12 White-Light Emissive Materials Based on Supramolecular …
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AC@BrNp-β-CD complex showed noticeable broad dual emission peaks, which
was assignable to the emission of coumarin group at 400 nm (blue-purple band) and
the BrNp group emission at 512 and 537 nm (yellow-green band). It is interesting to
note that almost pure WLE with the CIE coordinates calculated as (0.29, 0.33) was
realized when BrNp-β-CD was incorporated with 0.1 equiv. of AC under excitation
at 295 nm.
Recently, an amphiphilic AIE cage system with tetraphenylpyrazole (TPP) was
synthesized by stepwise nucleophilic aromatic substitution (S n Ar) reaction with
TPP-4OH (Fig. 12.13a) (Feng et al. 2018b). The TTP-cage emitted strong blue
fluorescence at 397 nm with photoluminescence quantum yield of 34.4% in THF
solution under 365 nm UV irradiation due to the restriction of intramolecular rotation of the TTP unit. The emission remained unchanged when up to 60% of water was
added to the THF solution. The information of the structural feature came from UV
and CD measurements. The UV spectrum in THF exhibited an absorption maximum
at 360 nm due to π–π* transition. It is interesting to note that Cotton effect was
observed in the absorption regions of the phenol rings and TPP units. It indicated
that the propeller-like TPP adopted either clockwise (P) or anticlockwise (M) rotational patterns. Crystal structure of TPP-Cage analog indicated that TPP-Cage
could adopt a cubic prism structure, where the distance between the top and the
bottom pyrazine cores was about 4.50 Å, and the distance between the two triazine
ring nitrogen atoms was about 11.23 Å. The size of the cavity was large enough to
encapsulate many guest molecules. In addition, π–π stacking, C–H–π, and C–H–N
interaction allowed TPP-Cage to pack to form a grid-like porous structure. Given
the blue emission of TPP-Cage, DPP was used as a guest molecule that emits a
yellow and its molecular size enabled it to thread into the cavity of the cage system,
forming a host-guest complex (Fig. 12.13b). WLE was easily obtained by adding
water to the complex. As shown in Fig. 12.13c, TPP-Cage exhibited a deep blue
emission at 397 nm when excited at 365 nm, which shifted to 430 nm upon adding
water, whereas the glaring yellow emission of DPP was quenched by water addition
due to the ACQ effect. However, the amphiphilic nature of the cage compound by
introducing 2-[2-(2-methoxyethoxy)ethoxy]ethyloxy group allowed it to serve as a
light harvesting platform to encapsulate DPP in its hydrophobic cavity in an aqueous
solution, as evidenced from
1 H NMR and
1 H1 H 2D NOESY NMR measurement.
Subsequently, aggregation-induced quenching of DPP was avoided through such
encapsulation. Indeed, a new peak assignable to the emission band of DPP encapsulated in the cavity was observed at 555 nm, with increasing water fraction in THF
(Fig. 12.13c). Interestingly, the complementary emission colors of TPP and DPP
enabled the complex to emit white light in the aggregation state.
12.5 Self-assembly
Organic assemblies from solution to solid substrates emerge as one of the most
facile and promising way to retain the pure WLE, which is relevant for device
423
AC@BrNp-β-CD complex showed noticeable broad dual emission peaks, which
was assignable to the emission of coumarin group at 400 nm (blue-purple band) and
the BrNp group emission at 512 and 537 nm (yellow-green band). It is interesting to
note that almost pure WLE with the CIE coordinates calculated as (0.29, 0.33) was
realized when BrNp-β-CD was incorporated with 0.1 equiv. of AC under excitation
at 295 nm.
Recently, an amphiphilic AIE cage system with tetraphenylpyrazole (TPP) was
synthesized by stepwise nucleophilic aromatic substitution (S n Ar) reaction with
TPP-4OH (Fig. 12.13a) (Feng et al. 2018b). The TTP-cage emitted strong blue
fluorescence at 397 nm with photoluminescence quantum yield of 34.4% in THF
solution under 365 nm UV irradiation due to the restriction of intramolecular rotation of the TTP unit. The emission remained unchanged when up to 60% of water was
added to the THF solution. The information of the structural feature came from UV
and CD measurements. The UV spectrum in THF exhibited an absorption maximum
at 360 nm due to π–π* transition. It is interesting to note that Cotton effect was
observed in the absorption regions of the phenol rings and TPP units. It indicated
that the propeller-like TPP adopted either clockwise (P) or anticlockwise (M) rotational patterns. Crystal structure of TPP-Cage analog indicated that TPP-Cage
could adopt a cubic prism structure, where the distance between the top and the
bottom pyrazine cores was about 4.50 Å, and the distance between the two triazine
ring nitrogen atoms was about 11.23 Å. The size of the cavity was large enough to
encapsulate many guest molecules. In addition, π–π stacking, C–H–π, and C–H–N
interaction allowed TPP-Cage to pack to form a grid-like porous structure. Given
the blue emission of TPP-Cage, DPP was used as a guest molecule that emits a
yellow and its molecular size enabled it to thread into the cavity of the cage system,
forming a host-guest complex (Fig. 12.13b). WLE was easily obtained by adding
water to the complex. As shown in Fig. 12.13c, TPP-Cage exhibited a deep blue
emission at 397 nm when excited at 365 nm, which shifted to 430 nm upon adding
water, whereas the glaring yellow emission of DPP was quenched by water addition
due to the ACQ effect. However, the amphiphilic nature of the cage compound by
introducing 2-[2-(2-methoxyethoxy)ethoxy]ethyloxy group allowed it to serve as a
light harvesting platform to encapsulate DPP in its hydrophobic cavity in an aqueous
solution, as evidenced from
1 H NMR and
1 H1 H 2D NOESY NMR measurement.
Subsequently, aggregation-induced quenching of DPP was avoided through such
encapsulation. Indeed, a new peak assignable to the emission band of DPP encapsulated in the cavity was observed at 555 nm, with increasing water fraction in THF
(Fig. 12.13c). Interestingly, the complementary emission colors of TPP and DPP
enabled the complex to emit white light in the aggregation state.
12.5 Self-assembly
Organic assemblies from solution to solid substrates emerge as one of the most
facile and promising way to retain the pure WLE, which is relevant for device