Spectroscopy and molecular structure of efficient laser dyes: Vibronic spin-orbit interactions in heterocyclics

Some characteristics of selected laser dyes are reviewed, and the effect of heterocyclic atom substitutions on triplet (pi, pi*) transitions is studied experimentally. Specifically, the intensities (oscillator strengths f) of the lowest-energy singlet-singlet (S-S) and triplet-triplet (T-T) transitions of anthracene and some of its heterocyclic analogs were measured. It is shown thai, this type of substitution of carbon atoms by heteroatoms results in a considerable reduction of intensity of T-T transitions. This observation is important to laser dye technology. The effect is explained by the existence of an efficient vibronic coupling mechanism between (n, pi*) and (pi,pi*) triplet states in heteroatom molecules. Some general guidelines for how to find efficient laser dyes are proposed. (C) 1997 Optical Society of America.