Effects of π-Conjugation on the Solid-State Photoresponsive Coloring Behavior of Bipyridine-Boronium Complexes

Solid-state photoinduced coloring of boronium complexes consisting of 9-borabicyclononane and 2,2′-bipyridine with π-conjugated substituents at the 4,4′- or 5,5′-positions were investigated. The substitution position affected the highest occupied molecular orbital distribution and determined coloring capability. The 4,4′-substituted complexes exhibited coloration upon irradiation, whereas most of 5,5′-substituted complexes did not.