8-Phenyl-Substituted Dipyrromethene·BF2 Complexes as Highly Efficient and Photostable Laser Dyes

We report on the synthesis and the photophysical and lasing properties of two new dipyrromethene·BF2 dyes, analogues of the commercial dye PM567, dissolved in liquid solutions or in polymeric matrices of poly(methyl methacrylate) and as solid copolymers with methyl methacrylate, where the chromophore is covalently bound to the polymeric chains. The new dyes have the 8 position substituted by the group p-(acetoxypolymethylene)phenyl or p-(methacryloyloxypolymethylene)phenyl (number of methylenes = 1 or 3). Good correlations between the photophysical properties in dilute solutions and the lasing characteristics in moderately concentrated solutions have been observed. The presence of the 8-phenyl substituent does not significantly modify the photophysics of the chromophore. Theoretical calculations were performed to rationalize this behavior. Under transversal pumping at 534 nm, laser efficiencies up to 46% were obtained for liquid solutions, which were found to be nearly independent of the nature of the solvent and the length of the polymethylene chain. For solid samples, lasing efficiencies of up to 23% and good photostabilities, with 96% of the initial laser output after 100 000 pump pulses at 10 Hz, were established.