Synthesis and Optoelectronic Properties of Thiophene-Based Semiconducting Oligomers

Three new semiconducting oligomers (BT, TT and TT2) made of thiophene based donors, bithiazole weak acceptor and rhodanine based acceptors were designed and synthesized using Suzuki and Stille coupling. Oligomers exhibited excellent absorption in the visible region because of the pi-pi* transition as well as intramolecular charge transfer between the donor and acceptor moieties. The packing of oligomers in the film state was studied using 2D grazing incidence X-ray diffraction (GIXRD) analysis and the percentage of edge-on orientation was found to be greater compared to face-on orientation in all three oligomers. HOMO and LUMO energy levels of the oligomers in film state were calculated from ultraviolet photoelectron yield spectroscopy analysis and onset of absorption, respectively. Detailed time-resolved microwave conductivity experiments proved that the oligomers can act as n-type materials making these oligomers promising for optoelectronic device applications.