Electron transfer from anthracenes. Comparison of photoionization, charge-transfer excitation and electrochemical oxidation

Abstract

Quantitative measures of electron detachment from anthracene and various meso-substituted derivatives (D) are examined in the gas phase and in solution. The photoelectron spectra show well-resolved bands for E1 corresponding to the first ionization [Formula: see text] from a π-molecular orbital (HOMO) with maximum electron density at the 9,10-positions. The same series of anthracenes form 1:1 electron donor–acceptor complexes with tetracyanoethylene [D,TCNE], which exhibit distinctive colors associated with charge transfer transitions hvCT to the ion pair[Formula: see text]. These measures of the gas phase energetics of electron transfer from the anthracenes are compared with their standard oxidation potentials [Formula: see text] determined from the reversible cyclic voltammograms in methylene chloride and trifluoroacetic acid solutions. Although there are direct, linear free energy relationships between E1and hvCT as well as E1and [Formula: see text], the best correlation is observed between [Formula: see text] and hvCT. The validity of the latter is discussed in terms of offsetting effects arising from differences in solvation energy and steric effects attendant upon 9,10-substitution in anthracenes.