The isomeric chlorination of the conjugated side chain is an effective method to improve the photoelectronic properties of polymers, but has not been well investigated in electrochromic performance. Herein, two new D-A-D type isomeric monomers, EQx-α-Cl and EQx-β-Cl, based on 2,3-bis(5-chloro-4-(2-ethylhexyl)thioph-en-2-yl)-6,7-difluoro-5,8-di(thiophen-2-yl)quinoxaline (Qx-α-Cl) and 2,3-bis(4-chloro-5-(2-ethylhexyl)thiophen-2-yl)-6,7-difluoro-5,8-di(thiophen-2-yl)quinoxaline (Qx-β-Cl) as the acceptor units by the isomeric chlorination of the different position of the conjugated thiophene side chain were designed and synthesized. Then their D-A-D type polymers (PEQx-α-Cl and PEQx-β-Cl) were synthesized by electrochemical polymerization. EQx-α-Cl not only exhibits slight red-shifted absorption onset and much stronger absorption with molar extinction coefficient of 1.16 × 10⁵ M⁻¹ cm⁻¹ but also shows lower onset oxidation potential (E_onset) of 0.65 V compared with those of EQx-β-Cl (7.26 × 10⁴ M⁻¹ cm⁻¹ and 0.73 V). And PEQx-α-Cl displayed yellow green at neutral state and dark green at oxidation state, respectively, and showed much better electrochemical stability and electrochromic performance including the higher optical contrast 37.7 % and the CE value of 319 cm² C⁻¹ at 890 nm in comparison with PEQx-β-Cl, which was beneficial to design the electrochromic materials toward adaptive camouflage application. These results demonstrated that the isomeric chlorination strategy of conjugated side chain is a promising approach which may open up a new horizon for designing and synthesizing the high-performance electrochromic polymers.

中文翻译：

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基于喹喔啉的共轭噻吩侧链异构氯化反应设计高性能电致变色聚合物


共轭侧链的异构氯化是改善聚合物光电性能的有效方法，但在电致变色性能方面尚未得到很好的研究。本文以2,3-双（5-氯-4-（2-乙基己基）硫代-2-基）-6,7-二氟-5,8-二（噻吩-2-基）喹啉（Qx-α-Cl）和2,3-双（4-氯-5-（2-乙基己基）噻吩-2-基）-6,7-二氟-5,8-二（噻吩-2-基）喹啉（Qx-β-Cl）为受体单元为基础，通过共轭噻吩侧链不同位置的异构氯化反应，设计合成了两种新的D-A-D型异构体单体EQx-α-β Cl.然后，通过电化学聚合合成了它们的 D-A-D 型聚合物 （PEQx-α-Cl 和 PEQx-β-Cl）。EQx-α-Cl 不仅表现出轻微的红移吸收起始和更强的吸收，摩尔消光系数为 1.16 ×^{10 5 M-1 cm-1}，而且与 EQx-β-Cl 相比，其起始氧化电位（E_起始）较低，为 0.65 V（7.26 × 10^{4 M-1 cm-1} 和 0.73 V）。PEQx-α-Cl 在中性态和氧化态分别呈黄绿色和深绿色，与 PEQx-β-Cl 相比，电化学稳定性和电致变色性能明显提高，包括更高的光学对比度 37.7 % 和 890 nm 处 319 cm² C⁻¹ 的 CE 值，有利于设计面向自适应伪装应用的电致变色材料。 这些结果表明，共轭侧链的异构氯化策略是一种很有前途的方法，可能为设计和合成高性能电致变色聚合物开辟新的视野。