A Novel Donor-Acceptor Thiophene-Containing Oligomer Comprising Dibenzothiophene-S, S-dioxide Units for Solution-Processable Organic Field Effect Transistor

Abstract

A π-conjugated thiophene-containing oligomer with a D-A-D-A-D (D: Donor, A: Acceptor) architecture, namely, 2, 6-bis {[4-(7-n-hexylthiophen-2-yl) thiophen-2-yl]- (dibenzothiophene-5,5-dioxide-3,3΄-diyl)}-bis((2-ethyl-hexyl)oxy) benzo [1,2-b:4,5-b’]dithiophen (BDT(DBTOTTH)2), was synthesized by Stille coupling reactions. There are obvious shifts in the Ultraviolet-visible (UV-vis) and photoluminescence (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(DBTOTTH)2. The optical band gap of the oligomer determined from its absorption onset in UV-Vis spectra is 2.25 eV. It agrees with the value of 2.29 eV determined from the cyclic voltammetry (CV) measurement. Its highest occupied and lowest unoccupied molecular orbital (HOMO/LUMO) energy levels, which were calculated from its onset of oxidation and reduction waves in CV curve, are −5.51 and −3.22 eV, respectively. The oligomer is a P-type semiconductor material with a good thermal stability and solubility, which can be used to fabricate organic field effect transistors (OFETs) by the spin coating technique. The OFET with n-octadecanylltrichlorosilane (OTS)-modified SiO2 dielectric layer exhibited a mobility of 1.6 ×10−3 cm2/Vs.