Solution phase and surface photoisomerization of a hydrazone switch with long thermal half-life

Photoswitches can be employed for various purposes, with the half-life being a crucial parameter to optimize for the desired application. The switching of a photochromic hydrazone functionalized with a C6 alkyl thiolate spacer (C6 HAT) was characterized on a number of metal surfaces. C6 HAT exhibits a half-life of 789 years in solution. Tip-enhanced Raman spectros-copy (TERS) was used to study the photoisomerization of the C6 HAT self-assembled monolayers (SAM) on Au, Ag and Cu sur-faces. The unique spectroscopic signature of the E isomer at 1580 and 1730 cm-1 in TER spectra allowed for its discrimination from the Z isomer. It was found that C6 HAT switches on Au and Cu surfaces when irradiated with 415 nm, however it cannot isomerize on Ag surfaces, unless higher energy light is used. Based on this finding, and supported by density functional theory calculations, we propose a substrate-mediated photoisomerization mechanism to explain the behavior of C6 HAT on these different metal sur-faces. This insight...