Prediction of laser action properties of organic dyes from their structure and the polarization characteristics of their electronic transitions

Effects of substitution by auxochromic groups on the electronic spectra of aromatic compounds are discussed. Depending on the location and direction of the singlet-singlet (S-S) relative to the triplet-triplet (T-T) oscillators within the molecular frame, substitution by an auxochromic group may cause T-T absorption bands to move into or out of the fluorescence region, or they may be left unchanged. Predictions can thus be made of potential dye laser materials based on substitutional effects on the spectral properties of aromatic compounds. The predictions are incorporated in a graph that presents possible arrangements of low-energy SS oscillators relative to a T-T oscillator located in the fluorescence region of the aromatic compound. Depending on short- or long-axis substitution, the red shifts of the S-S and T-T absorption bands result in two promising constellations (structures) for low T-T absorption over the fluorescence region. The laser action properties of coumarin and some of its derivatives are discussed.