GAUSSIAN DISTRIBUTIONS OF THE DECAY TIMES OF THE SINGLET EXCITED-STATE OF AROMATIC-AMINES DISPERSED IN POLYMER-FILMS

The fluorescence maximum of amino-substituted 1,3,5-triphenylbenzenes dispersed in polystyrene and polycarbonate is shifted to longer wavelengths compared to isooctane, and this shift is larger in polycarbonate than in polystyrene. The shift is attributed to a partial relaxation of the matrix around the dispersed molecules during the excited-state lifetime. The nonexponential fluorescence decays obtained at different emission wavelengths can be analyzed globally assuming a Gaussian distribution of decay rates with a standard deviation that does not depend upon the emission wavelength. This Gaussian distribution of decay rates is attributed to a distribution of sites with different interaction with the polymer matrix. The sites giving the largest excited-state stabilization are characterized by the slowest average decay rate.