Substituent effect of diarylethenes on IR spectra for application of non‐destructive readout of photochromic recording

Photochromic diarylethene derivatives, 1,2‐bis(2‐methyl‐5‐phenyl‐3‐thienyl)perfluorocyclopentene (1), 1,2‐bis(2,4‐dimethyl‐5‐phenyl‐3‐thienyl)perfluorocyclopentene (2), and 1,2‐bis(2‐methoxy‐5‐phenyl‐3‐thienyl) perfluorocyclopentene (3) were prepared to study substituent effects on IR spectra. The origin of the change of IR spectra due to the substituents may be categorized into (1) change in structure, (2) change in charge distribution, and (3) new normal modes due to the newly introduced substituent, which was examined by ab initio quantum chemical calculations. Comparisons between the experimental and computational IR spectra clarified the difference of the substituent effects between open‐ and closed‐ring isomers. Such understanding should be useful for designing diarylethene derivatives in use for non‐destructive readout by IR light.