Anomalous fluorescence and laser emission from 7-alkylamino coumarins in acid solutions

The fluorescence emission from alcoholic solutions of 7-monoalkylamino-4-methyl coumarins shifts from blue to blue-green on the addition of acid. Fluorescence and excitation spectra measured at various concentrations show that with increasing concentration, a new excitation peak appears which is the source of the blue-green emission in the presence of acid. It is suggested that this new species is a dimer of the coumarin. The analyses of the amplified fluorescence spectra with a streak camera indicate that the blue-green emission is due to a transient excited species, consistent with a model based on the addition of H+ to the excited dimeric state. © 1974.