FLUORESCENCE QUENCHING OF 1,3,5-TRIARYL-2-PYRAZOLINE DERIVATIVES WITHACCEPTOR SUBSTITUENTS IN THE 5-PHENYL RADICAL

Luminescence spectra of 1,3,5-triphenyl-2-pyrazoline with acceptor sub stituents or with substituents in a 5-phenyl ring having an extended c onjugated system are studied. These compounds exhibit considerably low er fluorescence quantum yield compared to that of the unsubstituted co mpound. Experimental and calculation data suggest that the fluorescenc e quenching of these bichromophore molecules with unconjugated chromop hores could be related to a thermal population of ''mixed'' excited sl ates involving occupied molecular orbitals of one chromophore and unoc cupied orbitals of another.