Fluorescence and electronic structure of the laser dye DCM in solutions and in polymethylmethacrylate

The photophysical properties and polarization of the fluorescence of the laser dye 4-dicyanomethylene-2-methyl-6(p(dimethylamino)styryl)-4-Hpyran (DCM) in solutions of different polarities and in polymethylmethacrylate (PMMA) at 293 and 77 K were investigated by stationary and pulsed fluorescent spectroscopy. Based on the data of polarized fluorescence, an oscillator model has been suggested, according to which the electronic absorption spectrum of DCM in the 240-500nm range is formed by at least three electron transitions. The quantum yield of fluorescence Φ f increases linearly with increase in the polarity of a solvent in a toluene dimethylsulfoxide (DMSO) mixture from 0.08 (toluene) to 0.80 (DMSO). An increase of Φ f to 0.90 was also observed on increase in the rigidity of the medium by freezing a solution of DCM in npropanol at 77 K or introducing of a dye to the polymeric matrix of PMMA at room temperature (Φ f = 0.76). The fluorescencedecay kinetics of DCM in toluene, npropanol, and PMMA at 293 K follows a biexponential law, whereas in nhexane and vaseline oil at 293 K and in npropanol at 77 K it follows a monoexponential law. The mechanisms underlying radiationless deactivation of the electronexcitation energy in solutions and in polymeric media are discussed.