The interrelation between polarographic half-wave potentials and the energies of electronic excited states

Abstract

The polarographic half-wave oxidation and reduction potentials, singlet and triplet energies of a series of (i) monocyclic aza-aromatics, (ii) polycyclic aza-aromatics and their N-oxides, (iii) condensed aromatic hydrocarbons, and (iv) substituted benzene derivatives are reported. The interrelation between the spectroscopic and electrochemical data is developed and discussed in regard to theoretical and experimental parameters. A linear free-energy relationship between the triplet energies and the absolute difference between the oxidation and reduction potentials of the first three series was found. These correlations were utilized to estimate the triplet energies of other molecules in the series, to predict the true half-wave oxidation potential of some heteroaromatic N-oxides and to compute the coulomb repulsion integral. No correlation between E T (π, π*) and (E 1/2 °x − E 1/2 R ) for substituted benzenes was found. The various reasons for this deviation were discussed.