Photochromism of salicylideneanilines bearing super bulky substituents: Single-crystal UV-vis spectroscopic examination of bleaching under variable temperature and visible-light irradiation

[Display omitted] •A new class of salicylideneanilines that show exclusive photochromism was prepared.•The photobleaching process under various temperatures was precisely analyzed.•A new kinetic model provided a distinct classification of photobleaching behavior. Three types of Schiff bases of anilines were derived from a salicylaldehyde bearing super bulky substituents, the dinuclear zinc complex [Zn2(bpsal)(CH3CO2)2](BF4)2 (Hbpsal = 3,5-bis(N, N-bis(2-pyridylmethyl)aminomethyl)-2,4-dihydroxybenzaldehyde). These Schiff bases formed isomorphous crystal structures, which exhibited almost similar photochromism and no detectable thermochromism. Single-crystal microscopic UV–vis absorption spectroscopy was performed to track the time course of the photoproduct at various temperatures between −75 and 135 °C. The decay curves were characterized by two parameters, k1 and k2, which contribute to linear and quadratic terms, respectively, in terms of the extent of reaction. The effects of temperature and visible-light intensity on the parameters were discussed. The analyzed data were compared to another series of Schiff bases with moderately bulky substituents derived from 3,5-di(tert-butyl)salicylaldehyde. The results suggested that the crystal packing is much more important than the electronic substituent effects in determining the photochromic properties.