Tuning Molecular Electron Affinities against Atomic Electronegativities by Spatial Expansion of a π-System

2,1,3-Benzochalcogenadiazoles C6R4N2E (E/R; E=S, Se, Te; R=H, F, Cl, Br, I) and C6H2R2N2E (E/R'; E=S, Se, Te; R=Br, I) are 10 pi-electron hetarenes. By CV/EPR measurements, DFT calculations, and QTAIM and ELI-D analyses, it is shown that their molecular electron affinities (EAs) increase with decreasing Allen electronegativities and electron affinities of the E and non-hydrogen R (except Cl) atoms. DFT calculations for E/R+e* -> [E/R]* electron capture reveal negative (sic)G values numerically increasing with increasing atomic numbers of the E and R atoms; positive (sic)S has a minor influence. It is suggested that the EA increase is caused by more effective charge/spin delocalization in the radical anions of heavier derivatives due to contributions from diffuse (a real-space expanded) p-AOs of the heavier E and R atoms; and that this counterintuitive effect might be of the general character.

Automated summary

By employing CV/EPR measurements, DFT calculations, and QTAIM and ELI-D analyses, we have observed that the molecular electron affinities (EAs) of 2,1,3-benzochalcogenadiazoles and C6H2R2N2E increase as the Allen electronegativities and electron affinities of the E and non-hydrogen R (except Cl) atoms decrease. DFT calculations also reveal that the electron capture process results in increasing (sic)G values with higher atomic numbers of the E and R atoms, while positive (sic)S has a negligible effect. Our findings suggest that this counterintuitive EA increase is attributed to the more effective charge/spin delocalization in the radical anions of heavier derivatives due to contributions from diffuse p-AOs of the heavier E and R atoms, which may have a broad significance.