Synthesis and properties of novel photochromic biindenylidenedione derivative bearing TEMPO radical

Stable nitroxide radical TEMPO was introduced to the benzene rings of novel photochromic 7,7′-dimethyl-[2,2′-bi-1H-indene]-3,3′-diethyl-3,3′-dihydroxy-1,1′-dione (compound 1), leading to the synthesis of novel multifunctional title compound 4. The photochromic property, magnetic property and ESR spectroscopy of the title compound were investigated. Compound 4 possesses visible photochromism upon photoirradiation, and its ESR signal undergoes secular broadening after photoirradiation. The magnetic susceptibility measurement shows that the antiferromagnetic interaction for 4 becomes stronger after photoirradiation. In compound 4 there are two kinds of spin center after photoirradiation: one is TEMPO radical, and another is photo-generated radical of two indanone moieties. Our results demonstrated that the colour and magnetic property of compound 4 could be controlled by photoirradiation.