PHOTOCHROMISM OF 1-PHENOXYANTHRAQUINONES

The photochromic phenomenon of 1-phenoxyanthraquinone (1) was investigated by IR and nuclear magnetic resonance (NMR) spectroscopy and decay of the colored species. On the basis of the spectral data the benzene ring of the phenoxyl group in the colored species was concluded to orientate with the carbonyl group within the molecule. From the kinetic analysis of the decay of the colored species, the consecutive production of two colored species, X(1) and X(2) (X(1)-->X(2), was elucidated. The activation enthalpies of the reversion process from X(1) to 1 and of the process from X(1) to X(2) were evaluated to be 8.9 and 43.2 kJ mol(-1) respectively. The low activation enthalpy of the reversion process suggests that the structure of X(1) is a rotational isomer of 1. X(2) is assigned as a. structural isomer, 9-phenoxy-1,10-anthraquinone.