Conjugated Polymers Based on 3,6-Dichlorothieno[3,2-b]thiophene Synthesized by Direct Arylation Polycondensation and Their Semiconductor Properties
Direct arylation polycondensation(DArP)is an atom-economic and environmentally benign protocol for the synthesis of conjugated polymers.However,this method often suffered from low reactivity and poor selectivity of C—H bonds.In this study,a β-chlorinated thiophene derivative,3,6-dichlorothieno[3,2-b]thiophene(2ClTT),was used as the C—H monomer for DArP.The introduction of chlorine atoms at the β-positions of thieno[3,2-b]thiophene significantly enhances the reactivity of a-C—H bonds and evades the unwanted C—H activation.Theoretical calculations revealed that the DArP reactivity of 2ClTT is comparable to that of highly reactive β-chlorinated thiophene-based C—H monomers reported in previous literature.Two conjugated polymers,i.e.,DPP-2ClTT and IID-2ClTT,were synthesized by using 2ClTT as the C—H monomer and bromothienyl-flanked diketopyrrolopyrrole(DPPThBr)or brominated isoindigo(IIDBr)as the C—Br monomers.The photophysical and electrochemical properties of these two polymers were investigated.The absorption spectrum of DPP-2ClTT was redshift by～200 nm compared to that of IID-2ClTT.This can be ascribed to the planar backbone of DPP-2ClTT due to the presence of Cl… S intramolecular interactions.Furthermore,the strong electronegativity of chlorine atoms resulted in a reduction of frontier orbital energy levels of the polymers.The HOMO/LUMO energy levels of DPP-2ClTT and IID-2ClTT were-5.35/-3.66 eV and-5.88/-3.73 eV,respectively.The charge transport properties of DPP-2ClTT and IID-2ClTT were characterized by top gate/bottom contact(TG/BC)organic thin-film transistors(OTFTs).Due to the favourable HOMO and LUMO energy levels,as well as the well delocalized HOMO and LUMO orbitals,DPP-2ClTT exhibited ambipolar transport characteristics in OTFT devices with the highest electron and hole mobilities of up to 1.36 and 0.89 cm2N/s,respectively.However,owing to the deep-positioned HOMO energy level and relatively localized HOMO orbitals,IID-2ClTT displayed n-type transport characteristics in OTFT devices with the highest electron mobility of 0.029 cm2N/s.The higher electron mobility of DPP-2ClTT,compared to that of IID-2ClTT,can be attributed to its good backbone planarity,highly packing ordered thin-film,and favourable thin-film morphology.
NETL
NSTL
万方数据
维普
