An example of a three-component co-assembly for induced CPL is shown
in Fig. 11.14 [36]. Interestingly, the helix of Fmoc-Glu assembly could be
triggered by the achiral nucleobase (guanine (G) or adenine (A)). Furthermore, this
supramolecular chirality transferred to the achiral cationic dye ThT. It should
be noted that only the second achiral molecule is introduced; the co-assembly
of Fmoc-Glu and ThT exhibits helicity at the nanoscale level, finally leading to a
distinct CPL.
On the other hand, chiral confined spaces or environments can also endow achiral
components with chirality. Figure 11.15 shows a general approach to fabricate
CPL-active assembly nanotubes through loading achiral AIE luminophores
(AIEgens) [37]. As illustrated in Fig. 11.15a, the hexagonal nanotube structures
can be constructed by C 3 symmetric chiral gelators L-/D-14, and the intrinsic
chirality of the substituted glutamate moieties can transfer to the supramolecular
nanotubes during the self-assembly process. Furthermore, the achiral AIE
luminophores could be embedded into the confined nanotubes via co-assembly,
and achiral AIE dyes aggregated during the gelation process, which showed
enhanced fluorescence intensity (Fig. 11.15b) and distinct circularly polarized
luminescence by direct excitation. Meantime, the polarization of the CPL
is regulated by the supramolecular chirality of the nanotubes. As shown in
Fig. 11.15c, through simply altering the doped dyes, mirror-imaged CPL signals
from 425 to 595 nm, covering the full-color from blue via green and yellow
to orange-red color, can be tuned.
A proton-triggered CPL switch in a co-assembled gel system consisted of a chiral
gelator and an achiral fluorophore was showed in Fig. 11.16 [38]. A co-gel could be
formed by chiral gelator L-/D-15 and achiral perylene bisimide (PBI) in ethanol and
gelation-induced chirality of PBI was transferred from L-/D-15. Due to low luminescence efficiency of PBI, no CPL signal could be observed. However, after
exposing the co-gel to an acid atmosphere, significantly increased emission intensity
Fig. 11.14 Left: Schematic illustration of the achiral nucleobase-assisted helical self-assembly
based on the Fmoc-Glu and supramolecular chirality transfer from Fmoc-Glu to achiral ThT. Right:
CPL spectra of Fmoc-(L/D)-Glu/A/ThT. Reproduced with permission [36]. Copyright 2016, WileyVCH
266
T. Zhao et al.
in Fig. 11.14 [36]. Interestingly, the helix of Fmoc-Glu assembly could be
triggered by the achiral nucleobase (guanine (G) or adenine (A)). Furthermore, this
supramolecular chirality transferred to the achiral cationic dye ThT. It should
be noted that only the second achiral molecule is introduced; the co-assembly
of Fmoc-Glu and ThT exhibits helicity at the nanoscale level, finally leading to a
distinct CPL.
On the other hand, chiral confined spaces or environments can also endow achiral
components with chirality. Figure 11.15 shows a general approach to fabricate
CPL-active assembly nanotubes through loading achiral AIE luminophores
(AIEgens) [37]. As illustrated in Fig. 11.15a, the hexagonal nanotube structures
can be constructed by C 3 symmetric chiral gelators L-/D-14, and the intrinsic
chirality of the substituted glutamate moieties can transfer to the supramolecular
nanotubes during the self-assembly process. Furthermore, the achiral AIE
luminophores could be embedded into the confined nanotubes via co-assembly,
and achiral AIE dyes aggregated during the gelation process, which showed
enhanced fluorescence intensity (Fig. 11.15b) and distinct circularly polarized
luminescence by direct excitation. Meantime, the polarization of the CPL
is regulated by the supramolecular chirality of the nanotubes. As shown in
Fig. 11.15c, through simply altering the doped dyes, mirror-imaged CPL signals
from 425 to 595 nm, covering the full-color from blue via green and yellow
to orange-red color, can be tuned.
A proton-triggered CPL switch in a co-assembled gel system consisted of a chiral
gelator and an achiral fluorophore was showed in Fig. 11.16 [38]. A co-gel could be
formed by chiral gelator L-/D-15 and achiral perylene bisimide (PBI) in ethanol and
gelation-induced chirality of PBI was transferred from L-/D-15. Due to low luminescence efficiency of PBI, no CPL signal could be observed. However, after
exposing the co-gel to an acid atmosphere, significantly increased emission intensity
Fig. 11.14 Left: Schematic illustration of the achiral nucleobase-assisted helical self-assembly
based on the Fmoc-Glu and supramolecular chirality transfer from Fmoc-Glu to achiral ThT. Right:
CPL spectra of Fmoc-(L/D)-Glu/A/ThT. Reproduced with permission [36]. Copyright 2016, WileyVCH
266
T. Zhao et al.