ON THE PHOTOISOMERIZATION COORDINATE OF TETRAPHENYLETHYLENE

The existence of two energetically distinct minima on the biradicaloid triplet state surface of tetraphenylethylene (TPE) was detected via A M1 and 3-21G UHF ab initio calculations. The interconversion between the minima proceeds through a large amplitude rotation of the interloc king phenyl rings. The importance of the presence of two excited state minima and the possibility of conformational trapping are discussed i n context of the recent spectroscopic and opto-calorimetric measuremen ts on TPE. The most favorable pathway for the combined cis-trans photo isomerization and enantiomerization of TPE is postulated.