Single-photon induced conductivity of solutes in nonpolar solvents

Synchrotron radiation was used for determining single-photon photoconductivity thresholds for various solutes in nonpolar solvents. For anthracene as a solute the thresholds (Eth) are 6.14, 6.07, and 5.87 eV in 2,2,4-trimethylpentane, 2,2,4,4-tetramethylpentane, and tetramethylsilane, respectively. The threshold decreases as the conduction band energy (V0) decreases. The polarization energy (P+) of the anthracene cation, as derived from the data for 2,2,4-trimethylpentane, is one-third larger in magnitude than that reported for the polarization energy of the anthracene anion in this solvent, which suggests that the cation is smaller than the anion. Thresholds were also measured for 1,2-benzanthracene, azulene, perylene, triphenylamine, and diazabicyclo-octane. The thresholds in solution and solvation terms are related quantitatively by the expression Eth=I.P.+V0+P+.