Electric field quenching of recombination fluorescence in photoionized nonpolar solutions. I. Free electron quantum yield determination

The field dependence of the relative decrease of fluorescence ΔF/F0 and of the photocurrent, i, is measured for dilute solutions of N,N,N′,N′-tetramethylparaphenylenediamine (TMPD) in 2,2,4-trimethylpentane (TMP) and tetramethylsilane (TMSi). In carefully purified and degassed solutions, irradiated by 5.90 eV photons, at 292 K, and E=45 kV cm−1, one obtains: ΔF/F0=3.9×10−2 in TMP and 11.8×10−2 in TMSi. The data are in good agreement with a model based on Onsager theory for electron escape. It is shown how the combined measurement of ΔF/F0 and i permits the determination of the free electron quantum yield at zero field, Φe0. For TMP:Φe0 =1.4×10−2 and for TMSi:Φe0=6.98×10−2. Finally it is shown that the field dependence of Φe, the free electron quantum yield at E, may be calculated from the experimental data.