Abstract
To improve the laser action properties of the pyrromethene-BF2 (P-BF2) complexes, we studied substitution effects at different positions of the dye molecule on the electronic spectra of several derivatives. Specifically, we used laser photoselection spectroscopy to measure the triplet–triplet (T–T) absorption and polarization spectra as well as the fluorescence and visible absorption singlet–singlet (S–S) spectra of the following compounds: 1,2,3,5,6,7,8-heptamethyl; 8-acetoxymethyl-1,3,5,7-tetramethyl-2,6-diethyl; 1,3,5,7-tetramethyl-8-p-methoxyphenyl; 3,5-dimethyl-1,7-diphenyl; and 1,3,5,7,8-pentamethyl-2,6-diphenyl P-BF2 complexes. The 1,3,5,7-tetramethyl P–BF2 complex itself exhibits weak T–T absorption, which stretches from the green to the near-IR spectral region. This band consists of two overlapping (differently polarized) T–T transitions. Short molecular axis (i.e., 8 and 1,7 positions) substitution causes the positively polarized T–T transition to gain considerably in intensity. Significantly, the negatively, long-axis-polarized T–T transition was unaffected by the long-axis 2,6-position disubstitution. Therefore, only the 2,6-position disubstitution is expected to produce superior new P-BF2 complex laser dyes. Substitution effects from strongly interacting groups with chromophores on S–S as well as T–T absorption spectra, together with cw laser photoselection spectroscopy, are briefly reviewed.
© 1992 Optical Society of America
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