Photochemical and thermal interconversions of three dimers of 2,4,5-triphenylimidazolyl (lophyl).

Two photochromic lophyl dimers, A and B, are interconverted by uv irradiation, while these two dimers and thermochromic dimer C can be equilibrated in benzene at 100°C. Compositions at equilibrium using the corresponding three dimers of 2-(p-tolyl)-4,5-diphenylimidazolyl are A:B = 96:4 and A:B:C = 14:18:68, respectively.