QUANTITATIVE STUDY OF THE PHOTOSTABILITY OF SPIROPYRANS

A quantitative method of determining the quantum yield of irreversible photodegradation (ϕC) of photochromic spiropyrans (SPP) was proposed for the first time. The ϕC of a large number of SPP of different types (with a different heterocyclic part) were determined. It was shown that for all of the SPP studied (except for dithiolane SPP), ϕC is almost independent of the heterocyclic part and is determined by the structure of the chromene part of the SPP. In addition to photodegradation, photooxidation takes place as a result of the reaction of the triplet state of the closed form of the SPP with O2 for nitrosubstituted SPP of all types. The value of ϕC is determined by the efficiency of the reaction of isomer X of the colored form with the solvent or impurities, i.e., the lifetime of this isomer.