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 (andvice versa), with a large thermal isomerization barrier (ΔG‡= 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.