This study is led by Prof. Dr. Xu-Min Cai (Nanjing Forestry University), Prof. Dr. Shenlin Huang (Nanjing Forestry University), Prof. Dr. Zheng Zhao (The Chinese University of Hong Kong, Shenzhen) and Prof. Dr. Ben Zhong Tang (The Chinese University of Hong Kong, Shenzhen). It is a significant task to develop more BioAIEgens. The researchers successfully synthesized Chromene derivatives with AIE characteristics in an aqueous micellar system. At the molecular level, the 6-substituted products exhibit a stronger red-shifted emission compared to the 7-substituted products. Density functional theory (DFT) calculations suggest that the 6-substituted products have stronger charge transfer (CT) effects and smaller band gaps than the 7-substituted products, resulting in more red-shifted emission. TDDFT calculations reveal that the 6-substituted products have quinone-like structures in their excited states, which restrict molecular motion, whereas the 7-substituted products have semi-quinone-like structures in their excited states, leading to more active molecular motion and comparatively weaker emission.
When in the solid state, the 6-substituted products still exhibit a stronger red-shifted emission compared to the 7-substituted products, indicating that the aggregate properties can be effectively modulated by regiostructure-dependent at the molecular level. However, unlike in the molecular level, the solid-state 6- and 7-substituted products exhibit blue-shifted emission, suggesting the crucial role of the aggregate structure in their photophysical properties. Additionally, CATB-6-OMe and CATB-6-Me show significant mechanochromic properties, with weakened and red-shifted emission observed after grinding the crystals, which is closely related to the crystallization-induced emission (CIE) effect. Grinding the crystals results in the disruption of the crystalline structure, leading to the formation of non-crystalline surfaces and the disruption of intermolecular interactions, resulting in more active intramolecular motion. The crystals undergo the Frank-Condon channel to excited states with smaller energy gaps and stronger non-radiative decay, resulting in red-shifted and weakened emission.
The two crystal structures of CATB-6-OMe (Cb and Cg) reveal that the sky-blue emissive crystals (Cb) display a helical propeller conformation. Such twisted conformation gives rise to intensive rigidifications with C-H···p and C-H···O interactions, restricting their molecular motions in the excited state and producing a quantum yield of 21.72%. Interestingly, when the benzyl moiety rotates to the tosyl group, a green emissive crystal (Cg) with dramatic torsion angle change can be obtained, providing another conformation with distinct spatial orientation. This unique conformation resulted in fewer intermolecular C-H···p and C-H···O interactions, leading to comparatively strong molecular motion and a lower QY (1.71%).
Imaging results confirm the successful use of Chromene derivatives for ER-specific imaging. Cell experiments also emphasize the potential of modulating the cell viability and imaging behaviors of these BioAIEgens by altering the substituents on the Chromene scaffold, providing more possibilities for exploring excellent BioAIEgens based on this system.
This study proposes a new strategy for constructing novel BioAIEgen scaffold structures through "in water" synthesis, providing insights for the development of new BioAIEgens.
