Theoretical study on the mechanism for the excited-state double proton transfer process of an asymmetric Schiff base ligand

Abstract

Excited-state double proton transfer (ESDPT) in the 1-[(2-hydroxy-3-methoxy-benzylidene)-hydrazonomethyl]-naphthalen-2-ol (HYDRAVH2) ligand was studied by the density functional theory and time-dependent density functional theory method. The analysis of frontier molecular orbitals, infrared spectra, and non-covalent interactions have cross-validated that the asymmetric structure has an influence on the proton transfer, which makes the proton transfer ability of the two hydrogen protons different. The potential energy surfaces in both S0 and S1 states were scanned with varying O–H bond lengths. The results of potential energy surface analysis adequately proved that the HYDRAVH2 can undergo the ESDPT process in the S1 state and the double proton transfer process is a stepwise proton transfer mechanism. Our work can pave the way towards the design and synthesis of new molecules.

Photochemical Mechanisms of Hydroxyquinoline Benzimidazole: Insights from Electronic Structure Calculations and Nonadiabatic Dynamics Simulations

“…In recent years, the excited-state intramolecular double proton transfer (ESIDPT) has gradually received widespread attention. ESIDPT has been proven to be closer to the proton transfer process of biomolecules such as DNA and proteins than ESIPT; thus, the ESIDPT process is crucial for the applications of fluorescent probes and the recognizing of fundamental biological processes. − In 1969, Taylor et al first discovered ESIDPT in the hydrogen-bonded dimerization of 7-azaindole (7-AI) . Since then, this special proton transfer has been extensively investigated.…”