Handbook of Aggregation-Induced Emission, Volume 3. Группа авторов

rel="nofollow" href="#ulink_59c1bd6f-7ac2-5123-bb76-792597f0851a">Figure 2.3) with AIE and delayed fluorescence properties [22]. In a toluene solution, these molecules exhibited obvious mirror image CPL signals with |g_lum| in the range of 0.5–1.2 × 10⁻³. Besides, 26–29 were used as emitting layers in CP‐OLED devices, and exhibited external quantum efficiency up to 9.3 and 3.5% with dissymmetry electroluminescence factor (g_EL) as high as +0.026/−0.021 and +0.06/−0.06 for the doped film and the neat film, respectively.

Figure 2.3 Molecular structures of chiral AIEgens 26–29 [22].

In 2019, Ye et al. prepared a novel chiral AIEgen 30 through the incorporation of a chiral BINOL moiety and two TPE units via Suzuki reaction (Figure 2.4a) [23]. 30 exhibited a typical AIE feature and showed bright yellow luminescence in the aggregated state (Figure 2.4b). CPL spectra demonstrated that the enantiomers generated mirror image CPL signals centered at 532 nm in the aggregated state (f_w = 99%) with g_lum of −2.7 × 10⁻³ and +2.8 × 10⁻³ for R‐30 and S‐30, respectively. In the spin‐coated film, CPL was observed at 532 nm with higher g_lum of −3.2 × 10⁻³ and +3.6 × 10⁻³ for R‐30 and S‐30, respectively (Figure 2.4c). Besides, R‐30 and S‐30 were also used as CP‐OLED emitters for nondoped device and showed CPL centered at 534 nm with g_EL of −3.0 × 10⁻³ and +3.2 × 10⁻³.

Figure 2.4 (a) Molecular structure of chiral AIEgen enantiomers 30 and corresponding g_lum. (b) PL spectra of 30 in various THF/H₂O mixtures. (c) CPL spectra of R‐30 and S‐30 in spin‐coated films.

      Source: Reproduced with permission [23]. Copyright 2019, American Chemical Society.

In 2019, Chen et al. reported a novel AIEgen 31 (Figure 2.5) with unique mechanoluminescence activities, which was rarely found in AIE‐active enantiomers [24]. With the existence of point chirality, 31 exhibited intense CPL centered at 479 nm with g_lum of +3.4 × 10⁻³ and −3.7 × 10⁻³ for R‐31 and S‐31, respectively.

Figure 2.5 Molecular structures of chiral AIEgens R‐31 and S‐31 and corresponding g_lum [24].

In 2019, Cai and coworkers synthesized three chiral TPE‐modified sulfono‐ γ ‐AApeptides, and one of them, molecule 32, was shown in Figure 2.6a [25]. Crystal structures indicated the presence of a helical scaffold of these molecules in an aqueous solution due to hydrogen bonding, which probably rendered the restriction of intramolecular rotations of TPE units (Figure 2.6b–e). Following a well‐defined right‐handed helical scaffold, the luminescent TPE units were arranged in a helical fashion and exhibited CPL around 460 nm with g_lum up to +1.2 × 10⁻². Later in 2020, the same group synthesized several TPE‐sulfono‐ γ ‐AApeptides with a left‐handed helix [26]. They found these helical foldamers emitted strong luminescence both in solution and in the aggregated state and can generate CPL with g_lum up to +5.0 × 10⁻³.

Figure 2.6 (a) Molecular structure of chiral AIEgen 32 and corresponding g_lum. (b–e) Crystal structure of molecule 32.

      Source: Reproduced with [25]. Copyright 2019, American Chemical Society.

2.3 Macrocycles and Cages

      Most of the typical AIE‐active molecules such as TPE, hexaphenylsilole (HPS), and their derivatives possess propeller‐shaped structures. In solution, these AIE luminophores are generally achiral due to the rapid conformational switching via intramolecular rotation. In the aggregated state, the intramolecular rotation is restricted; however, the random distribution of P‐type and M‐type conformations can only lead to chiroptical silence. Consequently, it becomes a significant challenge to produce CPL directly from simple AIE luminophores.

In 2016, Zheng et al. reported a pair of TPE tetracycles (P‐33 and M‐33) with stable chirality in a dilute solution (Figure 2.7a) [27]. They prepared the tetracycles by intramolecular cyclization and successfully immobilized the propeller‐shaped conformation of the TPE unit. The helical configurations of the P and M enantiomers were found to be remarkably stable at room temperature and can be isolated by chiral high performance liquid chromatography (HPLC). Since the phenyl rings were fixed by the intramolecular linkers and thus prevented from rotation, the tetracycle showed strong luminescence even in solution. The quantum yield of 33 reached up to 97% in a THF solution and 80% in the aggregated state. Mirror image CD and CPL spectra (Figure 2.7b–d) were observed for the tetracycle enantiomers, with g_lum of −3.3 × 10⁻³ (505 nm) and +3.1 × 10⁻³ (505 nm) for P‐33 and M‐33, respectively, in a THF solution (Figure 2.7c), and −5.0 × 10⁻³ (500 nm) and +6.2 × 10⁻³ (500 nm), respectively, in the aggregated state (Figure 2.7d).

Figure 2.7 (a) Molecular structures of TPE tetracycle enantiomers P‐33 and M‐33 and