A competitive excited state dynamical process for the 2,2′-((1E,1′E)-((3,3′-dimethyl-[1,1′-biphenyl]-4,4′-diyl)-bis(azanylylidene))bis(methanylylidene))-diphenol system

Abstract

By applying density functional theory (DFT) and time-dependent DFT (TDDFT) methods, we theoretically investigate the excited state dynamical process for the 2,2′-((1E,1′E)-((3,3′-dimethyl-[1,1′-biphenyl]-4,4′-diyl)-bis(azanylylidene))bis(methanylylidene))-diphenol (YT) system. Our results show that two intramolecular hydrogen bonds in YT strengthen in the S₁ state, which may trigger an excited state proton transfer (ESPT) process. By exploring the frontier molecular orbitals (MOs), we confirm that charge redistribution indeed has effects on excited state dynamical behavior. Furthermore, this implies the tendency of the ESPT reaction. Analyzing the constructed S₁-state potential energy surface (PES), we find three excited state potential barriers which are low enough for a complete excited state double proton transfer (ESDPT) process. Comparing barriers, we confirm a competitive process for stepwise and simultaneous ESDPT pathways.