Synthesis and characterization of new donor-acceptor oligothiophene derivative with pyrido[1,2,5]thiadiazole as electron accepting unit

Abstract

A π-conjugated oligothiophene derivative with a D-A-D-A-D (D: donor, A: acceptor) architecture, namely, 2,6-bis[2-(4-n-hexylphenyl)thiophene-[1,2,5]thiadiazolo[3,4-C]pyridine]-4,8-bis((2-ethyl-hexyl)oxy)benzodithiophen (BDT(PTTPH)2), was synthesized by Stille cross-coupling reactions. The chemical structure of oligothiophene derivative was characterized by Fourier infrared spectrophotometer (FTIR) and nuclear magnetic resonance spectrometer (NMR). There are obvious shifts in the Ultraviolet-visible (UV–vis) and pho-toluminescence (PL) spectra of the thin film relative to its solution, indicating the existence of the π-π stacking in the solid state of the oligomer BDT(PTTPH)2. The optical band gap of the oligomer determined from its absorption onset in UV–vis spectra is 1.53 eV. It agrees with the value of 1.52 eV determined from the cyclic voltammetry (CV) measurement. Its highest occupied and lowest unoccupied molecular orbital (HOMO/LUMO) energy levels are -5.31 and -3.79 eV, respectively. According to initial thermogravimetric analysis (TGA) we found that the thermogravimetric temperature of the oligomer BDT(PTTPH)2 is 289 °C. The oligomer is a potential semiconductor material with a good thermal stability and solubility for fabricating organic solar cells.