Polarization of phosphorescence in nitroaromatics

Polarization of phosphorescence of several aromatic nitro compounds has been studied by the photo-selection technique. It is shown that the 0, 0 band of the pi* -> pi phosphorescence of 2-nitronaphthalene is largely in-plane, Iong-axis polarized. The result is suggested to arise from the contributions of the dipole moments of the ground state and the lowest triplet state to the transition moment of the phosphorescence. Intramolecular charge-transfer transitions do not appear to he the important sources of the intensity to the phosphorescence of nitronaphthalenes.