Lattice solvent controlled photochromism of tripyridyl-triazine-based zinc bromide complexes

Abstract

The development of new stimuli-responsive materials with controllable properties has been highly desirable in the past decade owing to their increasing application demand in various areas. In this work, two tripyridyl-triazine-based zinc bromide complexes, [ZnBr₂(2-TPT)] (1) and [ZnBr₂(2-TPT)]·C₆H₅CH₂OH (2) (2-TPT = 2,4,6-tri(2-pyridyl)-1,3,5-triazine), have been prepared through the solvent evaporation method, and exhibit lattice solvent controlled photochromic performance in the crystalline state as well as solvent-induced photochromism in the solution state. Furthermore, the two complexes display tunable photochromic and photoluminescence properties in the crystalline state through the reversible desorption–adsorption of lattice benzyl alcohol molecules. Crystalline 1 and 2 are very sensitive to triple photostimulation (sunlight, ultraviolet light and X-ray irradiation) and exhibit excellent photochromic behaviors with distinct coloration contrast (light blue for 1vs. deep blue for 2), which is ascribed to different supramolecular frameworks via weak interactions (lone pair–π and π⋯π interactions). Meanwhile, crystalline 1 and 2 also exhibit completely different quenching efficiency during the coloration–decoloration processes, which is a typical example of a photo-stimuli dual-output responsive system and could be potentially applied in optical switches. The photochromic mechanism of photoinduced intermolecular electron transfer (PIET) has been carefully verified by the combination of experimental and theoretical investigations.