基于氟代异靛蓝并[7,6-g]异靛蓝的共轭聚合物的合成及其半导体性质

采用Stille缩聚,合成了3个异靛蓝并7,6-g]异靛蓝(DIID)和乙烯单元交替排列的共轭聚合物P0F、P2F和P4F,三者在DIID单元中分别含0、2和4个氟原子(F).3个聚合物均具有良好的平面性,前线分子轨道几乎在整个共轭骨架上离域.它们均具有宽的吸收光谱,吸收范围在400~1000 nm,光学带隙约为1.25 eV;随着氟原子数目的增加,聚合物的最高占有分子轨道(HOMO)和最低空分子轨道(LUMO)能级依次下降0.1~0.2 eV.以这3个聚合物作为活性层,制备了顶栅-底接触型有机场效应晶体管器件,随着氟原子数目的增加,聚合物的传输性质由双极传输变为n型传输.P0F和P2F是双极传输型聚合物,空穴迁移率(μ_h)分别达到0.11和0.30 cm~2 V~(-1) s~(-1),电子迁移率(me)分别达到0.22和1.19 cm~2 V~(-1) s~(-1).P4F是n型聚合物,me达到0.18 cm~2 V~(-1) s~(-1).

Synthesis and Semiconducting Properties of Conjugated Polymers Based on Fluorinated Isoindigo [7,6-g]isoindigo

Three alternating conjugated polymers of isoindigo7,6-g]isoindigo (DIID) and vinylene,i.e.,P0F,P2F and P4F,in which DIID units contain 0,2 and 4 fluorine (F) atoms,respectively,were synthesized via Stille polycondensation.The number-average molecular weights (Mn) were 3.94 × 104,4.45× 104 and 1.93× 104 for P0F,P2F and P4F,respectively.All these three polymers are largely planar and their frontier molecular orbitals are well-delocalized along conjugated backbones as revealed by density functional theory (DFT) calculation.Their 5 wt％ weight loss temperatures are above 360 ℃.They all have very broad absorption spectra in the range of 400 ～ 1000 nm and their optical band-gaps are ca.1.25 eV.With an increase of F atoms,both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels decreased,from-5.26 and-3.57 eV for P0F to-5.48 and-3.68 eV for P2F,and further to-5.62 and-3.82 eV for P4F.Thin films of the polymers were characterized by X-ray diffraction and atomic force microscopy (AFM).All these polymers formed ordered structure in their films with conjugated backbone adopting an edge-on arrangement.The portion of the ordered structure in the films increased from P0F to P4F,along with the increase in F-atoms in DIID unit.Top-gate and bottom-contact (TGBC) organic field-effect transistors (OFETs) of the polymers were fabricated with poly(methylmethacrylate) as dielectric via solution spin casting with o-dichlorobenzene.The device performance was measured under ambient conditions.With increasing the number of F atoms,the transfer behaviour of the devices based on the polymers changed from ambipolar to unipolar n-type.P0F and P2F were ambipolar polymers.Their hole mobility was 0.11 and 0.30 cm2V-1 S-1,respectively,and the electron mobility was 0.22 and 1.19 cm2 V-1 s-1,respectively.P4F was a typical unipolar n-type semiconductor and its electron mobility was up to 0.18 cm2V-1 s-1.The relatively lower mobility of P4F was attributed to its lower molecular weight.This study shows that DIID is a promising building block for conjugated polymers with high mobility and low band-gap.