The influence of the excited‐state substituent effect on the reduction potentials of Schiff bases

The reduction potentials ( E Red ) of 30 N ‐(phenyl‐ethylene)‐anilines (XArC(Me)=NArY) were determined, and the effect of substituents on E Red was investigated. During the reduction process, a molecule obtains an electron to form a radical anion; the electron distribution is somewhat similar to that of the excited state. Therefore, the substituent effect cannot be described thoroughly only with Hammett parameter, which is a classic descriptor for electronic effect of substituent in ground state. Excited‐state substituent constant σ cc ex was employed as a structural descriptor characterizing the stability of radical anion. The performances of quantitative structure‐reduction potential relationship model can be largely improved by introducing excited‐state substituent constant σ cc ex to the model, which has been confirmed by the investigations of reduction potentials of disubstituted N ‐benzylidenebenzenamines, aryl‐substituted acetophenone azines, and 1‐substituted naphthalenes. It is indicated that the excited‐state substituent effect is very important to the correlation of reduction potentials of Schiff bases. Copyright © 2015 John Wiley & Sons, Ltd.