intermolecular H-bond was stronger than π–π stacking interaction. Thus, the
anthracene chromophores formed twisted stacks with partially overlapped excimer.
At 25
C, the main driving force was π–π stacking for self-assembly. Thus, a
Sandwich-type excimer was formed by the anthracene fluorophores in the
excited state (Fig. 11.5a). Meanwhile, the obtained gel from gelator 4 with
the Sandwich-type excimer can emit intense CPL, with a dissymmetry factor of
3.2 Â 10
À3 (Fig. 11.5b). In addition, intermolecular interaction became weak
at 45
C; therefore, most anthracene fluorophores could not form an excimer and
no CPL could be observed. Therefore, temperature-controlled fluorescence and
CPL of organogel was accomplished.
Photon upconversion, in which the higher-energy excited state could be
populated by lower-energy light, provides a novel view for achieving higher-energy
emission. Duan and Liu et al. proposed an idea to modulate triplet–triplet
annihilation-based photon upconversion (TTA-UC) in chiral assembly system,
in which they designed a self-assembly system based on anthracene-derived
chiral gelator (L-/D-5) as acceptor and achiral Pd
II octaethylporphyrin derivative
(6) as sensitizer [23]. Interestingly, the co-assembly of 6 and L-/D-5 via co-gelation
could not only generate chirality transfer from L-/D-5 to 6, but also realize triplet–
triplet energy transfer (TTET) from 6 to L-/D-5. Thus, dual upconverted (460 nm)
and downconverted CPL (550–750 nm) emission was detected in the co-gels
under excitation of 532 nm laser (Fig. 11.6a). As shown in Fig. 11.6b, L-5/6
and D-5/6 co-gels in deaerated toluene showed the mirror-imaged upconverted
circularly polarized luminescence (UC-CPL) signal at 460 nm. More interestingly,
under high excitation laser power, strong CPL signal could be observed in the
wide emission range of 550–750 nm (Fig. 11.6c). This strongly suggested that a
downconverted CPL could be emitted from 6 in the co-gels at deaerated condition.
Thus, a dual circularly polarized light emission involving upconverted CPL
at 460 nm and downconverted CPL was realized in co-gels. Two channels of
chirality and energy-transfer process were successfully integrated, and the interplay
of energy and chirality transfer to produce a dual CPL emission was revealed
simultaneously.
Except for glutamic acid-based gelator, an L-histidine-derived gelator was
designed and the CPL property has been investigated in Fig. 11.7 [24]. As
shown in Fig. 11.7a, it was found that a supramolecular gel with CPL properties
could be formed by gelator 7 upon sonication. The calculated g lum was Æ5.0 Â 10
À4
at 370 nm. In addition, combined with achiral benzoic acids, 7 could form
two-component co-gels. Although the benzoic acid is achiral, the co-gels exhibited
unexpected enhanced CPL and one order of magnitude amplification of the largest
g lum value is detected (Æ 3.0 Â 10
À3 ). The possible mechanism for this CPL
enhancement was illustrated in Fig. 11.7b. A bilayer structure could be constructed
by gelator 7 due to the H-bond between the imidazole moieties and urea and π–π
stacking between the naphthalene. For the co-assembly, a C 3 -like secondary unit was
firstly formed by 7 and benzoic acid, then this unit further self-assembly into
hexagonal structures. The tight π–π interaction in this hexagonal stacking resulted
in better chirality transfer from gelator 7 to the supramolecular assembles, which
11 Circularly Polarized Luminescence from Gelator Molecules: From Isolated. . .
255
anthracene chromophores formed twisted stacks with partially overlapped excimer.
At 25
C, the main driving force was π–π stacking for self-assembly. Thus, a
Sandwich-type excimer was formed by the anthracene fluorophores in the
excited state (Fig. 11.5a). Meanwhile, the obtained gel from gelator 4 with
the Sandwich-type excimer can emit intense CPL, with a dissymmetry factor of
3.2 Â 10
À3 (Fig. 11.5b). In addition, intermolecular interaction became weak
at 45
C; therefore, most anthracene fluorophores could not form an excimer and
no CPL could be observed. Therefore, temperature-controlled fluorescence and
CPL of organogel was accomplished.
Photon upconversion, in which the higher-energy excited state could be
populated by lower-energy light, provides a novel view for achieving higher-energy
emission. Duan and Liu et al. proposed an idea to modulate triplet–triplet
annihilation-based photon upconversion (TTA-UC) in chiral assembly system,
in which they designed a self-assembly system based on anthracene-derived
chiral gelator (L-/D-5) as acceptor and achiral Pd
II octaethylporphyrin derivative
(6) as sensitizer [23]. Interestingly, the co-assembly of 6 and L-/D-5 via co-gelation
could not only generate chirality transfer from L-/D-5 to 6, but also realize triplet–
triplet energy transfer (TTET) from 6 to L-/D-5. Thus, dual upconverted (460 nm)
and downconverted CPL (550–750 nm) emission was detected in the co-gels
under excitation of 532 nm laser (Fig. 11.6a). As shown in Fig. 11.6b, L-5/6
and D-5/6 co-gels in deaerated toluene showed the mirror-imaged upconverted
circularly polarized luminescence (UC-CPL) signal at 460 nm. More interestingly,
under high excitation laser power, strong CPL signal could be observed in the
wide emission range of 550–750 nm (Fig. 11.6c). This strongly suggested that a
downconverted CPL could be emitted from 6 in the co-gels at deaerated condition.
Thus, a dual circularly polarized light emission involving upconverted CPL
at 460 nm and downconverted CPL was realized in co-gels. Two channels of
chirality and energy-transfer process were successfully integrated, and the interplay
of energy and chirality transfer to produce a dual CPL emission was revealed
simultaneously.
Except for glutamic acid-based gelator, an L-histidine-derived gelator was
designed and the CPL property has been investigated in Fig. 11.7 [24]. As
shown in Fig. 11.7a, it was found that a supramolecular gel with CPL properties
could be formed by gelator 7 upon sonication. The calculated g lum was Æ5.0 Â 10
À4
at 370 nm. In addition, combined with achiral benzoic acids, 7 could form
two-component co-gels. Although the benzoic acid is achiral, the co-gels exhibited
unexpected enhanced CPL and one order of magnitude amplification of the largest
g lum value is detected (Æ 3.0 Â 10
À3 ). The possible mechanism for this CPL
enhancement was illustrated in Fig. 11.7b. A bilayer structure could be constructed
by gelator 7 due to the H-bond between the imidazole moieties and urea and π–π
stacking between the naphthalene. For the co-assembly, a C 3 -like secondary unit was
firstly formed by 7 and benzoic acid, then this unit further self-assembly into
hexagonal structures. The tight π–π interaction in this hexagonal stacking resulted
in better chirality transfer from gelator 7 to the supramolecular assembles, which
11 Circularly Polarized Luminescence from Gelator Molecules: From Isolated. . .
255