On the Relationship between Molecular Geometry and Photochemical Properties of 1,2-Substituted 1,2-Di-9-anthrylethylenes

Article abstract of DOI:10.1021/jo00232a027

Starting from either 1,2-di-9-anthrylethanone or di-9-anthrylcyclopropenone, a series of cis-trans isomeric 1,2-di-9-anthrylethylenes substituted at the central ethylene bond has been synthesized, and their photochemical properties in terms of geometric isomerization and intramolecular cycloaddition have been investigated.By substitution of the ethylene bond with methoxy and methyl, the quantum yields of both photochemical trans->cis isomerization and intramolecular <4+4> cycloaddition of the cis isomers are greatly increased.Substituents such as formyl and methoxycarbonyl apparently enhance intersystem crossing so as to induce isomerization by <4+2> cycloaddition.Photochemical isomerization of 1,2-di-9-anthryl-1-hydroxypropene proceeds by hydrogen shift and results in the dearomatization of one anthracene moiety.Monosubstituted cis-dianthrylethylenes in solution are nonfluorescent.The fluorescence of cis-1-methoxy-2-methyl-1,2-di-9-anthrylethylene is suggested to originate from an intramolecular excimer state.For the corresponding trans isomer, the fluorescence is found to be dependent on solvent polarity as is typical of a twisted intramolecular charge-transfer state.