Polarization of the T1 → S0 phosphorescence and S0 → Sn phosphorescence excitation of aromatic hydrocarbons prototype for π,π* states. A reappraisal

The polarization of phosphorescence and phosphorescence excitation in benzene, naphthalene, phenanthrene and their corresponding perdeuterated forms in EPA at 77 K were examined using the photoselection method with both vertically and horizontally polarized light in conjunction with a delay between excitation and detection of emission. Based on the results, polarization in the spectral regions examined is consistent with a situation where the excitation and emission are at an angle near to 90° (i.e., where the polarization it is close to −0.33); this confirms that the phosphorescence of the compounds studied is polarized in the plane normal to the molecular plane. Consequently, any vibronic mixing and singlet-state mixing mechanisms potentially involved in the strengthening of T1 → S0 transitions in these compounds must posses a polarization normal to the molecular plane.