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 a grid-like arrangement of the anion.
Most of the salts exhibit a disorder of cations. For all the salts,
the reaction cavity between the pyridinium ring of the cation and
the adjacent anion was determined based on their crystal structures.
The reaction cavity volumes in the photochromic salts were larger
than those in other salts (>8.9 Å3). These results
demonstrate that the crystalline-state photochromism depends on the
size of the reaction cavity necessary for structural isomerization.
Additionally, shear stress also induces the isomerization of the cations
of all the salts in the solid state.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.