Synthesis and properties of acceptor–donor–acceptor molecules based on oligothiophenes with tunable and low band gap

A series of acceptor–donor–acceptor molecules (DCN3T, DCN5T and DCN7T) based on oligothiophenes with low band gap are synthesized. The UV–vis absorption spectra of solution show that the introduction of electron-accepting groups results in a shift of the absorption onset towards longer wavelengths. Moreover, the optical spectra of their films show a large bathochromic shift and broadening of the bands with respect to the spectra in solution. The optical band gaps of film of these A–D–A molecules are 1.90, 1.74 and 1.68 eV, respectively. Cyclic voltammetry shows that all these compounds present a reversible first oxidation process whose potential decreases with the lengthening of oligothiophene cores. Electrochemical band gaps are 2.14, 1.88 and 1.71 eV, respectively.