Solvent dependent photocyclization and photophysics of some 2-ethynylbiphenyls

摘要

The spectroscopic properties and photochemical behavior of molecules having 2-ethynylbiphenyl or 2-phenyldiphenylacetylene structures are reported. These molecules undergo photocyclization reactions to yield plienanthrene and dihydrophenanthrene products via putative isophenanthrene (cyclic allene) intermediates. Phenanthrene formation from the isophenanthrenc intermediates does not occur via a unimolecular sigmatropic hydrogen shift, but rather by protonation or hydrogen abstraction mechanisms involving the solvent. Cyclization efficiencies are much lower than is the case for previously-investigated 2-vinylbiphenyl systems. The 2-phenyidiphenylacetylenes have high fluorescence quantum yields and long singlet lifetimes when compared to diphenylacetylene. The 2-ethynylbiphenyls decay via a combination of fluorescence and intersystem crossing.