Synthesis And Charge Transport Properties Of DPP And ?G-Based Conjugated Polymers

Polymeric semiconductor materials, compared with inorganic semiconductor materials, have a great potential applications in constructing low-cost, large-area and mechanically flexible electronic devices, owing to their unique advantages of lightweight, solution processing, good flexibility, easy purification, and so on. The molecular structure of polymers is closely related to solubility, film forming and the stacking mode of materials, which has a crucial influence on device performance. This paper aims at exploring the structure-property relationships of polymers with excellent OFET performance reported in the literatures, on this basis, rationally designing and synthesizing polymers with the desired device performance for OFETs:1. In order to further understand the influence of extending ?-unsubstituted oligothiophene conjugation chain on the device performance, we prepared four D-A conjugated polymers with long conjugated chains, diketopyrrolopyrrole (DPP) was used as acceptor unit, and ?-unsubstituted oligothiophene units were used as donor units. The target polymers were purified by Soxhlet extraction using different solvents. The basic photophysical and electrochemiscal properties of polymers (chlorobenzene fraction) were characterized by thermal gravimetric analysis (TGA), UV-vis absorption spectra and cyclic voltammetry (CV). The results showed that these polymers had narrow optical bandgap and low HOMO/LUMO energy levels, introducing of stronger electron donor would result in blue shift of maximum absorption wavelengths and increment of the HOMO/LUMO energy levels.2. In order to investigate the effect of different materials-design methodology on device performance, we synthesized two polymers PIIG-BTz (A-A'type) and PIIG-TzTz (D-A1-D-A2 type) by polymerization of 2,2'-bithiazole (acceptor unit) and 2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole (donor-acceptor unit) with isoindigo (acceptor unit), respectively, the target polymers were purified by Soxhlet extraction using different solvents. The photophysical and electrochemical properties of PIIG-BTz-dcb (dichlorobenzene fraction) and PIIG-TzTz-cb (chlorobenzene fraction) as well as OFET performance of PIIG-BTz-dcb were measured systematically. The results indicated the two polymers have low LUMO energy levels due to the increasing of electron-withdrawing groups, PIIG-BTz showed balanced ambipolar charge transport properties, the maximum hole and electron mobilities were up to 0.030 and 0.022 cm2V-1s-1, respectively, annealed at 150?.3. In order to investigate the influence of more electron-acceptor units on device performance, we synthesized three D-A conjugated polymers by using pyridine-capped DPP as the acceptor unit,2,3-di(thiophen-2-yl)acrylonitrile,1,2-di(thiophen-2-yl)ethene and 2,2'-bithiophene as donor units. Meanwhile, a novel D-A1-D-A2 polymer (PDBPyDT2FBT) was also prepared in which pyridine-capped DPP, 5,6-difluorobenzo[c][1,2,5]thiadiazole and thiophene are used as A1, A2 and D unit, respectively, four target polymers were obtained by Soxhlet extraction using chloroform. The basic photophysical and electrochemical properties of four polymers as well as OFET performance of PDBPyDT2FBT were measured systematically, the results showed that introducting electron-withdrawing moieties into main chains would lower the HOMO/LUMO levels. PDBPyDT2FBT exhibited high-performance ambipolar charge transport characterization at low annealing temperatures due to the extendence of conjugated main chain, the maximum electron and hole mobilities were up to 0.65 and 0.24 cm2V-1s-1, respectively.4. Considering D-A1-D-A2 polymers maybe potential ambipolar charge transport properties, we synthesized a novel D-A1-D-A2 polymer in which DPP, 1,2-di(pyrazin-2-yl)diazene and thiophene are used as A1, A2 and D unit, respectively, the target polymer were obtained by Soxhlet extraction using chlorobenzene. The photophysical and electrochemical properties of the polymer was characterized, the result indicated the polymer had narrow optical band gap and low HOMO/LUMO levels, which implied that the polymer may have stable hole and electron transport properties.5. In order to enhance the solubility of polymer semiconductor materials, we constructed a D-A conjugated polymer (PBMDPP-co-TT) using DPP with alkoxy chain as acceptor unit, thiophene and thiophthene as donor unit, as a comparison, we also synthesized a similar polymer (PBDPP-co-TT) with hydrocarbon chains, the two target production was purified by Soxhlet extraction. The basic photophysical and electrochemical properties were characterized, it was found that two polymers have both narrow optical bandgap and low HOMO/LUMO energy levels, the substituting the hydrocarbon chains with the alkoxy chains at the nitrogen atoms of DPP unit was expected to lower the maximum absorption wavelength and the HOMO/LUMO energy levels.