media. Dalt. Trans. \u003cstrong\u003e50\u003c/strong\u003e, 3816\u0026minus;3824 (2021)\u003c/li\u003e\n \u003cli\u003eM. A. Andres, M. T. Vijjapu, S. G. Surya, O. Shekhah, K. N. Salama, C. Serre, M. Eddaoudi, O. Roubeau, I. Gascon, Methanol and Humidity Capacitive Sensors Based on Thin Films of MOF Nanoparticles. ACS. Appl. Mater. Interfaces. \u003cstrong\u003e12\u003c/strong\u003e, 4155\u0026minus; 4162 (2020)\u003c/li\u003e\n \u003cli\u003eJ.-X. Wang, J. Yin, O. Shekhah, O. M. Bakr, M. Eddaoudi, O. F. Mohammed, Energy Transfer in Metal\u0026ndash;Organic Frameworks for Fluorescence Sensing. ACS Appl. Mater. Interfaces. \u003cstrong\u003e14\u003c/strong\u003e (8), 9970\u0026ndash;9986 (2022)\u003c/li\u003e\n \u003cli\u003eC. E. Kivi, D. Song, A luminescent cationic metal\u0026ndash;organic framework featuring [Cu\u0026ndash;pyrazolate] 3 units for volatile organic compound sensing. \u003cstrong\u003eDalton Trans.\u003c/strong\u003e\u003cstrong\u003e\u003cstrong\u003e45,\u0026nbsp;\u003c/strong\u003e\u003c/strong\u003e17087-17090 \u003cstrong\u003e(\u003c/strong\u003e2016)\u003c/li\u003e\n \u003cli\u003eS. Hui, P. C. Saha, S. Guha, P. Mahata, Two-Dimensional Cu-Based MOF for Selective Staining of the Cellular Nucleus through Fluorescence Imaging and Selective Sorption of Dye Molecules in Aqueous Medium. Inorg. Chem.\u0026nbsp;\u003cstrong\u003e63\u003c/strong\u003e (29), 13439\u0026ndash;13449 (2024)\u003c/li\u003e\n \u003cli\u003eE. Moradi, R. Rahimi, Vahid Safarifard, Ultrasound-assisted preparation nanostructures of Cu2(BDC)2(BPY)-MOF: Highly selective and sensitive luminescent sensing of THF small molecule and Cu\u003csup\u003e2+\u003c/sup\u003e and Pb\u003csup\u003e2+\u003c/sup\u003e ions. J. Solid State Chem. \u003cstrong\u003e288\u003c/strong\u003e, 121397 (2020)\u003c/li\u003e\n \u003cli\u003eJ. Yang, J. Che, X. Jiang, Y. Fan, D. Gao, J. Bi, Z. Ning, A Novel Turn-On Fluorescence Probe Based on Cu(II) Functionalized Metal\u0026ndash;Organic Frameworks for Visual Detection of Uric Acid.\u0026nbsp;\u003cem\u003eMolecules\u003c/em\u003e \u003cem\u003e\u003cstrong\u003e27\u003c/strong\u003e,\u0026nbsp;\u003c/em\u003e4803 \u003cem\u003e(\u003c/em\u003e2022)\u003c/li\u003e\n \u003cli\u003eJ. Jia, H. Zhang, J. Qu, Y. Wang, N. Xu, Immunosensor of Nitrofuran Antibiotics and Their Metabolites in Animal-Derived Foods: A Review. Front. Chem. \u003cstrong\u003e10\u003c/strong\u003e, 813666 (2022)\u003c/li\u003e\n \u003cli\u003eJ. Points, D. Thorburn Burns, M.J. Walker, Forensic issues in the analysis of trace nitrofuran veterinary residues in food of animal origin. Food Control. \u003cstrong\u003e50\u003c/strong\u003e, 92-103 (2015)\u003c/li\u003e\n \u003cli\u003eL. Molognoni, H. Daguer, R.B. Hoff, Chapter 12 - Analysis of nitrofurans residues in foods of animal origin, in: C.M. Galanakis (Ed.) Food Toxicology and Forensics. Academic Press. 379-419 (2021)\u003c/li\u003e\n \u003cli\u003eJ. Buasakun, P. Srilaoong, K. Chainok, C. Raksakoon, R. Rattanakram, T. Duangthongyou, Novel zinc(II) coordination polymers (CPs) based on flexible aliphatic carboxylic acids and an N-donor ligand for fluorescence sensors. Inorg. Chim. Acta. \u003cstrong\u003e511\u003c/strong\u003e, 119839 (2020)\u003c/li\u003e\n \u003cli\u003eJ. Buasakun, P. Srilaoong, K. Chainok, C. Raksakoon, R. Rattanakram, T. Duangthongyou, Dual luminescent coordination polymers based on flexible aliphatic carboxylate ligands supplemented by rigid bipyridyl ligands for 2,4-dinitrophenol (DNP) and iron(III) ion detection. Polyhedron. \u003cstrong\u003e204\u003c/strong\u003e, 115265 (2021).\u003c/li\u003e\n \u003cli\u003eM. Brezovan, V. Kuchtanin, J. Moncol, J. Pavlik, Ľ. Dlh\u0026aacute;ň, P. Segľa, Four novel cobalt(II) succinate coordination polymers with \u003cem\u003eN\u003c/em\u003e-heterocyclic ligands: crystal structures, spectral properties, magnetism and computational study.\u0026nbsp;Chem. Pap. \u003cstrong\u003e74\u003c/strong\u003e 3741\u0026ndash;3753 (2020)\u003c/li\u003e\n \u003cli\u003eM. Brezovan, J. Jur\u0026aacute;kov\u0026aacute;, J. Moncol, Ľ. Dlh\u0026aacute;ň, M. Korabik, I. \u0026Scaron;alitro\u0026scaron;, J. Pavlik, P. Segľa, The Role of the Bridge in Single-Ion Magnet Behaviour: Reinvestigation of Cobalt(II) Succinate and Fumarate Coordination Polymers with Nicotinamide.\u0026nbsp;\u003cem\u003eInorganics.\u003c/em\u003e \u003cem\u003e\u003cstrong\u003e10\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e,\u0026nbsp;\u003c/em\u003e128 (2022).\u003c/li\u003e\n \u003cli\u003eX. Wu, X. Xiong, J.L. Li, D. Luo, K. Wu, Y.B. Wei, X.Y. Liu, W. Lu, D. Li, J. He, An Adenine‐Based Biological Metal‐Organic Framework as an Efficient Luminescent Sensor for Tetracycline Detection. Eur. J. Inorg. Chem. \u003cstrong\u003e23\u003c/strong\u003e, e202200278 (2022)\u003c/li\u003e\n \u003cli\u003eA. Eskemech, D. Gambhir, H. Kaur, A. Karmakar, R. R. Koner , Amino decorated adenine based metal\u0026ndash;organic framework for multi-faceted applications. \u003cstrong\u003eDalton Trans.\u003c/strong\u003e\u003cstrong\u003e52,\u0026nbsp;\u003c/strong\u003e8275-8283.\u003cstrong\u003e\u0026nbsp;(\u003c/strong\u003e2023)\u003c/li\u003e\n \u003cli\u003eD. Jonckheere, E. Coutino-Gonzalez, W. Baekelant, B. Bueken, H. Reinsch, I. Stassen, O. Fenwick, F. Richard, P. Samor\u0026igrave;, R. Ameloot, J. Hofkens, M. B. J. Roeffaers, D. E. De Vos, Silver-induced reconstruction of an adeninate-based metal\u0026ndash;organic framework for encapsulation of luminescent adenine-stabilized silver clusters. \u003cstrong\u003eJ. Mater. Chem. C\u003c/strong\u003e\u003cstrong\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/strong\u003e, 4259-4268 (2016)\u003c/li\u003e\n \u003cli\u003eS. S. Nagarkar, B. Joarder, A. K. Chaudhari, S. Mukherjee, S. K. Ghosh, Highly selective detection of nitro explosives by a luminescent metal-organic framework. Angew. Chem. Int. Ed. \u003cstrong\u003e52\u003c/strong\u003e (10), 2881-2885 (2013)\u003c/li\u003e\n \u003cli\u003eR. Goswami, S. C. Mandal, B. Pathak, S. Neogi, Guest-Induced Ultrasensitive Detection of Multiple Toxic Organics and Fe\u003csup\u003e3+\u003c/sup\u003e Ions in a Strategically Designed and Regenerative Smart Fluorescent Metal\u0026ndash;Organic Framework. ACS Appl. Mater. Interfaces, \u003cstrong\u003e11\u003c/strong\u003e (9), 9042-9053 (2019)\u003c/li\u003e\n \u003cli\u003eSAINT and SADABS; Bruker AXS Inc.: Madison, WI, USA, 2003.\u003c/li\u003e\n \u003cli\u003eO.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschman, LESS: A New GUI Implementation of the Least-Squares Refinement Program for Crystal Structure Analysis. J. Appl. Cryst. \u003cstrong\u003e42\u003c/strong\u003e, 339 \u0026ndash; 341 (2009)\u003c/li\u003e\n \u003cli\u003eG.M. Sheldrick, A Short History of SHELX. Acta Cryst. \u003cstrong\u003eA64\u003c/strong\u003e, 112 \u0026ndash; 122 (2008)\u003c/li\u003e\n \u003cli\u003eRunge, Erich; E. K. U. Gross, Density-Functional Theory for Time-Dependent Systems. Phys. Rev. Lett. \u003cstrong\u003e52\u003c/strong\u003e (12), 997\u0026ndash;1000 (1984)\u003c/li\u003e\n \u003cli\u003eM. J. Frisch et al., Gaussian 09, Revision D.01, Gaussian, Inc., Wallingford CT, 2009.\u003c/li\u003e\n \u003cli\u003eA.D. Becke, Density-functional thermochemistry. III. The role of exact exchange. J.Chem.Phys. \u003cstrong\u003e98\u003c/strong\u003e, 5648-5652 (1993)\u003c/li\u003e\n \u003cli\u003eC. Lee, W. Yang, R.G. Parr, Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B \u003cstrong\u003e37\u003c/strong\u003e, 785-789 (1988)\u003c/li\u003e\n \u003cli\u003eS.H. Vosko, L. Wilk, M. Nusair, Accurate spin-dependent electron liquid correlation energies for local spin density calculations: a critical analysis. Can. J. Phys. \u003cstrong\u003e58\u003c/strong\u003e, 1200-1211 (1980)\u003c/li\u003e\n \u003cli\u003eP.J. Stephens, F.J. Devlin, C.F. Chabalowski, M.J. Frisch, Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. J. Phys. Chem. \u003cstrong\u003e98\u003c/strong\u003e, 11623-11627 (1994)\u003c/li\u003e\n \u003cli\u003eS. Grimme, J. Antony, S. Ehrlich, and S. Krieg, A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. \u003cstrong\u003e132\u003c/strong\u003e, 154104 (2010).\u003c/li\u003e\n \u003cli\u003eS. Grimme, S. Ehrlich, and L. Goerigk, Effect of the damping function in dispersion corrected density functional theory. J. Comput. Chem. \u003cstrong\u003e32\u003c/strong\u003e, 1456 (2011).\u003c/li\u003e\n \u003cli\u003eJ. Tomasi, B. Mennucci, R. Cammi, Quantum Mechanical Continuum Solvation Models. Chem. Rev. \u003cstrong\u003e105\u003c/strong\u003e(8), 2999-3094 (2005)\u003c/li\u003e\n \u003cli\u003eS. Gai, J. Zhang, R. Fan, K. Xing, W. Chen, K. Zhu, X. Zheng, P. Wang, X. Fang, Y. Yang, Highly Stable Zinc-Based Metal-Organic Frameworks and Corresponding Flexible Composites for Removal and Detection of Antibiotics in Water. ACS Appl Mater Interfaces, \u003cstrong\u003e12\u003c/strong\u003e(7) 8650-8662 (2020)\u003c/li\u003e\n \u003cli\u003eS.-L. Sun, X.-Y. Sun, Q. Sun, E.-Q. Gao, Highly efficient fluorescent chemosensor for nitro antibiotic detection based on luminescent coordination polymers with 2, 6-di(4-carboxyphenyl)pyrazine. CrystEngComm. \u003cstrong\u003e23\u003c/strong\u003e(17), 3167-3174 (2021)\u003c/li\u003e\n \u003cli\u003eR.-Q. Jia, G. Tan, Y.-J. Chen, L.-Y. Zuo, B. Li, L.-Y. Wang, Cu\u003csup\u003eII\u003c/sup\u003e Ion Doping Enhances the Water Stability of Luminescent Metal\u0026ndash;Organic Framework, Realizing the Detection of Fe\u003csup\u003e3+\u003c/sup\u003e and Antibiotics in Aqueous Solutions.\u0026nbsp;\u003cem\u003eFront. Chem.\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, 860232 (2022)\u003c/li\u003e\n \u003cli\u003eZ.-L. Mu, Y.-Q. Ma, Y. Zhu, Z. Chen, H.-P. Xiao, X. Li, H.-Y. Wang, J.-Y. Ge, Two Stable Bifunctional Zinc Metal\u0026ndash;Organic Frameworks with Luminescence Detection of Antibiotics and Proton Conduction. Inorg. Chem. \u003cstrong\u003e62\u003c/strong\u003e(49) 20314-20324 (2023)\u003c/li\u003e\n \u003cli\u003eP. Srilaoong, P. Puengtham, J. Buasakun, C. Raksakoon, S. Suramitr, K. Chainok, P. Harding, D. J. Harding, T. Duangthongyou, Zn-metal organic framework containing electron rich linkers and film preparation for applications in antibiotic detection. Inorg. Chim. Acta \u003cstrong\u003e559\u003c/strong\u003e, 121780 (2024)\u003c/li\u003e\n \u003cli\u003eH. H.Hammud, K. H. Bouhadir, M. S. Masoud, A. M. Ghannoum, S.A. Assi, Solvent Effect on the Absorption and Fluorescence Emission Spectra of Some Purine Derivatives: Spectrofluorometric Quantitative Studies. J. Solution Chem. \u003cstrong\u003e37\u003c/strong\u003e(7), 895\u0026ndash;917 (2008)\u003c/li\u003e\n \u003cli\u003eZ. Zara, J. Iqbal, K. Ayub, M. Irfan, A. Mahmood, R. A. Khera, B. Eliasson, A comparative study of DFT calculated and experimental UV/Visible spectra for thirty carboline and carbazole based compounds. J. Mol. Struct. \u003cstrong\u003e1149\u003c/strong\u003e, 282\u0026ndash;298 (2017)\u003c/li\u003e\n \u003cli\u003eJ. M. Jean, 2-Aminopurine fluorescence quenching and lifetimes: Role of base stacking. Proceedings of the National Academy of Sciences. \u003cstrong\u003e98\u003c/strong\u003e(1), 37\u0026ndash;41(2000). doi:10.1073/pnas.011442198\u003c/li\u003e\n \u003cli\u003eJ. Liang, S. Matsika, Pathways for Fluorescence Quenching in 2-Aminopurine \u0026pi;-Stacked with Pyrimidine Nucleobases. J. Am. Chem. Soc. \u003cstrong\u003e133\u003c/strong\u003e(17), 6799\u0026ndash;6808 (2011)\u003c/li\u003e\n \u003cli\u003eM. Kasha, Characterization of electronic transitions in complex molecules. Discuss. Faraday Soc. \u003cstrong\u003e9\u003c/strong\u003e, 14-19 (1950)\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-inorganic-and-organometallic-polymers-and-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"joip","sideBox":"Learn more about [Journal of Inorganic and Organometallic Polymers and Materials](https://www.springer.com/journal/10904)","snPcode":"10904","submissionUrl":"https://submission.nature.com/new-submission/10904/3","title":"Journal of Inorganic and Organometallic Polymers and Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Adenine-based MOF, Fluorescence quenching, Photoinduced electron transfer (PET), Antibiotic sensing, TDDFT calculations","lastPublishedDoi":"10.21203/rs.3.rs-6562459/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6562459/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAn adenine–succinate-based metal–organic framework, [Cu(adenine)(succinate)]ₙ (CuAS), was synthesized via a solvothermal method and structurally characterized by single-crystal X-ray diffraction, PXRD, IR, TGA, and elemental analysis. CuAS forms a three-dimensional framework featuring two directional channels along the \u003cem\u003ea\u003c/em\u003e- and \u003cem\u003eb\u003c/em\u003e-axes, with amino groups oriented toward the cavities. The material exhibits solid-state fluorescence at 440 nm (λₑₓ = 330 nm) and, when dispersed in methanol, emits at 430 nm (λₑₓ = 350 nm), consistent with intraligand transitions of adenine. CuAS was employed as a fluorescent sensor for antibiotics, showing high selectivity toward nitrofurantoin (NFT) and nitrofurazone (NFZ), with strong fluorescence quenching driven mainly by photoinduced electron transfer (PET). Stern–Volmer analysis revealed K\u003csub\u003esv\u003c/sub\u003e values of 5.98 × 10⁴ M⁻¹ (NFZ) and 5.88 × 10⁴ M⁻¹ (NFT), with detection limits of 0.136 ppm and 0.110 ppm, respectively. DFT and TDDFT calculations support the PET mechanism, indicating that π-stacked interactions between adenine and NFZ/NFT facilitate electron transfer upon excitation. In contrast, bulky antibiotics show minimal quenching due to steric hindrance. These findings provide molecular-level insights into fluorescence sensing mechanisms and establish CuAS as a promising selective sensor for nitrofuran antibiotics.\u003c/p\u003e","manuscriptTitle":"Structural and Mechanistic Insights into a Cu-Adenine MOF for Selective Fluorescence Sensing of Antibiotics: Experimental and TDDFT Approaches","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-08 20:33:20","doi":"10.21203/rs.3.rs-6562459/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-05-14T01:52:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-11T17:18:21+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-11T09:48:25+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-10T16:02:39+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"287175602353052364667549599902415902814","date":"2025-05-03T04:38:02+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"65137123217187178912764066173305386530","date":"2025-05-02T14:11:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"141810492890955464949227251078014444000","date":"2025-05-01T06:02:07+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-01T02:55:56+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-04-30T17:51:30+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-30T13:55:08+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Inorganic and Organometallic Polymers and Materials","date":"2025-04-30T07:39:01+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-inorganic-and-organometallic-polymers-and-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"joip","sideBox":"Learn more about [Journal of Inorganic and Organometallic Polymers and Materials](https://www.springer.com/journal/10904)","snPcode":"10904","submissionUrl":"https://submission.nature.com/new-submission/10904/3","title":"Journal of Inorganic and Organometallic Polymers and Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"1553dec1-6133-409d-8b65-67d422d2e1da","owner":[],"postedDate":"May 8th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-07-14T16:00:36+00:00","versionOfRecord":{"articleIdentity":"rs-6562459","link":"https://doi.org/10.1007/s10904-025-03928-9","journal":{"identity":"journal-of-inorganic-and-organometallic-polymers-and-materials","isVorOnly":false,"title":"Journal of Inorganic and Organometallic Polymers and Materials"},"publishedOn":"2025-07-07 15:57:18","publishedOnDateReadable":"July 7th, 2025"},"versionCreatedAt":"2025-05-08 20:33:20","video":"","vorDoi":"10.1007/s10904-025-03928-9","vorDoiUrl":"https://doi.org/10.1007/s10904-025-03928-9","workflowStages":[]},"version":"v1","identity":"rs-6562459","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6562459","identity":"rs-6562459","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}