Synthesis and Properties of Thiophene-Quinone Helicenes with Different Molecular Curvature

Naphthothiophene-quinone helicenes with different molecular curvatures, i. e., NTQ, 2,3-NDTQ and 2,6-NDTQ, are synthesized in seven steps. Diels−Alder reaction between p-benzoquinone and silyl enol ether derived from the corresponding naphthothiophenes was used as a key step. Both UV-Vis and fluorescence spectroscopy, cyclic voltammetry experiments, including DFT calculation demonstrated that, in comparison to the basic thiophene-quinone system, both M-shaped (2,3-NDTQ) and S-shaped (2,6-NDTQ) structures possessed a narrower HOMO−LUMO band gap than C-shaped NTQ, implying the effect of extended conjugation. The change of molecular shape resulted in the shift in both UV-Vis and fluorescence spectra, but the strong electron withdrawing effect of benzoquinone is more dominant.