even no emission performance of luminophores in the aggregated state, the CPL
performance of most luminophores becomes even worse from isolate molecule
to aggregated state. Fortunately, Tang’s group advanced an excellent idea to solve
this problem by combined aggregation-induced emission (AIE) effect with chiral
assembly [25]. AIE luminophore incorporated with the chiral component to fabricate
novel CPL-active materials has become an efficient way to achieve both large g lum
values and high emission efficiency in condensed phase [26]. Cyano-substituted
stilbene (CNSB) is a well-known compound with AIE property. When CNSB
conjugated with a glutamic-derived gelaton, an AIE gelator was obtained (L-/D-8)
[27]. As shown in Fig. 11.8, the chiral donor (gelator 8) and achiral acceptor (BPEA)
could form a composite nanohelix through co-assembly, in which both energy and
chirality transfer were observed simultaneously. Amazingly, not only the chirality
transfer happened in the complex, but also the dissymmetry of CPL was significantly
amplified during the energy transfer. Thanks to the π–π stacking of CNSB and the
H-bond between the amide groups, an ordered nanohelix structure could be obtained
from gelator 8 through self-assembly. During the self-assembly process, not only
the emission intensity of 8 remarkably increased, but also the molecular level
chirality transferred to the supramolecular level, resulting in the excellent CPL
properties. When 8 co-assembled with achiral BPEA, the acceptor BPEA was
inserted into the nanohelix through the weak π–π stacking to form the co-gel
(Fig. 11.8a). Interestingly, the achiral acceptors could be endowed with CPL
caused by chirality transfer from the nanohelix. As shown in Fig. 11.8b, the detected
CPL g lum value was Æ1.2 Â 10
À3 by directly exciting the acceptor (at 400 nm),
while the g lum for the acceptor by exciting the donor (at 320 nm) showed a significant
enhancement (up to Æ3 Â 10
À3 ). This result exhibited that g lum value of CPL
was amplified more than 2.5 times through the energy-transfer process. This might
be resulted from the enhancement of acceptor emission via the energy transfer,
which seems to further amplify the g lum values.
Encouraged by the result of energy transfer amplified CPL, Liu et al.
further investigated a cooperative chirality and sequential energy transfer in a
supramolecular co-assembly system to explore its mechanism. In this work, a
cyanostilbene-appended glutamate gelator 9 and two kinds of achiral acceptors,
thioflavin T (ThT) and acridine orange (AO), were employed to from a co-gel
[28]. Similar to gelator 8, the chiral gelator 9 could form supramolecular nanotubes
with CPL activity. In addition, the supramolecular chirality could transfer to
these two achiral acceptors through co-assembly. Meantime, the excited-state energy
of 9 nanotubes could directly transfer to ThT but only be sequentially transferred
to AO. More interestingly, compared with CPL from directly exciting AO, a
stepwise amplified CPL could be observed when exciting the donor 9 or intermediate
donor ThT in the 9/ThT/AO ternary system (Fig. 11.9).
It should be noted that energy transfer boosted CPL was considerable, and a
possible analysis was proposed. When donor 9 nanotubes are excited by unpolarized
light, a CPL is obtained due to its intrinsic chirality. However, when acceptors
were added, the excited-state energy with chiral information will transfer to
acceptors, resulting in a new CPL from the acceptor. Based on a theoretical
258
T. Zhao et al.
performance of most luminophores becomes even worse from isolate molecule
to aggregated state. Fortunately, Tang’s group advanced an excellent idea to solve
this problem by combined aggregation-induced emission (AIE) effect with chiral
assembly [25]. AIE luminophore incorporated with the chiral component to fabricate
novel CPL-active materials has become an efficient way to achieve both large g lum
values and high emission efficiency in condensed phase [26]. Cyano-substituted
stilbene (CNSB) is a well-known compound with AIE property. When CNSB
conjugated with a glutamic-derived gelaton, an AIE gelator was obtained (L-/D-8)
[27]. As shown in Fig. 11.8, the chiral donor (gelator 8) and achiral acceptor (BPEA)
could form a composite nanohelix through co-assembly, in which both energy and
chirality transfer were observed simultaneously. Amazingly, not only the chirality
transfer happened in the complex, but also the dissymmetry of CPL was significantly
amplified during the energy transfer. Thanks to the π–π stacking of CNSB and the
H-bond between the amide groups, an ordered nanohelix structure could be obtained
from gelator 8 through self-assembly. During the self-assembly process, not only
the emission intensity of 8 remarkably increased, but also the molecular level
chirality transferred to the supramolecular level, resulting in the excellent CPL
properties. When 8 co-assembled with achiral BPEA, the acceptor BPEA was
inserted into the nanohelix through the weak π–π stacking to form the co-gel
(Fig. 11.8a). Interestingly, the achiral acceptors could be endowed with CPL
caused by chirality transfer from the nanohelix. As shown in Fig. 11.8b, the detected
CPL g lum value was Æ1.2 Â 10
À3 by directly exciting the acceptor (at 400 nm),
while the g lum for the acceptor by exciting the donor (at 320 nm) showed a significant
enhancement (up to Æ3 Â 10
À3 ). This result exhibited that g lum value of CPL
was amplified more than 2.5 times through the energy-transfer process. This might
be resulted from the enhancement of acceptor emission via the energy transfer,
which seems to further amplify the g lum values.
Encouraged by the result of energy transfer amplified CPL, Liu et al.
further investigated a cooperative chirality and sequential energy transfer in a
supramolecular co-assembly system to explore its mechanism. In this work, a
cyanostilbene-appended glutamate gelator 9 and two kinds of achiral acceptors,
thioflavin T (ThT) and acridine orange (AO), were employed to from a co-gel
[28]. Similar to gelator 8, the chiral gelator 9 could form supramolecular nanotubes
with CPL activity. In addition, the supramolecular chirality could transfer to
these two achiral acceptors through co-assembly. Meantime, the excited-state energy
of 9 nanotubes could directly transfer to ThT but only be sequentially transferred
to AO. More interestingly, compared with CPL from directly exciting AO, a
stepwise amplified CPL could be observed when exciting the donor 9 or intermediate
donor ThT in the 9/ThT/AO ternary system (Fig. 11.9).
It should be noted that energy transfer boosted CPL was considerable, and a
possible analysis was proposed. When donor 9 nanotubes are excited by unpolarized
light, a CPL is obtained due to its intrinsic chirality. However, when acceptors
were added, the excited-state energy with chiral information will transfer to
acceptors, resulting in a new CPL from the acceptor. Based on a theoretical
258
T. Zhao et al.