Structure of photochromic spiroxazines. II. 1',3',3'‐Trimethylspiro{anthra[2,1‐f][1,4]benzoxazine‐2,2'‐indoline}‐7,12‐dione

The asymmetric unit comprises two crystallographically independent molecules. The molecule consists of a substituted indoline ring orthogonally linked to an anthraquinone-benzo-oxazine moiety through a spiro C atom having regular sp 3 hybridization. The length of the C spiro -O bond, that undergoes cleavage upon photoexcitation, is larger than that normally observed for other spiroxazines having lower photocolourability than the title compound