STUDIES ON PHOTOCHROMISM OF A THERMALLY STABLE FULGIDE IN THE CRYSTALLINE STATE - X-RAY CRYSTALLOGRAPHIC INVESTIGATION OF )-2-ISOPROPYLIDENE-3-(1-NAPHTHYLMETHYLENE)SUCCINIC ANHYDRIDE

)-2-Isopropylidene-3-(1-naphthylmethylene)succinic anhydride, C18H14O3 , M(r) = 278.31, monoclinic, P2(1)/c, a = 13.408 (1), b = 8.762 (1), c = 13.431 (1) angstrom, beta = 117.50 (1)-degrees, V = 1399.5 (3) angs trom3, Z = 4, D(m) = 1.32, D(x) = 1.321 Mg m-3, Cu Kalpha, lambda = 1. 5418 angstrom, mu = 0.69 mm-1, F(000) = 584, T = 298 K, R = 0.057 for 1777 observed reflections. The electrocyclic ring closure that the ti tle compound undergoes in the solid state is viewed in terms of releva nt geometrical parameters. The photochromism of the compound observed in the solid state appears to occur at defect sites, surfaces and micr ocavities.