The Strategy for Molecular Design of Aggregation-Induced Emission Units Further Modified by Substitutes

Zhe Peng, Ying Chun Ji, Zihan Huang, Bin Tong, Jianbing Shi, Yuping Dong

Index: 10.1039/C8QM00096D

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Abstract

The Aggregation-induced emission (AIE) molecules with strong luminescence in aggregated states have attracted persistent attentions in recently years. Developing new structure AIE units and further modifying with functional groups to satisfy more specialized applications are important research fields. But the research works about molecular design associated with functional modification of AIE units are absence. 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 the electron-withdrawing groups on phenyl groups in 1,4-positions and electron-donating groups on the phenyl groups in 2,5-positions of pyrrolo[3,2-b]pyrrole core showed AIE characteristics. While the others showed aggregation-caused quenching (ACQ) characteristics. The absorption and photoluminescence (PL) emission spectra of the AIE compounds exhibited weak intramolecular charge transfer (ICT) absorption and possessed the largest Stokes shift, while the ACQ derivatives showed obvious ICT absorption. Desinity functional theoretical (DFT) calculation results suggested that HOMO and LUMO of the four AIE compounds were spatially isolated, which weakened the twisted intramolecular charge transfer (TICT) effect and minimized fluoscrence reabsorption in the aggregated states. Single crystal analysis also confirmed that the AIE properties could be realized by the suppression of both TICT effect and the close π···π interactions in the aggregated states. These results are beneficial to understand the relationship between molecular structure and AIE properties. The resulting structural information provides the basis for future rationalization of functional modification of AIE materials.