Observation of the Relative Polarizations of Electronic Transitions

The polarization of fluorescence of several aromatic systems in a rigid glass of propylene glycol at —78°C has been determined. Polarized exciting radiation absorbed in a single electronic band was used, enabling the determination of the polarization of higher electron transitions relative to that of the lowest singlet-singlet transition. Results are in agreement with current theoretical ideas for anthracene and several of its derivatives. Results for peri-condensed systems suggest the need for a more thorough examination of the free electron model for this type of system.