Transfer of Electronic Excitation Energy from 2,2-Diphenylethanol to 2,6-Diphenylpyridine in Solvents of Different Viscosity

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Abstract Measurement of emission spectra indicates that in diluted solution of 2,2-diphenylethanol (DPE)–2,6-diphenylpyridine (DPP) system in solvents of different viscosity, the rate parameters kxy associated with nonradiative energy transfer from donor X (DPE) to acceptor Y (DPP) decrease with increasing viscosity of the medium. Further kxy values are higher than diffusion controlled rates kd. The Förster critical transfer distance R0 is much greater than the sum of the radii of the donor and acceptor, rx+ry. The observations seemingly indicate that energy-transfer from donor DPE to acceptor DPP mainly occurs by coulombic interaction over the dipole–dipole interaction distance which exceeds the molecular dimensions. In the DPE–DPP system, there is no evidence of external quenching.