Theoretical Investigation of Excited-State Intramolecular Double-Proton Transfer Mechanism of Substituent Modified 1, 3-Bis (2-Pyridylimino)-4,7-Dihydroxyisoindole in Dichloromethane Solution

In this paper, density functional theory (DFT) and time-dependent DFT (TDDFT) methods were used to investigate substituent effects excited-state intramolecular double-proton transfer (ESIDPT) in 1, 3-bis (2-pyridylimino)-4, 7-dihydroxyisoindole (BPI–OH) its derivatives. The results of a systematic study the electron-withdrawing groups (F, Cl Br) on adjacent sites benzene ring regulate photophysical properties molecules dynamics proton-transfer process. Geometric structure comparisons infrared (IR) spectroscopic analysis confirmed that strengthening hydrogen bond first excited state (S 1 ) facilitated proton transfer. Functional reduced gradient these conclusions. Double-proton BPI–OH is considered occur two steps, i.e., (N) [Formula: see text] (T 2 ), ground 0 S state. potential-energy curves (PECs) for two-step scanned both states clarify mechanisms pathways stepwise path which protons are consecutively transferred has low energy barrier more rational favorable. This shows presence or absence coordinating groups, type group, affect hydrogen-bond strength. A group enhances formation, it promotes (ESIPT).