Abstract
Energy transfer from 3,5-xylenol to 2,6-diphenylpyridine (DPP) in a very dilute solution of the molecules in solvents of different viscosity, from 0.29 to 4.30 Cp, at 300 K is discussed. Excited xylenol does not form an exciplex with DPP. Non-radiative deactivation of the excited state of the xylenol proceeds through dissipation of excitational energy from the S 1 state of xylenol to the S 1 state of DPP. A suitable relation that takes into account the low concentrations of 3,5-xylenol and DPP in different solvents has been used to calculate the energy transfer quantum efficiency, f XY. In non-polar or polar solvents, the non-radiative part of energy transfer efficiency increases and the radiative part decreases as the concentration of DPP is increased. The non-radiative energy transfer rate constant, K XY, for the system of xylenol and DPP in solvents of different viscosity gradually decreases with increasing viscosity of the medium. In all solvents, the value of K XY, is larger than the collisional diffusion controlled rate and the Förster critical transfer distance, R O, is much greater than the collisional separation distance r X + r Y, the sum of the radii of xylenol (X) and DPP (Y) molecules. It is suggested that a diffusion-assisted long range dipole-dipole interaction is mainly responsible for energy transfer from xylenol to DPP. The efficiency of energy migration is negligibly small.
Published Version
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