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

Abstract

In this paper, density functional theory (DFT) and time-dependent DFT (TDDFT) methods were used to investigate substituent effects and excited-state intramolecular double-proton transfer (ESIDPT) in 1, 3-bis (2-pyridylimino)-4, 7-dihydroxyisoindole (BPI–OH) and its derivatives. The results of a systematic study of the substituent effects of electron-withdrawing groups (F, Cl and Br) on the adjacent sites of the benzene ring were used to regulate the photophysical properties of the molecules and the dynamics of the proton-transfer process. Geometric structure comparisons and infrared (IR) spectroscopic analysis confirmed that strengthening of the intramolecular hydrogen bond in the first excited state (S1) facilitated proton transfer. Functional analysis of the reduced density gradient confirmed these conclusions. Double-proton transfer in BPI–OH is considered to occur in two steps, i.e., BPI–OH (N) [Formula: see text] BPI–OH (T1) [Formula: see text] BPI–OH (T2), in the ground state (S0) and the S1 state. The potential-energy curves (PECs) for two-step proton transfer were scanned for both the S0 and S1 states to clarify the mechanisms and pathways of proton transfer. The stepwise path in which two protons are consecutively transferred has a low energy barrier and is more rational and favorable. This study shows that the presence or absence of coordinating groups, and the type of coordinating group, affect the hydrogen-bond strength. A coordinating group enhances hydrogen-bond formation, i.e., it promotes excited-state intramolecular proton transfer (ESIPT).

Insights into photo‐induced excited state intramolecular proton transfer behavior for the novel 2‐([1, 1′‐biphenyl]‐4‐yl)‐3‐hydroxy‐4H‐chromen‐4‐one system: Effects of solvent polarity

“…As one of the most basic chemical processes, excited state intramolecular or on intermolecular proton transfer (ESIPT) proceeds along with hydrogen bond, which plays important roles in photosystem, fluorescent protein, and other relative biological systems. [10][11][12][13][14][15] In particular, more and more novel chromophores based on ESIPT properties have been developed and designed in light emitting materials and organic photoelectric materials in recent years. Due to the importance of ESIPT processes in chemical and biological systems, its unique photo-physical properties, and huge application potential, the experimental and theoretical research of ESPT system has attracted more and more attention and becomes an active topic among researchers.…”

“…As one of the most basic chemical processes, excited state intramolecular or on intermolecular proton transfer (ESIPT) proceeds along with hydrogen bond, which plays important roles in photosystem, fluorescent protein, and other relative biological systems 10–15 . In particular, more and more novel chromophores based on ESIPT properties have been developed and designed in light emitting materials and organic photoelectric materials in recent years.…”