Theoretical approach to the problem of finding effective luminophors in the isocarbostyril series

Abstract

It has been established that the main reason for the low fluorescence quantum yield of unsubstituted isocarbostyril (I) is the thermally activated intersystem crossing Sππ ⇝ Tnπ. The positions in the molecule at which the introduction of substituents should cause the greatest bathochromic displacement of the absorption spectra have been determined on the basis of data from quantum-chemical calculations. Lowering of the S1 level results in a decrease in the probability of intersystem crossing and, as a consequence, in an increase in the quantum yield. A number of derivatives of I have been synthesized, and their luminescence-spectroscopic properties have been investigated. The causes of the instability of 4-hydroxy- and 4-NH2-isocarbostyrils have been discussed.