Progress in research on side chain-controlled conjugated polymer semiconductor performance

[ Instrument Network Instrument Development ] In recent years, organic conjugated polymers have received extensive attention due to their excellent semiconductor properties and application prospects in many fields. Carrier mobility is an important parameter for the performance of organic semiconductors. Many research groups at home and abroad mainly adjust the electronic structure and aggregate structure of molecules by designing and synthesizing new conjugated molecules and polymers, thereby improving the carrier mobility. In recent years, the results show that the structure of the alkyl side chain in the conjugated molecule and the polymer not only improves the solubility of the conjugated molecule and the polymer, but also affects the ordering of the molecules (conjugated main chain). Affect the transmission performance of semiconductors.

Under the support of the Strategic Pilot Science and Technology Project B of the Chinese Academy of Sciences and the National Natural Science Foundation of China, Zhang Deqing, the key laboratory of organic solids of the Institute of Chemistry, Chinese Academy of Sciences, focused on the conjugated (high) molecular aggregate structure and current carrying of alkyl side chains. In-depth research has been carried out on the regulation of sub-transmission performance and the construction of new functions, and a series of research progress has been made. They successfully prepared "linear/branched" conjugated polymers by changing the alkyl side chain structure of DPP-based conjugated DA polymers. The mobility of the "straight chain/branched" conjugated polymer film was remarkably improved without changing the structure of the conjugated main chain, reaching 9.4 cm 2 V -1 s -1 (Chem. Mater. 2018, 30, 3090). They have enhanced the crystallinity and order of the aggregated film by introducing a urea group into the side chain of the alkyl group, and the carrier mobility is remarkably improved to 13.1 cm 2 V -1 s -1 (J. Am. Chem. Soc. 2016, 138, 173). Zhenan Bao, a professor at Stanford University, and Simon Rondeau-Gagné and Yuning Li, professors at the University of Windsor and Waterloo, used this strategy to introduce urea and amide groups into the alkyl side chain to increase the mobility and conjugate of the conjugated polymer film. The mechanical properties of polymers. Recently, they designed and synthesized a DPP conjugated polymer containing a thymine group. It is found that the introduction of thymine groups can not only improve the mobility of carriers, but also utilize the coordination of thymine groups with metal ions to successfully construct an organic field-effect transistor CO sensor with high sensitivity and high selectivity. (Chem. Mater. 2019, 31, 1800). In addition to hydrogen bonding groups, they also introduce other functional groups into the side chain, exploring new functions of organic field effect transistors. For example, they introduced the azobenzene group into the side chain of the polymer for the first time, and the photo-controlled bistable transistor device prepared by the same has the advantages of reversibility and stability, fast response, high mobility, etc. (Adv. Funct Mater. 2019, 29, 1807176).

They also found that the introduction of tetramethylammonium iodide molecules into the DPP conjugated polymer film can increase carrier mobility by nearly a factor of 10. Combined with theoretical analysis, they proposed a mechanism for increasing the mobility, that is, the introduction of ionic groups can inhibit the rotation of the alkyl side chain, thereby improving the order of the polymer chains and facilitating the transport of carriers (Sci. Adv. 2016, 2, e1600076). Recently, they introduced a photochromic hexaarylbisimidazole derivative into a p-type organic conjugated polymer film and used it as a semiconductor layer to construct an optical/thermally responsive organic thin film field effect transistor, and demonstrated the transistor. Application in constructing non-volatile memory devices. Hexaarylbisimidazole (HABI) is a class of photochromic molecules that are UV/heat reversible. They used a mixture of a nitro-substituted hexaaryl imidazole derivative (p-NO2-HABI) and a p-type conjugated polymer (PDPP4T) as a semiconductor layer and OTS-modified silica as an insulating layer to construct a bottom-gate contact. Organic thin film field effect transistor device. The experiment found that the transistor device has a highly sensitive response to ultraviolet light (365 nm), and the current change can reach 106 before and after illumination, and the state can be stabilized for a long time. By heating, the device current can be restored to the initial state. The on/off state of the electrical signal of the device can be achieved by multiple cycles of UV illumination/heating without significant signal loss (Adv. Mater. DOI: 10.1002/adma.201902576).

Based on advances in the study of conjugated (high) molecular alkyl side chain functionalization, they were invited to the subject of Modification of side-chains of conjugated molecules and polymers for charge mobility enhancement and sensing functionality in Acc. Chem. Res. A review paper was written (Acc. Chem. Res. 2018, 51, 1422). Recently, they were invited to summarize and discuss the research work on related conjugated (high) molecular alkyl side chains on Adv. Mater., and prospects for the study of alkyl side chain strategy to control the performance of organic semiconductors (Adv Mater. DOI: 10.1002/adma.201903104).