Photochemistry of sulphur compounds related to the 1,2-dithiole system. Part 6. Photoisomerization of 1,6,6aλ4-trithiapentalenes

Abstract

A series of 1,6,6aλ⁴-trithiapentalenes are transformed upon irradiation into photoproducts which revert to starting materials by a dark process obeying first-order kinetics. The photoproducts have been assigned a trans-1,2-dithiol-3-ylidene thione structure. The stability of the trans-forms has been shown to be controlled mainly by steric factors; it is strongly dependent on the ability of the thiocarbonyl group to be coplanar with the dithiole ring. The rate constants and energy and entropy of activation for the thermal back reactions are reported.