Proton Transfer Behavior Research Articles

Tuning the Crowding Effect of Water and Imidazole in Covalent Organic Frameworks for Proton Conduction.

The proton conduction of imidazole under confined conditions has attracted widespread attention from researchers. Under anhydrous conditions, the proton transfer behavior is primarily governed by the molecular dynamics of imidazole. However, within a water-mediated system, the crowding effect of water and imidazole in a confined space may outweigh the intrinsic properties of imidazole itself. In this study, we have meticulously adjusted the structural fragments within the covalent organic frameworks (COFs), fine-tuning the saturation level of imidazole loading and adjusting the crowding degree of imidazole and water molecules. As a result, the two COF composites exhibit distinctly different proton conduction mechanisms from 32 to 100% relative humidity (RH), of which one possesses proton conduction progressively shifting from the Grotthuss mechanism to the vehicle mechanism, while the other has proton conduction undergoing a transition from the vehicle mechanism at 32% RH through the Grotthuss mechanism at 75% RH and finally back to the vehicle mechanism at 100% RH. These results highlight the critical role of the crowding effect of water and imidazole within confined spaces in proton conduction.

Excited-state antioxidant activity for apigenin based on external electric field-modulated ESIPT behavior: TD-DFT and molecular docking calculations.

Apigenin (Api), a flavonoid possessing dual features of antioxidant activity and intramolecular hydrogen bond (IMHB), is subjected to an external electric field (EEF) to investigate its excited-state antioxidant activity after excited state intramolecular proton transfer (ESIPT) behavior employing the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, as well as molecular docking. The existence of IMHB is demonstrated by structural parameters and AIM topological analysis, where Api in the enol⁎ form under an EEF of +60×10-4a.u. possesses strong IMHB. The potential energy curves confirm that the ESIPT process varies from barrierless to barriered as the positive EEF grows, thus determining the excited-state form. Api exhibits strong excited-state antioxidant activity in vitro whether or not under an EEF, especially under the EEF of -40×10-4a.u., utilizing HOMO energy. According to average local ionization energy (ALIE), the electrophilic reaction site also changes after ESIPT process under the EEF, and the activity is significantly increased. Furthermore, activation of the antioxidant Keap1-Nrf2-ARE pathway in vivo, namely, the interaction of Keap1 protein with Api, calculated by molecular docking, suggests that an interaction between the Keap1 and excited-state Api exists accompanying lower and variable bind energy under the distinct EEFs. Taken together, combining the modulation of the ESIPT process with the excited-state antioxidant activity is an effective approach to enhance the antioxidant activity of compounds.

A TDDFT exploration on the excited-state intramolecular proton transfer in 2-(2'-hydroxyphenyl)-benzimidazole derivatives.

Excited-state intramolecular proton transfer (ESIPT) reactions are one of the fundamental energy transformation reactions in catalysis and biological process. The combining ESIPT with the twisted intramolecular charge transfer (TICT) brings the richness of optical, photoelectronic performances to certain functional compounds. Delineating the mechanism of ESIPT+TICT reactions and further understanding why a specific functional group dominates are fundamentally crucial for the design and application of the functionally photoelectric materials. In this paper, six 2-(2'-hydroxyphenyl) benzimidazole (HBIgens) derivatives involved in ESIPT+TICT were investigated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations to have an insight into the photophysical and photochemical process in acetonitrile. The optimized geometries indicated that the intramolecular hydrogen bonds (-O-H···N-) were enhanced in the corresponding first singlet, which provided the fundamentally outstanding prerequisites of the ESIPT reactions. By further charge analysis, it is indicated that the introduction of substitutes to the different positions would determine the Stokes' shifts, and the electron-adopting p-cyanophenyl group mainly contributed to the TICT structure. Constraint scanning the potential energy curves of both ground and first singlet excited states, the electron-adopting N,N-diethylamino group on the meta position could enhance the barrier and inhibit the ESIPT reaction. Furthermore, the nucleus independent chemical shift (NICS(1)_ZZ) values of phenol groups indicate the relationship between the reversal aromaticity and the barrier of ESIPT, both of which were proved to be negatively correlated in the ESIPT reaction. It is concluded that not only both types and positions of substituents can tune the excited-state proton transfer behaviors in HBIgen derivatives, but also the aromatic rule can easily be applied to elaborate the ESIPT reaction.

Tactfully regulating the ESIPT mechanism of novel benzazolyl-4-quinolones fluorophore by atomic electronegativity

The effects of atomic electronegativity (O, S and Se) on the excited state intramolecular proton transfer (ESIPT) behavior of fluorescent benzazolyl-4-quinolones derivatives have been investigated theoretically. Analysis of structure parameters and infrared vibrational spectra indicate that the intramolecular hydrogen bonds (O1H1⋯N1) are gradually strengthened in the first (S1) excited state as the atomic electronegativity diminishes (O → S → Se). The topological parameters, reduced density gradient (RDG) scatter plots and interaction region indicator (IRI) isosurface further confirm our results. The energy gap of molecular orbitals reflect that the less atomic electronegativity prompt greater excited state reactivity. In addition, the constructed potential energy curves (PECs) reveal that Se substituent has lower potential barrier (0.42 kcal/mol), which is more likely to accelerate the occurrence of ESIPT process. These results show that the atomic electronegativity helps to regulate the ESIPT process, which will pave the way for the design and synthesis of ESIPT-based fluorophores in future.

“AIE+ESIPT” based naphthothiazole fluorescent probes for live cell imaging

Dual-functional organic fluorophores with aggregation induced emission (AIE) behavior and excited-state intramolecular proton transfer (ESIPT) behavior are of great significance to the design of imaging probes to bioimage systems. However, the pursuit of probes exhibiting dual AIE+ESIPT effects for live cell imaging remains an ongoing research challeng. Herein, we have successfully developed naphthothiazole fluorescent probes, HNBT-H and HNBT-G, based on the "AIE+ESIPT" effect. These probes were designed by incorporating responsive units for β-galactosidase (β-gal) and H2O2 into the pre-existing "AIE+ESIPT" HNBT fluorophore framework. The HNBT-H probe demonstrated the capability to distinguish various levels of H2O2. Furthermore, the applicability of HNBT-H and HNBT-G have been examined in living systems. These probes exhibit a good biocompatibility and low toxicity, the cell imaging experiments demonstrate the capability of HNBT-H and HNBT-G for fluorescence visualization in response to β-gal and H2O2 in RAW264.7 cells and PC12 cells.

Theoretical study on the atomic substitution effect on the aromaticity and ESIPT behavior of a novel chalcone-based fluorophore

Recently, a new ESIPT-based fluorophore (E)-2-(4-(dimethylamino) benzylidene)-7-hydroxy-1-indanone (7HIN) was designed and obtained experimentally. We investigated the excited state intramolecular proton transfer (ESIPT) behavior and photophysical properties of 7HIN based on density functional theory (DFT) and time-dependent DFT. Two derivatives of 7HIN (4HID and 4HBF) were obtained by replacing the CH2 group in the five-membered ring with NH group and O atom to study the atomic substitution effect on the proton transfer reactions and fluorescent features of 7HIN. All data from structural parameters, infrared frequencies and electron density showed that the intramolecular hydrogen bonds (IHB) in 7HIN and its derivatives were strengthened in the excited state (S1), which will accelerate the ESIPT process. The potential energy curves (PECs) indicated that the proton transfer can easily occur in the S1 state because of the lower energy barrier. The electron-hole analysis revealed that the S0 → S1 transition is an intramolecular charge transfer transition. The NH- and O-substitution led to a weakening of IHB, increased the ESIPT barrier and red-shifted the absorption/emission wavelength of 7HIN. The PBE38 functional in this work is very reliable since the experimental absorption/fluorescence wavelength of 7HIN was reproduced well.

Effects of amino‐ and dimethylamine‐groups on the fluorescent properties of novel flavone‐based derivatives with ESIPT behavior: A TD‐DFT study

AbstractIn this work, the effects of different functional groups on the excited‐state intramolecular proton transfer behavior and fluorescent features of 3‐hydroxy‐2‐(naphthalen‐2‐yl)‐4H‐chromen‐4‐one (HFN) are explored in detail. Three new compounds (HFN‐1, HFN‐2, and HFN‐3) are designed based on the HFN by introducing the electron‐donating groups (–NH2, –N(CH3)2). The mainly geometrical parameters of optimized configuration showed that the intramolecular hydrogen bonds of the studied compounds are enhanced in the excited (S1) state, confirming by the ground (S0) and excited states infrared spectra, electron densities and reduced density gradient isosurfaces. The S0 → S1 transitions of HFN derivatives are dominated by ππ* charge transfer transition. The introduction of electron‐donating group (–NH2, –N(CH3)2) weakens the intramolecular hydrogen bond, increases the excited‐state intramolecular proton transfer barrier and red‐shifts the absorption/fluorescence peak. The coexistence of –NH2 and –N(CH3)2 make the absorption and fluorescence wavelengths of HFN‐1/HFN‐2 red‐shift/blue‐shift.

Computational explorations about the solvent-polarity-associated excited state proton transfer behaviors for the novel F-BSD compound.

Inspired by the excellent potential application prospects from the precisely controlled attributes displayed by fluorine-substituted-bis(salicylidene)-1,5-diaminonaphthalene (F-BSD) and its derivatives in the domains of photochemistry and photophysics, our present undertaking predominantly focuses on exploring the complexities of photo-induced excited state reactions for F-BSD fluorophores dissolved in solvents with diverse levels of polarity. Our simulations reveal that the excited state intramolecular double proton transfer (ESIDPT) reaction for F-BSD chemosensor can be significantly regulated by solvent polarity-dependent hydrogen bonding interactions and charge recombination induced by photoexcitation, which result from variations in geometries and vertical excitation charge reorganizations. By constructing potential energy surfaces (PESs), we also demonstrate that the stepwise ESIDPT reaction of F-BSD occurs with alternative dual intramolecular hydrogen bonds (O1-H2···N3 or O4-H5···N6). Interestingly, we affirm polar solvents should be conducive to the first-step of ESIDPT process, while nonpolar solvents are in favor of the second step. We sincerely hope solvent polarity-dependent ESIDPT behavior will pave the way for future design of novel luminescent materials. The molecular geometries were optimized by DFT//TDDFT D3-B3LYP/TZVP theoretical level with IEFPCM solvent model in S0 and S1 states, respectively. This work also explores the energy level of target molecules with the computational vertical absorption spectra by TDDFT. All the simulations were carried out based on Gaussian 16 software. The core-valence bifurcation (CVB) indexes were obtained by using Multiwfn 3.8. Potential energy surfaces were constructed by the DFT//TDDFT D3-B3LYP/TZVP level based on restricted optimization, also the transition state (TS) forms were searched using the same level.

Different functional groups dependent fluorescent properties for ESIPT-based ABTN derivatives: A theoretical study

On the basis of density functional theory (DFT) and time-dependent DFT (TD-DFT), 2-amino-3-(benzo[d]thiazol-2-yl)benzaldehyde derivatives (ABTN-1, ABTN-2, ABTN-3) are selected as models to theoretically explore the effect of different functional groups on the fluorescent properties and excited state intramolecular proton transfer (ESIPT) behavior. The optimized configurations, infrared vibrational frequencies and topological parameters are used to analyze the intensity of intramolecular hydrogen bond (IHB). The absorption and fluorescence emission spectra are simulated, and the frontier molecular orbital as well as electron-hole distribution are investigated. In addition, the ground state (S0) and excited state (S1) potential energy curves (PECs) are constructed. The–CN group has little effect on the absorption and fluorescence wavelengths of ABTN. The –N(CH3)2 group red-shifts the absorption and fluorescence wavelengths exceeding 100 nm. The coexistence of –CN and –N(CH3)2 groups has almost the same effect on the absorption and fluorescence peaks as the–N(CH3)2 group.

Electrofluorochromic Hydrogels by Oligothiophene-Based Color-Tunable Fluorescent Dye Doping.

Soft electronic materials hold great promise for advancing flexible functional devices. Among the various soft materials available, hydrogels are particularly attractive for soft electronic device development due to their inherent properties, including transparency, shape adaptability through swelling/deswelling, and self-healing capabilities. Transparent hydrogels contribute to the creation of advanced smart devices such as sensors, smart windows, and anticounterfeiting technologies. Poly(vinyl alcohol) hydrogels are used as a platform for creating electrofluorochromic (EFC) devices in combination with oligothiophene-conjugated benzothiazole derivatives (OCBs) as fluorescent emitters. OCBs demonstrated excited-state intramolecular proton transfer (ESIPT) behavior with a large Stokes shift and emission changes responsive to solvent polarity and pH stimuli. Even in the solid state, OCBs exhibited strong fluorescence emission across a wide range of colors from blue to red, making them exceptionally well-suited for EFC device development. Their quantum yields in the powder state were obtained between 2.3% and 19.9%. Through the incorporation of OCBs into a PVA hydrogel (OCB@PVA), we achieved the successful fabrication of flexible EFC devices, including electronic paper and smart panels. When electric potentials (-2.4 and +2.4 V) were applied in OCB@PVA, fluorescence color changes were observed by an electrochemically induced pH change owing to electrohydrolysis of water. These devices demonstrated the potential of OCB@PVA hydrogels in the realm of flexible electronics. They could be used to create innovative and versatile devices with stimuli-responsive fluorescence properties.

Confinement effect of FeMOFs glass enhances the proton coupled electron transfer reaction for the organic pollutants polymerization toward sustainable water purification

Polymerization-driven removal of pollutants in advanced oxidation processes (AOPs) offers a sustainable way for the simultaneous achievement of contamination abatement and resource recovery, supporting a low-carbon water purification approach. In this work, metal–organic frameworks (MOFs) glass complexes (g-ZIF-62@8) were used as a platform to enhance proton transfer through the confinement effect of nanopores, modulating proton coupled electron transfer (PCET) reaction to promote organic pollutant polymerization. The results show that the confinement effect of nanopores in ZIF-62 glass can significantly improve the proton and electron transfer behavior, the proton diffusion coefficient is increased by 4.9 times (2.91*10−3 to 1.43*10−2), the energy barrier of the PCET reaction can be reduced by 1.9 eV, and the reaction kinetic rate constant is increased from 0.0198 min−1 to 0.20118 min−1. Photogenerated holes and Fe(IV = O), as the main reactive oxygen species (ROS), undergo PCET reaction with Bisphenol A (BPA) to convert them into phenoxy radicals, which are then polymerized into macromolecular organic compounds. PCET with proton-electron synergy was identified as a key driver of pollutant polymerization. This enables low-carbon purification and organic carbon recovery in wastewater. Our work provides new insights into the application of confinement effects to enhance proton and electron behavior to regulate pollutant polymerization toward sustainable water purification.

Concerning for the solvent-polarity-dependent conformational equilibrium and ESIPT mechanism in Pz3HC system: A novel insight

In this report, we propose a new insight into the interaction between the solvent-polarity-dependent conformational equilibrium and excited state intramolecular proton transfer (ESIPT) behavior of Pz3HC system in four different polar solvents (polarity order: ACN > THF > TOL > CYC). Using quantum chemistry method, we first announce a coexistence mechanism between Pz3HC-1 and Pz3HC-3 in the ground state in four solvents based on the Boltzmann distribution. In particular, Pz3HC-1 is the principal configuration in non-polar solvent, but Pz3HC-3 is the principal configuration in polar solvent. In addition, the simulated fluorescence spectra interprets the negative solvatochromism effect of Pz3HC-1 and Pz3HC-3 in four solvents. The evidence from intramolecular hydrogen bonding (IHB) parameters and electronic perspective collectively confirms the light-induced IHB enhancement and intramolecular charge transfer (ICT) properties in Pz3HC-1 and Pz3HC-3, which raises the likelihood of the ESIPT process. Combining the calculation of potential energy curve (PEC) and intrinsic reaction coordinate (IRC), we demonstrate that the ESIPT ease of Pz3HC-1 in different polar solvents obeys the order of CYC > TOL > THF > ACN, while the order of ESIPT ease in Pz3HC-3 is opposite. Notably, the ESIPT process of Pz3HC-3 in CYC solvent is accompanied by the twisted intramolecular charge transfer (TICT) process. In addition, we also reveal that the enol* and keto* fluorescence peaks of Pz3HC-3 in CYC solvent are quenched by ISC and TICT process, respectively. Our work not only provides a satisfactory explanation of the novel dynamics mechanism for Pz3HC system, but also brings light to the design and application of new sensing molecules in the future.

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.

Theoretical explorations about solvent polarity associated excited state proton transfer behaviour for 2-benzoxazol-2-yl-6-triethylsilanylethynyl-phenol fluorophore

Theoretical explorations about solvent polarity associated excited state proton transfer behaviour for 2-benzoxazol-2-yl-6-triethylsilanylethynyl-phenol fluorophore

Insights into solvent polarity associated geometries and ESIPT behaviours for Prz3HC: a theoretical study

Given the potential significance of 3-hydroxychromone derivatives, our focus in this study is to investigate the solvent-polarity-associated photo-induced behaviours for 3-hydroxy-2-(1-ethyl-1H-pyrazol-3-yl)-4H-chromen-4-one (Prz3HC). We firstly examine the coexistence of three conformations (i.e. Prz3HC-I, Prz3HC-II and Prz3HC-III) and present a mechanism for their coexistence between Prz3HC-I and Prz3HC-III. Notably, non-polar solvents contain mainly Prz3HC-I while polar solvents contain mainly Prz3HC-III. Analysing infrared vibrational spectra and geometrical variations between S0 and S1 states, we demonstrate a hydrogen bonding strengthening phenomenon that facilitates excited-state intramolecular proton transfer (ESIPT) behaviour for both Prz3HC-I and Prz3HC-III. To qualitatively investigate photo-induced behaviours, by frontier molecular orbitals (MOs), we have discovered that charge redistribution significantly enhances the propensity for ESIPT. By comparing the barriers of potential energy curves (PECs) for twisting dihedral angles and ESIPT paths, we have unequivocally ruled out any mutual transformations in the S1 state. We also propose a solvent-polarity-regulated ESIPT behaviour for Prz3HC-I and Prz3HC-III. Furthermore, through an exploration of transition states (TS), we have further scrutinised the intricate mechanism underlying ESIPT. We sincerely hope this study can elucidate the solvent-polarity-regulated excited-state behaviours of Prz3HC while simultaneously paving the way for future explorations and applications of other 3-hydroxychromone derivatives.

Theoretical investigation on regulating photophysical properties and proton transfer behavior by electronegativity for near-infrared emitting styryl dyes.

Our main focus is to explore the atomic electronegativity-dependent photoinduced behavior of styryl derivatives (HBO, HBS, and HBSe). The results of structural parameter calculation by the DFT method show that the intramolecular hydrogen bonds of normal and tautomer form are strengthened and weakened, respectively, in an excited state (S1), which is conducive to the excited intramolecular proton transfer (ESIPT) process. The enhancement of excited hydrogen bond is beneficial to the ESIPT process from the aspects of infrared vibration frequency (IR), Mulliken's charge analysis, and density gradient reduction (RDG). Additionally, by determining the bond energy with the band critical point (BCP) parameter, we found that the lower the electronegativity of the atom, the larger the hydrogen bond strength at the excited state and the more likely ESIPT reaction occurs. Meanwhile, the intramolecular H-bonds O-H…N in HBO, HBS, and HBSe are enhanced with the weakened electron-withdrawing capacity of the atom (from O to S and Se). Subsequently, frontier molecular orbital (FMOs) and charge density difference (CDD) analyses essentially revealed that electron redistribution induces the ESIPT process. Low atomic electronegativity exhibits the high chemical activity of the excited state. Furthermore, to demonstrate the electronegativity-dependent ESIPT behavior of the system, we built potential energy curves (PECs) and located the transition states (TS) of proton transfer processes.

An investigation into proton conduction of ga doped boehmite based memristor with simulated synaptic behavior

Artificial synapses based on protonic memristor have great potential in constructing neural morphological computing system. However, further investigation is still required to understand the proton conduction mechanism of protonic memristors. Here, we present a new type of Ga doped boehmite based memristors with artificial synapse functionality, which can achieve variations in conductance levels by precise control of the Ga doping content. Compared with undoped boehmite, there is no obvious change in crystal structure, particle morphology and chemical bond doped with different of concentration Ga. The change in the electrical conductance is found to be a result of proton transfer, closely resembling what takes place in biological neurons. Furthermore, the first-principle density functional theory (DFT) calculation is conducted to elucidate the proton conduction mechanism and zig-zag-like pathways for proton transfer in the memristor was proposed. The results establish a precedent for tuning the proton transfer behaviour in memristor-based neural devices, thereby enhancing their practicality. It provides a novel approach for studying the resistance switching behavior in proton transfer-based memristors.

Effects of substitution and conjugation on photophysical properties of ESIPT-based fluorophores with the core of 4-aminophthalimide

4-Aminophthalimide is a highly fluorescent signaling unit with excellent photophysical properties and wide application foregrounds. Based on this, a range of theoretical investigations are conducted on the fluorescent probe (E)-5-((2-hydroxybenzylidene) amino) isoindoline-1, 3-dione (HID) with the core of 4-aminophthalimide using density functional theory (DFT) and time-containing density functional theory (TD-DFT) methods in this paper. The optimized configurations, vertical excitation and emission energies, electronic characteristics and excited-state intramolecular proton transfer (ESIPT) behaviors of the probe HID are discussed in detail. Furthermore, to enhance the luminescent properties of HID, five novel compounds have been designed based on the structure of HID by introducing amino, methoxy and naphthalene groups (–NH2, –OMe and C10H8). Our work thoroughly explores how the property and position of substituents and conjugation affect photophysical characteristics and ESIPT processes. We find that the ESIPT dynamics can be modulated by the substitution and conjugation effects. Specifically, the introduction of amino and methoxy groups at the ortho-position and the introduction of the naphthalene group promote the ESIPT behavior of HID1, whereas the introduction of amino and methoxy groups at the meta-position exhibits the contrary impact. Therefore, we boldly infer that the introduction of electron-donating groups in the ortho-position and the introduction of the conjugated group make the ESIPT process more effortless to occur, whereas the introduction of substituents with opposing natures in the meta-position makes the ESIPT process more difficult to occur. In addition, the ionization potentials (IP), electron affinities (EA) and reorganization energies (λh and λe) of molecules are calculated to assess their potential as luminescent materials. Our work not only reveals the luminescence and ESIPT mechanism of the probe HID1, but also proposes to modulate the ESIPT process through the substitution and conjugation effects. In particular, the designed molecules have better photoelectric properties as a result of their red-shifted absorption and fluorescence spectra, smaller energy gaps, larger transferred charges and greater charge transferred distances, which offers some valuable ideas for the experimental development of more efficient organic luminescent materials with ESIPT properties.

Effects of substituted chalcogen atoms on excited state reaction for 1-(benzo[d]thiazol-2-yl)-6-substituted-naphthalen-2-ol derivatives

Inspired by the brilliant photophysical properties of novel organic molecules containing chalcogenide substitution, in this work, effects of atomic electronegativity of chalcogen (O, S and Se) on hydrogen bond interactions and proton transfer (PT) reaction are focused. We present the characteristic CN-BTN is the main objective to explore the influence of atomic electronegativity on the hydrogen bond interaction and excited state intramolecular proton transfer (ESIPT) behaviour by photoexcitation. By comparing the structural changes and infrared (IR) vibrational spectra of the CN-BTN derivatives (CN-BTN-O, CN-BTN-S and CN-BTN-Se) fluorophores in S0 and S1 states, combined with the preliminary detection of hydrogen bond interaction by core-valence bifurcation (CVB) index, we can conclude that hydrogen bond is strengthened in S1 state, which is favourable for the occurrence of ESIPT reaction. The charge recombination behaviour of hydrogen bond induced by photoexcitation also further illustrates this point. Via constructing potential energy curves (PECs) based on restrictive optimisation and searching transition state (TS) configuration, we finally clarify the ESIPT mechanism for CN-BTN derivatives. Specially, we confirm change of atomic electronegativity has a regulatory effect on the ESIPT behaviour of CN-BTN derivatives, that is, the lower the atomic electronegativity is more conducive to the ESIPT reaction.

Computational Insights into Excited State Intramolecular Double Proton Transfer Behavior Associated with Atomic Electronegativity for Bis(2'-benzothiazolyl)hydroquinone.

Inspired by the distinguished regulated photochemical and photophysical properties of 2-(2'-hydroxyphenyl)benzazole derivatives, in this work, the novel bis(2'-benzothiazolyl)hydroquinone (BBTHQ) fluorophore is explored, looking at its photo-induced behaviors associated with different substituted atomic electronegativities, i.e., BBTHQ-SO, BBTHQ-SS and BBTHQ-Se compounds. From the structural changes, infrared (IR) vibrational variations and simulated core-valence bifurcation (CVB) indexes for the dual hydrogen bonds for the three BBTHQ derivatives, we see that low atomic electronegativity could be conducive to enhancing hydrogen bonding effects in the S1 state. Particularly, the O4-H5⋯N6 of BBTHQ-SO and the O1-H2⋯N3 of BBTHQ-SSe could be strengthened to be more intensive in the S1 state, respectively. Looking into the charge recombination induced by photoexcitation, we confirm a favorable ESDPT trend deriving from the charge reorganization of the dual hydrogen bonding regions. By constructing the potential energy surfaces (PESs) along with the ESDPT paths for the BBTHQ-SO, BBTHQ-SS and BBTHQ-Se compounds, we not only unveil stepwise ESDPT behaviors, but also present an atomic electronegativity-regulated ESDPT mechanism.