INTRA-MOLECULAR FLUORESCENCE QUENCHING OF PHENYLALKYLAMINES

Intramolecular normal fluorescence quenching of phenylalkylamines has been studied by means of fluorometry and nanosecond time-resolved spectroscopy. No intramolecular exciplex emission was observed. The quenching involving intramolecular electron transfer and subsequent proton transfer is significantly dependent upon the number of methylene units, solvent polarity, and temperature. In nonpolar and weakly polar solvents, static quenching resulting from a sandwich-like or holding structure occurs markedly for C3, but not for C1 and C2. In strongly polar solvents, dynamic quenching takes place in the order of C1, C3, and C2. The quenching rate constants in EtOH can be elucidated in terms of intramolecular electron transfer as a function of rotational diffusion (ke = α′Τη-1 + β). Large activation energies for electron transfer in the excited state observed in EtOH may be attributed to slight electron overlapping between the benzene ring and amino group in the excited state and to negatively large activation energy for solvent viscosity of EtOH. Through-bond CT interaction was scarcely observed in the sample molecules. © 1979 American Chemical Society.