Electron affinities of aza-substituted polycyclic aromatic hydrocarbons

Electron affinities for aza-substituted polycyclic aromatics were determined from measurements of electron transfer equilibria in the dilute gas phase with a pulsed electron high pressure mass spectrometer (PHPMS). These are (in kcal/mol): quinazoline (12.7), quinoxaline (15.8), cinnoline (16.0), acridine (20.3), benzo[c]cinnoline (20.6), pyrido[2,3-b]pyrazine (22.5), phenazine (29.5). Solvation energies of the corresponding radical anions in acetonitrile and dimethylformamide are derived from the gas phase data and literature on electron reduction potentials in solution. An observed linear relationship between the electron affinities and the reduction potentials allows estimates of electron affinities to be made for 12 aza compounds whose EA's are too low to be measured with the present method. Keywords: aza-substituted aromatic hydrocarbons, electron affinities, electron transfer, radical anions, reduction potentials, solvation energies of radical anions, stabilities of radical anions.