Anisotrope Fluoreszenz langgestreckter Moleküle in Lösungen / The Anisotropie Fluorescence of Prolate Molecules in Solutions

Abstract

Abstract Quantum chemical investigations of the electric dipole moments in the ground and excited states and also transition moments of 2,2′-p-phenylenebis (5-phenyloxazole) (POPOP) and 2,2′-p-phenylenebis (4-methvl-5-phenylaxazole) (2MPOPOP) were carried out with the PPP-CI-method. It was established that the transition moments of POPOP and 2MPOPOP are parallel to the long axis, whereas the electric dipole moments are mutually parallel and perpendicular to the long axis of these molecules. Further, the emission anisotropics r of the fluorescence of the prolate molecules POPOP. 2MPOPOP and the non-polar diphenvlenestilbene (DPS) in solvents of different viscosities η were investigated. Also for these substances the non-linear dependence of 1/r on T/η was confirmed. This deviation from the linear dependence is stipulated essentially through the length of the molecule. The effective volumes and the rotational relaxation times in different solvents of the studied molecules were determined.