Benzothiazolyl substituted spiropyrans with ion-driven photochromic transformation

Abstract The present work is devoted to the synthesis and detailed investigation of new 8-benzothiazole containing spiropyrans. The investigated spiropyrans exist under colorless spirocyclic isomers exhibiting positive photochromism with thermo- and photoinduced back reaction. UV light irradiation leads to their effective coloration with quantum yields up to 44%. The efficiency of the back photocyclization induced by visible light does not exceed 0.1%. This feature distinguishes them from the previously studied benzoxazole analogs. The enhancement of electron-withdrawing properties of the indoline fragment substituents promotes an increase in photo-coloration efficiency. The lifetime of the colored form varies from 17 to 200.8 s (acetone, 293 K) depending on substituents. Due to the presence of the benzothiazole moiety, merocyanines can effectively bind Zn2+, Co2+, Ni2+, Cu2+, Cd2+, Mn2+ ions. The addition of salts of these ions to spiropyran solutions results in the stabilization of the merocyanine in the form of intensely colored complexes. Composition, stability and spectroscopic characteristics of complexes have been investigated depending on the metal ion nature and substituents in ligand molecules. The colored complexes possess negative photochromism. The visible light irradiation causes their bleaching with quantum yields up to 48%. The benzothiazole substituted spiropyrans demonstrate ion driving photochromic transformation.