Synthesis And Properties Of D-A Copolymers Used Benzothiophene Derivatives As Electron Donor

D-A copolymer is a conjugated copolymer that has electron donor(D)unit and electron acceptor(A)unit in the main chain.It has strong intramolecular charge transfer(ICT)capability due to the special bipolar structure,is therefore widely used in the polymer solar cells and field effect transistors.The benzothiophene structure has high degree of conjugation flatness and strong electron donating ability,while the benzodipyrrolidone structure has high degree of conjugation,flatness and strong electron accepting ability,both of which are expected to build D-A conjugated copolymers.In this dissertation,three benzothiophene monomers were designed and synthesized,which were used as donor units to copolymerize with two benzodipyrrolidone monomers by Stille polycondensation.A series of D-A copolymers were prepared to study the influences of side chain modification,degree of conjugation and bridging groups on the photophysical and electrochemical properties of the copolymers.1.Dithienobenzodithiophene(DTBDT)molecule was designed and synthesized,and its side chain was modified by alkoxy and alkylthiophene to obtain monomers DTBDT(OR)and DTBDT(TR).Then thiophene and benzene were used to modify the benzodipyrrolidone(BDP)molecules to obtain monomers BDPT and BDPP.Four D-A copolymers PDTBDT(OR)-BDPT,PDTBDT(TR)-BDPT,PDTBDT(OR)-BDPP and PDTBDT(TR)-BDPP were obtained by Stille polycondensation from these monomers,and the relationship between polymer structures and performances was discussed.Four copolymers show good thermal stability,the thermal decomposition temperatures are 320 ℃,360 ℃,280 ℃ and 320 ℃,respectively.The absorption ranges of the four polymers in the thin film state are 300~1150 nm,300~1200 nm,300~900 nm,and 300~1000 nm,respectively.According to the ultraviolet spectrums in the thin film state,the optical energy gaps are 1.23 eV,1.19 eV,1.56 eV and 1.42 eV,respectively.PDTBDT(TR)-BDPT has the widest absorption range and the lowest optical band gap,indicating that the thiophene π-bridge and alkylthiophene side chain can effectively increase the spectral absorption range and reduce the optical energy gap.The electrochemical energy gaps of the four polymers are 1.41 eV,1.38 eV,1.67 eV and 1.63 eV,respectively.The electrochemical energy gap of PDTBDT(TR)-BDPT is lowest,indicating that the thiophene π-bridge and alkylthiophene side chain can reduce the electrochemical energy.Thiophene has stronger electron donating ability than that of benzene,and thiophene π-bridge can improve the coplanarity of copolymers,these factors are beneficial to intramolecular charge transfer,thereby increasing the absorption range and reduce the energy gap.Alkylthiophene side chain can extend the degree of conjugation of the copolymers compared to alkoxy side chains,thereby reduce the energy gap.2.Benzotrithiophene(BTT)molecule was designed and synthesized,it was modified by thiophene derivatives to obtain monomer BTT(T).Then thiophene and benzene were used to modify the benzodipyrrolidone(BDP)molecules to obtain monomers BDPT and BDPP.Two D-A copolymers PBTT(T)-BDPT and PBTT(T)-BDPP were obtained by Stille polycondensation from these monomers,and the relationship between polymer structures and performances was discussed.Both polymers show good thermal stability,the thermal decomposition temperatures are 380 ℃ and 335 ℃,respectively.The absorption ranges of the two polymers in the thin film state are 300~1200 nm and 300~900 nm,respectively.According to the ultraviolet spectrums in the thin film state,the optical energy gaps are 1.11 eV and 1.57 eV,respectively.Compared with BTT-based polymers,it was proved that extending the degree of conjugation can reduce the optical energy gap and electrochemical energy gap.