Synthesis of low-bandgap small molecules by extending the π-conjugation of the termini in quinoidal compounds,Journal of Materials Chemistry C

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Synthesis of low-bandgap small molecules by extending the π-conjugation of the termini in quinoidal compounds
Journal of Materials Chemistry C ( IF 5.7 ) Pub Date : 2021-1-11 , DOI: 10.1039/d0tc04962j
Cheng Wang _{1,

2,

3,

4} , Tian Du _{1,

2,

3,

4} , Ziqi Liang _{1,

2,

3,

4} , Jiangyu Zhu _{1,

2,

3,

4} , Jie Ren _{1,

2,

3,

4} , Yunfeng Deng _{1,

2,

3,

4}

Affiliation

Low-bandgap π-conjugated small molecules have multiple applications. However, it is still a big challenge to develop such materials because of the scarcity of effective synthetic strategies. In this study, we adopt a feasible strategy, by extending the π-conjugation of the termini in quinoidal compounds, to construct low-bandgap π-conjugated small molecules. With this strategy, we synthesized four indandione-terminated quinoidal compounds, i.e., QIDT-H, QIDT-4F, QSiIDT-H and QSiIDT-4F. Owing to their closed-shell structures, which were confirmed by X-ray crystallographic analysis and ¹H NMR spectroscopy, these compounds showed good air stability. Absorption spectroscopy revealed that the terminal benzene rings effectively extended the π-conjugation of these compounds and endowed them with a low bandgap. QIDT-H and QSiIDT-H showed similar bandgaps of ∼1.23 eV, which was smaller than that of a dicyanomethylene-terminated analogue (1.38 eV). Introducing fluorine atoms on the terminal benzene rings further reduced the bandgap, thus QIDT-4F and QSiIDT-4F showed very small bandgaps of 1.06 and 0.91 eV, respectively. These values are among the lowest reported to date for small molecules. The lowest unoccupied molecular orbital energy levels of these compounds were below −4.0 eV, giving them good electron-transport characteristics in organic thin-film transistors. Our findings demonstrate that extending the π-conjugation of the termini in quinoidal compounds is an effective strategy for developing low-bandgap π-conjugated small molecules.

中文翻译：

通过扩展喹啉化合物中末端的π共轭来合成低带隙小分子

低带隙π共轭小分子具有多种应用。但是，由于缺乏有效的合成策略，开发这类材料仍然是一个巨大的挑战。在这项研究中，我们采取可行的策略，通过扩展喹啉化合物中末端的π-共轭来构建低带隙π-共轭小分子。与此策略，我们合成了4种茚满二酮封端的醌型化合物，即，QIDT-H ，QIDT-4F，QSiIDT-H和QSiIDT-4F。由于其闭壳结构，通过X射线晶体学分析和¹1 H NMR光谱显示，这些化合物显示出良好的空气稳定性。吸收光谱表明，末端苯环有效地扩展了这些化合物的π-共轭，并赋予它们低的带隙。QIDT-H和QSiIDT-H显示出相似的〜1.23 eV的带隙，小于双氰基亚甲基封端的类似物（1.38 eV）。在末端苯环上引入氟原子进一步降低了带隙，因此QIDT-4F和QSiIDT-4F显示出非常小的带隙，分别为1.06和0.91 eV。这些值是迄今为止报道的小分子中最低的值。这些化合物的最低未占据分子轨道能级低于-4.0 eV，使其在有机薄膜晶体管中具有良好的电子传输特性。我们的发现表明，延长喹啉化合物中末端的π共轭作用是开发低带隙π共轭小分子的有效策略。

更新日期：2021-01-18

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