Measurement of the Circular Polarization of the Luminescence of Photoselected Samples under Artifact-Free Conditions

The measurement of the Circular Polarization of the Luminescence (CPL) in viscous solvents is hampered by the occurrence of artifacts. These arise when the emitted radiation is partially linearly polarized due to the photoselection effect. It is shown that there are two configurations of the CPL spectrometer in which such linear polarization artifacts are virtually negligible: one requires perpendicular excitation and emission channels as well as horizontally polarized incident radiation; the other involves a 180° geometry and unpolarized excitation light. In both options, essentially artifact-free CPL data are obtained, enabling the study of the directional dependence of the optical activity in emission. This is illustrated for the case of the 3 ππ* → S 0 phosphorescence of the cross-conjugated dienone α-santonin.