In Situ Control of Photochromic Behavior through Dual Photo-Isomerization Using Cobaloxime Complexes with Salicylidene-3-aminopyridine and 3-Cyanopropyl Ligands

Abstract

In situ control of crystalline-state photochromism was achieved using a photo-isomerization reaction of cobaloxime complexes. These dual photoreactive complexes that have the photochromic salicylideneaniline ligand and 3-cyanopropyl group as the axial alkyl group were synthesized and crystallographically characterized. When each crystal was exposed to visible light, the 3-cyanopropyl group isomerized to a 1-cyanopropyl group while retaining the single crystal form. Although both 3-cyanopropyl and 1-cyanopropyl group complex crystals showed the yellow (or orange) to orange (or light brown) photochromism upon UV light irradiation, the fading rate of the photochromic color was significantly changed after the 3–1 isomerization. The differences in fading rates can be rationalized by a change of the volume of the cavity around the carbon–nitrogen bonds of the three salicylideneaniline derivatives, which is caused by the 3–1 photo-isomerization in the crystal. Also, the reactivity of 3–1 photo-isomerization was explained by the cavity around the 3-cyanopropyl group.