Structural Tuning of Curved TTFAQ-AQ as a Redox-Active Supramolecular Partner for C70 Fullerene

A series of saddle-shaped donor-acceptor pi-systems, termed TTFAQ-AQs, were designed and synthesized. The molecular structures of TTFAQ-AQs feature a pi-fused framework containing an anthraquinodimethane extended tetrathiafulvalene (TTFAQ) as the donor and an anthraquinone (AQ) unit as the acceptor. As such, TTFAQ-AQs show enhanced intramolecular charge-transfer properties, which result in amphoteric redox behavior and narrow electronic energy band gaps. Detailed structural and electronic properties were investigated by UV-vis absorption, cyclic voltammetric, and single-crystal X-ray diffraction (SCXRD) analyses. The supramolecular interactions of TTFAQ-AQs with C-60 and C-70 fullerenes were examined in both the solution and solid phases. Our results showed that the benzoannulated TTFAQ-AQ derivative favors interaction with C-70 fullerene through complementary concave-convex interactions. Detailed energetics involved in the TTFAQ-AQ/C-70 interactions were assessed by means of density functional theory (DFT) calculations.