Based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, the detailed excited state intramolecular proton transfer (ESIPT) mechanism of 2,2 0 -dihydroxy-1,1 0naphthalazine (P.Y. 101) has been investigated theoretically. Unlike previous theoretical investigation of P.Y. 101, our calculated results not only reproduce the absorption and fluorescence spectra reported in the previous experiment, but also were completed with considering solvent effect. It further demonstrates that the TDDFT theory we adopted is very reasonable and effective. The calculations of main bond lengths and bond angles involving in the hydrogen bondings (O 1 -H 2 /N 3 and O 4 -H 5 /N 6 ) as well as the infrared vibrational spectra and as well as the calculated hydrogen bonding energies demonstrated the intramolecular hydrogen bond was strengthened in the S 1 state. In addition, qualitative and quantitative intramolecular charge transfer based on the frontier molecular orbitals provided the possibility of the ESIPT reaction. The potential energy surfaces of ground state and the first excited state have been constructed to illustrate the ESIPT mechanism. Based on our calculations, the equilibrium ESIPT process exists in the S 1 state. And after the radiative transition, reversed GSIPT can also occur in the S 0 state.

The single and dual cooperated proton transfer dynamic process in the excited state of 1,5-dihydroxyanthraquinone (1,5-DHAQ) was theoretically investigated, taking solvent effects (ethanol) into account. The absorption and fluorescence spectra were simulated, and dual fluorescence exhibited, which is consistent with previous experiments. Analysis of the calculated IR and Raman vibration spectra reveals that the intramolecular hydrogen bonding interactions (O20–H21···O24 and O22–H23···O25) are strengthened following the excited proton transfer process. Finally, by constructing the potential energy surfaces of the ground state, first excited singlet state, and triplet state, the mechanism of the intramolecular proton transfer of 1,5-DHAQ can be revealed.

In this work, vibration-resolved photoinduced electron transfer of an organic conjugated DA system subjected to an external electric field was theoretically investigated. The ground and excited state vibrational relaxation energies were quantitatively characterized. The effective high frequency, ω, could be estimated from the variation in energy of the excited-state equilibrium geometries of acceptor and donor sites as well as the analysis of the vibrational modes upon electron transfer. For a PCDTBT:PCBM blend in an external electric field, the vibronic modes affected the charge separation process differently from the charge recombination process. The simulated results indicated that the vibrational quantum tunneling effect facilitated the charge recombination process to a large extent. Thus, for electron transfer reactions, considering the vibrational excitation influence and perturbed nucleus-electron interactions is essential. These results provide a feasible way to enhance the efficiency in yielding the electron transfer process products.

The excited‐state intramolecular proton transfer (ESIPT) process of 6‐amino‐2‐(2′‐hydroxyphenyl) benzoxazole (6A‐HBO) was investigated using density functional theory and time‐dependent density functional theory methods with B3LYP and TZVP basis sets. n‐Heptane, dichloromethane, methanol, and acetonitrile were chosen as a series of polar solvents in calculations using the IEFPCM model. To obtain a more comprehensive ESIPT mechanism, we constructed the S0 and S1 states' potential energy surfaces (PESs) by incrementally twisting the ─OH bond and increasing the distance of O–H bond. Based on the analysis of the bond lengths, the IR vibrational spectra, and the frontier molecular orbits (MOs), the intramolecular hydrogen bonding (O─H...N) is clearly strengthened, and the charge is redistributed in the S1 state. The results of calculated absorption spectrum are in accord with the experimental data. The fluorescence spectrum of 6A‐HBO‐enol showed a normal red shift, but the red shift of the 6A‐HBO‐keto is larger and increases with the solvent polarity, indicating a charge transfer. Analysis of the PESs indicates a lower potential energy barrier in S1 state for the proton transfer from the O atom to the N atom, with the excited state potential barrier slightly decreasing with the increase of the solvent polarity.