Abstract

The polarized luminescence when excited by light of time coherence that is less than specific rotational period of molecular top is a result of oscillator orientational selectivity by excitation followed by regular rotation spacial dispersion. Excitation by light of time coherence exceeding the rotational period leads to resonant interaction of light wave and molecular top rotation producing an additional orientational selection. The mechanism results in dependence of excited molecules, angular momentum orientation and of fluorescence polarization along rotational contour. Little-nown experimental data support the conclusion, but for the present the extent of generality and trends of the dependence are obscured. To clear up the situation we studied the fluorescence polarization along rotational excitation contour of jet-cooled organic polycyclics: thriphendioxazine (C₁₈H₁₀N₂O₂), 1, 4-diamino-9, 10-anthraquinone (C₁₄H₁₀N₂O₂), tetracene (C₁₈H₁₂), 4, 7-diamino-1H-isoin-dole-1, 3 (2H)-dione (C₈H₇N₃O₂) a.o. The molecules have different intramolecular orientation of transition dipole moment and are related to various kinds of asymmetric tops. The measurements were performed using dye-laser excitation (bandwidth 0.08 cm⁻¹). To avoid effects of nonlinearity the pumping power did not exceed 60 W cm⁻².

© 1994 IEEE