Excimer formation of pyrene in a solid/polymer solution interface layer. A time-resolved total internal reflection fluorescence study

By the use of time-resolved total internal reflection (TIR) fluorescence spectroscopy, pyrene excimer formation has been investigated in an interface layer of a sapphire/polymer solution (a toluene solution containing 3.3 × 10^-4 mol dm^-3 of poly(methyl methacrylate) (MW = 120 000)). The fluorescence intensity of a pyrene excimer relative to that of a pyrene monomer is reduced in the sapphire/polymer solution interface layer compared to that in the bulk solution. In addition, the rise and decay rates of the excimer fluorescence are decelerated in an interface layer less than 60 nm in thickness. Simulations of incidence- and observation-angle dependences of fluorescence intensities suggest a pyrene concentration gradient in which the pyrene concentration is higher in the interface layer than in the bulk solution. Furthermore, the viscosity of the interface layer has been proven to be increased compared to that of the bulk polymer solution by means of fluorescence depolarization studies of 1,6-diphenyl-1,3,5-hexatriene as well as analyses of rate constants for the excimer formation.