title: Synthesis, Structural Characterization, and Field-Effect Transistor Properties of n-Channel Semiconducting Polymers Containing Five-Membered Heterocyclic Acceptors: Superiority of Thiadiazole Compared with Oxadiazole.
abstract: Five-membered 1,3,4-oxadiazole (OZ) and 1,3,4-thiadiazole (TZ) heterocycle-based copolymers as active layer have long been ignored in solution-processable n-channel polymer field-effect transistors (PFETs) despite the long history of using OZ or TZ derivatives as the electron-injecting materials in organic light-emitting devices and their favorable electron affinities. Herein, we first report the synthesis and PFETs performance of two n-channel conjugated polymers bearing OZ- or TZ-based acceptor moieties, i.e., PNOZ and PNTZ, where simple thiophene units are utilized as the weak donors and additional alkylated-naphthalenediimides units are used as the second acceptors. A comparative study has been performed to reveal the effect of different heterocyclic acceptors on thermal properties, electronic properties, ordering structures, and carrier transport performance of the target polymers. It is found that both polymers possess low-lying LUMO values below -4.0 eV, indicating high electron affinity for both heterocycle-based polymers. Because of strong polarizable ability of sulfur atom in TZ heterocycle, PNTZ exhibits a red shift in maximal absorption and stronger molecular aggregation even in the diluted chlorobenzene solution as compared to the OZ-containing PNOZ. Surface morphological study reveals that a nodule-like surface with a rough surface morphology is observed clearly for PNOZ films, whereas PNTZ films display highly uniform surface morphology with well interconnected fiber-like polycrystalline grains. Investigation of PFETs performance indicates that both polymers afford air-stable n-channel transport characteristics. The uniform morphological structure and compact π-π stacking endow PNTZ with a high electron mobility of 0.36 cm2V-1s-1, much higher than that of PNOZ (0.026 cm2V-1s-1). These results manifest the feasibility in improving electron-transporting property simply by tuning heteroatom substitutes in n-channel polymers; further demostrate that TZ derivatives possess much superior potential for developing high-performance n-channel polymers compared to OZ derivatives.
authors.affiliation: Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, and Key Laboratory of Advanced Functional Polymeric Materials of College of Hunan Province, College of Chemistry, Xiangtan University , Xiangtan 411105, P. R. China.
authors.forename: Huajie
authors.initials: H
authors.lastname: Chen
authors.affiliation: Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, and Key Laboratory of Advanced Functional Polymeric Materials of College of Hunan Province, College of Chemistry, Xiangtan University , Xiangtan 411105, P. R. China.
authors.forename: Zhaoxia
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Chinese Academy of Sciences , Beijing 100190, P. R. China.
authors.forename: Zhiyuan
authors.initials: Z
authors.lastname: Zhao
authors.affiliation: Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, and Key Laboratory of Advanced Functional Polymeric Materials of College of Hunan Province, College of Chemistry, Xiangtan University , Xiangtan 411105, P. R. China.
authors.forename: Liping
authors.initials: L
authors.lastname: Zheng
authors.affiliation: Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, and Key Laboratory of Advanced Functional Polymeric Materials of College of Hunan Province, College of Chemistry, Xiangtan University , Xiangtan 411105, P. R. China.
authors.forename: Songting
authors.initials: S
authors.lastname: Tan
authors.affiliation: Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, and Key Laboratory of Advanced Functional Polymeric Materials of College of Hunan Province, College of Chemistry, Xiangtan University , Xiangtan 411105, P. R. China.
authors.forename: Zhihong
authors.initials: Z
authors.lastname: Yin
authors.affiliation: Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, and Key Laboratory of Advanced Functional Polymeric Materials of College of Hunan Province, College of Chemistry, Xiangtan University , Xiangtan 411105, P. R. China.
authors.forename: Chunguang
authors.initials: C
authors.lastname: Zhu
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Chinese Academy of Sciences , Beijing 100190, P. R. China.
authors.forename: Yunqi
authors.initials: Y
authors.lastname: Liu
keywords: 1,3,4-oxadiazole; 1,3,4-thiadiazole; air-stable; high performance; n-channel field-effect transistors