SPECTROSCOPIC STUDIES OF 7-DIETHYLAMINO-3-STYRYL COUMARINS

The absorption and fluorescence characteristics of four 7-diethylamino -3-styryl coumarins (dyes I-IV), containing either an extended formyl or acetyl substituent at the 3-position, in solvents of different pola rity (chloroform, dimethylsulphoxide and dimethyiformamide) were studi ed with regard to the influence of the flexibility of the chromophoric system in both the ground and excited states. The photophysical measu rements show that the dyes are very weakly fluorescent. The fluorescen ce lifetimes are in the region of 0.01 ns and the non-radiative rate c onstant is very high when compared with the radiative rate constant. T hese observations indicate that the reduction of the acceptor strength of the substituent at the 3-position, as in the present case, in a 7- diethylaminocoumarin dye does not always result in sustained fluoresce nce in polar, aprotic solvents. Therefore these dyes are not technical ly important as laser dyes.