Picosecond polarized fluorescence studies of anisotropic fluid media. II. Experimental studies of molecular order and motion in jet aligned rhodamine6G and resorufin solutions

New polarized time resolved fluorescence techniques are implemented to dete rmine the full angular motion of a probe molecule in an anisotropic environ ment. Studies of rhodamine 6G and resorufin molecules aligned in a free eth ylene glycol jet show that the presence of net molecular order is accompani ed by a distinct anisotropy in alignment relaxation following photoselectio n. Diffusion coefficients for phi and theta motion (D-parallel to and D-per pendicular to) in a jet fixed axis system are determined from the cylindric ally symmetric and asymmetric alignment relaxation rates for the isotropic and anisotropic regions of the jet. The presence of net negative molecular alignment as the free jet is formed is seen to correspond to restricted phi motion (D-parallel to < D-perpendicular to), with a net positive steady st ate alignment the anisotropy in the diffusion dynamics is reversed. The dif ferences in D-parallel to and D-perpendicular to are attributed to anisotro py in the solvent viscosity as a consequence of flow. The combination of li near and circular polarization techniques is seen to provide useful informa tion on cylindrical asymmetry and relaxation dynamics hitherto unobserved b y conventional fluorescence polarization techniques. (C) 2000 American Inst itute of Physics. [S0021-9606(00)00217-8].