Search

[Display omitted] • The enhanced hydrogen bonding provides the impetus to promote the ESIPT reaction. • Photo-induced increased electronic densities around O 14 atom plays vital roles in attracting hydroxyl proton. • Atomic electronegativity could be more favorable for the ESIPT behavior of 4M3HF system. In view of the potential applications via regulating excited state behaviors, in this work, excited state dynamics of 4-methoxy-3-hydroxyflavone (4M3HF) with different atomic electronegativities (i.e., 4M3HF-O, 4M3HF-S and 4M3HF-Se) are explored theoretically. Dominating chemical parameters, infrared (IR) spectra, and bond critical point (BCP) analyses reveal hydrogen bond could be enhanced in S 1 state. Via light-induced excitation, by comparing the energy gaps of frontier molecular orbitals (MOs) and charge recombination, we find low atomic electronegativity promotes ESIPT reaction. Insights into potential energy curves (PECs) and transition state (TS) forms, we present low atomic electronegativity facilitates ESIPT behavior for 4M3HF system. [ABSTRACT FROM AUTHOR]

In this work, based on density functional theory (DFT) and time‐dependent DFT (TDDFT) methods, we theoretically explore the excited state behavior for a novel dye molecule 3,3′‐(5,5′‐((1E,1E′)‐hydrazine‐1,2‐diylidenebis (methanylylidene))bis(2‐morpholinothiazole‐5,4‐diyl))bis(4‐hydroxy‐2H‐chromen‐2‐one) (CS‐Azine). Coupling with atoms in molecules, we investigate the intramolecular dual hydrogen bonds of CS‐Azine system and verify the formation of them. Via study the primary bond distances, bond angle, and infrared vibrational spectra involved in hydrogen bonding moieties, we find O1‐H2···N3 and O4‐H5···N6 of CS‐Azine should be strengthened in the S1 state. When exploring the photo‐excitation process, we confirm that the charge redistribution around hydrogen bonding moieties reveals the tendency of ESIPT reaction. To further investigate whether single or double proton transfer occurs in the S1 state, we consider two kinds of reaction paths (ie, the stepwise and synergetic ESIPT reactions). And the constructed potential energy curves demonstrate that only the single proton transfer reaction should be the most supported in the S1 state from CS‐Azine to CS‐Azine‐SPT form due to the low potential energy barrier. This work not only clarifies the excited state behavior and mechanism about CS‐Azine system but also paves the way for further applying CS‐Azine dye in future. Highlights: Although two hydrogen bonds exist for CS‐Azine system, only the single proton transfer reaction should be the most supported one in the S1 state. [ABSTRACT FROM AUTHOR]

Abstract A novel fluorescence molecule (2‑hydroxy‑4‑methoxyphenyl)(phenyl)‑methanone azine (HMPM) has been explored theoretically in this present work. Based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we investigate the excited state hydrogen bonding behaviors and excite state intramolecular proton transfer (ESIPT) process for HMPM molecule. Via simulating the reduced density gradient (RDG) versus sign(λ 2)ρ, we firstly verify the double intramolecular hydrogen bonds (O1 H2⋯N3 and O4 H5⋯N6) for HMPM system. Comparing with the changes about these two hydrogen bonds (i.e., bond distances, bond angles and infrared (IR) vibrational spectra), we find that they should be enhanced in the first excited state upon the photo-excitation. The shortened hydrogen bonding distance of H2⋯N3 and H5⋯N6 provide the possibility for ESIPT reaction. Given the photo-excitation process, we confirm the charge redistribution around the hydrogen bonding moieties plays an important role as a driving force for the ESIPT process. Further, via constructing S 0 -state and S 1 -state potential energy surfaces (PESs), we confirm the excited state double proton transfer (ESDPT) is excludable since the high optimized energy and high potential energy barrier. While the low potential barrier for excited state single proton transfer path results in the ultrafast ESIPT reaction, which explains why the initial HMPM fluorescence peak cannot be detected in previous experimental phenomenon. This work not only clarifies the excited state dynamical behavior for HMPM system, but also explains previous experimental phenomenon and attributions about steady state spectra. We hope this work can facilitate novel applications based on the novel HMPM system in future. Graphical Abstract Unlabelled Image Highlights • Hydrogen bond of HMPM should be strengthened in the first excited state. • Charge transfer facilitates the ESIPT process for HMPM molecule. • Only the excited state single proton transfer process occurs for HMPM molecule. [ABSTRACT FROM AUTHOR]

In this work, density functional theory (DFT) and time‐dependent density functional theory (TDDFT) methods are used to explore the excited‐state intramolecular proton transfer (ESIPT) mechanism of a novel system 4′‐dimethylaminoflavonol (DAF). By analyzing the molecular electrostatic potential (MEP) surface, we verify that the intramolecular hydrogen bond in DAF exists in both the S0 and S1 states. We calculate the absorption and emission spectra of DAF in two solvents, which reproduce the experimental results. By comparing the bond lengths, bond angles, and relative infrared (IR) vibrational spectra involved in the hydrogen bonding of DAF, we confirm the hydrogen‐bond strengthening in the S1 state. For further exploring the photoexcitation, we use frontier molecular orbitals to analyze the charge redistribution properties, which indicate that the charge transfer in the hydrogen‐bond moiety may be facilitating the ESIPT process. The constructed potential energy curves in acetonitrile and methylcyclohexane solvents with shortened hydrogen bond distances demonstrate that proton transfer is more likely to occur in the S1 state due to the lower potential barrier. Comparing the results in the two solvents, we find that aprotic polar and nonpolar solvents seem to play similar roles. This work not only clarifies the excited‐state behaviors of the DAF system but also successfully explains its spectral characteristics. Hydrogen bond should be formed in the S0 state for 4′‐dimethylaminoflavonol (DAF), as shown via Atoms in Molecules (AIM) analysis. The intramolecular hydrogen bond of DAF should be strengthened in the S1 state, which provides the tendency for the excited‐state intramolecular proton transfer (ESIPT) reaction. The charge redistribution and low potential energy barriers of DAF facilitate the ESIPT reaction. [ABSTRACT FROM AUTHOR]

Abstract: In this present work, using density functional theory and time‐dependent density functional theory methods, we theoretically study the excited‐state hydrogen bonding dynamics and the excited state intramolecular proton transfer mechanism of a new 2‐phenanthro[9,10‐d]oxazol‐2‐yl‐phenol (2PYP) system. Via exploring the reduced density gradient versus sign(λ2(r))ρ(r), we affirm that the intramolecular hydrogen bond O1‐H2⋯N3 is formed in the ground state. Based on photoexcitation, comparing bond lengths, bond angles, and infrared vibrational spectra involved in hydrogen bond, we confirm that the hydrogen bond O1‐H2⋯N3 of 2PYP should be strengthened in the S1 state. Analyses about frontier molecular orbitals prove that charge redistribution of 2PYP facilitates excited state intramolecular proton transfer process. Via constructing potential energy curves and searching transition state structure, we clarify the excited state intramolecular proton transfer mechanism of 2PYP in detail, which may make contributions for the applications of such kinds of system in future. [ABSTRACT FROM AUTHOR]

In the present work, using density functional theory and time-dependent density functional theory methods, we investigated and presented the excited-state intramolecular proton transfer (ESIPT) mechanisms of a novel Compound 1 theoretically. Analyses of electrostatic potential surfaces and reduced density gradient (RDG) versus sign(λ2)ρ, we confirm the existence of intramolecular hydrogen bond O1-H2···N3 for Compound 1 in the S0 state. Comparing the primary structural variations of Compound 1 involved in the intramolecular hydrogen bond, we find that O1-H2···N3 should be strengthened in the S1 state, which may facilitate the ESIPT process. Concomitantly, infrared (IR) vibrational spectra analyses further verify the stability of hydrogen bond. In addition, the role of charge transfer interaction has been addressed under the frontier molecular orbitals, which depicts the nature of electronical excited state and supports the ESIPT reaction. The theoretically scanned and optimized potential energy curves according to variational O1-H2 coordinate demonstrate that the proton transfer process should occur spontaneously in the S1 state. It further explains why the emission peak of Compound 1-enol was not reported in previous experiment. This work not only presents the ESIPT mechanism of Compound 1 but also promotes the understanding of this kind of molecules for further applications in future. [ABSTRACT FROM AUTHOR]

The excited-state intramolecular proton transfer (ESIPT) mechanism of a new compound ( E)-1-((2,2-diphenylhydrazono)methyl)naphthalen-2-ol ( EDMN) sensor, reported and synthesized by Mukherjee et al. [ Sensors Actuat. B-Chem. 2014, 202, 1190], is investigated in detail theoretically. The calculations on primary bond lengths, bond angles, and the corresponding infrared (IR) vibrational spectra and hydrogen-bond energy involved in intramolecular hydrogen bond between the S0 and S1 states confirm that the intramolecular hydrogen bond is strengthened in the S1 state, which reveals the tendency of ESIPT reaction. The fact that the experimental absorption and emission spectra are well reproduced demonstrates the rationality and effectiveness of the time-dependent density functional theory (TDDFT) level of theory we adopt here. Furthermore, intramolecular charge transfer based on the frontier molecular orbitals (MOs) gives indication of the ESIPT reaction. The constructed potential energy curves of both the S0 and S1 states while keeping the O─H distance of EDMN fixed at a series of values are used to illustrate the ESIPT process. The lower barrier of ~3.934 kcal/mol in the S1 state potential energy curve (lower than the 8.254 kcal/mol in the S0 state) provides the transfer mechanism. [ABSTRACT FROM AUTHOR]

In this present work, we theoretically investigate a novel system 3‐hydroxy‐2‐(5‐(5‐(5‐(3‐hydroxy‐4‐oxo‐4H‐chromen‐2‐yl)thiophen‐2‐yl)thiophen‐2‐yl)thiophen‐2‐yl)‐4H‐chromen‐4‐one (FT) based on density functional theory (DFT) and time‐dependent DFT (TDDFT) methods. Via calculating the reduced density gradient (RDG) versus sign(λ2) ρ, we firstly verify the formation of the dual intramolecular hydrogen bonds (O1─H2···O3 and O4─H5···O6) for FT form in the S0 state. Then comparing the primary structural parameters and corresponding infrared (IR) vibrational spectra involved in hydrogen bonds between S0 and S1 state, we demonstrate that these two intramolecular hydrogen bonds should be strengthened in the S1 state. Insights into the vertical excitation process, our theoretical results reproduced experimental absorption nature, which confirms that the theoretical level (B3LYP/TZVP) is reasonable and effective in this work. And frontier molecular orbitals (MOs) depict the nature of electronically excited state and support the excited‐state intramolecular proton transfer (ESIPT) reaction. According to the calculated results of potential energy curves along stepwise and synergetic O1─H2 and O4─H5 coordinates, we verify that only the excited‐state single‐proton transfer could occur for FT molecule in the S1 state, although it possesses two intramolecular hydrogen bonds. We not only investigate the detail excited‐state behaviors for FT system and elaborate the ESIPT mechanism but also explain previous experimental results. Dual intramolecular hydrogen bonds should be strengthened upon photoexcitation. The charge redistribution reveals the tendency of ESIPT reaction. We confirm that only single proton transfer occurs in the S1 state. [ABSTRACT FROM AUTHOR]

Using the density functional theory (DFT) and time‐dependent density functional theory (TDDFT) methods, we theoretically explore a novel fluorescent sensor molecule (abbreviated as "2") (Sensors Actuat B‐Chem. 2018, 263, 585). Because of its symmetry, three stable structures can be located, ie, 2‐enol, 2‐SPT, and 2‐DPT forms in both S0 and S1 states. Via comparing the bond lengths and bond angles involved in the hydrogen bonding moieties, we find the dual intramolecular hydrogen bonds should be strengthened in the S1 state. And based on infrared (IR) vibrational simulations, we further confirm the strengthening dual hydrogen bonds. Upon the photo‐excitation process, the charge redistribution via frontier molecular orbitals (MOs) reveals the tendency of excited state intramolecular proton transfer (ESIPT) reaction. In addition, the constructed S0‐state and S1‐state potential energy curves demonstrate that the excited state single proton transfer (ESSPT) should be the most supported one from 2‐enol to 2‐SPT form. In view of the S1‐state stable 2‐SPT and 2‐DPT structures as well as the fluorescence peaks of them, we can further confirm the ESSPT mechanism for 2 chemosensor. This work not only clarifies the excited state behaviors of 2 system but also successfully explain the previous experimental phenomenon. The strengthening dual intramolecular hydrogen bonds (O1H2···N3 and O4H5···N6) of 2 provides the possibility for ESIPT process.The redistribution of charge involved in the hydrogen bonding moieties facilitates the ESIPT reaction.Potential energy curves and emission spectra confirm that the excited state single proton transfer should occur for 2 system. [ABSTRACT FROM AUTHOR]