The Synthesis And Characterization Of Two Novel Donor-Acceptor Oligothiophene Derivatires

Oligothiophene derivatives have excellent photoelectric properties and good environmental stability.They are kinds of organic semiconductor materials,which have potential applications in those semiconductor devices such as organic solar cells(OPVs),organic field effect transistors(OFETs)and organic light emitting diodes(OLEDs).If the donor-acceptor structure was introduced into oligothiophene derivatives,it would be effective to promote the charge transfer between the electron-donating unit and the electron-accepting unit in molecules,and control the orbital energy level.In this paper,two novel donor-acceptor oligothiophene derivatives were designed and synthesized by using dibenzothiophene-S,S-dioxide as the acceptor units.Moreover,their structures,physical and chemical properties were investigated using infrared absorption spectroscopy(IR),nuclear magnetic resonance(1H NMR),mass(MS),ultraviolet-visible(UV-vis)absorption,photoluminescence(PL),cyclic voltammetry(CV),thermogravimetric analysis and so on.The specific contents and results are as follows:(1)3,7-bis(5'-hexyl-2,2'-bithiophen-5-y1)dibenzo[b,d]thiophene-S,S-dioxide(37HBTDBTSO),a novel oligothiophene derivative with dibenzothiophene-S,S-dioxide core and hexyldithienyl end-capped unites,forming a new D-A-D type,had been designed and synthesized by lithiation,stannylation and Stille cross-coupling reaction when thiophene was used as a starting material.The solid of 37HBTDBTSO had good solubility in dichloromethane,chloroform,tetrahydrofuran and other organic solvents.UV-vis absorption spectroscopy and PL spectroscopy of 37HBTDBTSO in films had a larger chemical shift than in solution.This indicated that there were strong ?-? interactions between neighboring molecules in solid state.The molecular orbital level of 37HBTDBTSO was measured by CV.It had been found that 37HBTDBTSO had a highest occupied molecular orbital(HOMO)level of-5.63 eV,a lowest unoccupied molecular orbital(LUMO)level of-3.30 eV.Its energy gap was 2.33 eV,which was similar to the optical energy gap of 2.48 eV measured by ultraviolet-visible(UV-vis)absorption spectroscopy.The thermogravimetric analysis showed that 37HBTDBTSO had good thermal stability and its onset of thermal decomposition temperature was higher than 430 ?.(2)The other novel oligothiophene derivative had been designed and synthesized by using bromination,oxidation,reduction and Stille cross-coupling reaction.It is 2,6-(7-(5'-hexyl-[2,2'-bithiophen]-5-y1)-S,S-dioxidodibenzo[b,d]thiophen-3-y1)-4,8-bis((2-ethyl-hexyl)oxy)benzo[1,2-b:4,5-b']dithiophen-2-y1)(HBTBDTDBTSO)with dibenzo thiophene-S,S-dioxide core,hexyl dithienyl end-capped unites and two dibenzothiophene-S,S-dioxide intermediaries,forming a new D-A-D-A-D type.Compared to 37HBTDBTSO,the oligomer HBTBDTDBTSO had a larger conjugated chain,resulting in a narrower optical bandgap(2.25 eV).HBTBDTDBTSO had a HOMO level of-5.51 eV and a LUMO level of-3.22 eV.It had good thermal stability,and its thermal decomposition temperature was higher than 450?.There were some ?-? interactions between neighboring molecules in the solid state.In addition,the solid state was in a layered arrangement under optical microscope,indicating that the oligomer HBTBDTDBTSO had an ordered ?-? stack.(3)Two novel oligothiophene derivatives both had moderate bandgaps and energy levels,and there were some ?-? interactions between molecules.At the same time,they had good thermal stability and good solubility.They are expected to be used in the preparation of organic thin film field effect transistors and organic solar cells as new materials.