FLUORESCENCE AND LASING PROPERTIES OF RHODAMINE DYES

New rhodamine dyes with amino endgroups that are rigidized by 5- and 6-membered rings have been synthesized. The fluorescence quantum yield in ethanolic solution is, independent of temperature, close to unity. A derivative with amino groups incorporated in a single 6-membered ring lases more efficiently than rhodamine 6G. In an attempt to improve pumping by an excimer laser the rhodamine chromophore was connected via methylene bridges with 2,5-diphenyloxazole (PPO) which absorbs strongly at 308 nm. In these antenna dyes complete energy transfer from PPO to rhodamine is observed, yet lasing efficiency is influenced by some unexpected excited state interaction between the chromophores. We studied with other multichromophoric dyes also the influence of nitrobenzene and anthracene moieties on the fluorescence efficiency of the rhodamine chromophore. Linkages consisting of two methylene groups permit a stronger interaction between chromophores than those consisting of a single methylene group.