Zur Photo-Dimerisation des Stilbens

Abstract

Formation of 1,2,3,4-tetraphenyl-cyclobutane by photochemical dimerization of stilbene only occurs when starting from the trans-form. It has been shown that the absence of dimerization of the cis-isomer even in the pure liquid phase is caused by the very small lifetime of this molecule in the first excited singlet state. In the crystal state trans-stilbene in contrast to trans-cinnamic acid does not formate a photodimer for the distance between the ethylene bonds of two molecules in the unit cell exceeds the critical value of 4.0 Å.