Dual-emission organic materials with aggregation-induced emission (AIE) and aggregation-induced quenching (ACQ) effects are rarely reported in the literature, and multicolor fluorescence emission can be achieved by regulating the aggregation degree of these organic molecules. Professor Du Pingwu of the University of Science and Technology of China (USTC) has synthesized the first chiral bicyclic molecule with aggregate tunable double emission properties, and in collaboration with Professor Yang Shangfeng's group, enhanced the circularly polarized luminescence properties (CPL) through the AIE effect. The research results were recently published in the international academic journal Nature Communications as "An unexpected dual-emissive luminogen with tunable aggregation-induced emission. and enhanced chiroptical property "(Nat.Commun.2022,13,3543).

The aggregation-induced emission phenomenon has great potential applications in biological probes, chemical sensors and photoelectric materials. In many traditional systems, ACQ emitters usually emit strong light in solution, but encounter different degrees of quenching effect caused by aggregation. Compared to typical ACQ molecules, AIE luminaires (FIG. 1a) have a significant advantage in the aggregated state. However, few materials with both AIE and ACQ effects have been reported in the literature. Solution and aggregated double-emission materials can completely fill the gap between ACQ and AIE materials, providing many potential applications, such as aggregatively tunable multicolor fluorescence emission and single molecule white light emission can be used to prepare light-emitting devices. In addition, for CPL active chiral molecules, AIE effect can make them obtain enhanced circular polarization luminescence properties in the aggregated state.

Figure 1. a) Example of a traditional AIE emitter; b) Chiral bicyclic molecules with tunable dual emission properties (SCPP [8]).

Recently, based on the previous work on conjugated conjoined double rings (Angew.chem.in.ed.2021, 60, 17368-17372), the collaborative research team has fixed 1,2,4, 5-tetraphenylbenzene with AIE activity with p-phenylene units. The first chiral organic bicyclic molecule with aggregate tunable double emission properties, called SCPP[8], was successfully synthesized (FIG. 1b). The fluorescence of SCPP[8] was studied in tetrahydrofuran and water mixtures containing different water volumes (FWS). SCPP[8] can emit blue-blue fluorescence in solution and red fluorescence in the aggregated state, which has a redshift of up to 102nm compared to the dilute solution (FIG. 2a). More importantly, multicolor fluorescence emission of cyan-white-red can be achieved by regulating the aggregation degree of SCPP[8], and near-white light emission of a single molecule can be achieved with CIE coordinates of about (0.33, 0.37)(FIG. 2b-c). SCPP[8] has a novel non-racemic chiral structure. Two chiral isomers (M)/(P)-SCPP[8] were separated by an efficiency liquid chromatograph, and the excellent stability of its configuration was confirmed by variable temperature circular dichroism (FIG. 2d). In addition, the circularly polarized luminescence properties of the two chiral isomers in the aggregated state and in solution were measured by circular polarization fluorescence spectrometer, confirming that the CPL properties of (M)/(P)-SCPP[8] can be enhanced by AIE effect (FIG. 2e).

Figure 2. (a) Fluorescence spectra of SCPP[8] in a mixture of tetrahydrofuran and water; (b)CIE chromaticity diagram; (c) Multi-colour fluorescence emission photographs; (d) variable-temperature circular dichrogram; (e) CPL diagram of SCPP[8] in solution and aggregation.

(Hefei National Research Center for Microscale Matter Science, College of Chemistry and Materials Science, Key Laboratory of Energy Conversion, Collaborative Innovation Center for Energy Materials Chemistry, Department of Scientific Research, Chinese Academy of Sciences)

Source: China University of Science and Technology News