Jeffrey E. Elbert

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.

A new synthetic route to 2-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecane

Abstract A new, general synthetic method for the title compound has been developed, based on the nitration of 2-benzyl-1,4,7,10-tetraazacyclododecane (64 % yield), which provides higher yields and easier purification for scale-up than previously reported methods.

Investigation of the photochemistry and photophysics of para-substituted tertiary thiocinnamamides

We report the synthesis and photochemical investigation of a new series of compounds, the tertiary, p-substituted thiocinnamamides. The synthesis centers on a one-pot conversion of the corresponding cinnamamide to the thiocinnamamide via Lawesson’s reagent. Results of semi-empirical calculations predict a frontier orbital structure for the thiocinnamamides that is similar to the analogous cinnamamides. One important difference is the inclusion of the sulfur non-bonding orbital as the highest occupied orbital of the thiocinnamamides. The oxygen non-bonded orbital of the cinnamamides is considerably lower in energy, and does not contribute significantly to the frontier orbital structure. The absorption and emission spectra were measured and are described. The quantum yields for E-Z photoisomerization at various wavelengths were measured and the quantum yields were not found to vary with wavelength. The photostationary states were measured and found to depend on the absorbance of the E and Z isomers at the irradiation wavelength as was expected. Analysis of photoproducts and triplet quenching studies suggest the importance of a triplet state in the photoreactivity of the tertiary thiocinnamamides.