Spectral, luminescent, and lasing properties of 3-(benzothiazolyl-2)-7-hydroxy-and-8-hydroxycoumarins

Abstract

The spectral and luminescent properties of 3-(benzothiazolyl-2)-7-hydroxy-and-8-hydroxycoumarins and their protolytic forms are studied experimentally and with the help of quantum-chemical calculations using the method of intermediate neglect of differential overlap with spectroscopic parameterization. The photophysical processes in these compounds are analyzed. The fluorescence of 3-(benzothiazolyl-2)-8-hydroxycoumarin is shown to be extremely weak due to intercombination conversion of the excitation energy. The introduction of a proton-accepting substituent next to the hydroxy group of the molecule (at position 8) leads to intramolecular proton transfer, resulting in formation of a zwitterion, with the probability of the proton transfer increasing in the excited S1 state. The lasing ability of the protolytic forms of the molecules under excitation with a XeCl excimer laser is studied. It is shown that the compounds have the highest lasing efficiency in the anionic form.