Structures and chromotropic properties of imidazole derivatives produced from 3,6-bis(4,5-diphenyl-2H-imidazol-2-ylidene)cyclohexa-1,4-diene

Abstract

Addition of acetic acid to 3,6-bis (4,5-diphenyl-2H-imidazol-2-ylidene) cyclohexa-1,4-diene (1) afforded 2-[4-(4-acetoxy-4,5-diphenyl-4H-imidazol-2-yl) phenyl]-4,5-diphenyl-1H-imidazole (2). Lead dioxide oxidation of (2) in acetic acid yielded 1,4-bis(4-acetoxy-4,5-diphenyl-4H-imidazol-2-yl)-benzene (13) but hexacyanoferrate(III) oxidation in alkaline solution gave a 2,2′-imidazolyl dimer (7) derived via 2-[4-(5-oxo-4,4-diphenyl-4,5-dihydro-1H-imidazol-2-yl)phenyl]-4,5-diphenyl-1H-imidazole (4).

Irradiation of compounds (2) and (13) with u.v. light resulted in the formation of the starting quinonoid compound (1) as indicated by its deep blue colour. However, the dimeric compound (7) shows chromotropism caused by radical dissociation of the dimer during irradiation, heating, or grinding. Particularly rapid reversible photochromic behaviour was observed for (7).