EMISSION AND THE EXCITATION-SPECTRA OF SOME AROMATIC ESTERS

The luminescence spectra of methyl-, ethy-, propyl-, butyl-, and benzyl- benzoates, ethyl phenyl acetate, benzyl acetate and benzyl propionate have been studied in ethanol and in n-hexane rigid solutions at 77 K. In benzoic acid esters the fluorescence is very weak whereas the phosphorescence is intense. In the other esters, both the fluorescence and the phosphorescence appear with comparable intensity. The experimental results suggest that in these molecules the fluorescence and the phosphorescence are due to Sππ* → S and Tππ* → S transitions respectively. Phosphorescence excitation spectra show both S→ Sππ* and S→ Tππ* absorption bands for all the esters. In benzoic acid esters and additional absorption band has been observed. From the solvent effect on this band and from large Φp/Φf values this has been assigned to the S→ Tππ* band. © 1979.