Solid-State Photochromism of Salts of Cationic Spiropyran with Various Anions: A Correlation between Reaction Cavity Volumes and Reactivity

The salts of cationic spiropyran with various anions ([PSP]X; X = I, NO3, SCN, BF4, ClO4, PF6, CF3BF3, OTf, and BPh4) were prepared, and their crystalline-state photochromism and crystal structures were investigated. Four salts (X = I, NO3, SCN, and BPh4) exhibited photochromism in the crystalline state. In all the crystals, the cations and anions are alternately arranged to form mixed-stacked columns, with the exception of [PSP]BPh4, which has...