Closed-to-Open-Shell Molecular Sensing Enables Highly Selective Detection of Chemical Warfare Agents

Closed-to-Open-Shell Molecular Sensing Enables Highly Selective Detection of Chemical Warfare Agents | 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 Article Closed-to-Open-Shell Molecular Sensing Enables Highly Selective Detection of Chemical Warfare Agents Hongwei Ma, Yunhui Meng, Shuqi Zou, Mingyang Wu, Xiaobai Li, Kun Song, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8614974/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Highly selective detection of chemical warfare agents (CWAs) is critical for public safety but remains extremely challenging due to the poor specificity of conventional fluorescent sensing reactions. Herein, an innovative sensing system based on a closed-to-open-shell transformation is reported. This system enables distinct and analyte-specific optical responses toward typical CWA simulants, including diethylchlorophosphate (DCP), bis(trichloromethyl) carbonate (BTC) and 2-chloroethylethyl sulfide (2-CEES), while also differentiating from the key interferent, HCl. Upon reaction with these analytes, the designed dithienylethene (DTE) derivatives generate stable luminescent radicals exhibiting clearly distinguishable fluorescence and colorimetric signatures. Mechanistic investigations reveal that the exceptional selectivity arises from the competition between Kasha- and anti-Kasha-rule radical emissions, giving each analyte a unique optical fingerprint. This work thus establishes a closed-to-open-shell sensing paradigm that integrates chemical specificity with multimodal optical response, offering a conceptual and practical advance toward selective and real-time detection of CWAs at the molecular level. Physical sciences/Materials science/Materials for optics Physical sciences/Chemistry/Analytical chemistry/Fluorescent probes Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Chemical warfare agents (CWAs) are among the most toxic chemicals known to humankind, posing a severe threat to public safety even at trace concentrations 1 . Despite the strict prohibition of CWAs under the Chemical Weapons Convention, accidental releases and malicious uses over the past century have repeatedly caused mass casualties and global concern 2 , 3 . To mitigate such threats, the development of highly sensitive and selective fluorescent sensing materials has emerged as an effective strategy for early warning and rapid detection 4 , 5 . In particular, donor-acceptor (D-A) type fluorophores equipped with nucleophilic functional groups (e.g., N -heterocycles, -NH 2 , -C = N-, -N = N-, or -OH) can undergo specific nucleophilic substitution or addition reactions with electrophilic CWAs, thereby producing distinct fluorescence changes 6 , 7 . Depending on molecular design, such fluorescence responses are typically governed by intramolecular charge transfer (ICT) 8 , 9 , photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET) 10 , 11 , or excited-state intramolecular proton transfer (ESIPT) mechanisms 12 , 13 . For safety reasons, less toxic analogues such as diethylchlorophosphate (DCP), bis(trichloromethyl) carbonate (BTC), and 2-chloroethylethyl sulfide (2-CEES) are generally used as simulants for sarin, phosgene, and mustard gas, respectively (Fig. 1 a). Nevertheless, achieving precise detection of CWAs in complex environments remains extremely challenging. The main difficulty lies in the lack of reaction specificity for most electrophilic sensing systems, leading to cross-interference from structurally similar CWAs and other electrophilic species 14 – 16 . Furthermore, many CWAs and their analogues undergo hydrolysis in humid air, generating protonic acids that induce false positive signals 17 , 18 . As highlighted in several recent reviews 19 – 21 , overcoming this intrinsic selectivity limitation has become a critical research frontier in CWA sensing 22 . Efforts to enhance selectivity include the design of o -phenylenediamine-based probes capable of distinguishing between phosgene and DCP 23 , dual-site probes containing o -hydroxythioxane moieties for differentiating phosgene and mustard gas 24 , and conjugated microporous polymer films incorporating acid-scavenging additives such as K 2 CO 3 or nano -SiO 2 to suppress acid interference 25 , 26 . Although these approaches have improved sensing reliability to some extent, a universal molecular platform that enables one-to-many specific recognition of multiple CWAs with high anti-interference capability remains elusive. Herein, a conceptually new fluorescent sensing system is developed based on a closed-to-open-shell sensing reaction to enable multi-signal (fluorescence and colorimetric) discrimination of CWAs (Fig. 1 b). Investigation of dithienylethene (DTE) photochromic systems revealed the formation of stable, luminescent radicals upon light irradiation. Based on this finding, two DTE derivatives (DTE-3PCz and DTE-3NCz) were designed and synthesized to investigate the reaction mechanism. Detailed spectroscopic analyses revealed that the photogenerated radicals exhibit dual radiative transitions — Kasha- and anti-Kasha-rule-compliant — allowing distinct fluorescence colors depending on the interacting analyte. For instance, DTE-3PCz (HCl) radical favors orange kasha emission (D 1 →D 0 ), whereas DTE-3PCz (DCP) radical induces indigo anti-Kasha emission (D 2 →D 0 ), accompanied by corresponding colorimetric changes (Fig. 1 c). This unique closed- to open-shell transformation not only ensures molecular-level selectivity toward different CWAs but also provides a new optical response mechanism based on singlet-to-doublet transitions. Furthermore, DTE-3PCz films demonstrate remarkable sensitivity and portability, enabling wireless, real-time vapor detection of DCP, as well as excellent cellular permeability, low cytotoxicity, and high biocompatibility. Overall, this work introduces a novel radical-based fluorescence sensing paradigm that enables simultaneous multi-channel response, enhanced specificity, and practical applicability in detecting CWAs. Results Synthesis and photophysical properties DTE-3PCz and DTE-3NCz were synthesized through a sequence of Friedel-Crafts acylation reaction, McMurry coupling, and Suzuki reaction (Supplementary Fig. 1). Their structures were verified by liquid chromatography-mass spectrometry (LC-MS), 1 H NMR, and 13 C NMR analyses. Comprehensive information was available in Supplementary Figs. 2–10. Upon irradiation with 365 nm UV light, both of DTE-3PCz and DTE-3NCz in DCM undergo pronounced photochromism: a new absorption band at ~ 500 nm appears, consistent with the open-ring to closed-ring transformation of DTE derivatives, accompanied by quenching of the ~ 400 nm fluorescence band. Unexpectedly, prolonged UV irradiation generated an additional absorption band at ~ 600 nm (Fig. 2 a and Supplementary Fig. 11a), along with dual-emission peaks centered at ~ 475 nm and ~ 600 nm (Fig. 2 b and Supplementary Fig. 11b). The corresponding emission color evolved from blue (CIE: 0.16, 0.05) to orange (CIE: 0.42, 0.34) within 60 s (Fig. 2 c and Supplementary Fig. 11c), indicating that a second photochemical process occurs concurrently with the canonical photocyclization 27 . To probe this transformation, electron paramagnetic resonance (EPR) spectra were employed for DTE-3PCz and DTE-3NCz in toluene (Fig. 2 d and Supplementary Fig. 11d). No detectable signal is observed in the EPR spectra of DTE-3PCz before UV irradiation, while obvious signal peaks ranging from 3500–3520 G appear after UV irradiation. The extracted g value 2.003, falls within typical range of neutral carbon radicals ( g = 1.99–2.01) 28 , demonstrating that DTE-3PCz and DTE-3NCz generate stable open-shell species under UV irradiation. Additionally, the ultraviolet absorption spectra and high-performance liquid chromatography (HPLC) of the molecule after combining with the radical scavenger 2,2,6,6-tetramethylpiperidine oxide (TEMPO) under UV irradiation exposure were studied. As shown in the Supplementary Fig. 12, following the addition of TEMPO, the absorption band near ~ 600 nm diminished, and a new peak with a retention time of 50.167 min appeared in the HPLC spectrum (Supplementary Fig. 13). It indicates that the generated radical molecules underwent covalent coupling with TEMPO, forming a new substance. Collectively, these results confirm the mechanism by which DTE-3PCz and DTE-3NCz induces radical generation under UV irradiation. Sensing performance of fluorescent probes to CWAs During radical-emission studies, it discovered that exposure of DTE-3PCz and DTE-3NCz to representative CWA simulants (DCP, 2-CEES, BTC) or to HCl produces markedly different fluorescence and colorimetric outputs upon identical UV irradiation (Fig. 3 , Supplementary Figs. 14 and 17). Take DTE-3PCz as an example, for DCP (Fig. 3 a), increasing concentration suppresses the ~ 600 nm band and attenuates the ~ 450 nm band, shifting the emission from bright blue to indigo and producing a blue colorimetric response. For HCl (Supplementary Figs. 14a), the ~ 600 nm emission intensifies while the ~ 450 nm band remains nearly unchanged, resulting in a blue to orange fluorescence shift and a colorless to red colorimetric shift. For BTC and 2-CEES (Supplementary Figs. 15a, c), the ~ 600 nm band decreases while the ~ 450 nm emission remains steady, producing bright blue to orange fluorescence and colorless to violet colorimetric transitions. The DTE-3PCz limit of detection (LOD) values for DCP, BTC, and 2-CEES were calculated as 0.19 µM (Fig. 3 b), 0.48 µM (Supplementary Fig. 15b), and 1.28 µM (Supplementary Fig. 15d), respectively. The CIE 1931 diagram, time-resolved PL decay curves, quantum yield analysis and interference studies (Figs. 3 f-i, Supplementary Fig. 16 and Supplementary Table 1), further highlight the exceptional selectivity of DTE-3PCz. UV-vis and EPR measurements reveal that CWAs enhance the 600 nm absorption band (Supplementary Figs. 17a, c) and preserve strong radical signatures (Fig. 3 c), suggesting that CWA analytes stabilize the radical species while modulating their excited-state dynamics to yield distinct optical fingerprints. Mechanism Research The photochromism of diarylethene derivatives is typically governed by classical photocyclization pathways 29 – 31 . As shown in Fig. 4 a, a mechanistic model is proposed in which UV irradiation first generates an excited state (1*) (a diradical like intermediates) that undergoes oxygen trapping to form an intermediate species (1’). These intermediate abstracts reactive hydrogen atoms or electrophilic groups (e.g., H-CHCl 2 , H-Cl, C 4 H 10 O 3 P-Cl), yielding a stable radical that accounts for the observed luminescent open-shell state. To validate this mechanism, LC-MS and 1 H NMR analysis on the products formed after UV irradiation between DCP and DTE-3PCz were performed. As shown in Fig. 4 c and Supplementary Figs. 18–19, LC-MS directly detected the masses of the substances formed after DTE-3PCz combined with HCl and DCP as m/z = 569.91 and m/z = 704.22, respectively, which are consistent with the theoretical values (theoretical values are m/z = 569.15 and m/z = 705.24). Additionally, the resulting steady-state solution exhibited complete disappearance of the 1 H NMR signals, consistent with the formation of a paramagnetic radical species, which is typically NMR-silent due to severe line broadening (Fig. 4 b and Supplementary Figs. 20–21) 32 . These results collectively support the proposed reaction mechanism. To elucidate the origin of the distinct emission responses of DTE-3PCz and DTE-3NCz to DCP and HCl under UV irradiation, a comparative investigation of the excited-state properties of the corresponding radical products (from DTE-3PCz and DTE-3NCz) was undertaken 33 – 35 . Under identical UV irradiation, DTE-3PCz solution display markedly different emission behaviors: in the presence of DCP, the ~ 475 nm band dominates over the ~ 600 nm band (Supplementary Fig. 22a), whereas in the presence of HCl, the ~ 600 nm emission becomes predominant (Supplementary Fig. 22b). Time-dependent density functional theory (TD-DFT) calculations indicate that the absorption bands around ~ 600 nm in both systems originate from βHOMO to βSOMO (D 0 -D 1 , λ abs = 535 ~ 540 nm) (Supplementary Tables. 2–3). Electrostatic potential maps (Fig. 5 c and Supplementary Fig. 23) reveal a negatively charged oxygen in the peroxyl radical and an electron-deficient phosphorus center in DCP, enabling nucleophilic attack of DCP on the radical oxygen. These theoretical results, inagreement with the experimental observations, indicating that two reaction pathways (with DCP and HCl) generate the same radical species. TD-DFT further shows that the first excited state (D 1 , βHOMO to βSOMO) possesses a weak oscillator strength (ƒ= 0.03–0.05), whereas the second excited state (D 2 , αSOMO to αLUMO) exhibits significantly larger oscillator strength (ƒ= 0.08–0.14). The distinct orbital compositions—D 1 mainly arising from the 148β→149β transition, and D 2 from the 149α→150α transition—lead to spatially separated electron distributions and different orbital orientations, resulting in minimal overlap (Fig. 5 d and Supplementary Figs. 24–30). Because D 1 and D 2 belong to different spin manifolds, internal conversion (IC) between them is strongly suppressed, giving rise to decoupled dual emission (Fig. 5 b). To verify that the ~ 475 nm band originates from a high-energy anti-Kasha transition, excitation-dependent emission measurements were performed. Excitation–emission experiments confirm that the ~ 475 nm and ~ 600 nm emissions arise from different excited states. Varying the excitation wavelength (360–400 nm) produces a noticeable redshift in emission (Supplementary Fig. 22c), and the excitation spectra monitored at 475 nm and 600 nm differ substantially (Supplementary Fig. 22d). At both 77 K and 298 K, the DTE-3PCz radical exhibits two distinct emission bands, which are assigned to anti-Kasha (D 2 →D 0 ) and Kasha (D 1 →D 0 ) transitions, respectively (Fig. 5 a and Supplementary Fig. 31). Importantly, the DTE-3PCz (DCP) radical shows a larger D 2 -D 1 energy gap than DTE-3PCz (HCl) radical. Consequently, IC from D 2 to D 1 is less efficient in the DCP system, which enhances the D 2 →D 0 emission while suppressing the D 1 →D 0 channel. As a result, the DTE-3PCz (DCP) radical exhibits dominant ~ 475 nm emission, whereas the DTE-3PCz (HCl) radical favors ~ 600 nm emission. Fluorescent film sensing Electrospun films of polyethylene oxide (PEO) doped with DTE-3PCz were fabricated (Fig. 6 a) to serve as a sensing platform for the real-time vapor detection of CWAs 36 . The resulting uniform, ultrafine fibers (0.15 µm diameter) provide a high surface area, facilitating efficient interaction with DCP vapor (Supplementary Fig. 32). A simple adsorption system was first established (Supplementary Fig. 33) to evaluate the adsorption capacities of DTE-3PCz films and blank film toward DCP vapor. Under UV irradiation, the adsorption capacity of rapidly increased within the first 150 min, then slowed due to saturation of active sites, and finally reached equilibrium at approximately 420 min. The maximum adsorption capacity of DTE-3PCz films reached 132 mg/g, whereas that of blank film was only 49 mg/g (Fig. 6 c). To elucidate the rate-limiting step of the DCP adsorption process, the data were fitted using the pseudo-first-order (PFO), pseudo-second-order (PSO), and intra-particle diffusion models (Figs. 6 d-e and Supplementary Fig. 34). The PSO model (R 2 > 0.985) provides a significantly better fit than the PFO model (R 2 < 0.965), indicating that the adsorption process is dominated by chemisorption. This result suggests that DTE-3PCz undergoes a chemical reaction with DCP under UV irradiation. Furthermore, the intra-particle diffusion model reveals two distinct linear regimes, indicating that both surface adsorption and particle diffusion contribute to the overall adsorption process. With increasing DCP concentration, the film color gradually changes from pale yellow to pale pink, while the fluorescence shifts from orange to purple (Fig. 6 b). The fluorescent-based mode offers higher sensitivity, enabling reliable visualization and quantitative detection of trace vapor-phase CWAs. DTE-3PCz film-based portable devices To facilitate practical deployment, a portable fluorescence-sensing device was developed. The system incorporates a DTE-3PCz film, an air pump, a 365 nm LED, a long-pass filter (λ ≥ 380 nm), a CCD sensor, and a Bluetooth transceiver. The internal structure and circuit diagram are shown in the Fig. 7 . The working principle is as follows: an STM 32 microcontroller unit (MCU) drives the CCD sensor to acquire fluorescence signals, which are then transmitted via the Bluetooth transceiver to a personal computer (PC) for data processing and analysis (Fig. 7 a). During data acquisition, the LED and CCD are synchronously switched on and off. Upon exposure to DCP vapor, the fluorescence intensity is quenched, and exhibiting a clear linear relationship with DCP concentration (Fig. 7 b). The device achieves a LOD of 4.0 ppb for DCP vapor and enables remote wireless sensing, thereby significantly reducing operator exposure risk (Fig. 7 c). These results demonstrate that the DTE-3PCz film-based sensor satisfies the practical CWA detection. In addition, the biocompatibility of the DTE-3PCz fluorescent probe was evaluated by in vitro cytotoxicity assays (CCK-8). The results show that DTE-3PCz exhibits low cytotoxicity, efficient cellular uptake, indicating its potential for live-cell fluorescence imaging (Supplementary Fig. 35). Discussion In summary, we establish a previously unexplored fluorescent sensing paradigm based on closed-to-open-shell transformations, which enables multi-channel (fluorescence and colorimetric) differentiation of CWAs simulants. The designed DTE-3PCz and DTE-3NCz molecules undergo photoinduced radical formation, and, the resulting open-shell species exhibit dual radiative pathways that comply with both Kasha and anti-Kasha rules. This uncommon coexistence of D 1 →D 0 and D n →D 0 emissions endows each analyte with a distinct optical fingerprint, thereby achieving molecular-level selectivity that traditional closed-shell sensing reactions can hardly deliver. Mechanistic investigations reveal that the unique singlet-to-doublet transition framework—together with analyte-dependent modulation of excited-state energy gaps—dictates the relative contributions of Kasha and anti-Kasha emissions. Such a controllable interplay between emissive excited states highlights an optical response mechanism rarely accessible in organic fluorophores and, more broadly, expands the fundamental photophysical landscape of organic radicals. Beyond the molecular mechanism, the DTE-R platform demonstrates high practical utility. The DTE-3PCz nanofiber films provide rapid, sensitive, and portable vapor-phase detection, achieving real-time, wireless monitoring of DCP with ppb-level sensitivity. Moreover, the probes exhibit excellent cellular permeability, low cytotoxicity, and good biocompatibility, underscoring their potential for biological sensing scenarios where acidic impurities or electrophilic interferents typically compromise selectivity. Overall, this study introduces a radical-enabled, multi-information optical sensing strategy that addresses long-standing challenges in CWA detection. By leveraging stable luminescent radicals and analyte-dependent competition between Kasha and anti-Kasha pathways, our work offers both a conceptual advance in radical photophysics and a practical sensing platform with broad applicability in environmental monitoring, security, and chemical defense. Methods Chemicals and measurement All the reagents were obtained from Aldrich, Kanto Chemicals, and TCL unless otherwise specified. DCP was purchased from sigma Aldrich. Unless otherwise specified, all reagents are used without further purification after purchase. The 1 H NMR and 13 C NMR spectra of the solution were recorded at 500 MHz using a Bruker AVANCE III HD NMR spectrometer in CDCl 3 with tetramethylsilane (TMS) as the internal standard. Mass spectrometry data were obtained using a triple quadrupole LC-MS/MS instrument, TSQ Quantis/Altis. UV-vis absorption spectra were detected by a Beijing PU-1901 UV-vis spectrophotometer. HPLC analyses were performed with a Water 1525 HPLC pump, Water 2489 UV/Vis detector, and 10 mm×10 mm C18 column. EPR spectra were acquired using an ELEXSYS-II E500 CW-EPR spectrometer from Bruker Instruments, Switzerland. Fluorescence lifetime measurements were performed with an FLS-980 fluorescence lifetime spectrometer coupled to an EPL-375 optical laser. Test solution concentrations ranged from 1.0×10 − 3 to 1.0×10 − 5 M. Baseline calibration was performed using pure DCM as the reference blank, with scanning conducted in the 400–700 nm range. Fluorescence spectra were measured using a Shimadzu RF-6000 fluorescence spectrophotometer. Fluorescent film structures were imaged using a high-resolution field emission scanning electron microscope manufactured by Thermo Fisher Scientific. Theoretical Calculation The radical properties of R-DTE were investigated using the Gaussian 09 D.01 package 37 . Geometric optimization and frequency calculations of the radical structure were performed at the 6–31 g(d, p) basis set level, employing the unrestricted density functional theory (UDFT) method and the M062X functional. Prior to further calculations, it was confirmed that the optimized structures resided at their minimum energy states without any imaginary frequencies. The ultraviolet absorption spectra of the radicals were calculated using the TD-DFT method at the uM062X/6–31 g(d, p) level. Spin density populations were analyzed using Multiwfn software and 38 , 39 visualized with VMD software 40 . Synthesis of compounds GDT-2Cl Glutaroyl chloride (2.25 g, 13.3 mmol), anhydrous aluminum trichloride (3.5 g, 26.25 mmol) were dissolved in a mixture of DCM (20 mL). The flask was placed in an ice-water bath and stirred for 0.5 h. Then, 2-chloro-5-methylthiophenol (2.65 g, 20 mmol) in DCM (10 mL) was slowly added to the round-bottom flask. After complete addition, the ice bath and allow the system were removed to react at room temperature for 2 h. Upon completion, the reaction was slowly quenched with ice water. The residue was extracted with DCM and H 2 O. The combined organic layer was dried over Mg 2 SO 4 . The mixture was purified by silica gel column, using petroleum ether/DCM (v/v = 1:10) as the eluent, the crude product obtained was recrystallized with toluene/anhydrous methanol, and pale-yellow powder (3.2 g) was obtained with a yield of 85%. Synthesis of compounds DTE-2Cl Zinc powder (3 g, 46.15 mmol) was dissolved in tetrahydrofuran (THF) (50 mL). Place the flask in an ice-water bath and titanium tetrachloride 4 mL (18.6 mmol) was slowly dropwise added under a nitrogen atmosphere. After completion of the addition, the system was purged with nitrogen gas three times to ensure a nitrogen atmosphere. The mixture was heated to 68°C and refluxed for 1 h. The temperature was lowered to 40°C. GDT-2Cl (1.8 g, 5 mmol) in THF (20 mL) was slowly added to the reaction flask using a syringe. The mixture was refluxed for 1 h. Upon completion, the reaction was slowly quenched with ice water. The residue was extracted with DCM and H 2 O. The combined organic layer was dried over Mg 2 SO 4 . The mixture was purified through a silica gel column, using petroleum ether as the eluent, the crude product obtained was recrystallized with toluene/anhydrous methanol, and white crystals (1.2 g) was obtained with a yield of 80%. 1 H NMR (500 MHz, CDCl 3 ) δ 6.58 (s, 2H), 2.71 (t, J = 7.5 Hz, 4H), 2.05–1.98 (m, 2H), 1.88 (s, 6H). 13 C NMR (126 MHz, CDCl 3 ) δ 133.79, 133.39, 132.25, 125.65, 124.16, 37.30, 21.79, 13.14. ESI-MS (m/z): [M + H] + calcd. for C 15 H 14 Cl 2 S 2 , 327.99; found 329.00. Synthesis of compounds DTE-3PCz DTE-2Cl (1.32 g, 4 mmol) was dissolved in THF (10 mL) into a three-neck round-bottom flask. Purge the flask three times with nitrogen gas. Cool the mixture to -78°C and n-butyllithium (1.6 mL) was slowly added. After addition, allow the mixture to react at room temperature for 15 min. Then tributyl borate (1.6 mL) was slowly added and continue stirring at room temperature for 3 h. The mixture was transferred to a two-neck flask. 3-bromo-9-phenylcarbazole (1.1 g, 3.39 mmol), palladium(II) tetratriphenylphosphide (0.28 g, 0.24 mmol) and K 2 CO 3 (12.0 mL, 20 wt%) were added. The reaction was heated to 80°C and stirred for 24 h under nitrogen. After removal of the solvent under reduced pressure, the residue was extracted with DCM and H 2 O. The combined organic layers were dried over Mg 2 SO 4 . The mixture was purified by silica gel column, using DCM/petroleum ether (v/v = 1:10) as the eluent, the crude product obtained was recrystallized with toluene/anhydrous methanol, and white powder (0.6 g) was obtained with a yield of 50%. 1 H NMR (500 MHz, CDCl 3 ) δ 8.25 (d, J = 1.7 Hz, 1H), 8.17 (d, J = 7.7 Hz, 1H), 7.62 (t, J = 7.7 Hz, 2H), 7.56 (ddd, J = 8.4, 4.0, 1.7 Hz, 3H), 7.50–7.46 (m, 1H), 7.43–7.40 (m, 2H), 7.37 (d, J = 8.5 Hz, 1H), 7.31 (ddd, J = 7.9, 5.7, 2.3 Hz, 1H), 7.03 (s, 1H), 6.68 (s, 1H), 2.90–2.86 (m, 2H), 2.78 (td, J = 7.4, 2.2 Hz, 2H), 2.06 (d, J = 18.0 Hz, 5H), 1.94 (s, 3H). 13 C NMR (126 MHz, CDCl 3 ) δ 140.31, 139.85, 139.13, 139.10, 136.51, 135.23, 134.53, 134.25, 132.53, 132.41, 132.27, 128.88, 126.50, 125.99, 125.87, 125.81, 125.18, 123.90, 122.98, 122.73, 122.25, 121.93, 119.41, 119.08, 116.13, 116.08, 108.99, 108.88, 37.44, 37.33, 21.93, 13.37, 13.21. ESI-MS (m/z): [M + H] + calcd. for C 33 H 26 ClNS 2 , 535.12; found 536.00. Synthesis of compounds DTE-3NCz DTE-2Cl (1.32 g, 4 mmol) was dissolved in THF (10 mL) into a three-neck round-bottom flask. Purge the flask three times with nitrogen gas. Cool the mixture to -78°C and n-butyllithium (1.6 mL) was slowly added. After addition, allow the mixture to react at room temperature for 15 min. Then tributyl borate (1.6 mL) was slowly added and continue stirring at room temperature for 3 h. The mixture was transferred to a two-neck flask. 3-bromo-9-(2-naphthyl)carbazole) (1.1 g, 3.39 mmol), palladium(II) tetratriphenylphosphide (0.28 g, 0.24 mmol) and K 2 CO 3 (12 mL, 20 wt%) were added. The reaction was heated to 80°C and stirred for 24 h under nitrogen. After removal of the solvent under reduced pressure, the residue was extracted with DCM and H 2 O. The combined organic layers were dried over Mg 2 SO 4 . The mixture was purified by silica gel column, using DCM/petroleum ether (v/v = 1:10) as the eluent, the crude product obtained was recrystallized with toluene/anhydrous methanol, and white powder (0.6 g) was obtained with a yield of 50%. 1 H NMR (500 MHz, CDCl 3 ) δ 8.26 (d, J = 1.8 Hz, 1H), 8.19 (d, J = 7.7 Hz, 1H), 8.10–8.04 (m, 2H), 8.00–7.97 (m, 1H), 7.92 (dd, J = 6.1, 3.3 Hz, 1H), 7.67 (dd, J = 8.7, 2.1 Hz, 1H), 7.58 (ddd, J = 16.8, 7.4, 2.5 Hz, 3H), 7.47–7.40 (m, 3H), 7.34–7.30 (m, 1H), 7.03 (s, 1H), 6.67 (s, 1H), 2.87 (t, J = 7.6 Hz, 2H), 2.80–2.74 (m, 2H), 2.11–2.02 (m, 5H), 1.93 (s, 3H). 13 C NMR (126 MHz, CDCl 3 ) δ 140.48, 139.85, 139.29, 135.25, 134.53, 134.25, 133.96, 132.96, 132.54, 132.44, 132.27, 131.40, 128.89, 126.92, 126.84, 125.93, 125.87, 125.52, 125.26, 124.26, 124.09, 123.91, 123.05, 122.84, 122.36, 121.96, 119.48, 119.21, 116.19, 109.04, 108.94, 37.45, 37.33, 21.94, 13.38, 13.21. ESI-MS (m/z): [M + H] + calcd. for C 37 H 28 ClNS 2 , 585.14; found 586.05. Preparation of DTE-3PCz films Polymer fibers were manufactured using equipment modified for electrospinning. Polyethylene oxide (600 mg, Mw = 1,000,000 Da) and DTE-3PCz (10 mg) were dissolved in 10 mL of DCM solution and stirred thoroughly. The mixture was loaded into a 5 mL syringe connected to a gauge needle. Prior to applying 10 kV, the distance between the needle tip and the grounding plate was adjusted to 18 cm. The solution was then sprayed onto the surface of a grounded aluminum plate and tin foil to form polymer fibers at a constant flow rate of 0.5 mL/h. Finally, the polymer fibers are retained in a sealed centrifuge tube for characterization of their structure via scanning electron microscopy. Adsorption kinetics formula The pseudo first-order (PFO) (Eq. 1), PSO (Eq. 2) model, and intraparticle diffusion model (Eq. 3) is as follows: $$\:\begin{array}{c}\text{ln}\left({\text{q}}_{\text{e}}\text{-}{\text{q}}_{\text{t}}\right)\text{=}\text{ln}{\text{q}}_{\text{e}}\text{-}{\text{k}}_{\text{1}}\text{t}\text{}（\text{1}）\end{array}$$ $$\:\begin{array}{c}\frac{\text{t}}{{\text{q}}_{\text{t}}}\text{=}\frac{\text{1}}{{\text{k}}_{\text{2}}{\text{q}}_{\text{e}}^{\text{2}}}\text{+}\frac{\text{t}}{{\text{q}}_{\text{e}}}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\left(\text{2}\right)\end{array}$$ $$\:\begin{array}{c}{\text{q}}_{\text{t}}\text{=}{\text{k}}_{\text{i}}{\text{t}}^{\text{1}/\text{2}}\text{+}\text{C}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\left(\text{3}\right)\end{array}$$ where t is the exposure time (h), q t (mg/g) and q e (mg/g) represent the adsorption capacity of DCP at time t and equilibrium, respectively. k 1 (1/h), k 2 (g/ (mg h)), k i (mg/ (g h 1/2 )) refer to the rate constant, and C (mg/g) is the intercept, which reflects the boundary layer effect. Declarations Competing interests The authors declare no competing interests. Author contributions H.M. and X.L. proposed the research direction, Y.M. synthesized and characterized the compounds. S.Z. performed the theoretical calculations. Y.M., A.A. and G.L. analyzed all data and wrote the manuscript with the help of M.W., K.S., L.Z. and Y.Y. All authors discussed the results and commented on the manuscript. Acknowledgements We are grateful for the financial supported by the National Natural Science Foundation of China (22374017; 22576031 and 62422404), Fundamental Research Funds for the Central Universities (2572025JT07), the Natural Science Foundation of Heilongjiang Province (2024ZXDXC28). References Lei Z, Yang YA, Concise Colorimetric (2014) Fluorimetric Probe for Sarin Related Threats Designed via the Covalent-Assembly Approach. J Am Chem Soc 136:6594–6597 Liu A et al (2024) Donor–Acceptor Type Solvatochromic Flavonoid Materials Fluorphores for Polarity Sensing and Real-Time Temperature Monitoring. Adv Funct Mater 35:2415250 Zhou P, Han K (2022) ESIPT-based AIE luminogens: Design strategies, applications, and mechanisms. Aggregate 3:e160 Li X et al (2019) Visualization of Ultrasensitive and Recyclable Dual-Channel Fluorescence Sensors for Chemical Warfare Agents Based on the State Dehybridization of Hybrid Locally Excited and Charge Transfer Materials. Anal Chem 91:10927–10931 Ren TB et al (2018) Enhancing the Anti-Solvatochromic Two‐Photon Fluorescence for Cirrhosis Imaging by Forming a Hydrogen‐Bond Network. Angew Chem Int Ed 57:7473–7477 Liu W et al (2024) Precise intramolecular-charge-transfer property modulation of D-A-type fluorescent probes for bifunctional detection of phosgene and nerve agent. Chem Eng J 498:155457 Huo B et al (2019) Covalent-Assembly-Based Fluorescent Probe for Detection of a Nerve-Agent Mimic (DCP) via Lossen Rearrangement. Anal Chem 91:10979–10983 Yan C et al (2021) Fluorescence umpolung enables light-up sensing of N-acetyltransferases and nerve agents. Nat Commun 12:3869 Yao J et al (2016) Concise and Efficient Fluorescent Probe via an Intromolecular Charge Transfer for the Chemical Warfare Agent Mimic Diethylchlorophosphate Vapor Detection. Anal Chem 88:2497–2501 Wu L et al (2020) Förster resonance energy transfer (FRET)-based small-molecule sensors and imaging agents. Chem Soc Rev 49:5110–5139 Xiong W et al (2019) Sensitive Discrimination of Nerve Agent and Sulfur Mustard Simulants Using Fluorescent Coassembled Nanofibers with Förster Resonance Energy Transfer-Enhanced Photostability and Emission. Anal Chem 91:1711–1714 Liu K et al (2023) Precise Manipulation of Excited-State Intramolecular Proton Transfer via Incorporating Charge Transfer toward High-Performance Film-Based Fluorescence Sensing. J Am Chem Soc 145:7408–7415 Sedgwick AC et al (2018) Excited-state intramolecular proton-transfer (ESIPT) based fluorescence sensors and imaging agents. Chem Soc Rev 47:8842–8880 Xiao F et al (2024) Coherent Modulation of the Aggregation Behavior and Intramolecular Charge Transfer in Small Molecule Probes for Sensitive and Long-term Nerve Agent Monitoring. Angew Chem Int Ed 63:e202400453 Kumar V et al (2023) Recent advances in fluorescent and colorimetric chemosensors for the detection of chemical warfare agents: a legacy of the 21st century. Chem Soc Rev 52:663–704 Zhang L et al (2025) Solid-state fluorescent films for detection of chemical warfare agents: Mechanisms, film engineering and integration with machine learning. Coord Chem Rev 540:216766 Zhang S et al (2023) Dual-State Fluorescent Probe for Ultrafast and Sensitive Detection of Nerve Agent Simulants in Solution and Vapor. ACS Sens 8:1220–1229 Fan S et al (2019) Challenges in Fluorescence Detection of Chemical Warfare Agent Vapors Using Solid-State Films. Adv Mater 32:1905785 Zhu B et al (2022) Molecular engineered optical probes for chemical warfare agents and their mimics: Advances, challenges and perspectives. Coord Chem Rev 463:214527 Safarkhani M et al (2024) Advances in sprayable sensors for nerve agent detection. Coord Chem Rev 509:215804 Meng W-Q et al (2023) Fluorescent probes for the detection of chemical warfare agents. Chem Soc Rev 52:601–662 Zhang Z et al (2025) Current status of research on chemical warfare agent detection technology. TRAC Trends Anal Chem 193:118474 Zhou X et al (2016) A Fluorescent Sensor for Dual-Channel Discrimination between Phosgene and a Nerve‐Gas Mimic. 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Angew Chem Int Ed 64:e202510141 Xie Z et al (2023) Realizing Photoswitchable Mechanoluminescence in Organic Crystals Based on Photochromism. Adv Mater 35:2212273 Cui L-S et al (2020) Fast spin-flip enables efficient and stable organic electroluminescence from charge-transfer states. Nat Photonics 14:636–642 de Jacquot H-P et al (2024) Viridium: A Stable Radical and Its π-Dimerization. J Am Chem Soc 147:1823–1830 Zhu Z et al (2024) Dual Channel Emissions of Kasha and Anti-Kasha from a Single Radical Molecule. Angew Chem Int Ed 63:e20240552 Li X et al (2022) A platform for blue-luminescent carbon-centered radicals. Nat Commun 13:5367 Li M et al (2025) Achieving a Record Photoluminescence Quantum Yield in Green Light-Emitting Carbon‐Centered Radicals with Nanosecond Emission Lifetimes. Adv Mater 37:2418324 Gao Q et al (2023) Electrospun fiber-based flexible electronics: Fiber fabrication, device platform, functionality integration and applications. Prog Mater Sci 137:101139 Frisch MJ, Schlegel GWTHB, Scuseria GE, Robb MA (2016) J. R. Gaussion 09 Rev. C.01. Wallingford, CT Lu T (2024) A comprehensive electron wavefunction analysis toolbox for chemists, Multiwfn. J Chem Phys 161:082503 Lu T, Chen F, Multiwfn (2012) A multifunctional wavefunction analyzer. J Comput Chem 33:580–592 Humphrey W et al (1996) Visual molecular dynamics. J Mol Graph 14:33–38 Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryInformation2026.1.16.docx Supplementary Information AfteraddingDCPandHCltotheDCMsolutionofDTE3PCzchangeswereobserved.mp4 The response of DTE-3PCz to DCP and HCl Cite Share Download PDF Status: Under Review Version 1 posted 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. 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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-8614974","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":580643518,"identity":"814f611a-49cd-4063-b9d1-4a778fe62689","order_by":0,"name":"Hongwei 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University","correspondingAuthor":false,"prefix":"","firstName":"Yuling","middleName":"","lastName":"Yang","suffix":""},{"id":580643526,"identity":"338493cc-4fb0-457f-85de-e324bebc48c4","order_by":8,"name":"Alim Abdurahman","email":"","orcid":"https://orcid.org/0000-0003-2419-3516","institution":"Jilin University","correspondingAuthor":false,"prefix":"","firstName":"Alim","middleName":"","lastName":"Abdurahman","suffix":""},{"id":580643527,"identity":"2b1cb76a-b3e3-4284-ba21-e9e71ca4aeed","order_by":9,"name":"Geyu Lu","email":"","orcid":"","institution":"State Key Laboratory of Integrated Optoelectronics, JLU Region, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China","correspondingAuthor":false,"prefix":"","firstName":"Geyu","middleName":"","lastName":"Lu","suffix":""}],"badges":[],"createdAt":"2026-01-16 03:41:06","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8614974/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8614974/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":101309647,"identity":"2e2aa5c4-da52-46f9-81d7-a7417293a094","added_by":"auto","created_at":"2026-01-28 10:41:58","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":152311,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eResearch outline.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e The schematic diagram of a traditional closed-shell D-π-A type probe. \u003cstrong\u003eb\u003c/strong\u003e The schematic diagram of closed-to-open shell D-π-A type probe in this work. \u003cstrong\u003ec\u003c/strong\u003e Visible and fluorescent color changes of DTE-3PCz upon the formation of its radical species in dichloromethane (DCM) solution containing DCP or HCl and proposed mechanism for DCP and HCl detection.\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8614974/v1/020b06897c7903734d216b50.jpg"},{"id":101309654,"identity":"9daf236f-3448-49fd-a786-be8ca9389469","added_by":"auto","created_at":"2026-01-28 10:42:02","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":150714,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePhotochemical properties and EPR spectra of DTE-3PCz solution\u003c/strong\u003e. \u003cstrong\u003ea \u003c/strong\u003eUV-vis absorption spectra and \u003cstrong\u003eb\u003c/strong\u003e fluorescence spectra of DTE-3PCz (1.0×10\u003csup\u003e-5\u003c/sup\u003e M in DCM) upon UV irradiation at room temperature. \u003cstrong\u003ec\u003c/strong\u003e Color shifts in the CIE 1931 diagram of DTE-3PCz (1.0×10\u003csup\u003e-5\u003c/sup\u003e M in DCM) under continuous of UV irradiation (0-60 s). \u003cstrong\u003ed \u003c/strong\u003eEPR spectra of DTE-3PCz before and after UV irradiation (in toluene).\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8614974/v1/0f3d0ce2b6c83214931bfa5d.jpg"},{"id":101309630,"identity":"554de97d-faff-4e73-beb2-ddcbcbcdc875","added_by":"auto","created_at":"2026-01-28 10:41:49","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":207790,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOptical and physical properties of molecules under different detection conditions.\u003c/strong\u003e Fluorescence spectra of DTE-3PCz \u003cstrong\u003e(a)\u003c/strong\u003e and DTE-3NCz \u003cstrong\u003e(d)\u003c/strong\u003e (1.0×10\u003csup\u003e-5\u003c/sup\u003e M in DCM) upon addition of\u003cstrong\u003e \u003c/strong\u003eDCP. Linear relationship between quenching efficiency of DTE-3PCz \u003cstrong\u003e(b)\u003c/strong\u003e and DTE-3NCz \u003cstrong\u003e(e)\u003c/strong\u003e (1.0×10\u003csup\u003e-5\u003c/sup\u003e M in DCM) solution upon addition of DCP. Error bars stand for standard deviation. \u003cstrong\u003ec\u003c/strong\u003e EPR spectra of DTE-3PCz solution upon addition of DCP and without DCP exposed to UV irradiation for the same duration. \u003cstrong\u003ef\u003c/strong\u003e Changes in color emission of DTE-3PCz (1.0×10\u003csup\u003e-5\u003c/sup\u003e M in DCM) upon addition of HCl, BTC, 2-CEES, DCP. \u003cstrong\u003eg\u003c/strong\u003e Time-resolved PL decay curves of DTE-3PCz (1.0×10\u003csup\u003e-5\u003c/sup\u003e M in DCM) upon addition of HCl, BTC, 2-CEES, DCP. \u003cstrong\u003eh\u003c/strong\u003e Fluorescence quantum yield of DTE-3PCz (1.0×10\u003csup\u003e-5\u003c/sup\u003e M in DCM) upon addition of HCl, BTC, 2-CEES, DCP. \u003cstrong\u003ei\u003c/strong\u003e The quenching efficiency of DTE-3PCz (1.0×10\u003csup\u003e-5\u003c/sup\u003e M in DCM) upon UV irradiation following the addition of DCP, HCl, or other interfering substances (10 equiv. each).\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8614974/v1/ff88ddcc903230807027cbbb.jpg"},{"id":101309640,"identity":"1427ccb8-251a-46b5-b6fb-264e787f1f15","added_by":"auto","created_at":"2026-01-28 10:41:54","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":157303,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStudy on the response mechanism of DTE-3PCz a\u003c/strong\u003e The radical generation process of DTE-3PCz in DCP and HCl. \u003cstrong\u003eb\u003c/strong\u003e \u003csup\u003e1\u003c/sup\u003eH NMR of DTE-3PCz in CDCl\u003csub\u003e3\u003c/sub\u003e solution without irradiation and with addition of 10 equiv. DCP and HCl. \u003cstrong\u003ec\u003c/strong\u003e LC-MS of the photoirradiation DTE-3PCz solution upon addition of 10 equiv. of DCP and HCl.\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8614974/v1/d8ba98e10a6a7f648a5002d1.jpg"},{"id":101309641,"identity":"0d8cb204-3821-428e-aae9-dfa710a11d73","added_by":"auto","created_at":"2026-01-28 10:41:55","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":182924,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStudy on the Response Mechanism and theoretical calculation of DTE-3PCz.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e The schematic illustration of the processes of Kasha and anti-Kasha emission. \u003cstrong\u003eb\u003c/strong\u003e The orbital transitions and electron-hole distributions corresponding to the D\u003csub\u003e2\u003c/sub\u003e and D\u003csub\u003e1\u003c/sub\u003e states of DTE-3PCz (HCl) radical. \u003cstrong\u003ec\u003c/strong\u003e ESP plots of DTE-3PCz before and after addition of DCP. \u003cstrong\u003ed\u003c/strong\u003e Orbital transitions and electron-hole distribution corresponding to the DTE-3PCz (DCP) radical.\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8614974/v1/2d50d9e5c6ea7297308d18be.jpg"},{"id":101309629,"identity":"1c0e1833-5e60-4c1f-ae9f-52dcf851c375","added_by":"auto","created_at":"2026-01-28 10:41:49","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":143138,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePreparation and performance study of fluorescent films.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Preparation process of films. \u003cstrong\u003eb\u003c/strong\u003e Testing process and colorimetric-fluorescence changes of films. \u003cstrong\u003ec \u003c/strong\u003eAdsorption capacity of DTE-3PCz films and blank sample for DCP. \u003cstrong\u003ed\u003c/strong\u003e PFO model. \u003cstrong\u003ee\u003c/strong\u003e PSO model.\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8614974/v1/5bb78104a45447de5303d785.jpg"},{"id":101309642,"identity":"7d6b8c2e-4dc5-4e4d-8132-665aec1c1938","added_by":"auto","created_at":"2026-01-28 10:41:55","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":197495,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDevice design and testing.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Internal structure and circuit schematic of the portable detection system. \u003cstrong\u003eb\u003c/strong\u003e Fluorescence signal data output by the portable detection system; the horizontal axis represents sensor unit number, while the vertical axis indicates corresponding fluorescence intensity. \u003cstrong\u003ec\u003c/strong\u003e The quenching efficiency of DTE-3PCz film to DCP vapor in the portable detection system.\u003c/p\u003e","description":"","filename":"Picture7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8614974/v1/af0d425a47bbdf79cbb5c961.jpg"},{"id":101309702,"identity":"5618b438-810c-46cf-93f1-8fc38481c392","added_by":"auto","created_at":"2026-01-28 10:42:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2071107,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8614974/v1/b82c85cc-4d95-4f4c-a039-17e9a589489d.pdf"},{"id":101309691,"identity":"541cc000-d78f-4e0f-b95e-95f3049ba9c8","added_by":"auto","created_at":"2026-01-28 10:42:17","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":8411114,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SupplementaryInformation2026.1.16.docx","url":"https://assets-eu.researchsquare.com/files/rs-8614974/v1/6242feb2568893a6a4798353.docx"},{"id":101309664,"identity":"716baaef-62ee-4576-a91e-d00dd2d70e98","added_by":"auto","created_at":"2026-01-28 10:42:11","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":19924287,"visible":true,"origin":"","legend":"The response of DTE-3PCz to DCP and HCl","description":"","filename":"AfteraddingDCPandHCltotheDCMsolutionofDTE3PCzchangeswereobserved.mp4","url":"https://assets-eu.researchsquare.com/files/rs-8614974/v1/6d63bcbab2d56efe06006130.mp4"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Closed-to-Open-Shell Molecular Sensing Enables Highly Selective Detection of Chemical Warfare Agents","fulltext":[{"header":"Introduction","content":"\u003cp\u003eChemical warfare agents (CWAs) are among the most toxic chemicals known to humankind, posing a severe threat to public safety even at trace concentrations\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. Despite the strict prohibition of CWAs under the Chemical Weapons Convention, accidental releases and malicious uses over the past century have repeatedly caused mass casualties and global concern\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. To mitigate such threats, the development of highly sensitive and selective fluorescent sensing materials has emerged as an effective strategy for early warning and rapid detection\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. In particular, donor-acceptor (D-A) type fluorophores equipped with nucleophilic functional groups (e.g., \u003cem\u003eN\u003c/em\u003e-heterocycles, -NH\u003csub\u003e2\u003c/sub\u003e, -C\u0026thinsp;=\u0026thinsp;N-, -N\u0026thinsp;=\u0026thinsp;N-, or -OH) can undergo specific nucleophilic substitution or addition reactions with electrophilic CWAs, thereby producing distinct fluorescence changes\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Depending on molecular design, such fluorescence responses are typically governed by intramolecular charge transfer (ICT)\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e, photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET)\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, or excited-state intramolecular proton transfer (ESIPT) mechanisms\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. For safety reasons, less toxic analogues such as diethylchlorophosphate (DCP), bis(trichloromethyl) carbonate (BTC), and 2-chloroethylethyl sulfide (2-CEES) are generally used as simulants for sarin, phosgene, and mustard gas, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea).\u003c/p\u003e \u003cp\u003eNevertheless, achieving precise detection of CWAs in complex environments remains extremely challenging. The main difficulty lies in the lack of reaction specificity for most electrophilic sensing systems, leading to cross-interference from structurally similar CWAs and other electrophilic species\u003csup\u003e\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. Furthermore, many CWAs and their analogues undergo hydrolysis in humid air, generating protonic acids that induce false positive signals\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. As highlighted in several recent reviews\u003csup\u003e\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e, overcoming this intrinsic selectivity limitation has become a critical research frontier in CWA sensing\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. Efforts to enhance selectivity include the design of \u003cem\u003eo\u003c/em\u003e-phenylenediamine-based probes capable of distinguishing between phosgene and DCP\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e, dual-site probes containing \u003cem\u003eo\u003c/em\u003e-hydroxythioxane moieties for differentiating phosgene and mustard gas\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e, and conjugated microporous polymer films incorporating acid-scavenging additives such as K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e or \u003cem\u003enano\u003c/em\u003e-SiO\u003csub\u003e2\u003c/sub\u003e to suppress acid interference\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. Although these approaches have improved sensing reliability to some extent, a universal molecular platform that enables one-to-many specific recognition of multiple CWAs with high anti-interference capability remains elusive.\u003c/p\u003e \u003cp\u003eHerein, a conceptually new fluorescent sensing system is developed based on a closed-to-open-shell sensing reaction to enable multi-signal (fluorescence and colorimetric) discrimination of CWAs (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Investigation of dithienylethene (DTE) photochromic systems revealed the formation of stable, luminescent radicals upon light irradiation. Based on this finding, two DTE derivatives (DTE-3PCz and DTE-3NCz) were designed and synthesized to investigate the reaction mechanism. Detailed spectroscopic analyses revealed that the photogenerated radicals exhibit dual radiative transitions \u0026mdash; Kasha- and anti-Kasha-rule-compliant \u0026mdash; allowing distinct fluorescence colors depending on the interacting analyte. For instance, DTE-3PCz (HCl) radical favors orange kasha emission (D\u003csub\u003e1\u003c/sub\u003e\u0026rarr;D\u003csub\u003e0\u003c/sub\u003e), whereas DTE-3PCz (DCP) radical induces indigo anti-Kasha emission (D\u003csub\u003e2\u003c/sub\u003e\u0026rarr;D\u003csub\u003e0\u003c/sub\u003e), accompanied by corresponding colorimetric changes (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). This unique closed- to open-shell transformation not only ensures molecular-level selectivity toward different CWAs but also provides a new optical response mechanism based on singlet-to-doublet transitions. Furthermore, DTE-3PCz films demonstrate remarkable sensitivity and portability, enabling wireless, real-time vapor detection of DCP, as well as excellent cellular permeability, low cytotoxicity, and high biocompatibility. Overall, this work introduces a novel radical-based fluorescence sensing paradigm that enables simultaneous multi-channel response, enhanced specificity, and practical applicability in detecting CWAs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis and photophysical properties\u003c/h2\u003e \u003cp\u003eDTE-3PCz and DTE-3NCz were synthesized through a sequence of Friedel-Crafts acylation reaction, McMurry coupling, and Suzuki reaction (Supplementary Fig.\u0026nbsp;1). Their structures were verified by liquid chromatography-mass spectrometry (LC-MS), \u003csup\u003e1\u003c/sup\u003eH NMR, and \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC NMR analyses. Comprehensive information was available in Supplementary Figs.\u0026nbsp;2\u0026ndash;10. Upon irradiation with 365 nm UV light, both of DTE-3PCz and DTE-3NCz in DCM undergo pronounced photochromism: a new absorption band at ~\u0026thinsp;500 nm appears, consistent with the open-ring to closed-ring transformation of DTE derivatives, accompanied by quenching of the ~\u0026thinsp;400 nm fluorescence band. Unexpectedly, prolonged UV irradiation generated an additional absorption band at ~\u0026thinsp;600 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and Supplementary Fig.\u0026nbsp;11a), along with dual-emission peaks centered at ~\u0026thinsp;475 nm and ~\u0026thinsp;600 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;11b). The corresponding emission color evolved from blue (CIE: 0.16, 0.05) to orange (CIE: 0.42, 0.34) within 60 s (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec and Supplementary Fig.\u0026nbsp;11c), indicating that a second photochemical process occurs concurrently with the canonical photocyclization\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTo probe this transformation, electron paramagnetic resonance (EPR) spectra were employed for DTE-3PCz and DTE-3NCz in toluene (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed and Supplementary Fig.\u0026nbsp;11d). No detectable signal is observed in the EPR spectra of DTE-3PCz before UV irradiation, while obvious signal peaks ranging from 3500\u0026ndash;3520 G appear after UV irradiation. The extracted \u003cem\u003eg\u003c/em\u003e value 2.003, falls within typical range of neutral carbon radicals (\u003cem\u003eg\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.99\u0026ndash;2.01)\u003csup\u003e28\u003c/sup\u003e, demonstrating that DTE-3PCz and DTE-3NCz generate stable open-shell species under UV irradiation. Additionally, the ultraviolet absorption spectra and high-performance liquid chromatography (HPLC) of the molecule after combining with the radical scavenger 2,2,6,6-tetramethylpiperidine oxide (TEMPO) under UV irradiation exposure were studied. As shown in the Supplementary Fig.\u0026nbsp;12, following the addition of TEMPO, the absorption band near ~\u0026thinsp;600 nm diminished, and a new peak with a retention time of 50.167 min appeared in the HPLC spectrum (Supplementary Fig.\u0026nbsp;13). It indicates that the generated radical molecules underwent covalent coupling with TEMPO, forming a new substance. Collectively, these results confirm the mechanism by which DTE-3PCz and DTE-3NCz induces radical generation under UV irradiation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSensing performance of fluorescent probes to CWAs\u003c/h3\u003e\n\u003cp\u003eDuring radical-emission studies, it discovered that exposure of DTE-3PCz and DTE-3NCz to representative CWA simulants (DCP, 2-CEES, BTC) or to HCl produces markedly different fluorescence and colorimetric outputs upon identical UV irradiation (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Supplementary Figs.\u0026nbsp;14 and 17). Take DTE-3PCz as an example, for DCP (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea), increasing concentration suppresses the ~\u0026thinsp;600 nm band and attenuates the ~\u0026thinsp;450 nm band, shifting the emission from bright blue to indigo and producing a blue colorimetric response. For HCl (Supplementary Figs.\u0026nbsp;14a), the ~\u0026thinsp;600 nm emission intensifies while the ~\u0026thinsp;450 nm band remains nearly unchanged, resulting in a blue to orange fluorescence shift and a colorless to red colorimetric shift. For BTC and 2-CEES (Supplementary Figs.\u0026nbsp;15a, c), the ~\u0026thinsp;600 nm band decreases while the ~\u0026thinsp;450 nm emission remains steady, producing bright blue to orange fluorescence and colorless to violet colorimetric transitions. The DTE-3PCz limit of detection (LOD) values for DCP, BTC, and 2-CEES were calculated as 0.19 \u0026micro;M (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb), 0.48 \u0026micro;M (Supplementary Fig.\u0026nbsp;15b), and 1.28 \u0026micro;M (Supplementary Fig.\u0026nbsp;15d), respectively. The CIE 1931 diagram, time-resolved PL decay curves, quantum yield analysis and interference studies (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef-i, Supplementary Fig.\u0026nbsp;16 and Supplementary Table\u0026nbsp;1), further highlight the exceptional selectivity of DTE-3PCz. UV-vis and EPR measurements reveal that CWAs enhance the 600 nm absorption band (Supplementary Figs.\u0026nbsp;17a, c) and preserve strong radical signatures (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec), suggesting that CWA analytes stabilize the radical species while modulating their excited-state dynamics to yield distinct optical fingerprints.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eMechanism Research\u003c/h3\u003e\n\u003cp\u003eThe photochromism of diarylethene derivatives is typically governed by classical photocyclization pathways\u003csup\u003e\u003cspan additionalcitationids=\"CR30\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, a mechanistic model is proposed in which UV irradiation first generates an excited state (1*) (a diradical like intermediates) that undergoes oxygen trapping to form an intermediate species (1\u0026rsquo;). These intermediate abstracts reactive hydrogen atoms or electrophilic groups (e.g., H-CHCl\u003csub\u003e2\u003c/sub\u003e, H-Cl, C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003eP-Cl), yielding a stable radical that accounts for the observed luminescent open-shell state. To validate this mechanism, LC-MS and \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR analysis on the products formed after UV irradiation between DCP and DTE-3PCz were performed. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec and Supplementary Figs.\u0026nbsp;18\u0026ndash;19, LC-MS directly detected the masses of the substances formed after DTE-3PCz combined with HCl and DCP as m/z\u0026thinsp;=\u0026thinsp;569.91 and m/z\u0026thinsp;=\u0026thinsp;704.22, respectively, which are consistent with the theoretical values (theoretical values are m/z\u0026thinsp;=\u0026thinsp;569.15 and m/z\u0026thinsp;=\u0026thinsp;705.24). Additionally, the resulting steady-state solution exhibited complete disappearance of the \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR signals, consistent with the formation of a paramagnetic radical species, which is typically NMR-silent due to severe line broadening (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb and Supplementary Figs.\u0026nbsp;20\u0026ndash;21)\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. These results collectively support the proposed reaction mechanism.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo elucidate the origin of the distinct emission responses of DTE-3PCz and DTE-3NCz to DCP and HCl under UV irradiation, a comparative investigation of the excited-state properties of the corresponding radical products (from DTE-3PCz and DTE-3NCz) was undertaken\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. Under identical UV irradiation, DTE-3PCz solution display markedly different emission behaviors: in the presence of DCP, the ~\u0026thinsp;475 nm band dominates over the ~\u0026thinsp;600 nm band (Supplementary Fig.\u0026nbsp;22a), whereas in the presence of HCl, the ~\u0026thinsp;600 nm emission becomes predominant (Supplementary Fig.\u0026nbsp;22b). Time-dependent density functional theory (TD-DFT) calculations indicate that the absorption bands around ~\u0026thinsp;600 nm in both systems originate from βHOMO to βSOMO (D\u003csub\u003e0\u003c/sub\u003e-D\u003csub\u003e1\u003c/sub\u003e, λ\u003csub\u003eabs\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;535\u0026thinsp;~\u0026thinsp;540 nm) (Supplementary Tables. 2\u0026ndash;3). Electrostatic potential maps (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec and Supplementary Fig.\u0026nbsp;23) reveal a negatively charged oxygen in the peroxyl radical and an electron-deficient phosphorus center in DCP, enabling nucleophilic attack of DCP on the radical oxygen. These theoretical results, inagreement with the experimental observations, indicating that two reaction pathways (with DCP and HCl) generate the same radical species. TD-DFT further shows that the first excited state (D\u003csub\u003e1\u003c/sub\u003e, βHOMO to βSOMO) possesses a weak oscillator strength (ƒ=\u0026thinsp;0.03\u0026ndash;0.05), whereas the second excited state (D\u003csub\u003e2\u003c/sub\u003e, αSOMO to αLUMO) exhibits significantly larger oscillator strength (ƒ=\u0026thinsp;0.08\u0026ndash;0.14). The distinct orbital compositions\u0026mdash;D\u003csub\u003e1\u003c/sub\u003e mainly arising from the 148β\u0026rarr;149β transition, and D\u003csub\u003e2\u003c/sub\u003e from the 149α\u0026rarr;150α transition\u0026mdash;lead to spatially separated electron distributions and different orbital orientations, resulting in minimal overlap (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed and Supplementary Figs.\u0026nbsp;24\u0026ndash;30). Because D\u003csub\u003e1\u003c/sub\u003e and D\u003csub\u003e2\u003c/sub\u003e belong to different spin manifolds, internal conversion (IC) between them is strongly suppressed, giving rise to decoupled dual emission (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). To verify that the ~\u0026thinsp;475 nm band originates from a high-energy anti-Kasha transition, excitation-dependent emission measurements were performed. Excitation\u0026ndash;emission experiments confirm that the ~\u0026thinsp;475 nm and ~\u0026thinsp;600 nm emissions arise from different excited states. Varying the excitation wavelength (360\u0026ndash;400 nm) produces a noticeable redshift in emission (Supplementary Fig.\u0026nbsp;22c), and the excitation spectra monitored at 475 nm and 600 nm differ substantially (Supplementary Fig.\u0026nbsp;22d). At both 77 K and 298 K, the DTE-3PCz radical exhibits two distinct emission bands, which are assigned to anti-Kasha (D\u003csub\u003e2\u003c/sub\u003e\u0026rarr;D\u003csub\u003e0\u003c/sub\u003e) and Kasha (D\u003csub\u003e1\u003c/sub\u003e\u0026rarr;D\u003csub\u003e0\u003c/sub\u003e) transitions, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and Supplementary Fig.\u0026nbsp;31). Importantly, the DTE-3PCz (DCP) radical shows a larger D\u003csub\u003e2\u003c/sub\u003e-D\u003csub\u003e1\u003c/sub\u003e energy gap than DTE-3PCz (HCl) radical. Consequently, IC from D\u003csub\u003e2\u003c/sub\u003e to D\u003csub\u003e1\u003c/sub\u003e is less efficient in the DCP system, which enhances the D\u003csub\u003e2\u003c/sub\u003e\u0026rarr;D\u003csub\u003e0\u003c/sub\u003e emission while suppressing the D\u003csub\u003e1\u003c/sub\u003e\u0026rarr;D\u003csub\u003e0\u003c/sub\u003e channel. As a result, the DTE-3PCz (DCP) radical exhibits dominant\u0026thinsp;~\u0026thinsp;475 nm emission, whereas the DTE-3PCz (HCl) radical favors\u0026thinsp;~\u0026thinsp;600 nm emission.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eFluorescent film sensing\u003c/h3\u003e\n\u003cp\u003eElectrospun films of polyethylene oxide (PEO) doped with DTE-3PCz were fabricated (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea) to serve as a sensing platform for the real-time vapor detection of CWAs\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. The resulting uniform, ultrafine fibers (0.15 \u0026micro;m diameter) provide a high surface area, facilitating efficient interaction with DCP vapor (Supplementary Fig.\u0026nbsp;32). A simple adsorption system was first established (Supplementary Fig.\u0026nbsp;33) to evaluate the adsorption capacities of DTE-3PCz films and blank film toward DCP vapor. Under UV irradiation, the adsorption capacity of rapidly increased within the first 150 min, then slowed due to saturation of active sites, and finally reached equilibrium at approximately 420 min. The maximum adsorption capacity of DTE-3PCz films reached 132 mg/g, whereas that of blank film was only 49 mg/g (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). To elucidate the rate-limiting step of the DCP adsorption process, the data were fitted using the pseudo-first-order (PFO), pseudo-second-order (PSO), and intra-particle diffusion models (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed-e and Supplementary Fig.\u0026nbsp;34). The PSO model (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.985) provides a significantly better fit than the PFO model (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.965), indicating that the adsorption process is dominated by chemisorption. This result suggests that DTE-3PCz undergoes a chemical reaction with DCP under UV irradiation. Furthermore, the intra-particle diffusion model reveals two distinct linear regimes, indicating that both surface adsorption and particle diffusion contribute to the overall adsorption process.\u003c/p\u003e \u003cp\u003eWith increasing DCP concentration, the film color gradually changes from pale yellow to pale pink, while the fluorescence shifts from orange to purple (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). The fluorescent-based mode offers higher sensitivity, enabling reliable visualization and quantitative detection of trace vapor-phase CWAs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eDTE-3PCz film-based portable devices\u003c/h3\u003e\n\u003cp\u003eTo facilitate practical deployment, a portable fluorescence-sensing device was developed. The system incorporates a DTE-3PCz film, an air pump, a 365 nm LED, a long-pass filter (λ \u0026ge; 380 nm), a CCD sensor, and a Bluetooth transceiver. The internal structure and circuit diagram are shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The working principle is as follows: an STM 32 microcontroller unit (MCU) drives the CCD sensor to acquire fluorescence signals, which are then transmitted via the Bluetooth transceiver to a personal computer (PC) for data processing and analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). During data acquisition, the LED and CCD are synchronously switched on and off. Upon exposure to DCP vapor, the fluorescence intensity is quenched, and exhibiting a clear linear relationship with DCP concentration (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb). The device achieves a LOD of 4.0 ppb for DCP vapor and enables remote wireless sensing, thereby significantly reducing operator exposure risk (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec). These results demonstrate that the DTE-3PCz film-based sensor satisfies the practical CWA detection. In addition, the biocompatibility of the DTE-3PCz fluorescent probe was evaluated by in vitro cytotoxicity assays (CCK-8). The results show that DTE-3PCz exhibits low cytotoxicity, efficient cellular uptake, indicating its potential for live-cell fluorescence imaging (Supplementary Fig.\u0026nbsp;35).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn summary, we establish a previously unexplored fluorescent sensing paradigm based on closed-to-open-shell transformations, which enables multi-channel (fluorescence and colorimetric) differentiation of CWAs simulants. The designed DTE-3PCz and DTE-3NCz molecules undergo photoinduced radical formation, and, the resulting open-shell species exhibit dual radiative pathways that comply with both Kasha and anti-Kasha rules. This uncommon coexistence of D\u003csub\u003e1\u003c/sub\u003e\u0026rarr;D\u003csub\u003e0\u003c/sub\u003e and D\u003csub\u003en\u003c/sub\u003e\u0026rarr;D\u003csub\u003e0\u003c/sub\u003e emissions endows each analyte with a distinct optical fingerprint, thereby achieving molecular-level selectivity that traditional closed-shell sensing reactions can hardly deliver. Mechanistic investigations reveal that the unique singlet-to-doublet transition framework\u0026mdash;together with analyte-dependent modulation of excited-state energy gaps\u0026mdash;dictates the relative contributions of Kasha and anti-Kasha emissions. Such a controllable interplay between emissive excited states highlights an optical response mechanism rarely accessible in organic fluorophores and, more broadly, expands the fundamental photophysical landscape of organic radicals. Beyond the molecular mechanism, the DTE-R platform demonstrates high practical utility. The DTE-3PCz nanofiber films provide rapid, sensitive, and portable vapor-phase detection, achieving real-time, wireless monitoring of DCP with ppb-level sensitivity. Moreover, the probes exhibit excellent cellular permeability, low cytotoxicity, and good biocompatibility, underscoring their potential for biological sensing scenarios where acidic impurities or electrophilic interferents typically compromise selectivity. Overall, this study introduces a radical-enabled, multi-information optical sensing strategy that addresses long-standing challenges in CWA detection. By leveraging stable luminescent radicals and analyte-dependent competition between Kasha and anti-Kasha pathways, our work offers both a conceptual advance in radical photophysics and a practical sensing platform with broad applicability in environmental monitoring, security, and chemical defense.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eChemicals and measurement\u003c/h2\u003e \u003cp\u003eAll the reagents were obtained from Aldrich, Kanto Chemicals, and TCL unless otherwise specified. DCP was purchased from sigma Aldrich. Unless otherwise specified, all reagents are used without further purification after purchase. The \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eH NMR and \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC NMR spectra of the solution were recorded at 500 MHz using a Bruker AVANCE III HD NMR spectrometer in CDCl\u003csub\u003e3\u003c/sub\u003e with tetramethylsilane (TMS) as the internal standard. Mass spectrometry data were obtained using a triple quadrupole LC-MS/MS instrument, TSQ Quantis/Altis. UV-vis absorption spectra were detected by a Beijing PU-1901 UV-vis spectrophotometer. HPLC analyses were performed with a Water 1525 HPLC pump, Water 2489 UV/Vis detector, and 10 mm\u0026times;10 mm C18 column. EPR spectra were acquired using an ELEXSYS-II E500 CW-EPR spectrometer from Bruker Instruments, Switzerland. Fluorescence lifetime measurements were performed with an FLS-980 fluorescence lifetime spectrometer coupled to an EPL-375 optical laser. Test solution concentrations ranged from 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e to 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e M. Baseline calibration was performed using pure DCM as the reference blank, with scanning conducted in the 400\u0026ndash;700 nm range. Fluorescence spectra were measured using a Shimadzu RF-6000 fluorescence spectrophotometer. Fluorescent film structures were imaged using a high-resolution field emission scanning electron microscope manufactured by Thermo Fisher Scientific.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eTheoretical Calculation\u003c/h2\u003e \u003cp\u003eThe radical properties of R-DTE were investigated using the Gaussian 09 D.01 package\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. Geometric optimization and frequency calculations of the radical structure were performed at the 6\u0026ndash;31 g(d, p) basis set level, employing the unrestricted density functional theory (UDFT) method and the M062X functional. Prior to further calculations, it was confirmed that the optimized structures resided at their minimum energy states without any imaginary frequencies. The ultraviolet absorption spectra of the radicals were calculated using the TD-DFT method at the uM062X/6\u0026ndash;31 g(d, p) level. Spin density populations were analyzed using Multiwfn software and\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e visualized with VMD software\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of compounds GDT-2Cl\u003c/h2\u003e \u003cp\u003eGlutaroyl chloride (2.25 g, 13.3 mmol), anhydrous aluminum trichloride (3.5 g, 26.25 mmol) were dissolved in a mixture of DCM (20 mL). The flask was placed in an ice-water bath and stirred for 0.5 h. Then, 2-chloro-5-methylthiophenol (2.65 g, 20 mmol) in DCM (10 mL) was slowly added to the round-bottom flask. After complete addition, the ice bath and allow the system were removed to react at room temperature for 2 h. Upon completion, the reaction was slowly quenched with ice water. The residue was extracted with DCM and H\u003csub\u003e2\u003c/sub\u003eO. The combined organic layer was dried over Mg\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. The mixture was purified by silica gel column, using petroleum ether/DCM (v/v\u0026thinsp;=\u0026thinsp;1:10) as the eluent, the crude product obtained was recrystallized with toluene/anhydrous methanol, and pale-yellow powder (3.2 g) was obtained with a yield of 85%.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of compounds DTE-2Cl\u003c/h2\u003e \u003cp\u003eZinc powder (3 g, 46.15 mmol) was dissolved in tetrahydrofuran (THF) (50 mL). Place the flask in an ice-water bath and titanium tetrachloride 4 mL (18.6 mmol) was slowly dropwise added under a nitrogen atmosphere. After completion of the addition, the system was purged with nitrogen gas three times to ensure a nitrogen atmosphere. The mixture was heated to 68\u0026deg;C and refluxed for 1 h. The temperature was lowered to 40\u0026deg;C. GDT-2Cl (1.8 g, 5 mmol) in THF (20 mL) was slowly added to the reaction flask using a syringe. The mixture was refluxed for 1 h. Upon completion, the reaction was slowly quenched with ice water. The residue was extracted with DCM and H\u003csub\u003e2\u003c/sub\u003eO. The combined organic layer was dried over Mg\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. The mixture was purified through a silica gel column, using petroleum ether as the eluent, the crude product obtained was recrystallized with toluene/anhydrous methanol, and white crystals (1.2 g) was obtained with a yield of 80%. \u003csup\u003e1\u003c/sup\u003eH NMR (500 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) δ 6.58 (s, 2H), 2.71 (t, J\u0026thinsp;=\u0026thinsp;7.5 Hz, 4H), 2.05\u0026ndash;1.98 (m, 2H), 1.88 (s, 6H). \u003csup\u003e13\u003c/sup\u003eC NMR (126 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) δ 133.79, 133.39, 132.25, 125.65, 124.16, 37.30, 21.79, 13.14. ESI-MS (m/z): [M\u0026thinsp;+\u0026thinsp;H]\u003csup\u003e+\u003c/sup\u003e calcd. for C\u003csub\u003e15\u003c/sub\u003eH\u003csub\u003e14\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003e, 327.99; found 329.00.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of compounds DTE-3PCz\u003c/h2\u003e \u003cp\u003eDTE-2Cl (1.32 g, 4 mmol) was dissolved in THF (10 mL) into a three-neck round-bottom flask. Purge the flask three times with nitrogen gas. Cool the mixture to -78\u0026deg;C and n-butyllithium (1.6 mL) was slowly added. After addition, allow the mixture to react at room temperature for 15 min. Then tributyl borate (1.6 mL) was slowly added and continue stirring at room temperature for 3 h. The mixture was transferred to a two-neck flask. 3-bromo-9-phenylcarbazole (1.1 g, 3.39 mmol), palladium(II) tetratriphenylphosphide (0.28 g, 0.24 mmol) and K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e (12.0 mL, 20 wt%) were added. The reaction was heated to 80\u0026deg;C and stirred for 24 h under nitrogen. After removal of the solvent under reduced pressure, the residue was extracted with DCM and H\u003csub\u003e2\u003c/sub\u003eO. The combined organic layers were dried over Mg\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. The mixture was purified by silica gel column, using DCM/petroleum ether (v/v\u0026thinsp;=\u0026thinsp;1:10) as the eluent, the crude product obtained was recrystallized with toluene/anhydrous methanol, and white powder (0.6 g) was obtained with a yield of 50%. \u003csup\u003e1\u003c/sup\u003eH NMR (500 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) δ 8.25 (d, J\u0026thinsp;=\u0026thinsp;1.7 Hz, 1H), 8.17 (d, J\u0026thinsp;=\u0026thinsp;7.7 Hz, 1H), 7.62 (t, J\u0026thinsp;=\u0026thinsp;7.7 Hz, 2H), 7.56 (ddd, J\u0026thinsp;=\u0026thinsp;8.4, 4.0, 1.7 Hz, 3H), 7.50\u0026ndash;7.46 (m, 1H), 7.43\u0026ndash;7.40 (m, 2H), 7.37 (d, J\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.31 (ddd, J\u0026thinsp;=\u0026thinsp;7.9, 5.7, 2.3 Hz, 1H), 7.03 (s, 1H), 6.68 (s, 1H), 2.90\u0026ndash;2.86 (m, 2H), 2.78 (td, J\u0026thinsp;=\u0026thinsp;7.4, 2.2 Hz, 2H), 2.06 (d, J\u0026thinsp;=\u0026thinsp;18.0 Hz, 5H), 1.94 (s, 3H). \u003csup\u003e13\u003c/sup\u003eC NMR (126 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) δ 140.31, 139.85, 139.13, 139.10, 136.51, 135.23, 134.53, 134.25, 132.53, 132.41, 132.27, 128.88, 126.50, 125.99, 125.87, 125.81, 125.18, 123.90, 122.98, 122.73, 122.25, 121.93, 119.41, 119.08, 116.13, 116.08, 108.99, 108.88, 37.44, 37.33, 21.93, 13.37, 13.21. ESI-MS (m/z): [M\u0026thinsp;+\u0026thinsp;H]\u003csup\u003e+\u003c/sup\u003e calcd. for C\u003csub\u003e33\u003c/sub\u003eH\u003csub\u003e26\u003c/sub\u003eClNS\u003csub\u003e2\u003c/sub\u003e, 535.12; found 536.00.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of compounds DTE-3NCz\u003c/h2\u003e \u003cp\u003eDTE-2Cl (1.32 g, 4 mmol) was dissolved in THF (10 mL) into a three-neck round-bottom flask. Purge the flask three times with nitrogen gas. Cool the mixture to -78\u0026deg;C and n-butyllithium (1.6 mL) was slowly added. After addition, allow the mixture to react at room temperature for 15 min. Then tributyl borate (1.6 mL) was slowly added and continue stirring at room temperature for 3 h. The mixture was transferred to a two-neck flask. 3-bromo-9-(2-naphthyl)carbazole) (1.1 g, 3.39 mmol), palladium(II) tetratriphenylphosphide (0.28 g, 0.24 mmol) and K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e (12 mL, 20 wt%) were added. The reaction was heated to 80\u0026deg;C and stirred for 24 h under nitrogen. After removal of the solvent under reduced pressure, the residue was extracted with DCM and H\u003csub\u003e2\u003c/sub\u003eO. The combined organic layers were dried over Mg\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. The mixture was purified by silica gel column, using DCM/petroleum ether (v/v\u0026thinsp;=\u0026thinsp;1:10) as the eluent, the crude product obtained was recrystallized with toluene/anhydrous methanol, and white powder (0.6 g) was obtained with a yield of 50%. \u003csup\u003e1\u003c/sup\u003eH NMR (500 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) δ 8.26 (d, J\u0026thinsp;=\u0026thinsp;1.8 Hz, 1H), 8.19 (d, J\u0026thinsp;=\u0026thinsp;7.7 Hz, 1H), 8.10\u0026ndash;8.04 (m, 2H), 8.00\u0026ndash;7.97 (m, 1H), 7.92 (dd, J\u0026thinsp;=\u0026thinsp;6.1, 3.3 Hz, 1H), 7.67 (dd, J\u0026thinsp;=\u0026thinsp;8.7, 2.1 Hz, 1H), 7.58 (ddd, J\u0026thinsp;=\u0026thinsp;16.8, 7.4, 2.5 Hz, 3H), 7.47\u0026ndash;7.40 (m, 3H), 7.34\u0026ndash;7.30 (m, 1H), 7.03 (s, 1H), 6.67 (s, 1H), 2.87 (t, J\u0026thinsp;=\u0026thinsp;7.6 Hz, 2H), 2.80\u0026ndash;2.74 (m, 2H), 2.11\u0026ndash;2.02 (m, 5H), 1.93 (s, 3H). \u003csup\u003e13\u003c/sup\u003eC NMR (126 MHz, CDCl\u003csub\u003e3\u003c/sub\u003e) δ 140.48, 139.85, 139.29, 135.25, 134.53, 134.25, 133.96, 132.96, 132.54, 132.44, 132.27, 131.40, 128.89, 126.92, 126.84, 125.93, 125.87, 125.52, 125.26, 124.26, 124.09, 123.91, 123.05, 122.84, 122.36, 121.96, 119.48, 119.21, 116.19, 109.04, 108.94, 37.45, 37.33, 21.94, 13.38, 13.21. ESI-MS (m/z): [M\u0026thinsp;+\u0026thinsp;H]\u003csup\u003e+\u003c/sup\u003e calcd. for C\u003csub\u003e37\u003c/sub\u003eH\u003csub\u003e28\u003c/sub\u003eClNS\u003csub\u003e2\u003c/sub\u003e, 585.14; found 586.05.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of DTE-3PCz films\u003c/h2\u003e \u003cp\u003ePolymer fibers were manufactured using equipment modified for electrospinning. Polyethylene oxide (600 mg, Mw\u0026thinsp;=\u0026thinsp;1,000,000 Da) and DTE-3PCz (10 mg) were dissolved in 10 mL of DCM solution and stirred thoroughly. The mixture was loaded into a 5 mL syringe connected to a gauge needle. Prior to applying 10 kV, the distance between the needle tip and the grounding plate was adjusted to 18 cm. The solution was then sprayed onto the surface of a grounded aluminum plate and tin foil to form polymer fibers at a constant flow rate of 0.5 mL/h. Finally, the polymer fibers are retained in a sealed centrifuge tube for characterization of their structure via scanning electron microscopy.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eAdsorption kinetics formula\u003c/h2\u003e \u003cp\u003eThe pseudo first-order (PFO) (Eq.\u0026nbsp;1), PSO (Eq.\u0026nbsp;2) model, and intraparticle diffusion model (Eq.\u0026nbsp;3) is as follows:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\text{ln}\\left({\\text{q}}_{\\text{e}}\\text{-}{\\text{q}}_{\\text{t}}\\right)\\text{=}\\text{ln}{\\text{q}}_{\\text{e}}\\text{-}{\\text{k}}_{\\text{1}}\\text{t}\\text{}（\\text{1}）\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\frac{\\text{t}}{{\\text{q}}_{\\text{t}}}\\text{=}\\frac{\\text{1}}{{\\text{k}}_{\\text{2}}{\\text{q}}_{\\text{e}}^{\\text{2}}}\\text{+}\\frac{\\text{t}}{{\\text{q}}_{\\text{e}}}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\left(\\text{2}\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{\\text{q}}_{\\text{t}}\\text{=}{\\text{k}}_{\\text{i}}{\\text{t}}^{\\text{1}/\\text{2}}\\text{+}\\text{C}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\text{}\\left(\\text{3}\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003et\u003c/em\u003e is the exposure time (h), \u003cem\u003eq\u003c/em\u003e\u003csub\u003et\u003c/sub\u003e (mg/g) and \u003cem\u003eq\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003e (mg/g) represent the adsorption capacity of DCP at time \u003cem\u003et\u003c/em\u003e and equilibrium, respectively. \u003cem\u003ek\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e (1/h), \u003cem\u003ek\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e (g/ (mg h)), \u003cem\u003ek\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e (mg/ (g h\u003csup\u003e1/2\u003c/sup\u003e)) refer to the rate constant, and \u003cem\u003eC\u003c/em\u003e (mg/g) is the intercept, which reflects the boundary layer effect.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003eH.M. and X.L. proposed the research direction, Y.M. synthesized and characterized the compounds. S.Z. performed the theoretical calculations. Y.M., A.A. and G.L. analyzed all data and wrote the manuscript with the help of M.W., K.S., L.Z. and Y.Y. All authors discussed the results and commented on the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eWe are grateful for the financial supported by the National Natural Science Foundation of China (22374017; 22576031 and 62422404), Fundamental Research Funds for the Central Universities (2572025JT07), the Natural Science Foundation of Heilongjiang Province (2024ZXDXC28).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLei Z, Yang YA, Concise Colorimetric (2014) Fluorimetric Probe for Sarin Related Threats Designed via the Covalent-Assembly Approach. 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J Mol Graph 14:33\u0026ndash;38\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-8614974/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8614974/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHighly selective detection of chemical warfare agents (CWAs) is critical for public safety but remains extremely challenging due to the poor specificity of conventional fluorescent sensing reactions. Herein, an innovative sensing system based on a closed-to-open-shell transformation is reported. This system enables distinct and analyte-specific optical responses toward typical CWA simulants, including diethylchlorophosphate (DCP), bis(trichloromethyl) carbonate (BTC) and 2-chloroethylethyl sulfide (2-CEES), while also differentiating from the key interferent, HCl. Upon reaction with these analytes, the designed dithienylethene (DTE) derivatives generate stable luminescent radicals exhibiting clearly distinguishable fluorescence and colorimetric signatures. Mechanistic investigations reveal that the exceptional selectivity arises from the competition between Kasha- and anti-Kasha-rule radical emissions, giving each analyte a unique optical fingerprint. This work thus establishes a closed-to-open-shell sensing paradigm that integrates chemical specificity with multimodal optical response, offering a conceptual and practical advance toward selective and real-time detection of CWAs at the molecular level.\u003c/p\u003e","manuscriptTitle":"Closed-to-Open-Shell Molecular Sensing Enables Highly Selective Detection of Chemical Warfare Agents","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-28 10:39:40","doi":"10.21203/rs.3.rs-8614974/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"1c44bdc4-cfc3-4eab-92ea-ef7bd9db0e10","owner":[],"postedDate":"January 28th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":61769350,"name":"Physical sciences/Materials science/Materials for optics"},{"id":61769351,"name":"Physical sciences/Chemistry/Analytical chemistry/Fluorescent probes"}],"tags":[],"updatedAt":"2026-03-09T16:51:40+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-28 10:39:40","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8614974","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8614974","identity":"rs-8614974","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}