Twisted Donor−π–Acceptor Carbazole Luminophores with Substituent-Dependent Properties of Aggregated Behavior (Aggregation-Caused Quenching to Aggregation-Enhanced Emission) and Mechanoresponsive Luminescence
2018-08-09T00:00:00Z (GMT) by
To get insight on how the donor (D)/acceptor (A) substitutions and their substitution pattern affect optical properties in solution and in the solid state, four novel carbazole derivatives C1–C4 with different terminal groups (N(CH3)2, H, Br, and CN) have been employed. Their single-crystal X-ray structures confirm that the twisted structures, intermolecular interactions, and loose molecular packing are functions of the terminal groups. Interestingly, they displayed substituent-dependent aggregation-induced behaviors and mechanochromic (MC) properties. C1 showed aggregation-caused quenching because of the strong intermolecular π–π interaction, whereas C2, C3, and C4 exhibit strong aggregation-enhanced emission characteristics, which contributed to the formation of J-aggregates. Different twisted conformations and molecular arrangements induce different mechanostimuli response behaviors for C1–C4 between green-yellow to red color along with large red-shifts of 63, 30, 56, and 49 nm, respectively. C1, C3, and C4 displayed obvious MC characteristics, but C2 displayed irreversible mechanostimulus behavior. Powder X-ray diffraction and single-crystal X-ray analysis revealed that planarization of the twisted structure extended the π-conjugation and the destruction of the crystalline structure accounted for the tuned solid-state fluorescence.