Excited-state Intramolecular Proton Transfer Research Articles

Mechanistic Insights into the Excited-State Intramolecular Proton Transfer (ESIPT) Process of 2-(2-Aminophenyl)naphthalene.

The 2-(2-aminophenyl)naphthalene molecule attracted much attention due to excited-state intramolecular proton transfer (ESIPT) from an amino NH2 group to a carbon atom of an adjacent aromatic ring. The ESIPT mechanisms of 2-(2-aminophenyl)naphthalene are still unclear. Herein, the decay pathways of this molecule in vacuum were investigated by combining static electronic structure calculations and nonadiabatic dynamics simulations. The calculations indicated the existence of two stable structures (S0-1 and S0-2) in the S0 and S1 states. For the S0-1 isomer, upon excitation to the Franck-Condon point, the system relaxed to the S1 minimum quickly, and then there exist four decay pathways (two ESIPT ones and two decay channels with C atom pyramidalization). In the ESIPT decay pathways, the system encounters the S1S0-PT-1 or S1S0-PT-2 conical intersection, which funnels the system rapidly to the S0 state. In the other two pathways, the system de-excited from the S1 to the S0 state via the S1S0-1 or S1S0-2 conical intersection. For the S0-2 structure, the decay pathways were similar to those of S0-1. The dynamics simulations showed that 75 and 69% of trajectories experienced the two ESIPT conical intersections for the S0-1 and S0-2 structures, respectively. Our simulations showed that the lifetime of the S1 state of S0-1 (S0-2) is estimated to be 358 (400) fs. Notably, we not only found the detailed reaction mechanism of the system but also found that the different ground-state configurations of this system have little effect on the reaction mechanism in vacuum.

Exploring electron donor and acceptor effects: DFT analysis of ESIPT/GSIPT in 2-(oxazolinyl)-phenols for photophysical and luminophore enhancement

Exploring electron donor and acceptor effects: DFT analysis of ESIPT/GSIPT in 2-(oxazolinyl)-phenols for photophysical and luminophore enhancement

Dual channel chemosensor for successive detection of environmentally toxic Pd2+ and CN− ions and its application to cancer cell imaging

BackgroundDetecting and neutralizing Pd2+ ions are a significant challenge due to their cytotoxicity, even at low concentrations. To address this issue, various chemosensors have been designed for advanced detection systems, offering simplicity and the potential to differentiate signals from different analytes. Nonetheless, these chemosensors often suffer from limited emission response and complex synthesis procedures. As a result, the tracking and quantification of residual palladium in biological systems and environments remain challenging tasks, with only a few chemosensing probes available for commercial use. ResultsIn this paper, a straightforward approach for the selective detection of Pd2+ ions is proposed, which involves the design, synthesis, and utilization of a propargylated naphthalene-derived probe (E)-N'-((2-(prop-2-yn-1-yloxy)naphthalen-1-yl)methylene)benzohydrazide (NHP). The NHP probe exhibits sensitive dual-channel colorimetry and fluorescence Pd2+ detection over other tested metal ions. The detection process is performed through a catalytic depropargylation reaction, followed by an excited state intramolecular proton transfer (ESIPT) process, the detection limit is as low as 11.58 × 10−7 M under mild conditions. Interestingly, the resultant chemodosimeter adduct (E)-N'-((2-hydroxynaphthalen-1-yl)methylene)benzohydrazide (NHH) was employed for the consecutive detection of CN− ions, exhibiting an impressive detection limit of 31.79 × 10−8 M. Validation of both detection processes was achieved through 1H nuclear magnetic resonance and density functional theory calculations. For real-time applications of the NHP and NHH probes, smartphone-assisted detection, and intracellular detection of Pd2+ and CN− ions within HeLa cells were studied. SignificanceThis research presents a novel naphthalene derivative for visually detecting environmentally toxic Pd2+ and CN− ions. The synthesized probe selectively binds to Pd2+, forming a chemodosimeter. It successfully detects CN− ions through colorimetry and fluorimetry, offering a low detection limit and quick response. Notably, it's the first naphthalene-based small molecule to serve as a dual probe for toxic analytes - palladium and cyanide. Moreover, it effectively detects Pd2+ and CN− intracellularly in cancer cells.

Specific detection of sarin gas Mimicking, diethylchlorophosphate employing solvent mediated in-situ generated hydroxyl functional group in a phthalimide-chromone coupled fluorogenic probe

Nerve agents are particularly hazardous substances and can result in fatality due to suppressing acetylcholinesterase function. This article introduced a fluorescent probe, (E)-5-(((4-hydroxy-2-methoxy-2H-chromen-3-yl)methylene)amino)isoindoline-1,3-dione (CMAD), which was exceptionally effective at detecting the sarin replacement diethylchlorophosphate (DCP), both in solution and vapor phase, respectively which exhibited quick response, excellent sensitivity and specificity. As a result of the gradual addition of DCP into the solution of the probe, the photoluminescence intensity at 476 nm is markedly increased, exhibiting bright cyan color fluorescence because of inhibition of the excited state intramolecular proton transfer (ESIPT) process, which is also clearly reflected in the estimation of photoluminescence quantum yield of phosphorylated CMAD (0.55 relatives to 4-aminophalimide) and the color chromaticity (CIE) diagram. The lowest detection limit and limit of quantification are 3.25 µM and 10.8 µM, respectively, within the stockpiles of other analogous analytes. Additionally, for on-the-spot detection, the probe may also be utilized in the test strips with superior selectivity for DCP. The ability to identify and measure DCP in the gas phase has also been established using a dip-stick and dipped-vial-conical-flask analysis. Moreover, we also performed the smartphone-based technique for the practical utility of CMAD for the on-spot quantification and detection of sarin gas in real threat situations. The effective demonstrations of practical usage, including soil analysis, inspire additional applications in different fields. Therefore, probe CMAD is a reliable, on-site monitoring fluorescence probe for precisely identifying DCP in the presence of additional competing nerve agents.

Effect of different substituted groups on excited state intramolecular proton transfer of BOHMB

Effect of different substituted groups on excited state intramolecular proton transfer of <scp>BOHMB</scp>

Versatile Aggregation Induced Emissive Molecular Probes Incorporating different Donor/Acceptor groups for Tunable Multiple Color Fluorescence

Excited state intramolecular proton transfer (ESIPT) and aggregation induced emission active multicolour fluorescent probes for bioimaging applications has grown popularly in recent years. Herein, we report a series of different donor/acceptor units (Cl, NO2 and O-CH3) bearing anthracene-salicylaldehyde based fluorescent probes and their antibacterial activity and fluorescence imaging of E. Coli bacteria and zebrafish embryos. All the compounds (ASA1, ASA2, ASA3 and ASA4) synthesized via facile one pot condensation reaction of anthracene hydrazide with Salicylaldehyde, 5-Chlorosalicylaldehyde, 5-Nitrosalicylaldehyde, 5-methoxysalicylaldehyde and characterized using all the possible spectroscopic techniques. The noteworthy tuneable emission wavelength shifts from 471 nm to 625 nm and ESIPT characteristics of the compounds were demonstrated through photophysical experiments and single crystal X-ray diffraction analysis. All the experimental results were completely analysed theoretically on the ground as well as the excited state using density functional theory (DFT) and time dependant density functional theory (TD-DFT) calculations. Compounds ASA1-ASA4 showed fascinating different colour fluorescent (Green, Yellow and Orange) aggregation induced emission features in the THF-H2O mixture. AIE characteristics of ASA1, ASA2, ASA3 and ASA4 were recognized using absorption, emission, fluorescence quantum yield (φ), DLS and SEM analysis. ASA1, ASA2, ASA3 and ASA4 showed excellent antibacterial activity and ROS generation against E. Coli bacteria. Further, owing to the multicolour fluorescent property of the compounds successfully applied for fluorescent imaging in E. Coli bacteria and live zebrafish embryos.

Investigating the Photophysical Aspects of a Naphthalene-Based Excited-State Proton Transfer Dye 1-(1H-Benzo[d]imidazol-2-yl)naphthalen-2-ol: pH-Dependent Modulation of Photodynamics.

The steady state and time-resolved photophysical behavior of a proton transfer dye 1-(1H-benzo[d]imidazol-2-yl)naphthalen-2-ol (H-BINO) was investigated. The excited state intramolecular proton transfer (ESIPT) reaction in H-BINO is predominant in nonpolar solutions (toluene and DCM) with a lifetime of ∼1.0 ns. However, in polar media (DMF and MeOH), the excited state photodynamics is characterized by a complex equilibrium of emission from the locally excited state (0.1-2.3 ns), the phototautomer (0.5-1.2 ns), and the anionic emission (2.1-5.4 ns). In the solid state, emission from the various aggregated states dictates the photobehavior. Interestingly, the photodynamics in aqueous solution changes starkly as a function of pH with the anionic (2.1 ns) and phototautomeric (0.5-1.0 ns) emissions guiding the photodynamics as the pH of the medium increases. Optimized structural parameters at the proton donor and acceptor sites for the enol and keto forms and the calculated potential energy curve along the proton transfer coordinate at the density functional theory (DFT) level with the B3LYP/6-311G++(d,p) theory support a favorable and barrierless ESIPT process. The current results will surely boost the ongoing research on small molecule emissive materials.

Effects of oxygen family elements on electron-withdrawing nitryl-substituted 2-(2’-hydroxyphenyl)benzazole derivatives: a theoretical investigation

The excited state intramolecular proton transfer (ESIPT) reaction is a well-studied photo reaction, based on this mechanism, many high-performance organic chromophores can be selected. It is widely acknowledged that the 2-(2’-hydroxyphenyl)benzazole (HBX) derivatives undergo the ESIPT process. This work mainly uses DFT and TDDFT methods to clarify the effects of oxygen family substituted elements on excited states for HBX derivatives. First, we probe into the molecular structures of HBX derivatives (HBX-O, HBX-S and HBX-Se) and explore their infrared (IR) vibrational behaviours. The results confirm that light excitation in S1 state enhances the hydrogen bonds of HBX dyes. Additionally, analysis of the frontier molecular orbitals shows that charge redistribution promotes the ESIPT process. This article provides a detailed explanation of the excited state reaction behaviours of three HBX dyes and demonstrates that substitution effects regulate the ESIPT processes of these dyes. This finding will contribute to the development of new photo-reactive substances in the future.

Heterocyclic fluorescent Schiff base chemosensors for the detection of Fe(III) and Cu(II) ions.

Two new Schiff bases were synthesized from 1-(2,4-dihydroxyphenyl)ethanone and pyridine derivatives. Both compounds were characterized using infrared, UV-Vis., 1H NMR, 13C NMR and mass spectral studies. Density functional theory (DFT) calculations were performed for both the Schiff bases with 6-31G(d, p) as the basis set. Vibrational frequencies calculated using the theoretical method were in good agreement with the experimental values. Both the Schiff bases were highly fluorescent in nature. The cation-recognizing profile of the compounds was investigated in aqueous methanol medium. The Schiff base 4-(1-(pyridin-4-ylimino)ethyl)benzene-1,3-diol (PYEB) was found to interact with Fe(III) and Cu(II) ions, whereas the Schiff base 4,4'-((pyridine-2,3-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (PDEB) was found to detect Cu(II) ions. The mechanism of recognition was established as combined excited state intramolecular proton transfer (ESIPT)-chelation-enhanced fluorescence (CHEF) effect and chelation-enhanced quenching (CHEQ) process for the detection of Fe(III) and Cu(II) ions, respectively. The stability constant of the metal complexes formed during the sensing process was determined. The limit of detection for Fe(III) and Cu(II) ions with respect to Schiff base PYEB was found to be 1.64 ×10-6 and 2.16 ×10-7M, respectively. With respect to Schiff base PDEB, the limit of detection for Cu(II) ion was found to be 4.54 ×10-4M. The Cu(II) ion sensing property of the Schiff base PDEB was applied in bioimaging studies for the detection of HeLa cells.

Influence of atomic electronegativity on ESIPT behaviour for the BTDI and its derivatives: Theoretical exploration

In this work, we theoretically explored the influence of atomic electronegativity on excited-state intramolecular proton transfer (ESIPT) behavior among novel fluorescent probes BTDI and its derivatives (BODI and BSeDI). A thorough examination of the optimized structural parameters and infrared vibrational spectra reveals an enhancement in intramolecular hydrogen bonding within BTDI and its derivatives upon light excitation. This finding is further reinforced by topological analysis and interaction region indicator scatter plots, which underscores the sensitivity of atomic electronegativity to variations in hydrogen bonding strength. With regards to absorption and fluorescence spectra, the decrease in atomic electronegativity leads to a pronounced redshift, primarily attributed to the narrowing of the energy gap. Additionally, an analysis of potential energy curves and the exploration of intrinsic reaction coordinate paths based on transition state structures afford a deeper understanding of the mechanism underlying ESIPT and being modulated through the manipulation of atomic electronegativity. We anticipate that this work on atomic electronegativity regulating ESIPT behavior will serve as a catalyst for novel fluorescent probes in the future, offering fresh perspectives and insights.

Aggregation-Induced Modulation of Ground and Excited State Photophysics of 5-(tert-Butyl)-2-Hydroxy-1,3-Isophthalaldehyde (5-tBHI).

5-(tert-Butyl)-2-hydroxy-1,3-isophthalaldehyde (5-tBHI) is a photochromic material susceptible to either excited state proton transfer or excited state intramolecular proton transfer, depending upon the solvent. However, it has also been found to aggregate in the presence of sodium dodecyl sulfate. In this current study, based on the steady-state and time-resolved spectroscopy, supported by crystallography, quantum chemical density functional theory calculation, and molecular dynamics (MD) simulation, we report on the aggregation of this potential single benzene-based emitter (SBBE) in neat solvents as well as solid phase to modulate its photophysics. It has been found that 5-tBHI forms mixed aggregates of different orders, owing to the presence of both enolic and tautomeric forms, to yield tunable emission, although the emission intensity is quenched. These findings suggest that the intramolecular hydrogen bonding of 5-tBHI not only limits intermolecular interactions but also promotes nonradiative deactivation pathways. Hence, designing and structural engineering, with a focus to suppressing intramolecular hydrogen bonding as well as increasing through space conjugation by replacing the aldehydic moieties with bulky aliphatic or aromatic ketonic groups, can be a plausible approach to yielding improved probes with tunable emission and higher fluorescence quantum yields.

Amination and Protonation Facilitated Novel Isoxazole Derivative for Highly Efficient Electron and Hole Separation.

It is of great importance to understand the intrinsic relationship between phototautomerization and photoelectric properties for the exploration of novel organic materials. Here, in order to chemically control the protonation process, the aminated isoxazole derivative (2,2'-(isoxazolo[5,4-d]isoxazole-3,6-diyl)dibenzenaminium, DP-DA-DPIxz) with -N═ as the proton acceptor was designed to achieve the twisted intramolecular charge transfer (TICT) state which was triggered by an excited-state intramolecular proton transfer (ESIPT) process. This kind of protonation enhanced the intramolecular hydrogen bonding, conjugative effect, and steric hindrance effects, ensuring a barrierless spontaneous TICT process. Through the intramolecular proton transfer, the configuration torsion and conjugation dissociation of the DP-DA-DPIxz molecule was favored, which led to efficient charge separation and remarkable variations in light-emitting properties. We hope the present investigation will provide a new approach to design novel optoelectronic organic materials and shine light on the understanding of the charge transfer and separation process in molecular science.

Nuclear Quantum Effects on Nonadiabatic Dynamics of a Green Fluorescent Protein Chromophore Analogue: Ring-Polymer Surface-Hopping Simulation.

Herein, we have used the "on-the-fly" ring-polymer surface-hopping simulation method with the centroid approximation (RPSH-CA), in combination with the multireference OM2/MRCI electronic structure calculations to study the photoinduced dynamics of a green fluorescent protein (GFP) chromophore analogue in the gas phase, i.e., o-HBI, at 50, 100, and 300 K with 1, 5, 10, and 15 beads (3600 1 ps trajectories). The electronic structure calculations identified five new minimum-energy conical intersection (MECI) structures, which, together with the previous one, play crucial roles in the excited-state decay dynamics of o-HBI. It is also found that the excited-state intramolecular proton transfer (ESIPT) occurs in an ultrafast manner and is completed within 20 fs in all the simulation conditions because there is no barrier associated with this ESIPT process in the S1 state. However, the other excited-state dynamical results are strongly related to the number of beads. At 50 and 100 K, the nuclear quantum effects (NQEs) are very important; therefore, the excited-state dynamical results change significantly with the bead number. For example, the S1 decay time deduced from time-dependent state populations becomes longer as the bead number increases. Nevertheless, an essentially convergent trend is observed when the bead number is close to 10. In contrast, at 300 K, the NQEs become weaker and the above dynamical results converge very quickly even with 1 bead. Most importantly, the NQEs seriously affect the excited-state decay mechanism of o-HBI. At 50 and 100 K, most trajectories decay to the S0 state via perpendicular keto MECIs, whereas, at 300 K, only twisted keto MECIs are responsible for the excited-state decay. The present work not only comprehensively explores the temperature-dependent photoinduced dynamics of o-HBI, but also demonstrates the importance and necessity of NQEs in nonadiabatic dynamics simulations, especially at relatively low temperatures.

Chemical bond reorganization in intramolecular proton transfer revealed by ultrafast X-ray photoelectron spectroscopy

Time-resolved X-ray photoelectron spectroscopy (TR-XPS) is used in a simulation study to monitor the excited state intramolecular proton transfer between oxygen and nitrogen atoms in 2-(iminomethyl)phenol. Real-time monitoring of the chemical bond breaking and forming processes is obtained through the time evolution of excited-state chemical shifts. By employing individual atomic probes of the proton donor and acceptor atoms, we predict distinct signals with opposite chemical shifts of the donor and acceptor groups during proton transfer. Details of the ultrafast bond breaking and forming dynamics are revealed by extending the classical electron spectroscopy chemical analysis to real time. Through a comparison with simulated time-resolved photoelectron spectroscopy at the valence level, the distinct advantage of TR-XPS is demonstrated thanks to its atom specificity.

Insights into the solvent-polarity-associated hydrogen bonding interactions and ESIPT reactions for DBOX fluorophore: a theoretical investigation

Inspired by the exquisite design of distinguished optical materials, novel organic molecules with remarkable characteristics of excited-state intramolecular proton transfer (ESIPT) have emerged as a prominent and captivating research topic. In this study, our primary focus lies in exploring the intricate dynamics of the excited state in 2-(5-(benzo[d]thiazol-2-yl)-1,3,4-oxadiazol-2-yl)-5-(diethylamino)phenol (DBOX), an extraordinary reversible molecular fluorophore that undergoes single-crystal-to-single-crystal transition. By investigating four distinct aprotic solvents with varying degrees of polarity, we unequivocally validate the significant impact of solvent polarity on photo-induced hydrogen bonding interactions, charge redistribution, and associated excited-state intramolecular proton transfer (ESIPT) phenomena. Through meticulous comparison and precise quantification of reaction barriers in diverse solvent environments, our groundbreaking findings strongly suggest that solvents with low polarities effectively facilitate the ESIPT reaction for DBOX fluorophore.

Dual-Channel Imine-Amine Photoisomerization in a Benzoimidazole and Benzothiazole Coupled System: Photophysics and Applications.

A molecule, namely 2-(1H-benzo[d]imidazol-2-yl)-6-(benzo[d]thiazol-2-yl)-4-bromophenol (BIBTB), having a two-way proton transfer unit of thiazole and imidazole moieties was synthesized and characterized by NMR, electrospray ionization mass spectrometry (ESI-MS), and single-crystal diffraction studies. Steady state and time-resolved spectral studies of BIBTB support excited state intramolecular proton transfer (ESIPT), causing imine-amine tautomerization through a two-way 6-membered H-bonded ring, where the N atoms of benzothiazole and the benzoimidazole unit are involved as proton acceptor sites. Interestingly, in a nonpolar and moderately polar solvent, photoisomerization in BIBTB is found to be favored toward the thiazole ring, whereas in a highly polar solvent, it is favored toward the imidazole ring. A spectral comparison of BIBTB with judicially designed molecules 2-(benzo[d]thiazol-2-yl)-4-bromophenol (HBT) and 2-(1H-benzo[d]imidazol-2-yl)-4-bromophenol (BIB) supports these inferences. Theoretical calculation using the Density Functional Theory (DFT) at CAM-B3LYP/6-311+G(d,p) level supports the existence of two low-energy 6-membered hydrogen-bonded planar conformers in the ground state in the gas phase and in solvents of different dielectrics. The potential energy curves (PECs) calculated along the proton transfer (PT) coordinate are found to have a high energy barrier in the ground state and to be barrierless or have a low energy barrier in the excited state for both the forms. The calculated vertical excitation and the emission energy from the relaxed excited and PT states show good correlation with the experimental spectral data. Aggregation of BIBTB in water with red shifted emission was established from X-ray single-crystal structure analysis, solid state emission, and Dynamic Light Scattering (DLS) measurement. The molecule BIBTB also acts as a fluorescence probe for sensing the explosive picric acid in the subnano scale and can be used to determine the proportion of water in dimethyl sulfoxide (DMSO) solvent.

2-Aryl-3H-1,3-benzazaphosphole Oxides: Synthesis, Optical Properties, and Excited State Intramolecular Proton Transfer.

Inclusion of a heteroatom to the phosphole ring is a promising strategy to intrinsically modulate the optical properties of phosphole derivatives. We report on a series of 2-aryl-3H-1,3-benzazaphosphole oxides that were efficiently prepared via sequential C-P cross-coupling, dehydrative [3 + 2] cycloaddition, and ring-oxidation reactions. The inclusion of one nitrogen atom into the benzophosphole framework caused red shifting of the absorption and emission maxima, reflecting the greater stabilization of the LUMO level.2-(2-Hydroxyphenyl)benzazaphosphole oxide underwent excited state intramolecular proton transfer and emitted a weak fluorescence from the excited state of the N-H tautomer.

Modulating the ESIPT Mechanism and Luminescence Characteristics of Two Reversible Fluorescent Probes by Solvent Polarity: A Novel Perspective.

As reversible fluorescent probes, HTP-1 and HTP-2 have favourable applications for the detection of Zn2+ and H2S. Herein, the impact of solvent on the excited-state intramolecular proton transfer (ESIPT) of HTP-1 and HTP-2 was comprehensively investigated. The obtained geometric parameters and infrared (IR) vibrational analysis associated with the intramolecular hydrogen bond (IHB) indicated that the strength of IHB for HTP-1 was weakened in the excited state. Moreover, structural torsion and almost no ICT behaviour indicated that the ESIPT process did not occur in HTP-1. Nevertheless, when the 7-nitro-1,2,3-benzoxadiazole (NBD) group replaced the H atom, the IHB strength of HTP-2 was enhanced after photoexcitation, which inhibited the twisting of tetraphenylethylene, thereby opening the ESIPT channel. Notably, hole-electron analysis and frontier molecular orbitals revealed that the charge decoupling effect was the reason for the fluorescence quenching of HTP-2. Furthermore, the potential energy curves (PECs) revealed that HTP-2 was more inclined to the ESIPT process in polar solvents than in nonpolar solvents. With a decrease in solvent polarity, it was more conducive to the ESIPT process. Our study systematically presents the ESIPT process and different detection mechanisms of the two reversible probe molecules regulated by solvent polarity, providing new insights into the design and development of novel fluorescent probes.

Development of a fluorescent scaffold by utilizing quercetin template for selective detection of Hg2+: Experimental and theoretical studies along with live cell imaging

Quercetin is an important antioxidant with high bioactivity and it has been used as SARS-CoV-2 inhibitor significantly. Quercetin, one of the most abundant flavonoids in nature, has been in the spot of numerous experimental and theoretical studies in the past decade due to its great biological and medicinal importance. But there have been limited instances of employing quercetin and its derivatives as a fluorescent framework for specific detection of various cations and anions in the chemosensing field. Therefore, we have developed a novel chemosensor based on quercetin coupled benzyl ethers (QBE) for selective detection of Hg2+ with “naked-eye” colorimetric and “turn-on” fluorometric response. Initially QBE itself exhibited very weak fluorescence with low quantum yield (Φ = 0.009) due to operating photoinduced electron transfer (PET) and inhibition of excited state intramolecular proton transfer (ESIPT) as well as intramolecular charge transfer (ICT) within the molecule. But in presence of Hg2+, QBE showed a sharp increase in fluorescence intensity by 18-fold at wavelength 444 nm with high quantum yield (Φ = 0.159) for the chelation-enhanced fluorescence (CHEF) with coordination of Hg2+, which hampers PET within the molecule. The strong binding affinity of QBE towards Hg2+ has been proved by lower detection limit at 8.47 µM and high binding constant value as 2 × 104 M−1. The binding mechanism has been verified by DFT study, Cyclic voltammograms and Jobs plot analysis. For the practical application, the binding selectivity of QBE with Hg2+ has been capitalized in physiological medium to detect intracellular Hg2+ levels in living plant tissue by using green gram seeds. Thus, employing QBE as a fluorescent chemosensor for the specific identification of Hg2+ will pave the way for a novel approach to simplifying the creation of various chemosensors based on quercetin backbone for the precise detection of various biologically significant analytes.

Light Induced Proton Coupled Charge Transfer Triggers Counterion Directional Translocation

We demonstrate directed translocation of ClO4‐ anions from cationic to neutral binding site along the synthetized BPym‐OH dye molecule that exhibits coupled excited‐state intramolecular proton‐transfer (ESIPT) and charge‐transfer (CT) reaction (PCCT). The results of steady‐state and time‐resolved spectroscopy together with computer simulation and modeling show that in low polar toluene the excited‐state redistribution of electronic charge enhanced by ESIPT generates the driving force, which is much stronger than by CT reaction itself and provides more informative gigantic shifts of fluorescence spectra signaling on ultrafast ion motion. The associated with ion translocation red‐shifted fluorescence band (at 750 nm, extending to near‐IR region) appears at the time ~ 83 ps as a result of electrochromic modulation of PCCT reaction. It occurs at substantial delay to PCCT that displayed fluorescence band at 640 nm and risetime of &lt; 200 fs. Thus, it becomes possible to visualize the manifestations of light‐triggered ion translocation and of its driving force by fluorescence techniques and to separate them in time and energy domains.