ELECTRON-AFFINITIES OF SOME POLYCYCLIC AROMATIC-HYDROCARBONS, OBTAINED FROM ELECTRON-TRANSFER EQUILIBRIA

The gas-phase electron attachment free energies DELTAG(a)degrees, where-DELTAG(a)degrees almost-equal-to EA, were measured for several polycyclic aromatic hydrocarbons with the electron-transfer equilibria technique. The EA values in kcal/mol are as follow: anthracene, 13.2; benz[a]pyrene, 18.2; perylene, 22.3; tetracene, 23.9; and pentacene, 31.2. These results, when combined with the literature value for naphthalene, -4.4 kcal/mol, based on electron transmission spectroscopy, lead to an approximately linear correlation with the one-electron (polarographic) reduction potentials determined in solution. However, the slope of the line is not equal to 1 as previously assumed. The deviation from unity is probably due to decreases of the solvation exothermicity of the radical anions, expected because of the increasing charge delocalization for the negative ion with increasing electron affinity of the neutral precursor.