Ultrafast dynamics of Auramine O in composite films

Ultrafast excited-state dynamics of Auramine O, a diphenylmethane dye, in polymethylmethacrylate (PMMA) and in hybrid organic/inorganic sol-gel based films have been studied by means of femtosecond fluorescence upconversion experiments. The fluorescence transients of the samples showed a fast decay (few picoseconds) and a long decay (hundreds of picoseconds) representing a rapid cooling of the excess excitation energy to the matrices and the excited-state lifetime of the dye molecules, respectively. Different dynamic Stokes shifts in PMMA and hybrid glasses have been observed, which is argued to be ascribed to the different couplings between the emissive and nonemissive excited states for the two types of matrices.