An easily accessible isospiropyran switch

Abstract

In the presence of SiCl₄, three molecules of 5′-bromo-2′-hydroxyacetophenone underwent an unexpected tandem aldol condensation to give a novel isospiropyran switch (69%), with X-ray crystallography confirming its structure. The strong Brønsted acid CH₃SO₃H turned the colorless isospiropyran into its protonated and open form possessing red color. This process was reversed using the Et₃N base, with the acid/base toggling repeatable for at least six times (UV-Vis). When printed on a silica plate, however, the isospiropyran formed a blue-colored product due to, as posited, its stabilization by hydrogen bonding (HB) to silica. An exposure to HB-competing ethyl acetate temporarily “erased” the print only to be brought back by subjecting the plate to a higher temperature for evaporating the solvent. The isospiropyran described here is an easily accessible, chromic, modular and switchable compound that one can incorporate into dynamic materials or use for building chemosensors, molecular machines and organic electronic devices.