Design,Synthesis And Characterization Of N-Type Conjugated Polymers Based On Strong Electron-Deficient Units

n-Type conjugated polymers are a class of very important conjugated polymers due to their applications in complementary metal-oxide semiconductor(CMOS),organic solar cells,thermoelectric devices.However,the development of n-type conjugated polymers greatly lags behind their p-type counterparts.To realize n-type transport behavior,both low-lying the highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO)energy levels are necessary,which could block hole injection and stabilize electron transport,respectively.For donor-acceptor(D-A)type conjugated polymers,the A units play an important role in determining their HOMO and LUMO levels.In the current thesis,we chose strong electron-deficient A units,i.e,3,6-di(5-bromopyridin-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione(Py DPP),6,6'-7,7'-azaisoindigo(AIID),and 3,3'-(1,1,4,4-tetraoxidothieno[3,2-b]thiophene-2,5-diylidene)bis(6-bromo-indolin-2-one)(IDOTT),to construct n-type conjugated polymers,and the relationships between polymer structures and properties have been studied in detail.The main results are as below:1.Four D-A type conjugated polymers based on Py DPP,i.e.,PPy DPP1-4FBT,PPy DPP2-4FBT,PPy DPP1-4FTVT and PPy DPP2-4FTVT,were synthesized via direct arylation polycondensation(DArP).The low-lying HOMO and LUMO energy levels endow polymers n-type transport properties.The branching positions of alkyl side chains significantly influence the polymer thin-film ordering and?-?stacking distances.With removing the branching point away from the polymer backbone,the thin-film order was increased and the?-?stacking distance was decreased,which in turn enhanced the charge transport performance.Among these polymers,PPy DPP2-4FBT showed the highest electron mobility of 2.45 cm²V^-1s^-1.2.AIID based n-type conjugated polymer,PAIID-4FTVT,was synthesized via DArP.The inhibitory effect of 7,7?-diazaisoindigo on DArP stemmed from the coordination of N atom with catalyst resulted in low molecular weight PAIID-4FTVT.Using DMAc as co-solvent,this inhibitory effect could be suppressed effectively,thus significantly improve the molecular weight of PAIID-4FTVT.By using the condition of Pd(OAc)₂/Piv OH/K₂CO₃/toluene:DMAc(5:1,V:V),PAIID-4FTVT with M_n up to109.7 k Da,have been successfully synthesized.Organic thin-film transistors demonstrated that the electron mobility of PAIID-4FTVT was strongly molecular-weight dependent.The polymer with the highest M_n showed the best electron transport performance with an electron mobility of 0.25 cm²V^-1s^-1.3.A thienoquinoidal unit,IDOTT,with isatin as the end-groups and thienothiophenas the central core has been developed,and three D-A conjugated polymers PIDOTT-BT,PIDOTT-TT and PIDOTT-T were synthesized based on IDOTT.All three polymers showed low-lying HOMO and LUMO levels due to the strong electron-deficient nature of IDOTT.By comparing these three polymers with the reference polymer PIDOBT-TT,we found that the monomer angle has significantly influence on the curvature of polymer backbone,thereby influence the crystallinity of the polymer thin-film.Due to the larger monomer angle of IDOTT relative to IDOBT,the polymers based on IDOTT showed lower curvature of polymer backbone,which in turn led to more ordered thin-film and higher electron mobility.The highest electron mobility of up to 0.49 cm²V^-1s^-1 was obtained for OTFTs based on PIDOTT-BT.