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

moiety. Due to the existence of two FRET pairs, deep‐red luminescence with large Stokes shifts was observed. In addition, the g_lum reached up to ±2.0 × 10⁻³ (around 650 nm) in the aggregated state (f_w = 99%).

Figure 2.26 Molecular structures of AIE‐active three‐component chiral conjugated polymers 76–80 and AIE‐active four‐component chiral conjugated polymers 81–82 and the corresponding g_lum [61, 62].

In 2018, Chen’s group synthesized a pair of conjugated polymers P‐83 and M‐83 with the TPE units and the chiral helical aromatic esters immobilized in the main chain (Figure 2.27) [63]. According to PL spectra, polymer 83 possessed a typical AIE feature with enhanced luminescence in the aggregated state. In THF solution, polymer 83 was CPL‐inactive. Upon mixing with water, AICPL centered at 500 nm was observed with g_lum of ±8.3 × 10⁻⁴.

Figure 2.27 (a) Molecular structures of AIE‐active chiral conjugated polymers P‐83 and M‐83 and corresponding g_lum. (b) PL, (c) CD spectra, and (d) CPL spectra of polymer 83 in various THF/H₂O mixtures.

      Source: Reproduced with permission [63]. Copyright 2018, The Royal Society of Chemistry.

In 2018, Tang’s group prepared an AIE‐active chiral polymer 84 by connecting alanine‐containing pendants and TPE units together via Cu(I)‐catalyzed click polymerization (Figure 2.28) [64]. In a dilute THF solution, the polymer exhibited weak CD and no apparent CPL signals. In the cast film, intense CPL around 500 nm was observed with g_lum of +4.5 × 10⁻³.

Figure 2.28 (a) Molecular structure of chiral conjugated polymer 84 and corresponding g_lum. (b) PL and CPL spectra of polymer 84 in a cast film.

      Source: Reproduced with permission [64]. Copyright 2018, The Royal Society of Chemistry.

2.7 Liquid Crystals

      CPL‐active liquid crystal (LC) systems based on AIEgens were also investigated. The helical orientation of the LC molecules appears to be critical for the CPL performance. Both helical stacking of chiral AIEgens and doping achiral AIEgens in chiral nematic LCs can generate CPL.

In 2015, Lu et al. prepared a novel AIE‐active chiral LC molecule 85 by introducing two cholesterol pendants into a TPE unit with long alkyl chains (Figure 2.29) [65]. With a flexible molecular structure, molecule 85 formed a cholesteric LC and exhibited temperature‐dependent chiroptical properties. The resulting LC showed a prominent CPL performance with g_lum of +2.5 × 10⁻² (483 nm) at 20 °C, and declined to +7.5 × 10⁻³ (480 nm) at 40–50 °C. Above 60 °C, the mixture was almost CPL‐inactive. The temperature‐sensitive CPL was consistent with the trend of CD signals. The fact that the CD and CPL signals changed with temperature was presumably due to the variations of the helical pitch of the cholesteric phase. Polarizing optical microscopy images further proved the hypothesis. In 2019, Yang et al. prepared two LC molecules by modifying a TPE unit with four cholesteric‐derived side chains [66]. Through ordered columnar self‐assembly, these molecules formed a liquid crystalline mesophase and generate CPL with g_lum up to +8.8 × 10⁻² (491 nm).

Figure 2.29 (a) Molecular structure of 85 and corresponding g_lum. (b) Schematic illustration of temperature‐dependent CPL. (c–g) Polarizing optical microscopy images of 85 at different temperatures: (c) 20 °C, (d) 50 °C, (e) 60 °C, (f) 75 °C, and (g) 90 °C, scale bar: 200 μm. (h–k) CPL spectra of 85 at different temperatures: (h) 20 °C, (i) 40 °C, (j) 50 °C, and (k) 60 °C. (l) g_lum factor vs. wavelength plot at different temperature.

      Source: Reproduced with permission [65]. Copyright 2015, The Royal Society of Chemistry.

In 2016, Tang et al. reported a CPL‐active system with achiral TPE‐derived molecule 86 (Figure 2.30) doped in a chiral nematic liquid crystal (N*LC) [67]. The resulting LC favored the fabrication of a display with |g_lum| as high as 0.4.

Figure 2.30 Molecular structure of achiral AIEgen 86 [66].

In 2018, Cheng et al. prepared an achiral emissive nematic liquid crystal by doping BINOL‐derived AIEgen enantiomers R/S‐87 into a common achiral nematic liquid crystal (N‐LC E7) (Figure 2.31) [68]. The products exhibited AICPL centered at 536 nm with high |g_lum| up to 0.41. Later in 2019, the same group reported a subsequent work on a three‐component chiral nematic liquid crystal system (Figure 2.32) [69]. As shown in Figure 2.32c, an achiral nematic liquid crystal was used as the host, and then doped with chiral BINOL‐derived dopant R/S‐88 and achiral AIEgens 89–92. The resulting chiral nematic liquid crystals showed strong CPL with |g_lum| in the range of 0.97–1.42 (505–610 nm). In 2019, Duan et al. also reported a doped chiral LC system with |g_lum| up to 0.27 [70]. Recently, Cheng et al. prepared two D–A type chiral AIEgens and prepared chiral nematic liquid crystals with strong CPL around 550 nm with g_lum of ±0.37 [71].

Figure 2.31 (a)