FLUORESCENCE ANISOTROPIES OF METHYLAMINO-OMEGA-DIPHENYLPHOSPHINYL-TRANS-STYRENE IN ISOTROPIC MEDIA IN THE CASE OF ONE-PHOTON AND 2-PHOTON EXCITATION

Fluorescence emission anisotropies, r, and mean lifetimes of methylami no-omega-diphenylphosphinyl-trans-styrene (DDPS) were measured in n-bu tanol at different temperatures from 20 to 80-degrees-C for one- and t wo-photon excitation. When increasing the temperature, the lifetime de creased from 32 to 12 ps, the r values, however, remained constant (0. 315 and 0.445 for one- and two-photon excitation, respectively) and we re found to be temperature independent. For DDPS in glycerol at -5-deg rees-C, where rotational diffusion does not occur during the excited s tate lifetime, the limiting emission anisotropies were r0=0.382 and r0 =0.545 for one- and two-photon excitation, respectively, very little d iffering from the fundamental emission anisotropies r(f) = 2/5 and r(f ) = 4/7. The small differences r(f)-r0 can be due to vibrations perfor med after excitation by the DDPS molecule as a result of the initial s hock.