Bichromophoric Compounds. Photophysics and Photochemistry of (1-Naphthyl)alkyl Esters of Fumaric, Maleic, and Oxalic Acids

Article abstract of DOI:10.1021/jo00206a029

Fumarate, maleate, and oxalate groups quench the excited singlet state of naphthalene.When the naphthalene chromophore is combined in the same molecule with one of these quenching groups, its fluorescence quantum yield is reduced to about 1percent of that of the corresponding (1-naphthyl)alkyl acetate as a result of efficient electron transfer to the diester.No exciplex emission is observed from the bichromophoric compounds.Although the rate of quenching is only weakly dependent on the number of atoms linking the two groups, ground-state charge-transfer interactions between the two groups were observed only in the di-1-naphthyl esters and were absent when the groups were separated by longer chains. (1-Naphthyl)alkyl fumarates and maleates undergo photochemical cis-trans isomerization with quantum yields on the order of 0.04.This photoisomerization was shown to proceed via the electron-transfer pathway and not by direct triplet energy transfer from the naphthalene chromophore to the unsaturated diester.The 1-naphthylmethyl esters yield 1-naphthaldehyde with quantum yields of 0.001.Free-radical chain addition to the fumarate double bond occurs on prolonged irradiation in solvents containing abstractable H, particularly in the presence of acetophenone or radical sources such as tert-butyl hydroperoxide.Even in thoroughly degassed benzene oligomerization of the fumarate group leads to partial loss of the double bond at long irradiation times.