Polarizations of Electronic Transitions from Azimuthal Variation in Fluorescence Intensity—with Application to Biphenyl

Abstract

It is shown that the angle between absorbing and emitting transition moment vectors may be obtained from a ratio of intensities measured in fluorescence; the intensities to be taken from an azimuthal circle with the propagation vector of the incident beam as polar axis. The incident light must be polarized and the intensities are measured at azimuthal stations selected according to the direction of polarization. Results are compared with those obtained using conventional polarized fluorescence—for aniline and for indole. The azimuthal ratio method is then used to obtain polarizations for biphenyl and substituted biphenyls. Use of the method may facilitate penetration into the region below 200 nm; in fact a determination using excitation at 197 nm has already been made. Finally, the results for biphenyl are interpreted so as to constitute several new assignments of electronic transitions.