A detailed experimental study of the photochemistry of dixanthylidene over a wide temperature range indicates the existence of three labile photoisomers, B, C, and P, all of which revert thermally to A. Light-stable B, formed from the excited triplet of the fundamental modification A, is thermally stable below -140°. The structure of B involves torsion of ca. 50° about the central double bond. C And its possible precursor P are photolabile isomers formed from excited singlet A. They are photocyclisation products of the 4a,4b-dihydrophenanthrene type: C is photoconvertible into A. The thermal stability of P is much less than that of C. Helixanthen is obtained on thermal dehydro-genation of C with molecular oxygen or iodine. The quantum yield of A →hv B drops with the temperature and is very small at -140° but can be strongly enhanced (up to 220-fold) by the spin-orbit coupling perturbers molecular oxygen, carbon disulphide, and ethyl iodide.
|Number of pages||6|
|Journal||Journal of the Chemical Society, Perkin Transactions 2|
|State||Published - 1976|