Xiaoyan Song

Exploring the excited state behavior for 2-(phenyl) imidazo[4,5-c]pyridine in methanol solvent

In this present work, we theoretically investigate the excited state mechanism for the 2-(phenyl)imidazo[4,5-c]pyridine (PIP-C) molecule combined with methanol (MeOH) solvent molecules. Three MeOH molecules should be connected with PIP-C forming stable PIP-C-MeOH complex in the S0 state. Upon the photo-excitation, the hydrogen bonded wires are strengthened in the S1 state. Particularly the deprotonation process of PIP-C facilitates the excited state intermolecular proton transfer (ESIPT) process. In our work, we do verify that the ESIPT reaction should occur due to the low potential energy barrier 8.785u2009kcal/mol in the S1 state. While the intersection of potential energy curves of S0 and S1 states result in the nonradiation transition from S1 to S0 state, which successfully explain why the emission peak of the proton-transfer PIP-C-MeOH-PT form could not be reported in previous experiment. As a whole, this work not only put forward a new excited state mechanism for PIP-C system, but also compensates for the defects about mechanism in previous experiment.

A theoretical study about the excited state intermolecular proton transfer mechanisms for 2-phenylimidazo[4,5-b]pyridine in methanol solvent

In this study, within the framework of density functional theory (DFT) and time-dependent DFT (TDDFT) methods, we theoretically investigated the novel system 2-phenylimidazo[4,5-b]pyridine (PIP) with respect to the dynamical behavior of its excited state in methanol (MeOH) solvents. Herein, two hydrogen-bonded networks have been discussed between PIP and MeOH, and it has been found that two MeOH connected to PIP (PIP–2MeOH) should be the best arrangement in both S0 and S1 states. Investigations on the electronic spectra of PIP–2MeOH have verified this point. Via analysis of hydrogen bond wires and corresponding infrared (IR) vibrational spectra, we have found that N1–H2⋯O3 of PIP–2MeOH undergoes the biggest change upon photoexcitation that reflects the tendency of the excited state intermolecular proton transfer (ESIPT) process. According to the results of our theoretical potential energy curves along different coordinates, we confirmed that ESIPT reaction should occur along the hydrogen bond wire N1–H2⋯O3 first. After the ESIPT reaction, proton transfer of PIP–2MeOH-PT* could proceed via intersystem crossing (ISC) process from S1 state to T1 state with a negligible energy gap 0.031 eV. Due to this non-radiation process, the fluorescence peak of PIP–2MeOH-PT* could be quenched. Our study not only explains previous successful experiment, but also proposes a new excited state dynamical mechanism for the PIP system.

Metallic VO2 monolayer as an anode material for Li, Na, K, Mg or Ca ion storage: a first-principle study

Using density functional theory (DFT), we assess the suitability of monolayer VO2 as promising electrode materials for Li, Na, K, Mg and Ca ion batteries. The metallic VO2 monolayer can offer an intrinsic advantage for the transportation of electrons in materials. The results suggest that VO2 can provide excellent mobility with lower diffusion barriers of 0.043xa0eV for K, 0.119 eV for Li, 0.098 eV for Na, 0.517 eV for Mg, and 0.306 eV for Ca. The specific capacities of Li, Na and Mg can reach up to 968, 613 and 815 mA h g−1 respectively, which are significantly larger than the corresponding value of graphite. Herein, with high open-circuit voltage the VO2 sheet could be a promising candidate for the anode material in battery applications.

Theoretical explorations about the excited state behaviors for two novel high efficient ESIPT compounds

Two high efficient excited state intramolecular proton transfer (ESIPT) compounds (i.e., 3-(5-([1,1′-biphenyl]-4-yl)oxazol-2-yl)-4′-(N,N-diphenylamino)-[1,1′-biphenyl]-4-ol (1) and 4′-(N,N-diphenylamino)-3-(5-(4′-(diphenylamino)-[1,1′-biphenyl]-4-yl)oxazol-2-yl)-5-methyl-[1,1′-biphenyl]-4-ol (2)) are explored theoretically. Based on DFT and time-dependent DFT (TDDFT) methods, we investigate the hydrogen bonding interactions and ESIPT mechanism. Via B3LYP/TZVP/IEFPCM (toluene) theoretical level, we reappear the experimental steady-state spectra, which demonstrate that the theoretical manner is reasonable and effective. Based on reduced density gradient (RDG) versus sign(λ2)ρ analyses, we confirm intramolecular hydrogen bond for both 1-enol and 2-enol. Investigating geometrical parameters and infrared (IR) vibrational spectra, we verify the O-H···N should be strengthened in the S1 state for 1-enol and 2-enol systems. Exploring frontier molecular orbitals (MOs) and charge density difference (CDD) maps, we find charge redistribution provides the tendency of ESIPT. The constructed potential energy curves demonstrate that the proton transfer should happen in the S1 state. Particularly, the low potential energy barriers of forward and backward ESIPT process for both 1 and 2 systems, the dynamical equilibrium could be verified, which means 1 and 2 systems should be potential for novel white light LEDs materials. This work not only explores and explains previous experimental phenomenon, but also makes a reasonable assignment about the ESIPT mechanism.

Exploring and elaborating the excited state mechanism of a novel AIE material 2-(5-(4-carboxyphenyl)-2-hydroxyphenyl)benzothiazole

A novel aggregation-induced emission material 2-(5-(4-carboxyphenyl)-2-hydroxyphenyl)benzothiazole (2-CHBT) has been investigated based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. Via reduced density gradient (RDG) versus sign(λ2)ρ analyses, we firstly verify the formation of intramolecular hydrogen bond in 2-CHBT system. Analyzing the primary geometrical parameters in 2-CHBT and comparing the changes about infrared (IR) vibrational spectra, we confirm that the hydrogen bond O-H···N is strengthened in the S1 state upon excitation. Exploring photo-excitation process, the frontier molecular orbitals (MOs) and charge density difference (CDD) analyses have been performed using TDDFT/B3LYP/TZVP theoretical level, based on which we verify the charge transfer phenomenon referring to the S0u2009→u2009S1 transition. And the CDD around the hydrogen bond moiety provides the tendency of ESIPT for 2-CHBT molecule. Comparing the energy gap between HOMO and LUMO orbitals in cyclohexane, toluene, chloroform, and DMSO solvents, we predict the ESIPT reaction might be more active in non-polar solvents. In addition, constructing potential energy curves and searching transition state (TS) structures, we further clarify the ESIPT mechanism and verify that non-polar solvents might facilitate the ESIPT process. Our simulated results reappear experimental spectral results and successfully explain experimental phenomenon.

Theoretical research on excited-state intramolecular proton coupled charge transfer modulated by molecular structure

At the TD-B3LYP/TZVP/IEFPCM theory level, we have theoretically studied the excited-state intramolecular proton coupled charge transfer (ESIPCCT) process for both 4′-N,N-diethylamino-3-hydroxyflavone (3HFN) and 2-{[2-(2-hydroxyphenyl)benzo[d]oxazol-6-yl]methylene}malononitrile (diCN-HBO) molecules. Our calculated hydrogen bond lengths and angles sufficiently confirm that the intramolecular hydrogen bonds O1–H1⋯O2 and O1–H1⋯N1 formed at the S0 states of 3HFN and diCN-HBO should be significantly strengthened in the S1 state, which is further supported by the results obtained based on the analyses of infrared spectra shifts, molecular orbitals and charge density differences maps. The significant strengthening of intramolecular hydrogen bonds O1–H1⋯O2 and O1–H1⋯N1 upon photoexcitation should facilitate the ESIPCCT process of the two title molecules. The scanned potential energy curves and confirmed excited-state transition states for both 3HFN and diCN-HBO show that the proton can be easily transferred from O1 to O2 (N1 for diCN-HBO) through the strengthened intramolecular hydrogen bonds upon photoexcitation to the S1 state.

A Theoretical Investigation About the Excited State Dynamical Mechanism for Doxorubicin Sensor

We theoretically investigate the excited state intramolecular proton transfer (ESIPT) mechanism about a novel doxorubicin (DOX) system based on density functional theory (DFT) and time-dependent DFT methods. We mainly focus on the double proton transfer process regarding the stepwise versus synchronous dual proton transfer mechanism. The changes in our calculated primary bond lengths and bond angles show that the intramolecular hydrogen bonds (O1–H2···O3 and O4–H5···O6) are both strengthened in the S1 state, which provides the possibility of the ESIPT process. Though our computational simulations, the DOX indicates the lowest absorption at around 490xa0nm. After excitation, we find three emission bands maximized at 656, 663 and 687xa0nm, which are ascribed to the tautomer. To further elucidate the ESIPT mechanism, we construct the potential energy surfaces (PESs) of both S0 and S1 states. Clearly, three kinds of stable structures could be located on the S1-state PES. We establish a new mechanism of DOX that excludes synchronous double proton transfer, while the stepwise double proton transfer mechanism is confirmed theoretically. We believe that the systematic investigation for photo-physical and photochemical properties of the antineoplastic drug DOX might be significant to obtain fundamental insight into the transport mechanism of DOX inside cultured cells.

Theoretical insights into the excited state hydrogen bond and ESIPT reaction for 2-amino-3-(2’-benzoxazolyl)quinoline and 2-amino-3-(2’-benzothiazolyl)-quinoline

Two N-H type excited state intramolecular proton transfer (ESIPT) systems (i.e., 2-amino-3-(2’benzoxazolyl)quinoline (ABO) and 2-amino-3-(2’-benzothiazolyl)-quinoline (ABT)) have been investigated. Adopting DFT and TDDFT methods coupling with B3LYP functional and TZVP basis set, our simulations about ABO and ABT molecules have successfully reappeared experimental results, based on which the rationality of our calculations is confirmed. Using Atoms in Molecules (AIM) analytical method, we firstly explore the interactions about chemical bond and verify the formation of hydrogen bond N-H•••N for ABO and ABT in the S0 state. Investigating the primary geometrical parameters involved in N-H•••N, we find it should be strengthened in the S1 state. Upon photoexcitation, charge transfer phenomenon is found via frontier molecular orbitals (MOs), and charge redistribution provides the tendency of ESIPT reaction for ABO and ABT. According to our constructed potential energy curves of both S0 and S1 states for ABO and ABT using two kinds of methods (i.e., the elongation of N-H single bond and the weakening of H•••N hydrogen bond), we clarify the ESIPT mechanisms and explain the recovery of four-level reaction cycle. Our searching transition state (TS) structures and simulated intrinsic reaction coordinate (IRC) path further confirm the ESIPT reaction.

Modulating N-H-based Excited-State Intramolecular Proton Transfer by Different Electron-Donating/Withdrawing Substituents in 2-(2’-aminophenyl)benzothiazole Compounds

At the B3LYP/6-311+G(d, p)/IEFPCM (in dichloromethane) theory level, the N-H-based excited-state intramolecular proton transfer (N-H-based ESIPT) process of 2-(2’-aminophenyl)benzothiazole (PBT-NH2) and its three derivatives 2-(2’-methylaminophenyl)benzothiazole(PBT-NHMe), 2-(2’acetylaminophenyl)benzothiazole (PBT-NHAc) and 2-(2’-tosylaminophenyl) benzothiazole (PBT-NHTs) have been explored by the time-dependent density functional theory (TD-DFT) method. Our calculated hydrogen bond lengths and angles sufficiently confirm that the intramolecular hydrogen bonds N1-H•••N2 formed at the S0 states of the four compounds should be significantly strengthened in the S1 state, which are further supported by the results obtained based on the analyses of infrared spectra shifts. The scanned potential energy curves reveal that the energy barriers of the first singlet excited state of the four titled compounds along the ESIPT reactions are predicted at 8.74, 8.98, 6.72 and 1.69 kcal/mol, respectively, suggesting that the inclusion of a strong electron-withdrawing tosyl (Ts) group can remarkably facilitate the occurrence of the ESIPT reaction, while the involvement of an electron-donating methyl group has slight opposite effect on the ESIPT process of the amino-type hydrogen-bonding system.