Effects of terminal substituents on electrochemical reduction of X-PhCH=NPhCH=CHPh-Y

Structural influence on the electrochemical properties of X-PhCH=NPhCH=CHPh-Y type of Schiff bases with long conjugated core were studied from the viewpoint of reduction potentials (E_(red)), which was determined by cyclic voltammetry on twenty-eight compounds. The effects of X and Y as terminal groups on E_(red) were also explored by means of computational methods. The results show that electronic effects, especially resonance effects caused by ending groups X and Y play a dominant role on the E_(red) values, while Y-group contributes less significantly than X-group does. Also, with lengthening of conjugated chain, the E_(red) values are more affected by the effect of excited state. Finally, a quantitative model was developed based on the respective effects of X and Y, which was used to scale the effects of remote substituents on E_(red). The quantitative computing model was proven reliable by the leave-one-out method, supporting that the effects of Y terminals on E_(red) are strengthened with increasing degree of core conjugation. The present study provides deeper insights into the effects of ending substituents on the electrochemical reduction of Schiff bases with long conjugated core.