Fig. 4
The influence of π–π interactions on the electron redistribution and RTP behavior. a The orbital interaction of π–π stacking in excited state: the electrons would redistribute in new orbitals for the π–π interactions, then three electrons are stabilized and one electron is destabilized, and thus the net stabilization is two electrons. b Depiction of the electrostatic model of substituent effects on π–π interactions from Hunter–Sanders model: electron-withdrawing substituents could enhance π–π interactions by decreasing the π-electron density of the substituted π-system and relieving the π–π repulsion, while electron-donating substituents hinder π–π stacking through the opposite mechanism. c Difference electrostatic potential (ESP) analysis of isolated CS-CH3O, CS-CH3 (a), CS-H, CS-Br, CS-Cl, and CS-F. The potential energy range is −0.015 to 0.015 H q-1 for all surfaces shown, red indicates areas with dense electron density, yellow for normal, while blue areas suggest less electron density
