Roles of functional group and intramolecular hydrogen bond in the S1/S0 energy Landscape: Hydrazone versus Schiff base

Abstract

We investigated the S1/S0 energy surfaces and energy-minimized conical intersections (MECIs) of Schiff bases and their hydrazone analogues. Time-dependent density functional theory revealed that proton transfers on the S1 surface involve minimal barriers, or are barrier-less. In the phenolic form, the MECIs of the Schiff bases are more sloped than their hydrazone counterparts, and the MECIs of the proton-transferred species are more sloped. The hydrogen bonds result in lower-energy vertical excitations and higher-energy MECIs. The MECIs of hydrazone featuring carbonyl-furan group have the largest dot products of the energy gradient of S1 and the g and h vectors.