A new insight into the push-pull effect of substituents via the stilbene-like model compounds

In this paper, authors report on 1-pyridyl-2-arylethenes, 1-furyl-2-arylethylenes, 1,2-diphenylpropylenes and substituted cinnamyl anilines as stilbene-like model compounds to investigate the factors dominating the push-pull effect of substituents via using the nuclear magnetic resonance chemical shift of bridging bond carbon atoms. It is demonstrated that the maximum push-pull effect is not always between the strong electron-donating D and strong electron-accepting A groups in D-pi-A compounds. The action mode of push-pull effect of substituents in D-pi-A compounds is dominated by their molecular parent structure. The contribution of field/inductive effect and conjugative effect of a group to the push-pull effect is unequal. When the D-pi-A parent molecule is in a plane, the influence of field/inductive effect of a group on the push-pull effect is greater than or close to that of its conjugative effect does. Although the parent molecule is sterically twisted, the push-pull effect is mainly dependent on the conjugative effect of a group. The results of this paper can provide us a new insight into the push-pull effect of substituents.