Suzanne L. Quillen

The singlet states of methyl cinnamate and methyl indenoate

The fluorescence lifetimes of methyl cinnamate and methyl indenoate have been investigated by means of picosecond laser spectroscopy. Values of <3 ps and 15 ± 2 ps for these esters are significantly shorter than those previously reported for ethyl cinnamate. The short lifetimes are tentatively attributed to the competition between fluorescence from the originally populated π,π* singlet state and its internal conversion to a lowest n,π* singlet state. The efficiency of isomerization is independent of solvent, but dependent upon temperature and excitation wavelength. Comparison of the quantum yields for direct and triplet-sensitized dimerization indicates that intersystem crossing is highly inefficient. Thus the isomerization which occurs upon direct irradiation occurs predominantly from the singlet manifold.