Photochromic compounds

摘要

Fulgimide derivatives are provided having the formula: <CHEM> wherein groups R<7>, R<8> and R<9> are hydrogen or are chosen to provide desired solubility, reactivity and spectral properties to the compound; X is a group -(CH2)n- or a group, <CHEM> in which case it links via a two or three atom chain with carbon atom C<a> of ring Z to form a fused bicyclic aromatic ring which may be optionally substituted and n is 0 or 1; Z is an optionally substituted six-membered aromatic or fused bicyclic aromatic ring containing carbon atoms and optionally no more than two atoms selected from oxygen, nitrogen and sulphur. The compounds are useful for imparting photochromic properties to materials by covalent and non-covalent association.