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 was investigated. The substitution position affected the highest occupied molecular orbital distribution and determined the coloring capability. The 4,4′-substituted complexes exhibited coloration upon irradiation, whereas most of the 5,5′-substituted complexes did not.