The auxochromic group in the triplet manifold

Abstract

The spectral locations of the low energy triplet-triplet ( T-T) and singlet-singlet ( S-S) maxima of coumarin, 6-methyl, 7-methoxy, 7-hydroxy, 7-hydroxy-4-methyl, 7-amino-4-methyl, 7-ethylamino-4,6-dimethyl, 7-dimethylamino-4-methyl, 7-diethylamino-4-methyl coumarin, coumarin 339 and LD 490 were measured. The spectral location of the fluorescence maxima of all the auxochromic group substituted coumarin derivatives were also determined. In addition, the low energy S-S absorption and T-T absorption and polarization spectra of coumarin and 7-diethylamino-4-methyl coumarin were recorded. The importance of polarization of S-S and T-T absorption bands as related to substitution effects is briefly reviewed. T-T laser photoselection spectroscopy is employed to furnish experimental data on the arrangement of singlet and triplet dipoles relative to each other within the molecular frame of a molecule. It was found that the order of effectiveness of the auxochromic group in causing spectral red shifts in the singlet manifold is the same as in the triplet manifold. Using wavelength units the spectral red shifts (bathochromic effect) in the triplet manifold are much larger when compared to the red shift as a result of the auxochromic group substitution in the singlet manifold. When expressed in wavenumbers (energy), however, the red shifts appear to be about the same. The importance of these red shifts, as related to the laser action properties of laser dyes, are discussed. It is concluded that laser dyes superior to the coumarin laser dyes could be synthesized.