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8405776 
Journal Article 
Intramolecular photocyclizations of o,o′-Bis-(2-arylvinyl)biphenyls 
Op Het Veld, PHG; Laarhoven, WH 
1977 
2 
268-273 
English 
In a series of o,o'-bis-(2-arylvinyl)biphenyls (1a-f) the quantum yields of the photocycloaddition to give trans,-trans,trans-1,2-diaryl-1.2,2a,10b- tetrahydrocyclobuta[/]phenanthrene (2a-f) (φcb). of their photocyclization to 4,9-diaryl-4,5,9,10-tetrahydropyrene (3a-f) (φthp). of trans-cis photoisomerization (φle), and of fluorescence (φ1) have been determined. An explanation, based on the different properties of the aryl groups, is given for the differences in product formation, which arise on irradiation of compounds (1a-f). Forthep-methoxyphenyl (1e) andp-dimethylaminophenyl (1f) derivatives an enhanced internal conversion from the singlet n → π * state to the ground state is responsible for the low values of φcb-. o,o'-Divinylbiphenyl (1g) cannot be converted into the cyclobutane derivative (2g). This is caused by the absorption characteristics of (1 g) and (2g). The stereoselective formation of the cyclobutane derivatives (2a-f) takes place in a concerted [π28 + π28] photocycloaddition via the S1 state of the trans,anti,irans,anti-conformers of (1). The photocyclization to the tetrahydropyrenes (3a-f) also arises from the S1 state.