A Schiff Base-Functionalized Triphenylamine Fluorescent Probe for Selective and Sensitive Detection of Cu2+ in Aqueous Media

A Schiff Base-Functionalized Triphenylamine Fluorescent Probe for Selective and Sensitive Detection of Cu2+ in Aqueous Media | 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 A Schiff Base-Functionalized Triphenylamine Fluorescent Probe for Selective and Sensitive Detection of Cu 2+ in Aqueous Media Long Liu, Jiayi Chen, Meijun Ye, Wen Huang, Xiang Liao, Hanqing Wu, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8247812/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Mar, 2026 Read the published version in Journal of Fluorescence → Version 1 posted 10 You are reading this latest preprint version Abstract Heavy metal Cu 2+ from industrial discharge continuously accumulates in ecosystems, posing threats to human health and ecological balance. Researchers successfully synthesized a novel fluorescent probe, TPA-OPD , via a Schiff base reaction between triphenylamine and o-phenylenediamine. TPA-OPD exhibits rapid, highly selective, and sensitive fluorescence quenching in response to Cu 2+ , along with excellent anti-interference capability. The binding mechanism between Cu²⁺ and TPA-OPD was confirmed by Job’s plot, Fourier-transform infrared spectroscopy, mass spectrometry, nuclear magnetic resonance, and Gaussian calculations. TPA-OPD effectively detects Cu 2+ in real-world environmental samples such as tap water and river water, demonstrating strong potential for monitoring Cu 2+ pollution. Organic fluorescence Sensor Schiff base Triphenylamine Cu2+ Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction With accelerating industrialization, environmental pollution has become increasingly prominent, with metal ions drawing significant attention due to their widespread presence and potential hazards [ 1 – 5 ] . As a vital industrial metal, copper plays an indispensable role in modern society. Its excellent electrical conductivity, thermal conductivity, and corrosion resistance have led to its extensive application across multiple sectors including power, electronics, construction, and transportation [ 6 – 9 ] . With the extensive use of copper and its compounds, copper ion pollution has gradually emerged as a significant issue. As a heavy metal pollutant, copper ions exert substantial impacts on both the environment and living organisms [ 10 – 15 ] . Simultaneously, copper ions are essential trace elements for the human body [ 16 ] , playing a crucial role in maintaining normal physiological functions. They participate in the activity of various enzymes, being vital for respiration, cell proliferation [ 17 ] , neurotransmitter biosynthesis [ 18 ] iron metabolism [ 19 ] , antioxidant defense systems [ 20 ] , connective tissue formation [ 21 ] and nervous system health [ 22 ] . Therefore, establishing efficient, sensitive, and selective copper ion detection methods holds significant value for environmental monitoring, food safety, and clinical diagnostics [ 23 , 24 ] . Current copper ion detection methods predominantly rely on instrumental analysis techniques, such as flame atomic absorption spectroscopy (AAS) [ 25 , 26 ] , electrochemical analysis [ 27 ] , inductively coupled plasma mass spectrometry (ICP-MS) [ 28 ] , high-performance liquid chromatography (HPLC) [ 29 ] , and solid-phase microextraction (SPME) [ 30 ] . These methods offer high accuracy and precision but are limited in widespread practical application due to expensive equipment, high detection limits, and cumbersome procedures [ 31 , 32 ] . The limitations inherent in such detection methods can be effectively addressed by fluorescence probe analysis [ 33 – 35 ] . This work designed and synthesized a novel AIE fluorescent probe, TPA-OPD , achieving highly selective and nanoscale ultrasensitive detection of Cu 2+ . Benefiting from its AIE properties, TPA-OPD effectively avoids aggregation quenching issues in aqueous solutions that plague traditional probes, significantly enhancing the signal-to-noise ratio in bioimaging. Through comprehensive analysis using NMR spectroscopy, pre- and post-binding mass spectrometry, and theoretical calculations, we systematically elucidated its coordination mode and response mechanism, establishing a clear "structure-property-mechanism" correlation. This work provides novel insights for developing high-performance metal ion probes with well-defined mechanisms, offering broad prospects for environmental and biomedical detection. 2. Experimental 2.1. Reagents and instruments Chemical reagents were purchased from Aladdin Co., Ltd. The nitrates were used for metallic salts. The sodium salts were used for anion salts. The TLC (Thin-layer chromatography) analyses were carried out on the precoated glass plates. NMR spectra were recorded on the Bruker-ARX 400 instrument, using TMS as inner standard. The MS spectra were recorded on the Bruker mass spectrometer. Varian UV-Vis spectrometer were recorded on UV-Vis spectra. Fluorescence spectra were recorded on a Hitachi F-4500 spectrometer. The density functional theory (DFT) method was used to perform the theoretical calculations on Gaussian 09 program at the B3LYP/6-31G(d) level. 2.2 Synthesis of Probe TPA-OPD As shown in Scheme 1 , compound 3 was first synthesized by referring to the literature method [ 36 ] . Subsequently, under nitrogen atmosphere, compound 3 (0.219 g, 0.60 mmol) and o-phenylenediamine (0.033 g, 0.3 mmol) were refluxed for 12 h in a mixture of 15 mL EtOH and 1 mL DCM. The reaction was monitored by TLC analysis. Upon completion, the organic solvents were removed by rotary evaporation. The crude product was purified by column chromatography (elution: PE/DCM = 10/1), yielding the target product TPA-OPD (yellow solid, 76.0% yield). UV-vis (DMSO) λ max : 370 nm; m.p. 153.6-155.4 ℃; 1 H NMR (400 MHz, CDCl 3 ) ( Fig. S1 ), δ : 7.03 – 7.08 (m, 4H, -ArH), 7.08 – 7.18 (m, 15H, -ArH), 7.25 (s, 2H, -CH), 7.29 (d, J = 8.0 Hz, 9H, -ArH), 7.32 – 7.36 (m, 2H, -ArH), 7.42 (d, J = 8.0 Hz, 2H, -ArH), 7.51 (d, J = 8.0 Hz, 4H, -ArH), 8.67 (s, 2H, -CH), 13.15 (s, 2H, -OH); 13 C NMR (101 MHz, CDCl 3 ) ( Fig. S2 ), δ : 115.1, 117.5, 123.2, 123.3, 124.8, 127.9, 129.4, 147.4, 163.0; MALDI-TOF MS m/z: Calcd for C 56 H 43 N 4 O 2 + [M + H] + , 802.3308, found: 803.335. 2.3 Experimental procedure for test paper Neutral paper strips were immersed in a DMSO-H 2 O (5:95) solution containing TPA-OPD (0.1 mM) for 3.0 minutes. The strips were then removed and air-dried naturally before being cut into circular discs for subsequent experiments. Subsequently, three drops each of TPA-OPD solution and solutions of common metal ions and anions (all guest concentrations 0.1 mM) at different equivalent concentrations were added to these discs. After drying again, the discs were observed under UV light (365 nm) and fluorescence photographs were taken. 3. Results and dis cussion 3.1 Photophysical properties First, the photophysical properties of TPA-OPD in different organic solvents were investigated via UV-Vis absorption and fluorescence spectroscopy, with results shown in Fig. 1 . Within the 375 – 390 nm wavelength range, TPA-OPD exhibits weak UV absorption in nonpolar solvents (Hex, PE) due to low solubility and tendency to aggregate, resulting in reduced effective concentration. Conversely, in polar-matched solvents, it disperses uniformly with stable concentration, yielding strong and stable absorption. Solvent polarity dominates absorption differences by influencing dissolution behavior. Simultaneously, the fluorescence emission intensity of TPA-OPD also exhibits significant variations across different solvents, as illustrated in Fig. 1 . Within the 500 – 600 nm range, TPA-OPD exhibits distinct fluorescence emission peaks, with a prominent peak at 548 nm. Notably, fluorescence emission intensity in low-polarity solvents ( Hex and PE) is markedly lower than in other solvents. These phenomena may arise because in pure nonpolar solvents (Hex and PE), the molecules form disordered, dense precipitates or large-scale aggregates due to extremely poor solubility. This leads to rapid dissipation of excited-state energy through nonradiative pathways (e.g., intermolecular collisions or excited-state quenching), thereby suppressing effective fluorescence emission. To systematically investigate the influence of aggregation behavior on fluorescence properties, DMSO was selected as the base solvent due to its high solubility, excellent fluorescence stability, and low toxicity, and was used to prepare DMSO-H 2 O mixtures with varying water fractions. As water content increased, TPA-OPD gradually aggregated due to reduced solubility, forming nanoaggregates or precipitates. This enabled systematic investigation of changes in luminescence intensity, wavelength, and stability across different aggregation states, revealing the structure-property relationship between the molecular microenvironment and luminescent performance. In DMSO-H 2 O mixed solvent systems, the UV-vis absorption spectrum of TPA-OPD remained essentially unchanged (as shown in Fig. S5 ), while its fluorescence emission behavior exhibited significant dependence on water content (as shown in Fig. 2 ). In pure DMSO, TPA-OPD exhibits pale green fluorescence under 365 nm UV irradiation, with a maximum emission peak at approximately 522 nm. As water content increases (0% - 30%), the fluorescence emission peak gradually redshifts, shifting the solution's luminescence color from pale green to yellow. This phenomenon can be attributed to either the excited-state intramolecular charge transfer (ICT) effect induced by enhanced solvent polarity or the formation of primary aggregates triggered by intermolecular weak interactions, both leading to reduced excited-state energy. When water content further increased to 95%, the emission wavelength stabilized, forming a strong, sharp emission peak at 548 nm, while fluorescence intensity significantly enhanced with rising water proportion. The aforementioned phenomena can be attributed to the following: as a poor solvent, water causes a sharp decrease in molecular solubility at high concentrations, leading to pronounced self-aggregation and the formation of nanoscale aggregates. The fluorescence enhancement occurs synchronously with the aggregation process, exhibiting typical Aggregation-Induced Emission (AIE) characteristics. intramolecular rotational (RIR) or vibrational (RIV) non-radiative transition pathways are spatially restricted by steric hindrance, effectively suppressing energy dissipation and enhancing radiative transition efficiency. 3.2 Responsiveness of the sensor TPA-OPD to ions Subsequently, the response characteristics of TPA-OPD to various ions were systematically investigated in a DMSO-H 2 O solution with 95% water content. The results are shown in Fig. 3 . It can be observed that after adding Na⁺, K⁺, Cs⁺, Mg 2+ , Al³⁺, Ca 2+ , Ba 2+ , Cd 2+ , N₂H₆ 2+ , Sr 2+ , NH₄⁺, Co 2+ , Zn 2+ , Cl − , NO₃ − , SO₄² − and CO 3 2− ions, the fluorescence emission peaks of TPA-OPD all centered around approximately 548 nm. The I/I₀ ratio measured at this wavelength (where I is the fluorescence intensity of TPA-OPD in the presence of different added ions, and I 0 is the fluorescence intensity of the pristine sample.) ranged from 0.93 to 1.04 at this wavelength. These values are close to unity, indicating that the fluorescence emission intensity remains essentially unchanged, consistent with that of pure TPA-OPD , indicating that the probe itself exhibits good spectral stability in the presence of various coexisting ions. However, upon the addition of Cu 2+ to the TPA-OPD solution, the fluorescence intensity at 548 nm dramatically decreased to approximately 10% of its original value, indicating significant fluorescence quenching. This robust and selective response toward Cu 2+ , in contrast to other tested metal ions, highlights the exceptional specificity of TPA-OPD for the recognition of copper ions. Notably, this fluorescence change was clearly discernible to the naked eye in actual observation, further highlighting its potential for visual detection. Experimental results demonstrate that TPA-OPD can specifically recognize Cu 2+ in a DMSO-H 2 O mixed solution system containing 95% water. This highly selective sensing behavior likely originates from the recognition unit in the TPA-OPD molecule, which features an open cavity structure capable of forming specific chelation with Cu 2+ .This coordination interaction may induce intramolecular charge transfer or alter the excited-state energy level structure, thereby suppressing radiative transitions and significantly reducing the fluorescence quantum yield, leading to fluorescence quenching. 3.3 Fluorescence titration of Cu 2+ After confirming the selective detection capability of TPA-OPD toward Cu 2+ , fluorescence titration experiments were carried out in a DMSO-H₂O (5:95) solvent system. As shown in Fig. 4 (a), the maximum fluorescence emission of TPA-OPD at 548 nm gradually decreased with increasing Cu 2+ concentration. This quenching behavior may be attributed to the weakening of intramolecular rotational restriction on the aromatic groups upon Cu²⁺ binding to the molecular cavity of TPA-OPD . As depicted in Fig. 4 (b), within the 0–1.0 uM range, the fluorescence intensity of TPA-OPD exhibits a linear dependence on Cu 2+ concentration, described by the equation:y = 1255.44–1096.64x (R² = 0.99332),where x is the molar concentration of Cu 2+ (mol/L). The high correlation coefficient indicates excellent linearity. Based on the detection limit formula LOD = 3σ/k, where σ is the standard deviation of the blank and k is the slope of the calibration curve, the detection limit for Cu 2+ was determined to be 20.47 nM. This value is significantly lower than those reported for other Cu 2+ detection methods ( Table S1 ), highlighting the promising potential of TPA-OPD for sensitive Cu 2+ sensing.Furthermore, the binding constant (K a ) between TPA-OPD and Cu 2+ was calculated to be 1.51 × 10⁷ M⁻¹ using the Benesi-Hildebrand equation. 3.4 Anti-interference test and response time To further validate the interference resistance of the TPA-OPD fluorescent probe in Cu 2+ detection, interference experiments were conducted on TPA-OPD . As shown in Fig. 5 , the variation in I/I₀ (where I is the fluorescence intensity of TPA-OPD in the presence of different added ions, and I 0 is the fluorescence intensity of the pristine sample.) measured at 548 nm remained between 0.97 and 1.06. This indicates that the presence of other coexisting ions has negligible effect on the detection of Cu 2+ by TPA-OPD . These results strongly confirm that TPA-OPD possesses excellent interference resistance, making it suitable for precise detection of Cu 2+ . Additionally, we investigated the effect of reaction time on the fluorescence response of TPA-OPD during Cu 2+ detection. The study revealed that as reaction time increased, the fluorescence intensity of TPA-OPD detecting Cu 2+ rapidly decreased, reaching a stable state within just 10 seconds. This characteristic demonstrates TPA-OPD 's capability for rapid response. As shown in Fig. 6 , the effect of pH (2 – 11) on the fluorescence intensity of TPA-OPD and its complex with Cu 2+ at 548 nm was investigated. Within the pH range of 4 – 8, the fluorescence intensity of TPA-OPD remained stable, demonstrating good optical stability. When pH 8.0, deprotonation of the phenolic hydroxyl group forms -O⁻, triggering enhanced intramolecular charge transfer and activating non-radiative transitions, leading to fluorescence quenching. The TPA-OPD + Cu 2+ exhibits significant and stable fluorescence quenching within the pH range of 4 – 8, indicating its recognition response possesses excellent pH adaptability. At pH 8.0, Cu 2+ undergoes hydrolysis to form Cu(OH) 2 precipitation, losing its coordination ability. In both cases, the fluorescence quenching effect of the probe weakens, and the fluorescence intensity recovers. These results further confirm that fluorescence quenching originates from the specific coordination between Cu 2+ and TPA-OPD , and this interaction remains stable and efficient within the optimal pH range. 3.5 The proposed binding model for TPA-OPD with Cu 2+ The recognition mechanism of the triphenylamine derivative fluorescent probe TPA-OPD toward Cu 2+ was elucidated through fluorescence calibration curves, mass spectrometry before and after binding, ¹H NMR, FT-IR spectroscopy, and Gaussian calculations. As shown in Fig. 7 , analysis of the fluorescence calibration curve revealed that fluorescence intensity was lowest when both TPA-OPD and Cu 2+ concentrations were 0.5×10 − 6 M. Increasing Cu 2+ concentration did not alter fluorescence intensity, indicating a 1:1 stoichiometric binding ratio between TPA-OPD and Cu 2+ . As displayed in Fig. S6 , the mass spectrum of TPA-OPD bound to Cu 2+ shows two characteristic ion peaks at 803.331 and 866.272, respectively, further validating the 1:1 stoichiometric ratio between TPA-OPD and Cu 2+ . As shown in Fig. S7 , ¹H NMR clearly demonstrates significant changes in the ligand TPA-OPD before and after coordination with Cu 2+ . The disappearance of the (-C = N-) proton signal (approximately 8.5 to 9.0 ppm) and the (-OH) proton signal peak at 13 ppm confirms that (-C = N-) and (-OH) participate in coordination with Cu 2+ . Furthermore, as shown in the infrared spectrum ( Fig. S8 ), after TPA-OPD coordinates with Cu 2+ , the (-OH) stretching vibration peak near 3400 cm⁻¹ significantly broadens and intensifies, indicating the participation of the phenolic hydroxyl group in coordination; while the peaks at 1640 cm⁻¹ (-C = N-) and 1300–1320 cm⁻¹ (C-N) decrease. Concurrently, the intensity of the aromatic ring skeletal vibration peak diminishes, suggesting perturbation of the molecular conjugated system. This further confirms the involvement of (-C = N-) and (-OH) in coordination with Cu 2+ . Based on molecular structure analysis, TPA-OPD forms a tetracoordinate planar complex with Cu 2+ via its two phenolic oxygen atoms and two imine nitrogen atoms. Based on the excellent mechanism of triphenylamine derivatives in detection, we propose a potential sensing mechanism as shown in Fig. S9 : Cu 2+ binds to the open cavity of TPA-OPD , forming a stable complex through coordination with the phenolic oxygen and imine nitrogen atoms. This binding process perturbs the electronic structure of the ligand. Additionally, we performed theoretical calculations on the proposed sensing model using the Gauss09 B3LYP/6-31G* method. As shown in Fig. 8 , the electron density initially distributes predominantly over the aromatic ring structure of TPA-OPD . However, upon coordination with Cu 2+ , the electron density of the HOMO remains concentrated on the conjugated backbone of the organic ligand, while the electron density of the LUMO is almost entirely localized at the Cu 2+ center. This result indicates that upon formation of the TPA-OPD + Cu 2+ complex, a significant ICT occurs within the system, involving a ligand-to-metal charge transfer (LMCT) from the ligand to the metal center. Calculations show that upon TPA-OPD binding to Cu 2+ , the HOMO-LUMO energy gap decreases markedly from 3.4088688 eV to 1.1411874 eV. This indicates that metal ion binding significantly alters the molecular electronic structure, potentially introducing low-energy LMCT states. Although the charge transfer process may become more favorable, the paramagnetism and strong spin–orbit coupling of Cu²⁺ greatly enhance non-radiative decay pathways, ultimately leading to efficient fluorescence quenching. 3.6 Test paper test for the detection of Cu 2+ in real samples The litmus paper test is a widely used method for evaluating fluorescent sensor performance, valued for its simplicity, rapidity, and capability for in situ detection. In this experiment, ordinary filter paper was immersed in a 0.1 mM solution of TPA-OPD in 95% DMSO-H₂O for 3 minutes. After drying, solutions of different guest molecules were added dropwise (5 drops each), followed by re-drying before observation under UV light (365 nm). Figure 9 shows the typical fluorescence responses of the test paper toward 21 guest species. Upon exposure to all analytes except Cu²⁺, distinct yellow fluorescence was observed. In contrast, the paper treated with Cu²⁺ showed significant fluorescence quenching, indicating selective recognition. 3.7 Application to the detection of Cu 2+ in real water samples By adding a specific amount of Cu 2+ to DMSO-H 2 O (5:95) (tap water or river water) solutions, Cu 2+ solutions of 1.0×10 − 5 M, 3.0×10 − 5 M, and 5.0×10 − 5 M were prepared. Separately, a 1.0×10 − 4 M TPA-OPD solution was prepared using DMSO-H 2 O (5:95). Subsequently, 1.0 mL of the prepared Cu 2+ solution at the corresponding concentration was mixed with 1.0 mL of the prepared TPA-OPD solution, and diluted to 10 mL with DMSO-H 2 O (5:95). Thus, in these solutions, the TPA-OPD concentration was 1.0×10 − 5 M. Therefore, in these solutions, the TPA-OPD concentration was 1.0×10 − 5 M. DMSO - H 2 O (5:95) to a final volume of 10 mL. Thus, in these solutions, the TPA-OPD concentration was 1.0×10 − 5 M, while the Cu 2+ concentrations were 1.0×10 − 6 M, 3.0×10 − 6 M, and 5.0×10 − 6 M, respectively. The fluorescence intensity of the resulting solutions was then measured by fluorescence spectroscopy (λ ex = 370 nm). Further comparison via fluorescence titration curves was performed to calculate the x value (x being the concentration equivalent of Cu 2+ in the mixed solution). The value of 10x represents the test concentration of the original TPA-OPD solution. The test concentrations are listed in Table 1 . All test data were obtained from three independent experiments, and the relative standard deviation (RSD) was subsequently calculated. Table 1 Recovery results of TPA-OPD in water samples. Sample Found Added (µM) Total found (µM) Recovery (%) Std Dev(%) HPLC found (µM ± RSD%) Tap water 0 1.00 1.09 109 3.15 1.01 ± 0.03 0 3.00 3.13 104 2.24 2.97 ± 0.02 0 5.00 4.94 98.8 3.31 4.98 ± 0.03 River water 0 1.00 0.96 96.0 3.46 0.99 ± 0.03 0 3.00 2.96 98.7 2.76 3.01 ± 0.03 0 5.00 4.84 96.8 2.73 5.02 ± 0.03 4. Conclusion This study designed and synthesized a triphenylamine derivative, TPA-OPD , based on the Schiff base reaction. This probe specifically recognizes Cu 2+ ions, undergoing fluorescence quenching to form a stable 1:1 complex. Mechanistic studies indicate that Cu 2+ coordination induces electronic rearrangement, potentially generating a low-energy LMCT state. Its enhanced paramagnetism promotes non-radiative transitions, leading to fluorescence quenching. Furthermore, TPA-OPD exhibits excellent water solubility and stability, enabling rapid and sensitive detection of Cu 2+ in tap water and lake water with outstanding recovery rates, demonstrating promising applications for environmental monitoring. This work provides new insights for developing highly efficient and selective fluorescent sensors. Declarations Data Availability The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request. Acknowledgments This research is financially supported by the Projects of Talents Recruitment of GDUPT (No.2024rcyj1039), the Sci-Tech Innovation Project of Graduate School of Guangdong University of Petrochemical Technology and the Sci-Tech Innovation Project for Joint Training Base of Professional Degrees Graduate of Maoming Green Chemical Industry Research Institute (No. 73123106625), the Maoming Science and Technology Plan, China (No.2022S040) and the Natural Science Foundation of Guangdong Province (No. 2614050002840). Funding This work was supported bythe Projects of Talents Recruitment of GDUPT (No.2024rcyj1039), the Sci-Tech Innovation Project of Graduate School of Guangdong University of Petrochemical Technology and the Sci-Tech Innovation Project for Joint Training Base of Professional Degrees Graduate of Maoming Green Chemical Industry Research Institute (No. 73123106625), the Maoming Science and Technology Plan, China (No.2022S040) and the Natural Science Foundation of Guangdong Province (No. 2614050002840). Author information Authors and Affiliations Guangdong University of Petrochemical Technology, Maoming, Guangdong 525000, China . Long Liu, Jiayi Chen,Meijun Ye, Wen Huang, Xiang Liao, Hanqing Wu, Jingshui Xu. Contributions Long Liu: Conceptualization, Resources, Data Curation, Formal analysis, Investigation, Writing - original draft, Methodology, Validation, Visualization, Funding acquisition. Jiayi Chen: Resources, Data Curation, Formal analysis, Investigation, Validation, Visualization. Meijun Ye: Resources, Writing - review & editing, Supervision. Wen Huang : Resources, Writing - review & editing, Supervision. Xiang Liao : Resources, Writing - review & editing, Supervision. Hanqing Wu: Data Curation, Formal analysis, Investigation. Jingshui Xu: Conceptualization, Writing - review & editing, Supervision. Corresponding author Correspondence toHanqing Wu, Jingshui Xu. Ethics declarations Ethics Approval Not applicable. Consent to Participate Informed consent was obtained from all individual participants included in the study. Competing Interests The authors declare no competing interests References Isaac R, Siddiqui S, Aldosari OF, Uddin MK (2023) Magnetic biochar derived from Juglans regia for the adsorption of Cu2 + and Ni2+: Characterization, modelling, optimization, and cost analysis. J Saudi Chem Soc 27(6):101749 Zhou Y, Li H, Tse E, Sun H (2024) Metal-detection based techniques and their applications in metallobiology. 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Anal Chim Acta, 1286, p. 341980, 2024/01/15/ 2024, doi: https://doi.org/10.1016/j.aca.2023.341980 Karawek A, Mayurachayakul P, Santiwat T, Sukwattanasinitt M, Niamnont N Electrospun nanofibrous sheet doped with a novel triphenylamine based salicylaldehyde fluorophore for hydrazine vapor detection. J Photochem Photobiol A, 404, p. 112879, 2021/01/01/ 2021, doi: https://doi.org/10.1016/j.jphotochem.2020.112879 Scheme 1 Scheme 1 is available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files SupplementaryMaterials.docx GRAPHICALABSTRACT.jpg Scheme1.jpg Scheme 1Synthetic route of compound TPA-OPD. Cite Share Download PDF Status: Published Journal Publication published 06 Mar, 2026 Read the published version in Journal of Fluorescence → Version 1 posted Editorial decision: Revision requested 24 Dec, 2025 Reviews received at journal 18 Dec, 2025 Reviews received at journal 16 Dec, 2025 Reviewers agreed at journal 11 Dec, 2025 Reviewers agreed at journal 11 Dec, 2025 Reviewers agreed at journal 11 Dec, 2025 Reviewers invited by journal 11 Dec, 2025 Editor assigned by journal 08 Dec, 2025 Submission checks completed at journal 08 Dec, 2025 First submitted to journal 01 Dec, 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. 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17:33:46","extension":"html","order_by":27,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":121158,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/6d281bb0724faabb07572a63.html"},{"id":98451804,"identity":"625542ad-4458-4801-a76e-e9f6cf02bd6c","added_by":"auto","created_at":"2025-12-17 17:33:27","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":65337,"visible":true,"origin":"","legend":"\u003cp\u003eThe emission spectra of \u003cstrong\u003eTPA-OPD\u003c/strong\u003e in different solvents (1.0×10\u003csup\u003e-5\u003c/sup\u003e M, λ\u003csub\u003eex\u003c/sub\u003e = 370 nm).\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/b1b9e1eac5746ec31202d4ba.jpg"},{"id":98451731,"identity":"a2760e98-4f7c-4f22-b295-eb704fae02c6","added_by":"auto","created_at":"2025-12-17 17:33:10","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":84871,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Emission spectra of\u003cstrong\u003e TPA-OPD \u003c/strong\u003ein DMSO-H\u003csub\u003e2\u003c/sub\u003eO mixed solvent (1×10\u003csup\u003e-5\u003c/sup\u003eM, λ\u003csub\u003eex\u003c/sub\u003e= 370 nm); (b) Corresponding maximum fluorescence wavelengths and intensities.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/30da72780d992a5d8ba7687b.jpg"},{"id":98451850,"identity":"07e06c75-ddc5-4b84-8aab-f956a6dc5e29","added_by":"auto","created_at":"2025-12-17 17:33:46","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":82008,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Fluorescence emission spectra and intensities of \u003cstrong\u003eTPA-OPD\u003c/strong\u003e in the absence and presence of various substances in DMSO-H₂O solution (95% H₂O, v/v; λ\u003csub\u003eex\u003c/sub\u003e = 370 nm, DMSO/H₂O = 5/95, 1 × 10⁻⁵ M). (b) Comparison of fluorescence intensities at 548 nm under conditions of 95% water content.None = 95% H\u003csub\u003e2\u003c/sub\u003eO, 1 = Cu²⁺, 2 = Na⁺, 3 = K⁺, 4 = Cs⁺, 5 = Mg²⁺, 6 = Al³⁺, 7 = Ca\u003csup\u003e2+\u003c/sup\u003e, 8 = Ba²⁺, 9 = Cd²⁺, 10 = N₂H₆²⁺, 11 = Sr²⁺, 12 = NH₄⁺, 13 = Co\u003csup\u003e2+\u003c/sup\u003e, 14 = Zn\u003csup\u003e2+\u003c/sup\u003e, 15 = Ag\u003csup\u003e+\u003c/sup\u003e, 16 = Ni²⁺, 17 = SO₄²⁻, 18 = CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e, 19 = Cl\u003csup\u003e-\u003c/sup\u003e , 20 = NO₃⁻, 21 = CH₃COO⁻.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/5cb05c78e643568a6bded8a0.jpg"},{"id":98451679,"identity":"abc132a7-f616-4fda-9059-63a572193d26","added_by":"auto","created_at":"2025-12-17 17:33:04","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":94547,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Fluorescence emission spectra of \u003cstrong\u003eTPA-OPD\u003c/strong\u003e upon addition of increasing equivalents of Cu\u003csup\u003e2+\u003c/sup\u003e (0-10.0 eq) (λ\u003csub\u003eex\u003c/sub\u003e = 370 nm, in DMSO/H₂O = 5/95, v/v; 1 × 10\u003csup\u003e-5\u003c/sup\u003e M). (b) Fluorescence intensity of \u003cstrong\u003eTPA-OPD \u003c/strong\u003eat 548 nm as a function of Cu\u003csup\u003e2+\u003c/sup\u003e concentration, used to determine the detection limit of \u003cstrong\u003eTPA-OPD \u003c/strong\u003efor Cu²⁺.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/27494b59e36f0a5bb825d9a1.jpg"},{"id":98451738,"identity":"e947ad2a-564b-4cbd-9ef5-b7c6e1570b07","added_by":"auto","created_at":"2025-12-17 17:33:10","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":52763,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Comparison of fluorescence intensities of \u003cstrong\u003eTPA-OPD + Cu\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e \u003c/strong\u003ewith various substances in DMSO-H\u003csub\u003e2\u003c/sub\u003eO solutions containing 95% H\u003csub\u003e2\u003c/sub\u003eO (λ\u003csub\u003eex\u003c/sub\u003e= 370 nm, DMSO/H\u003csub\u003e2\u003c/sub\u003eO = 5/95, 1×10\u003csup\u003e-5\u003c/sup\u003eM); (b) Comparison of fluorescence intensities at 548 nm of\u003cstrong\u003e TPA-OPD + Cu\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e + X \u003c/strong\u003eand\u003cstrong\u003e TPA-OPD + X \u003c/strong\u003esystems. None = 95% H\u003csub\u003e2\u003c/sub\u003eO, 1 = Cu²⁺, 2 = Na⁺, 3 = K⁺, 4 = Cs⁺, 5 = Mg²⁺, 6 = Al³⁺, 7 = Ca\u003csup\u003e2+\u003c/sup\u003e, 8 = Ba²⁺, 9 = Cd²⁺, 10 = N₂H₆²⁺, 11 = Sr²⁺, 12 = NH₄⁺, 13 = Co\u003csup\u003e2+\u003c/sup\u003e, 14 = Zn\u003csup\u003e2+\u003c/sup\u003e, 15 = Ag\u003csup\u003e+\u003c/sup\u003e, 16 = Ni²⁺, 17 = SO₄²⁻, 18 = CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e, 19 = Cl\u003csup\u003e-\u003c/sup\u003e , 20 = NO₃⁻, 21 = CH₃COO⁻.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/daefdd7ba69b795eb9abd9af.jpg"},{"id":98451853,"identity":"667dded9-a4d1-4bfe-8e63-6e351722813c","added_by":"auto","created_at":"2025-12-17 17:33:47","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":57926,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of pH on the maximum fluorescence intensity of \u003cstrong\u003eTPA-OPD\u003c/strong\u003e (548 nm) and \u003cstrong\u003eTPA-OPD + Cu²⁺\u003c/strong\u003e (548 nm) (λ\u003csub\u003eex\u003c/sub\u003e = 370 nm,\u003cstrong\u003e \u003c/strong\u003eDMSO/H₂O = 5/95 , 1×10⁻⁵ M , pH adjusted with hydrochloric acid or sodium hydroxide).\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/fd17b5c5711ad9e22991c42b.jpg"},{"id":98451791,"identity":"8fc5e0f0-c6e0-4e42-9829-bf49c47cdfce","added_by":"auto","created_at":"2025-12-17 17:33:23","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":45630,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Fluorescence titration curve of\u003cstrong\u003e TPA-OPD + Cu\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e \u003c/strong\u003ein DMSO/H\u003csub\u003e2\u003c/sub\u003eO (5/95) solution (λ\u003csub\u003eex\u003c/sub\u003e= 370 nm), total concentration [\u003cstrong\u003e TPA-OPD + Cu\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2+\u003c/strong\u003e\u003c/sup\u003e] = 1×10\u003csup\u003e-5\u003c/sup\u003eM; (b) Linear fit plot of fluorescence intensity versus Cu\u003csup\u003e2+\u003c/sup\u003e concentration based on data from (a), used to establish a quantitative detection model.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/d0cb1e04aed43e9ce8f8268f.jpg"},{"id":98451854,"identity":"32ee69c1-6032-49ed-8e4c-49c2f827fded","added_by":"auto","created_at":"2025-12-17 17:33:48","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":80117,"visible":true,"origin":"","legend":"\u003cp\u003eLUMO and HOMO orbitals of\u003cstrong\u003e TPA-OPD \u003c/strong\u003eand\u003cstrong\u003e TPA-OPD + Cu\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2+\u003c/strong\u003e\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/a9d37f976a9a82a9f737df0f.jpg"},{"id":98451540,"identity":"c1d904bd-06c6-4fd1-a097-97d4d035e51f","added_by":"auto","created_at":"2025-12-17 17:33:00","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":24988,"visible":true,"origin":"","legend":"\u003cp\u003eFluorescence photos of test paper with\u003cstrong\u003e TPA-OPD \u003c/strong\u003efor different species. None = 95% H\u003csub\u003e2\u003c/sub\u003eO, 1 = Cu²⁺, 2 = Na⁺, 3 = K⁺, 4 = Cs⁺, 5 = Mg²⁺, 6 = Al³⁺, 7 = Ca\u003csup\u003e2+\u003c/sup\u003e, 8 = Ba²⁺, 9 = Cd²⁺, 10 = N₂H₆²⁺, 11 = Sr²⁺, 12 = NH₄⁺, 13 = Co\u003csup\u003e2+\u003c/sup\u003e, 14 = Zn\u003csup\u003e2+\u003c/sup\u003e, 15 = Ag\u003csup\u003e+\u003c/sup\u003e, 16 = Ni²⁺, 17 = SO₄²⁻, 18 = CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e, 19 = Cl- , 20 = NO₃⁻, 21 = CH₃COO⁻.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/93b0b4c7f8366e4aa48f626a.jpg"},{"id":104250749,"identity":"834f1f7d-ff22-4f41-b637-5a596b717bd9","added_by":"auto","created_at":"2026-03-09 16:07:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1698097,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/bee334f8-6f52-4a9f-8178-64d442f3dcf6.pdf"},{"id":98451816,"identity":"373ed499-70d1-495e-9a4e-69ce39eea7ae","added_by":"auto","created_at":"2025-12-17 17:33:35","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":717216,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterials.docx","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/5873bf77da560c73983b8d85.docx"},{"id":98451470,"identity":"81fe8b27-2573-4437-b9a6-1f853ea484ec","added_by":"auto","created_at":"2025-12-17 17:32:53","extension":"jpg","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":76078,"visible":true,"origin":"","legend":"","description":"","filename":"GRAPHICALABSTRACT.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/7ca3f42215ece085a8061731.jpg"},{"id":98451789,"identity":"1bbefe4a-8658-4386-b2b4-e7863a1be57d","added_by":"auto","created_at":"2025-12-17 17:33:23","extension":"jpg","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":37364,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1\u003c/strong\u003eSynthetic route of compound\u003cstrong\u003e TPA-OPD\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"Scheme1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8247812/v1/9f005374b2497c8f946bb54c.jpg"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eA Schiff Base-Functionalized Triphenylamine Fluorescent Probe for Selective and Sensitive Detection of Cu\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e in Aqueous Media\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith accelerating industrialization, environmental pollution has become increasingly prominent, with metal ions drawing significant attention due to their widespread presence and potential hazards\u003csup\u003e[\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e. As a vital industrial metal, copper plays an indispensable role in modern society. Its excellent electrical conductivity, thermal conductivity, and corrosion resistance have led to its extensive application across multiple sectors including power, electronics, construction, and transportation\u003csup\u003e[\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. With the extensive use of copper and its compounds, copper ion pollution has gradually emerged as a significant issue. As a heavy metal pollutant, copper ions exert substantial impacts on both the environment and living organisms\u003csup\u003e[\u003cspan additionalcitationids=\"CR11 CR12 CR13 CR14\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e. Simultaneously, copper ions are essential trace elements for the human body\u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e, playing a crucial role in maintaining normal physiological functions. They participate in the activity of various enzymes, being vital for respiration, cell proliferation\u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e, neurotransmitter biosynthesis\u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e iron metabolism\u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e, antioxidant defense systems\u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e, connective tissue formation\u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e and nervous system health\u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e. Therefore, establishing efficient, sensitive, and selective copper ion detection methods holds significant value for environmental monitoring, food safety, and clinical diagnostics\u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eCurrent copper ion detection methods predominantly rely on instrumental analysis techniques, such as flame atomic absorption spectroscopy (AAS)\u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e, electrochemical analysis\u003csup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e, inductively coupled plasma mass spectrometry (ICP-MS)\u003csup\u003e[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e, high-performance liquid chromatography (HPLC)\u003csup\u003e[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003c/sup\u003e, and solid-phase microextraction (SPME)\u003csup\u003e[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e. These methods offer high accuracy and precision but are limited in widespread practical application due to expensive equipment, high detection limits, and cumbersome procedures\u003csup\u003e[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e. The limitations inherent in such detection methods can be effectively addressed by fluorescence probe analysis\u003csup\u003e[\u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThis work designed and synthesized a novel AIE fluorescent probe, \u003cb\u003eTPA-OPD\u003c/b\u003e, achieving highly selective and nanoscale ultrasensitive detection of Cu\u003csup\u003e2+\u003c/sup\u003e. Benefiting from its AIE properties, \u003cb\u003eTPA-OPD\u003c/b\u003e effectively avoids aggregation quenching issues in aqueous solutions that plague traditional probes, significantly enhancing the signal-to-noise ratio in bioimaging. Through comprehensive analysis using NMR spectroscopy, pre- and post-binding mass spectrometry, and theoretical calculations, we systematically elucidated its coordination mode and response mechanism, establishing a clear \"structure-property-mechanism\" correlation. This work provides novel insights for developing high-performance metal ion probes with well-defined mechanisms, offering broad prospects for environmental and biomedical detection.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Reagents and instruments\u003c/h2\u003e \u003cp\u003eChemical reagents were purchased from Aladdin Co., Ltd. The nitrates were used for metallic salts. The sodium salts were used for anion salts. The TLC (Thin-layer chromatography) analyses were carried out on the precoated glass plates. NMR spectra were recorded on the Bruker-ARX 400 instrument, using TMS as inner standard. The MS spectra were recorded on the Bruker mass spectrometer. Varian UV-Vis spectrometer were recorded on UV-Vis spectra. Fluorescence spectra were recorded on a Hitachi F-4500 spectrometer. The density functional theory (DFT) method was used to perform the theoretical calculations on Gaussian 09 program at the B3LYP/6-31G(d) level.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Synthesis of Probe \u003cb\u003eTPA-OPD\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eAs shown in Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, compound \u003cb\u003e3\u003c/b\u003e was first synthesized by referring to the literature method\u003csup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/sup\u003e. Subsequently, under nitrogen atmosphere, compound \u003cb\u003e3\u003c/b\u003e (0.219 g, 0.60 mmol) and o-phenylenediamine (0.033 g, 0.3 mmol) were refluxed for 12 h in a mixture of 15 mL EtOH and 1 mL DCM. The reaction was monitored by TLC analysis. Upon completion, the organic solvents were removed by rotary evaporation. The crude product was purified by column chromatography (elution: PE/DCM\u0026thinsp;=\u0026thinsp;10/1), yielding the target product \u003cb\u003eTPA-OPD\u003c/b\u003e (yellow solid, 76.0% yield). UV-vis (DMSO) λ\u003csub\u003emax\u003c/sub\u003e: 370 nm; m.p. 153.6-155.4 ℃; \u003csup\u003e1\u003c/sup\u003eH NMR (400 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) ( \u003cb\u003eFig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e), δ : 7.03\u003cb\u003e\u0026ndash;\u003c/b\u003e7.08 (m, 4H, -ArH), 7.08\u003cb\u003e\u0026ndash;\u003c/b\u003e7.18 (m, 15H, -ArH), 7.25 (s, 2H, -CH), 7.29 (d, J\u0026thinsp;=\u0026thinsp;8.0 Hz, 9H, -ArH), 7.32\u003cb\u003e\u0026ndash;\u003c/b\u003e7.36 (m, 2H, -ArH), 7.42 (d, J\u0026thinsp;=\u0026thinsp;8.0 Hz, 2H, -ArH), 7.51 (d, J\u0026thinsp;=\u0026thinsp;8.0 Hz, 4H, -ArH), 8.67 (s, 2H, -CH), 13.15 (s, 2H, -OH); \u003csup\u003e13\u003c/sup\u003eC NMR (101 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) (\u003cb\u003eFig. S2\u003c/b\u003e), δ : 115.1, 117.5, 123.2, 123.3, 124.8, 127.9, 129.4, 147.4, 163.0; MALDI-TOF MS m/z: Calcd for C\u003csub\u003e56\u003c/sub\u003eH\u003csub\u003e43\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e [M\u0026thinsp;+\u0026thinsp;H]\u003csup\u003e+\u003c/sup\u003e, 802.3308, found: 803.335.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Experimental procedure for test paper\u003c/h2\u003e \u003cp\u003eNeutral paper strips were immersed in a DMSO-H\u003csub\u003e2\u003c/sub\u003eO (5:95) solution containing \u003cb\u003eTPA-OPD\u003c/b\u003e (0.1 mM) for 3.0 minutes. The strips were then removed and air-dried naturally before being cut into circular discs for subsequent experiments. Subsequently, three drops each of \u003cb\u003eTPA-OPD\u003c/b\u003e solution and solutions of common metal ions and anions (all guest concentrations 0.1 mM) at different equivalent concentrations were added to these discs. After drying again, the discs were observed under UV light (365 nm) and fluorescence photographs were taken.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and dis cussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Photophysical properties\u003c/h2\u003e \u003cp\u003eFirst, the photophysical properties of \u003cb\u003eTPA-OPD\u003c/b\u003e in different organic solvents were investigated via UV-Vis absorption and fluorescence spectroscopy, with results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Within the 375\u003cb\u003e\u0026ndash;\u003c/b\u003e390 nm wavelength range, \u003cb\u003eTPA-OPD\u003c/b\u003e exhibits weak UV absorption in nonpolar solvents (Hex, PE) due to low solubility and tendency to aggregate, resulting in reduced effective concentration. Conversely, in polar-matched solvents, it disperses uniformly with stable concentration, yielding strong and stable absorption. Solvent polarity dominates absorption differences by influencing dissolution behavior. Simultaneously, the fluorescence emission intensity of \u003cb\u003eTPA-OPD\u003c/b\u003e also exhibits significant variations across different solvents, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Within the 500\u003cb\u003e\u0026ndash;\u003c/b\u003e600 nm range, \u003cb\u003eTPA-OPD\u003c/b\u003e exhibits distinct fluorescence emission peaks, with a prominent peak at 548 nm. Notably, fluorescence emission intensity in low-polarity solvents ( Hex and PE) is markedly lower than in other solvents. These phenomena may arise because in pure nonpolar solvents (Hex and PE), the molecules form disordered, dense precipitates or large-scale aggregates due to extremely poor solubility. This leads to rapid dissipation of excited-state energy through nonradiative pathways (e.g., intermolecular collisions or excited-state quenching), thereby suppressing effective fluorescence emission.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo systematically investigate the influence of aggregation behavior on fluorescence properties, DMSO was selected as the base solvent due to its high solubility, excellent fluorescence stability, and low toxicity, and was used to prepare DMSO-H\u003csub\u003e2\u003c/sub\u003eO mixtures with varying water fractions. As water content increased, \u003cb\u003eTPA-OPD\u003c/b\u003e gradually aggregated due to reduced solubility, forming nanoaggregates or precipitates. This enabled systematic investigation of changes in luminescence intensity, wavelength, and stability across different aggregation states, revealing the structure-property relationship between the molecular microenvironment and luminescent performance. In DMSO-H\u003csub\u003e2\u003c/sub\u003eO mixed solvent systems, the UV-vis absorption spectrum of \u003cb\u003eTPA-OPD\u003c/b\u003e remained essentially unchanged (as shown in \u003cb\u003eFig. S5\u003c/b\u003e), while its fluorescence emission behavior exhibited significant dependence on water content (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In pure DMSO, \u003cb\u003eTPA-OPD\u003c/b\u003e exhibits pale green fluorescence under 365 nm UV irradiation, with a maximum emission peak at approximately 522 nm. As water content increases (0%\u003cb\u003e-\u003c/b\u003e30%), the fluorescence emission peak gradually redshifts, shifting the solution's luminescence color from pale green to yellow. This phenomenon can be attributed to either the excited-state intramolecular charge transfer (ICT) effect induced by enhanced solvent polarity or the formation of primary aggregates triggered by intermolecular weak interactions, both leading to reduced excited-state energy. When water content further increased to 95%, the emission wavelength stabilized, forming a strong, sharp emission peak at 548 nm, while fluorescence intensity significantly enhanced with rising water proportion. The aforementioned phenomena can be attributed to the following: as a poor solvent, water causes a sharp decrease in molecular solubility at high concentrations, leading to pronounced self-aggregation and the formation of nanoscale aggregates. The fluorescence enhancement occurs synchronously with the aggregation process, exhibiting typical Aggregation-Induced Emission (AIE) characteristics. intramolecular rotational (RIR) or vibrational (RIV) non-radiative transition pathways are spatially restricted by steric hindrance, effectively suppressing energy dissipation and enhancing radiative transition efficiency.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Responsiveness of the sensor \u003cb\u003eTPA-OPD\u003c/b\u003e to ions\u003c/h2\u003e \u003cp\u003eSubsequently, the response characteristics of \u003cb\u003eTPA-OPD\u003c/b\u003e to various ions were systematically investigated in a DMSO-H\u003csub\u003e2\u003c/sub\u003eO solution with 95% water content. The results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. It can be observed that after adding Na⁺, K⁺, Cs⁺, Mg\u003csup\u003e2+\u003c/sup\u003e, Al\u0026sup3;⁺, Ca\u003csup\u003e2+\u003c/sup\u003e, Ba\u003csup\u003e2+\u003c/sup\u003e, Cd\u003csup\u003e2+\u003c/sup\u003e, N₂H₆\u003csup\u003e2+\u003c/sup\u003e, Sr\u003csup\u003e2+\u003c/sup\u003e, NH₄⁺, Co\u003csup\u003e2+\u003c/sup\u003e, Zn\u003csup\u003e2+\u003c/sup\u003e, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e, NO₃\u003csup\u003e\u0026minus;\u003c/sup\u003e, SO₄\u0026sup2;\u003csup\u003e\u0026minus;\u003c/sup\u003e and CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e ions, the fluorescence emission peaks of \u003cb\u003eTPA-OPD\u003c/b\u003e all centered around approximately 548 nm. The \u003cem\u003eI/I₀\u003c/em\u003e ratio measured at this wavelength (where \u003cem\u003eI\u003c/em\u003e is the fluorescence intensity of \u003cb\u003eTPA-OPD\u003c/b\u003e in the presence of different added ions, and \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e is the fluorescence intensity of the pristine sample.) ranged from 0.93 to 1.04 at this wavelength. These values are close to unity, indicating that the fluorescence emission intensity remains essentially unchanged, consistent with that of pure \u003cb\u003eTPA-OPD\u003c/b\u003e, indicating that the probe itself exhibits good spectral stability in the presence of various coexisting ions. However, upon the addition of Cu\u003csup\u003e2+\u003c/sup\u003e to the \u003cb\u003eTPA-OPD\u003c/b\u003e solution, the fluorescence intensity at 548 nm dramatically decreased to approximately 10% of its original value, indicating significant fluorescence quenching. This robust and selective response toward Cu\u003csup\u003e2+\u003c/sup\u003e, in contrast to other tested metal ions, highlights the exceptional specificity of TPA-OPD for the recognition of copper ions. Notably, this fluorescence change was clearly discernible to the naked eye in actual observation, further highlighting its potential for visual detection. Experimental results demonstrate that \u003cb\u003eTPA-OPD\u003c/b\u003e can specifically recognize Cu\u003csup\u003e2+\u003c/sup\u003e in a DMSO-H\u003csub\u003e2\u003c/sub\u003eO mixed solution system containing 95% water. This highly selective sensing behavior likely originates from the recognition unit in the \u003cb\u003eTPA-OPD\u003c/b\u003e molecule, which features an open cavity structure capable of forming specific chelation with Cu\u003csup\u003e2+\u003c/sup\u003e.This coordination interaction may induce intramolecular charge transfer or alter the excited-state energy level structure, thereby suppressing radiative transitions and significantly reducing the fluorescence quantum yield, leading to fluorescence quenching.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Fluorescence titration of Cu\u003csup\u003e2+\u003c/sup\u003e\u003c/h2\u003e \u003cp\u003eAfter confirming the selective detection capability of \u003cb\u003eTPA-OPD\u003c/b\u003e toward Cu\u003csup\u003e2+\u003c/sup\u003e, fluorescence titration experiments were carried out in a DMSO-H₂O (5:95) solvent system. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a), the maximum fluorescence emission of \u003cb\u003eTPA-OPD\u003c/b\u003e at 548 nm gradually decreased with increasing Cu\u003csup\u003e2+\u003c/sup\u003e concentration. This quenching behavior may be attributed to the weakening of intramolecular rotational restriction on the aromatic groups upon Cu\u0026sup2;⁺ binding to the molecular cavity of \u003cb\u003eTPA-OPD\u003c/b\u003e. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b), within the 0\u0026ndash;1.0 uM range, the fluorescence intensity of \u003cb\u003eTPA-OPD\u003c/b\u003e exhibits a linear dependence on Cu\u003csup\u003e2+\u003c/sup\u003e concentration, described by the equation:y\u0026thinsp;=\u0026thinsp;1255.44\u0026ndash;1096.64x (R\u0026sup2; = 0.99332),where x is the molar concentration of Cu\u003csup\u003e2+\u003c/sup\u003e (mol/L). The high correlation coefficient indicates excellent linearity. Based on the detection limit formula LOD\u0026thinsp;=\u0026thinsp;3σ/k, where σ is the standard deviation of the blank and k is the slope of the calibration curve, the detection limit for Cu\u003csup\u003e2+\u003c/sup\u003e was determined to be 20.47 nM. This value is significantly lower than those reported for other Cu\u003csup\u003e2+\u003c/sup\u003e detection methods (\u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e), highlighting the promising potential of \u003cb\u003eTPA-OPD\u003c/b\u003e for sensitive Cu\u003csup\u003e2+\u003c/sup\u003e sensing.Furthermore, the binding constant (K\u003csub\u003ea\u003c/sub\u003e) between \u003cb\u003eTPA-OPD\u003c/b\u003e and Cu\u003csup\u003e2+\u003c/sup\u003e was calculated to be 1.51 \u0026times; 10⁷ M⁻\u0026sup1; using the Benesi-Hildebrand equation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Anti-interference test and response time\u003c/h2\u003e \u003cp\u003eTo further validate the interference resistance of the \u003cb\u003eTPA-OPD\u003c/b\u003e fluorescent probe in Cu\u003csup\u003e2+\u003c/sup\u003edetection, interference experiments were conducted on \u003cb\u003eTPA-OPD\u003c/b\u003e. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the variation in \u003cem\u003eI/I₀\u003c/em\u003e (where \u003cem\u003eI\u003c/em\u003e is the fluorescence intensity of \u003cb\u003eTPA-OPD\u003c/b\u003e in the presence of different added ions, and \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e is the fluorescence intensity of the pristine sample.) measured at 548 nm remained between 0.97 and 1.06. This indicates that the presence of other coexisting ions has negligible effect on the detection of Cu\u003csup\u003e2+\u003c/sup\u003e by \u003cb\u003eTPA-OPD\u003c/b\u003e. These results strongly confirm that \u003cb\u003eTPA-OPD\u003c/b\u003e possesses excellent interference resistance, making it suitable for precise detection of Cu\u003csup\u003e2+\u003c/sup\u003e. Additionally, we investigated the effect of reaction time on the fluorescence response of \u003cb\u003eTPA-OPD\u003c/b\u003e during Cu\u003csup\u003e2+\u003c/sup\u003e detection. The study revealed that as reaction time increased, the fluorescence intensity of \u003cb\u003eTPA-OPD\u003c/b\u003e detecting Cu\u003csup\u003e2+\u003c/sup\u003e rapidly decreased, reaching a stable state within just 10 seconds. This characteristic demonstrates \u003cb\u003eTPA-OPD\u003c/b\u003e's capability for rapid response.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the effect of pH (2\u003cb\u003e\u0026ndash;\u003c/b\u003e11) on the fluorescence intensity of \u003cb\u003eTPA-OPD\u003c/b\u003e and its complex with Cu\u003csup\u003e2+\u003c/sup\u003e at 548 nm was investigated. Within the pH range of 4\u003cb\u003e\u0026ndash;\u003c/b\u003e8, the fluorescence intensity of \u003cb\u003eTPA-OPD\u003c/b\u003e remained stable, demonstrating good optical stability. When pH\u0026thinsp;\u0026lt;\u0026thinsp;4.0, the fluorescence intensity decreases, primarily attributed to protonation of the Schiff base structure (C\u0026thinsp;=\u0026thinsp;N) and potential hydrolysis. When pH\u0026thinsp;\u0026gt;\u0026thinsp;8.0, deprotonation of the phenolic hydroxyl group forms -O⁻, triggering enhanced intramolecular charge transfer and activating non-radiative transitions, leading to fluorescence quenching.\u003c/p\u003e \u003cp\u003eThe \u003cb\u003eTPA-OPD\u0026thinsp;+\u0026thinsp;Cu\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e exhibits significant and stable fluorescence quenching within the pH range of 4\u003cb\u003e\u0026ndash;\u003c/b\u003e8, indicating its recognition response possesses excellent pH adaptability. At pH\u0026thinsp;\u0026lt;\u0026thinsp;4.0, H⁺ competes with Cu\u003csup\u003e2+\u003c/sup\u003e for coordination sites, causing partial dissociation of Cu\u003csup\u003e2+\u003c/sup\u003e. At pH\u0026thinsp;\u0026gt;\u0026thinsp;8.0, Cu\u003csup\u003e2+\u003c/sup\u003e undergoes hydrolysis to form Cu(OH)\u003csub\u003e2\u003c/sub\u003e precipitation, losing its coordination ability. In both cases, the fluorescence quenching effect of the probe weakens, and the fluorescence intensity recovers. These results further confirm that fluorescence quenching originates from the specific coordination between Cu\u003csup\u003e2+\u003c/sup\u003e and \u003cb\u003eTPA-OPD\u003c/b\u003e, and this interaction remains stable and efficient within the optimal pH range.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.5 The proposed binding model for \u003cb\u003eTPA-OPD\u003c/b\u003e with Cu\u003csup\u003e2+\u003c/sup\u003e\u003c/h2\u003e \u003cp\u003eThe recognition mechanism of the triphenylamine derivative fluorescent probe \u003cb\u003eTPA-OPD\u003c/b\u003e toward Cu\u003csup\u003e2+\u003c/sup\u003e was elucidated through fluorescence calibration curves, mass spectrometry before and after binding, \u0026sup1;H NMR, FT-IR spectroscopy, and Gaussian calculations. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, analysis of the fluorescence calibration curve revealed that fluorescence intensity was lowest when both \u003cb\u003eTPA-OPD\u003c/b\u003e and Cu\u003csup\u003e2+\u003c/sup\u003e concentrations were 0.5\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e M. Increasing Cu\u003csup\u003e2+\u003c/sup\u003e concentration did not alter fluorescence intensity, indicating a 1:1 stoichiometric binding ratio between \u003cb\u003eTPA-OPD\u003c/b\u003e and Cu\u003csup\u003e2+\u003c/sup\u003e. As displayed in \u003cb\u003eFig. S6\u003c/b\u003e, the mass spectrum of \u003cb\u003eTPA-OPD\u003c/b\u003e bound to Cu\u003csup\u003e2+\u003c/sup\u003eshows two characteristic ion peaks at 803.331 and 866.272, respectively, further validating the 1:1 stoichiometric ratio between \u003cb\u003eTPA-OPD\u003c/b\u003e and Cu\u003csup\u003e2+\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in \u003cb\u003eFig. S7\u003c/b\u003e, \u0026sup1;H NMR clearly demonstrates significant changes in the ligand \u003cb\u003eTPA-OPD\u003c/b\u003e before and after coordination with Cu\u003csup\u003e2+\u003c/sup\u003e. The disappearance of the (-C\u0026thinsp;=\u0026thinsp;N-) proton signal (approximately 8.5 to 9.0 ppm) and the (-OH) proton signal peak at 13 ppm confirms that (-C\u0026thinsp;=\u0026thinsp;N-) and (-OH) participate in coordination with Cu\u003csup\u003e2+\u003c/sup\u003e. Furthermore, as shown in the infrared spectrum (\u003cb\u003eFig. S8\u003c/b\u003e), after \u003cb\u003eTPA-OPD\u003c/b\u003e coordinates with Cu\u003csup\u003e2+\u003c/sup\u003e, the (-OH) stretching vibration peak near 3400 cm⁻\u0026sup1; significantly broadens and intensifies, indicating the participation of the phenolic hydroxyl group in coordination; while the peaks at 1640 cm⁻\u0026sup1; (-C\u0026thinsp;=\u0026thinsp;N-) and 1300\u0026ndash;1320 cm⁻\u0026sup1; (C-N) decrease. Concurrently, the intensity of the aromatic ring skeletal vibration peak diminishes, suggesting perturbation of the molecular conjugated system. This further confirms the involvement of (-C\u0026thinsp;=\u0026thinsp;N-) and (-OH) in coordination with Cu\u003csup\u003e2+\u003c/sup\u003e. Based on molecular structure analysis, \u003cb\u003eTPA-OPD\u003c/b\u003e forms a tetracoordinate planar complex with Cu\u003csup\u003e2+\u003c/sup\u003e via its two phenolic oxygen atoms and two imine nitrogen atoms.\u003c/p\u003e \u003cp\u003eBased on the excellent mechanism of triphenylamine derivatives in detection, we propose a potential sensing mechanism as shown in \u003cb\u003eFig. S9\u003c/b\u003e: Cu\u003csup\u003e2+\u003c/sup\u003e binds to the open cavity of \u003cb\u003eTPA-OPD\u003c/b\u003e, forming a stable complex through coordination with the phenolic oxygen and imine nitrogen atoms. This binding process perturbs the electronic structure of the ligand.\u003c/p\u003e \u003cp\u003eAdditionally, we performed theoretical calculations on the proposed sensing model using the Gauss09 B3LYP/6-31G* method. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, the electron density initially distributes predominantly over the aromatic ring structure of \u003cb\u003eTPA-OPD\u003c/b\u003e. However, upon coordination with Cu\u003csup\u003e2+\u003c/sup\u003e, the electron density of the HOMO remains concentrated on the conjugated backbone of the organic ligand, while the electron density of the LUMO is almost entirely localized at the Cu\u003csup\u003e2+\u003c/sup\u003e center. This result indicates that upon formation of the \u003cb\u003eTPA-OPD\u0026thinsp;+\u0026thinsp;Cu\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e complex, a significant ICT occurs within the system, involving a ligand-to-metal charge transfer (LMCT) from the ligand to the metal center. Calculations show that upon \u003cb\u003eTPA-OPD\u003c/b\u003e binding to Cu\u003csup\u003e2+\u003c/sup\u003e, the HOMO-LUMO energy gap decreases markedly from 3.4088688 eV to 1.1411874 eV. This indicates that metal ion binding significantly alters the molecular electronic structure, potentially introducing low-energy LMCT states. Although the charge transfer process may become more favorable, the paramagnetism and strong spin\u0026ndash;orbit coupling of Cu\u0026sup2;⁺ greatly enhance non-radiative decay pathways, ultimately leading to efficient fluorescence quenching.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Test paper test for the detection of Cu\u003csup\u003e2+\u003c/sup\u003e in real samples\u003c/h2\u003e \u003cp\u003eThe litmus paper test is a widely used method for evaluating fluorescent sensor performance, valued for its simplicity, rapidity, and capability for in situ detection. In this experiment, ordinary filter paper was immersed in a 0.1 mM solution of \u003cb\u003eTPA-OPD\u003c/b\u003e in 95% DMSO-H₂O for 3 minutes. After drying, solutions of different guest molecules were added dropwise (5 drops each), followed by re-drying before observation under UV light (365 nm). Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e shows the typical fluorescence responses of the test paper toward 21 guest species. Upon exposure to all analytes except Cu\u0026sup2;⁺, distinct yellow fluorescence was observed. In contrast, the paper treated with Cu\u0026sup2;⁺ showed significant fluorescence quenching, indicating selective recognition.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.7 Application to the detection of Cu\u003csup\u003e2+\u003c/sup\u003e in real water samples\u003c/h2\u003e \u003cp\u003eBy adding a specific amount of Cu\u003csup\u003e2+\u003c/sup\u003eto DMSO-H\u003csub\u003e2\u003c/sub\u003eO (5:95) (tap water or river water) solutions, Cu\u003csup\u003e2+\u003c/sup\u003esolutions of 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e M, 3.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e M, and 5.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e M were prepared. Separately, a 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e M \u003cb\u003eTPA-OPD\u003c/b\u003e solution was prepared using DMSO-H\u003csub\u003e2\u003c/sub\u003eO (5:95). Subsequently, 1.0 mL of the prepared Cu\u003csup\u003e2+\u003c/sup\u003e solution at the corresponding concentration was mixed with 1.0 mL of the prepared \u003cb\u003eTPA-OPD\u003c/b\u003e solution, and diluted to 10 mL with DMSO-H\u003csub\u003e2\u003c/sub\u003eO (5:95). Thus, in these solutions, the \u003cb\u003eTPA-OPD\u003c/b\u003e concentration was 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003eM. Therefore, in these solutions, the \u003cb\u003eTPA-OPD\u003c/b\u003e concentration was 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003eM. DMSO\u003cb\u003e-\u003c/b\u003eH\u003csub\u003e2\u003c/sub\u003eO (5:95) to a final volume of 10 mL. Thus, in these solutions, the \u003cb\u003eTPA-OPD\u003c/b\u003e concentration was 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003eM, while the Cu\u003csup\u003e2+\u003c/sup\u003econcentrations were 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e M, 3.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e M, and 5.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e M, respectively. The fluorescence intensity of the resulting solutions was then measured by fluorescence spectroscopy (λ\u003csub\u003eex\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;370 nm). Further comparison via fluorescence titration curves was performed to calculate the x value (x being the concentration equivalent of Cu\u003csup\u003e2+\u003c/sup\u003e in the mixed solution). The value of 10x represents the test concentration of the original \u003cb\u003eTPA-OPD\u003c/b\u003e solution. The test concentrations are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. All test data were obtained from three independent experiments, and the relative standard deviation (RSD) was subsequently calculated.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRecovery results of TPA-OPD in water samples.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFound\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAdded (\u0026micro;M)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTotal found (\u0026micro;M)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRecovery (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eStd Dev(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eHPLC found (\u0026micro;M\u0026thinsp;\u0026plusmn;\u0026thinsp;RSD%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eTap water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e109\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e1.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e104\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e2.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e98.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e4.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eRiver water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e96.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e0.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e98.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e3.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e96.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e5.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThis study designed and synthesized a triphenylamine derivative, \u003cb\u003eTPA-OPD\u003c/b\u003e, based on the Schiff base reaction. This probe specifically recognizes Cu\u003csup\u003e2+\u003c/sup\u003e ions, undergoing fluorescence quenching to form a stable 1:1 complex. Mechanistic studies indicate that Cu\u003csup\u003e2+\u003c/sup\u003e coordination induces electronic rearrangement, potentially generating a low-energy LMCT state. Its enhanced paramagnetism promotes non-radiative transitions, leading to fluorescence quenching. Furthermore, \u003cb\u003eTPA-OPD\u003c/b\u003e exhibits excellent water solubility and stability, enabling rapid and sensitive detection of Cu\u003csup\u003e2+\u003c/sup\u003e in tap water and lake water with outstanding recovery rates, demonstrating promising applications for environmental monitoring. This work provides new insights for developing highly efficient and selective fluorescent sensors.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research is financially supported by the Projects of Talents Recruitment of GDUPT (No.2024rcyj1039), the Sci-Tech Innovation Project of Graduate School of Guangdong University of Petrochemical Technology and the Sci-Tech Innovation Project for Joint Training Base of Professional Degrees Graduate of Maoming Green Chemical Industry Research Institute (No. 73123106625), the Maoming Science and Technology Plan, China (No.2022S040) and the Natural Science Foundation of Guangdong Province (No. 2614050002840).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported bythe Projects of Talents Recruitment of GDUPT (No.2024rcyj1039), the Sci-Tech Innovation Project of Graduate School of Guangdong University of Petrochemical Technology and the Sci-Tech Innovation Project for Joint Training Base of Professional Degrees Graduate of Maoming Green Chemical Industry Research Institute (No. 73123106625), the Maoming Science and Technology Plan, China (No.2022S040) and the Natural Science Foundation of Guangdong Province (No. 2614050002840).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors and Affiliations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eGuangdong University of Petrochemical Technology, Maoming, Guangdong 525000, China\u003c/em\u003e\u003cem\u003e.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eLong Liu, Jiayi Chen,Meijun Ye, Wen Huang, Xiang Liao, Hanqing Wu, Jingshui Xu.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLong Liu:\u0026nbsp;\u003c/strong\u003eConceptualization, Resources, Data Curation, Formal analysis, Investigation, Writing - original draft, Methodology, Validation, Visualization, Funding acquisition. \u003cstrong\u003eJiayi Chen:\u0026nbsp;\u003c/strong\u003eResources, Data Curation, Formal analysis, Investigation, Validation, Visualization. \u003cstrong\u003eMeijun Ye:\u0026nbsp;\u003c/strong\u003eResources, Writing - review \u0026amp; editing, Supervision.\u003cstrong\u003eWen Huang\u003c/strong\u003e\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003eResources, Writing\u0026nbsp;-\u0026nbsp;review\u0026nbsp;\u0026amp;\u0026nbsp;editing, Supervision.\u0026nbsp;\u003cstrong\u003eXiang Liao\u003c/strong\u003e\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003eResources, Writing\u0026nbsp;-\u0026nbsp;review\u0026nbsp;\u0026amp;\u0026nbsp;editing, Supervision. \u003cstrong\u003eHanqing Wu:\u0026nbsp;\u003c/strong\u003eData Curation, Formal analysis, Investigation. \u003cstrong\u003eJingshui Xu:\u0026nbsp;\u003c/strong\u003eConceptualization, Writing\u0026nbsp;-\u0026nbsp;review\u0026nbsp;\u0026amp;\u0026nbsp;editing, Supervision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding author\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence toHanqing Wu, Jingshui Xu.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eInformed consent was obtained from all individual participants included in the study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eIsaac R, Siddiqui S, Aldosari OF, Uddin MK (2023) Magnetic biochar derived from Juglans regia for the adsorption of Cu2\u0026thinsp;+\u0026thinsp;and Ni2+: Characterization, modelling, optimization, and cost analysis. 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J Photochem Photobiol A, 404, p. 112879, 2021/01/01/ 2021, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jphotochem.2020.112879\u003c/span\u003e\u003cspan address=\"10.1016/j.jphotochem.2020.112879\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Scheme 1","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section.\u003c/p\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-fluorescence","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jofl","sideBox":"Learn more about [Journal of Fluorescence](https://www.springer.com/journal/10895)","snPcode":"10895","submissionUrl":"https://submission.nature.com/new-submission/10895/3","title":"Journal of Fluorescence","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Organic fluorescence, Sensor, Schiff base, Triphenylamine, Cu2+","lastPublishedDoi":"10.21203/rs.3.rs-8247812/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8247812/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHeavy metal Cu\u003csup\u003e2+\u003c/sup\u003e from industrial discharge continuously accumulates in ecosystems, posing threats to human health and ecological balance. Researchers successfully synthesized a novel fluorescent probe, \u003cstrong\u003eTPA-OPD\u003c/strong\u003e, via a Schiff base reaction between triphenylamine and o-phenylenediamine. \u003cstrong\u003eTPA-OPD\u003c/strong\u003e exhibits rapid, highly selective, and sensitive fluorescence quenching in response to Cu\u003csup\u003e2+\u003c/sup\u003e, along with excellent anti-interference capability. The binding mechanism between Cu²⁺ and \u003cstrong\u003eTPA-OPD\u003c/strong\u003e was confirmed by Job’s plot, Fourier-transform infrared spectroscopy, mass spectrometry, nuclear magnetic resonance, and Gaussian calculations.\u003cstrong\u003e TPA-OPD\u003c/strong\u003e effectively detects Cu\u003csup\u003e2+\u003c/sup\u003e in real-world environmental samples such as tap water and river water, demonstrating strong potential for monitoring Cu\u003csup\u003e2+\u003c/sup\u003e pollution.\u003c/p\u003e","manuscriptTitle":"A Schiff Base-Functionalized Triphenylamine Fluorescent Probe for Selective and Sensitive Detection of Cu2+ in Aqueous Media","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-17 17:25:39","doi":"10.21203/rs.3.rs-8247812/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-12-24T20:16:15+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-19T04:57:39+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-16T13:26:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"105670563616340516302551120963115852181","date":"2025-12-12T02:12:19+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"153865935475439913224318292183464365873","date":"2025-12-11T13:34:31+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"153373616927650798037784810615203163836","date":"2025-12-11T13:26:54+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-11T13:21:00+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-08T17:38:16+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-08T17:37:52+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Fluorescence","date":"2025-12-01T08:02:30+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-fluorescence","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jofl","sideBox":"Learn more about [Journal of Fluorescence](https://www.springer.com/journal/10895)","snPcode":"10895","submissionUrl":"https://submission.nature.com/new-submission/10895/3","title":"Journal of Fluorescence","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"61e52779-54b9-4a3c-8a67-e1973382eb67","owner":[],"postedDate":"December 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-09T16:03:50+00:00","versionOfRecord":{"articleIdentity":"rs-8247812","link":"https://doi.org/10.1007/s10895-026-04718-3","journal":{"identity":"journal-of-fluorescence","isVorOnly":false,"title":"Journal of Fluorescence"},"publishedOn":"2026-03-06 15:57:40","publishedOnDateReadable":"March 6th, 2026"},"versionCreatedAt":"2025-12-17 17:25:39","video":"","vorDoi":"10.1007/s10895-026-04718-3","vorDoiUrl":"https://doi.org/10.1007/s10895-026-04718-3","workflowStages":[]},"version":"v1","identity":"rs-8247812","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8247812","identity":"rs-8247812","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}