Visible‐Light Photoswitching by Azobenzazoles

Abstract

Abstract Three visible‐light responsive photoswitches are reported, azobis(1‐methyl‐benzimidazole) ( 1 ), azobis(benzoxazole) ( 2 ) and azobis(benzothiazole) ( 3 ). Photostationary distributions are obtained upon irradiation with visible light comprising approximately 80 % of the thermally unstable isomer, with thermal half‐lives up to 8 min and are mostly invariant to solvent. On protonation, compound 1 H + has absorption extending beyond 600 nm, allowing switching with yellow light, and a thermal half‐life just under 5 minutes. The two isomers have significantly different p K a values, offering potential as a pH switch. The absorption spectra of 2 and 3 are insensitive to acid, although changes in the thermal half‐life of 3 indicate more basic intermediates that significantly influence the thermal barrier to isomerization. These findings are supported by high‐level ab initio calculations, which validate that protonation occurs on the ring nitrogen and that the Z isomer is more basic in all cases.