Molecular System Based on Novel Photochromic Biindenylidenedione Derivative Demonstrating Photomodulation of Magnetism

Stable nitronyl nitroxide radical and imino nitroxide radical were incorporated into the benzene rings of novel photochromic 7,7＇-dimethyl-[2,2＇-bi-lH-indene]-3,3＇-diethyl-3,3＇-dihydroxy-l,l＇-dione （1）, leading to the synthesis of novel multifunctional compounds 4 and 5. The photochromic properties, ESR spectroscopy and magnetic proper- ties of the title compounds were investigated. Compounds 4 and 5 possess visible photochromism upon photoirra- diation, and their ESR signals undergo secular broadening after photoirradiation. The magnetic susceptibility meas- urement shows that the antiferromagnetic interaction of 4 and 5 becomes stronger after photoirradiation. In compounds 4 and 5 there are two kinds of spin centers after photoirradiation： one is nitroxide radical, and the other is photo-generated radicals from two indanone moieties. Our results demonstrated that the colour and magnetic properties of compounds 4 and 5 could be modulated by photoirradiation.