Chromogenic properties of heterocyclic compounds: Barochromic effect of indoline spiropyrans in the gas phase

Abstract

Spiropyrans of the indoline and benzothiazole series, which exist under normal conditions in a colored merocyanine form, have been obtained. Solutions of the synthesized compounds exhibit negative photochromism. Previously unknown chromogenic properties were found in the gas phase of the synthesized indoline spiropyrans, namely, the barochromic effect, consisting of the discoloration of a gas containing spiropyran molecules when the pressure of the air is reduced. This effect is due to the conversion of the merocyanine isomers absorbing in the visible region of the spectrum into cyclic isomers absorbing in the UV region of the spectrum. It has been established that solid-phase films of indoline series spiropyrans, which are in a stable merocyanine form under normal conditions, have the properties of negative T- and P-type photochromism. Extremely low values of the rate constants of reverse thermal reactions make it possible to consider them as reverse positive–negative media for recording and processing optical information.