Aggregation-induced emission (AIE) molecules with strong luminescence in aggregated states have attracted persistent attention in recent years. The development of new structures of AIE units and their further modification with functional groups to satisfy more specialized applications are important research fields. However, studies on the molecular design associated with the functional modification of AIE units have not been reported to date. Herein, we designed and synthesized 13 aryl-substituted pyrrolo[3,2-b]pyrrole derivatives. Among these compounds, DPP-1CN, DPP-1MF, DPP-1MF-2Me, and DPP-1MF-2IP with electron-withdrawing groups on the phenyl groups at the 1,4-positions and electron-donating groups on the phenyl groups at the 2,5-positions of pyrrolo[3,2-b]pyrrole core showed AIE characteristics, whereas others showed aggregation-caused quenching (ACQ) characteristics. The absorption and photoluminescence (PL) emission spectra indicated that the AIE compounds exhibited weak intramolecular charge transfer (ICT) absorption and possessed large Stokes shifts, whereas the ACQ derivatives showed obvious ICT absorption. Density functional theory (DFT) calculation results suggested that the HOMOs and LUMOs of the four AIE compounds were spatially isolated that weakened the twisted intramolecular charge transfer (TICT) effect and minimized fluorescence reabsorption in the aggregated states. Single-crystal analysis also confirmed that AIE properties could be realized by the suppression of both the TICT effect and the close π⋯π interactions in the aggregated state. These results are beneficial for understanding the relationship between molecular structure and AIE properties. The resulting structural information provides the basis for the future rationalization of functional modification of the AIE materials.

中文翻译：

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一种用于被取代基进一步改性聚合诱导的发光单元的分子设计策略†

近年来，在聚集状态中具有强发光的聚集诱导发射（AIE）分子引起了持续的关注。重要的研究领域是开发AIE单元的新结构并对其进行官能团的进一步修饰以满足更专业的应用。然而，迄今为止尚未报道与AIE单元的功能修饰相关的分子设计的研究。在这里，我们设计并合成了13个芳基取代的吡咯并[3,2- b ]吡咯衍生物。在这些化合物中，DPP-1CN，DPP-1MF，DPP-1MF-2Me和DPP-1MF-2IP在吡咯并[3,2- b]吡咯核表现出AIE特征，而其他表现出聚集引起的猝灭（ACQ）特征。吸收和光致发光（PL）发射光谱表明，AIE化合物显示出较弱的分子内电荷转移（ICT）吸收和较大的斯托克斯位移，而ACQ衍生物则显示出明显的ICT吸收。密度泛函理论（DFT）的计算结果表明，四种AIE化合物的HOMO和LUMO在空间上是隔离的，从而减弱了扭曲的分子内电荷转移（TICT）效应，并使聚集态的荧光重吸收最小化。单晶分析还证实，通过抑制TICT效应和在聚集状态下紧密的π⋯π相互作用，可以实现AIE特性。这些结果对于理解分子结构和AIE性质之间的关系是有益的。由此产生的结构信息为将来对AIE材料的功能修改进行合理化提供了基础。