Significant acceleration of E-Z photoisomerization induced by molecular planarity breaking

Abstract

E-Z photoisomerization constitutes the footstone of photosensitive proteins, molecular photoswitches and sunscreens and is believed to be controlled by photoinduced intramolecular charge transfer. In this work, we have made methylation on isomerizable alkene bond of plant sunscreen sinapate esters to break the coplanarity between phenol ring and CC double bond in ground state. Femtosecond transient absorption spectroscopy combined with time-dependent density functional theory calculations determine that this molecular planarity breaking triggers an immediate excited-state CC double bond twisting and thus accelerates the isomerization by more than one order of magnitude. These results highlight the role of molecular geometry on isomerization dynamics.