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

• 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 [Zn 2 (bpsal)(CH 3 CO 2) 2 ](BF 4) 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, k 1 and k 2 , 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. [ABSTRACT FROM AUTHOR]