STERICALLY OVERCROWDED ALKENES - A STEREOSPECIFIC PHOTOCHEMICAL AND THERMAL-ISOMERIZATION OF A BENZOANNULATED BITHIOXANTHYLIDENE

Enantiomerically pure sterically overcrowded 12H-benzo[a]thioxanthenyl-12-(2-'methyl-9'H-thioxanthene-9'-ylidene) shows a stereospecific photochemical and thermal isomerization of the P-trans into the M-cis isomer (and vice versa), with a large thermal isomerization barrier (DELTAG(double dagger) = 28.6 kcal mol-1) (1 cal = 4.184 J), making this type of molecule especially suitable as the key structural unit for applications as chiroptical molecular switches.