In situ control of photochromic behavior through dual photo-isomerization using cobaloxime complexes with a spiropyran derivative and 2-cyanoethyl ligands

Abstract

A new photochromic spiropyran derivative is synthesized and used with a 2-cyanoethyl group as an axial ligand in new dual photochromic cobaloxime complexes. Photoisomerization of the 2-cyanoethyl group by visible light is performed to control the photochromic behavior in situ of the spiropyran derivative. The color of the crystal containing 2-cyanoethyl groups changes from yellow to dark brown when the crystals are irradiated with UV light. The color returns to the original yellow color when the crystals are kept in the dark at room temperature. On exposure to visible light before UV irradiation, the 2-cyanoethyl group bonded to the central cobalt atom is isomerized to the 1-cyanoethyl group with retention of the single crystal form. The thermal color fading rates of the brown crystals are different from those without visible light irradiation. The difference is explained well by the cavity volume around the benzopyran moiety in each crystal.