SOLID-STATE PHOTODIMERIZATION OF 9-METHYLANTHRACENE AS STUDIED BY SOLID-STATE C-13 NMR

The locus of the photodimerization reaction of 9-methylanthracene in t he crystal was examined by high-resolution solid-state C-13 NMR techni ques. Examination of the C-13 spectra of the products showed that only the trans dimer is formed by the solid state photodimerization, while both trans and cis dimers are formed by the photodimerization in benz ene solution. The H-1 T-1 relaxation curves for the monomer and the di mer at various exposure times were separately observed via well-resolv ed C-13 peaks. The two T-1 curves exhibit characteristic features for relaxation of a weakly coupled two-spin system. By analyzing the T-1 c urves, the spin diffusion rates between the monomer and the dimer and the fraction of the dimer were obtained for various exposure times. Fr om the result, the maximum domain size of the minor component during t he photodimerization process was estimated to be ca. 0.3 mu m. The het erogeneous domain structure generated by the photodimerization indicat es that the reaction takes place at defects of the crystal in the mono mer. (C) 1998 Elsevier Science B.V. All rights reserved.