Abstract
AbstractA structureless, longwavelength fluorescence band, attributed to the excited (charge‐transfer) complex: A−D+, occurs when the fluorescence of aromatic hydrocarbons (A) is quenched by aryl amines (D). The relative intensity of this band is found to decrease strongly with increasing solvent polarity, so that ultimately in highly polar solvents (ε > 30) no complex emission can be observed even at high aryl amine concentration at which the normal hydrocarbon fluorescence is strongly quenched.Flash experiments carried out with solutions of aromatic hydrocarbons in acetonitrile (ε = 37) with high concentrations of diethylaniline show transient absorption spectra which are due to the triplet state of the hydrocarbon and to the radical ions A·− and D+ which are produced with quantum yields between 2 and 6%. Kinetic experiments (of fluorescence quenching) indicate that in polar solvents electron transfer can occur at an encounter distance of about 7 Å. A kinetic scheme which is consistent with these results and meets the energetic requirements is discussed.
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