Imide-Functionalized Thiazole-Based Polymer Semiconductors: Synthesis, Structure–Property Correlations, Charge Carrier Polarity, and Thin-Film Transistor Performance
journal contributionposted on 09.10.2018, 00:00 authored by Yongqiang Shi, Han Guo, Minchao Qin, Yuxi Wang, Jiuyang Zhao, Huiliang Sun, Hang Wang, Yulun Wang, Xin Zhou, Antonio Facchetti, Xinhui Lu, Ming Zhou, Xugang Guo
Imide-functionalized arenes, exemplified by naphthalene diimides (NDIs), perylene diimides (PDIs), and bithiophene imides (BTIs), are the most promising building blocks for constructing high-performance n-type polymers. In order to reduce the steric hindrance associated with NDI- and PDI-based polymers and to address the high-lying LUMO issue of BTI-based polymers, herein a highly electron-deficient imide-functionalized bithiazole, N-alkyl-5,5′-bithiazole-4,4′-dicarboximide (BTzI), was successfully synthesized via an efficient C–H activation. Single crystal of BTzI model compound showed a planar backbone with close π-stacking distances (3.2–3.3 Å). The N,N′-bis(2-alkyl)-2,2′-bithiazolethienyl-4,4′,10,10′-tetracarboxdiimide (DTzTI) was also used for constructing polymer semiconductors. Compared to DTzTI, BTzI is more electron-deficient, rendering it highly appealing for enabling n-type polymers. On the basis of BTzI and DTzTI, a series of polymers, including acceptor–acceptor homopolymers, and donor–acceptor and donor–acceptor–acceptor copolymers, were synthesized, which feature different contents of acceptor units in polymeric backbones. As imide content increases, the polymer FMO levels were gradually lowered, yielding a transition of charge carrier from ambipolarity to unipolar n-type in organic thin-film transistors (OTFTs). The acceptor–acceptor homopolymer PBTzI possesses the deepest LUMO/HOMO level of −3.94/-6.17 eV, enabling minimal off-current (Ioff) of 10–10–10–11 A in OTFTs. The highest electron mobility of 1.61 cm2 V–1 s–1 accompanied by small Ioff of 10–10–10–11 A and high on-current/off-current ratio (Ion/Ioff) of 107–108 was achieved from OTFTs using PDTzTI homopolymer, showing the pronounced advantages of acceptor-acceptor homopolymer approach for developing unipolar n-type polymer semiconductors. The correlations between the FMO levels and the transistor performances underscore the significance of FMO tuning for enabling unipolar electron transport. The results demonstrate that imide-functionalized thiazoles are excellent units for constructing high-performance n-type polymers. Moreover, the synthetic routes to these highly electron-deficient imide-functionalized thiazoles and the polymer structure–property correlations developed here are informative for materials invention in organic electronics.
Read the peer-reviewed publication
acceptor-acceptor homopolymer approachunipolar n-type polymer semiconductorshigh-lying LUMO issueThin-Film Transistor Performance Imide-functionalized arenesn-type polymersBTzI model compoundBTINDIPDIOTFTImide-Functionalized Thiazole-Based Polymer SemiconductorsCharge Carrier Polarityimide content increaseselectron-deficient imide-functionalized thiazolespolymer FMO levelselectron-deficient imide-functionalized bithiazoleunipolar electron transport