Open AccessCCS ChemistryRESEARCH ARTICLE3 Oct 2022Supramolecular Nanohelix Fabricated by Pillararene-Based Host–Guest System for Chirality Amplification, Transfer, and Circularly Polarized Luminescence in Water Krishnasamy Velmurugan, Adil Murtaza, Azhar Saeed, Jianing Li, Kaiya Wang, Minzan Zuo, Qian Liu and Xiao-Yu Hu Krishnasamy Velmurugan College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 211106 Google Scholar More articles by this author , Adil Murtaza School of Physics, MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi’an Jiaotong University, Xi’an 710049 Google Scholar More articles by this author , Azhar Saeed State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter, Xi’an Jiaotong University, Xi’an 710049 Google Scholar More articles by this author , Jianing Li School of Physics, MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi’an Jiaotong University, Xi’an 710049 Google Scholar More articles by this author , Kaiya Wang College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 211106 Google Scholar More articles by this author , Minzan Zuo College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 211106 Google Scholar More articles by this author , Qian Liu College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 211106 Google Scholar More articles by this author and Xiao-Yu Hu *Corresponding author: E-mail Address: [email protected] College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 211106 Google Scholar More articles by this author https://doi.org/10.31635/ccschem.022.202101749 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Amplified chirality and Förster resonance energy transfer (FRET)-assisted chirality transfer from molecular to nanoscale level have been shown to play a vital role in co-assembled nanohelix for potential energy transfer in biological systems. Herein, we have constructed a chiral host–guest complex donor system for chiral amplification via induced chirality of pillar[5]arene host and loaded it with an achiral dye acceptor to demonstrate how chirality-assisted excitation energy transfer occurred in the supramolecular nanohelix system in an aqueous medium. We found that the individual chiral copolymeric guest could self-assemble into nanohelixes. In the presence of pillar[5]arene host, the formed supramolecular host–guest complex also proceeded to form long helical fibers via J-aggregation of pillar[5]arene; thus, causing amplified chirality. After loading an achiral dye acceptor into the host–guest complex donor, it achieved co-assembled composite nanohelixes via electrostatic interactions and ordered stacking of the chromophoric dyes. In this hybrid supramolecular system, the loaded dye was uniformly dispersed, becoming the driving force for chirality transfer. Fascinatingly, this supramolecular system containing achiral dye could capture both chiral information and energy from the chiral donor, displaying supramolecular chirality and FRET-assisted amplified circularly polarized luminescence (CPL) in water with a large dissymmetry factor (glum = 1.32 × 10−2). Download figure Download PowerPoint Introduction Chirality is indispensable in nature and living organisms; it exists around us, including double-helix DNA, peptide assembly, and collagen triple-helix.1–4 Chiral amplification and transfer of both energy and chirality in hierarchical nanoassemblies have been carried out in biological systems. These assemblies are essential for various biological functions, from recognition to replication and catalytic reactions.5–8 Also, structural chirality- and energy-based information are transferred in living systems via multichannel.9–11 Inspired by nature, researchers have been devoted to mimicking chiroptical materials through supramolecular-/nano-assemblies.12,13 In particular, various chiral self-assembled superstructures have been achieved in a few liquid crystal systems and various chiral solvents.14,15 Although chiral amplification, transfer of both energy and chirality, as well as circularly polarized luminescence (CPL) were reported alone,16–21 it remains mysterious how these three sequential processes could combine in a single supramolecular self-assembled system. Self-assembly plays a crucial role in the construction of various supramolecular chiral superstructures/materials.22–24 Particularly, the host–guest approach has been promptly advanced into one of the major strategies in fabricating supramolecular chiral nanoassemblies with controlled chirality.25,26 In the host–guest system, two-/multi-components took part in the self-assembly process and produced amplified or state-of-the-art functions from these multi-component supramolecular nanocomposite systems. The main advantage of the supramolecular system is that complicated and well-ordered chiral superstructures could be achieved conveniently and with great potential to avoid the multi-step synthetic route. Especially, the achiral moiety could acquire chiroptical activity through chiral information transfer from the chiral donor to the achiral acceptor in the supramolecular host–guest self-assembled systems.27–29 The resulting supramolecular self-assembled chiral materials are responsive to circularly polarized light and could produce active CPL-signals with higher luminescence dissymmetry factor (glum) in an aqueous medium than that of normal systems in organic solvents or binary solvent mixtures (glum = 10−5 to 10−3).30–34 In order to extend the application of CPL-active materials, a high glum value of the resulting chiral luminescent materials is an important prerequisite. Therefore, the hierarchical supramolecular self-assembly approach has played an active role in improving the CPL activity. Thus, to explore efficient CPL systems via multichannel chiral transfer process, we designed a supramolecular host–guest self-assembled system from a chiral copolymer and a water-soluble pillar[5]arene host. This chiral supramolecular system was further loaded with an achiral dye, in which the host–guest complex acted as a chiral donor, and the dye molecule served as an achiral acceptor. With this robust design, we sought to gain an understanding of three critical fundamental concepts, (1) how the planar chirality of pillar[5]arene was amplified and stabilized in the presence of chiral copolymeric guest; (2) whether chiral information contained in the host–guest complex (donor) could be transferred to the achiral acceptor to assemble into a Förster resonance energy transfer (FRET)-based donor–acceptor system; (3) how the FRET mechanism might assist chirality transfer and active CPL signal. As predicted, we observed that the designed chiral copolymer could involve in the self-assembly to form chiral nanohelixes in an aqueous solution. When water-soluble pillar[5]arene ( WP5) host was mixed with this copolymeric solution, the obtained supramolecular system assembled into long nanohelix structures with amplified chirality via host–guest complexation, followed by J-aggregation of WP5 (Scheme 1). Subsequently, when an achiral dye [Eosin Y (EsY)/Fluorescein (FL)] acceptor was mixed with the above supramolecular host–guest complex (donor) solution, donor–acceptor composite nanohelixes were developed. Fascinatingly, the obtained composite nanohelixes exhibited efficient chirality transfer via electrostatic interactions between the positively charged surface of the supramolecular host–guest complex and the negatively charged dye, as well as ordered stacking of the chromophoric dyes. More importantly, the dye acceptor could capture the transferred energy from the donor through an efficient FRET process, leading to a strong CPL with a large dissymmetry factor (glum = 1.32 × 10−2). To the best of our knowledge, this is the first pillararene-based multichannel FRET-assisted chiral transfer system with active CPL and high glum value in an aqueous medium. Therefore, this work highlights the supramolecular chirality transfer from chiral host–guest system to an achiral moiety and the significance of FRET-assisted strong CPL signals in the self-assembled nanocomposite system. Scheme 1 | Self-assembly route for chiral amplification, transfer, and FRET-assisted CPL. Schematic illustrations of the possible self-assembly route for chiral amplification via host–guest complexation (WP5⊃L-1), transfer of chirality, and FRET-assisted amplified CPL in the donor (WP5⊃L-1)-acceptor (EsY/FL) composite nanohelix assemblies. Images of WP5⊃L-1/EsY (1∶1∶3) (yellow) and WP5⊃L-1/FL (1∶1∶3) (green) solutions were taken under UV-light (365 nm). Download figure Download PowerPoint Experimental Methods All chemicals, solvents, and reagents were purchased from Alfa Aesar Chemical Co., Ltd. (Shanghai, China), Aladdin Biochemical Technology Co., Ltd. (Shanghai, China), and used without any prior treatment and purification. Deionized water purification system UPT-I-10 was purchased from Shanghai Gaosen Instrument Co., Ltd. (Shanghai, China) and the obtained deionized water was used as a solvent for all our experiments. Nuclear magnetic resonance (NMR; 400 MHz) spectra were recorded using an Avance 400 MHz NMR spectrometer (Bruker, Switzerland) with tetramethylsilane (TMS) as an internal standard. The enantiomeric purity of monomer (L/D-4) was determined using high-performance liquid chromatography (HPLC) separations on the Daicel Chiralpak OD column (SPD-20A, SHIMADZU, Kyoto, Japan). The mobile phases comprised hexane∶isopropanol (70∶30, v/v). The flow rate was set at 1 mL/min, with a fixed detection wavelength of 254 nm and a temperature kept at 25 °C. Molecular weight and polydispersity index (PDI) were determined by gel permeation chromatography using the Agilent 1260 Infinity II Multi-detector system calibrated with standard PMMA (CA, United States). UV–vis absorption spectra, fluorescence spectra, circular dichroism (CD), linear dichroism (LD), and CPL spectra with 1 cm cuvette were recorded using Shimadzu UV-1780 (Kyoto, Japan), Angdong F-380 (Guangdong, China), JASCO J-810 (Tokyo, Japan), and JASCO CPL-300 (Tokyo, Japan) spectrometers, respectively. For CD spectra, the cuvette was kept perpendicularly to the light of the CD spectrometer and rotated within the cuvette plane at different angles (0°–180°) using a homemade rotator to avoid artifacts from the LD, linear birefringence, and circular birefringence. One drop of the sample in H2O was deposited on a carbon-coated copper grid and evaporated at room temperature for 1 day. Transmission electron microscopy (TEM) images were examined with a JEOL JEM-F200 microscope (Tokyo, Japan), operating at 200 kV. Spin-coated samples (Si wafer substrate) were used for atomic force microscopy (AFM) imaging, which was obtained in tapping mode by using a NanoDrive Controller with Bruker Innova scanning probe microscope (AZ, United States). Dynamic light scattering (DLS) analysis was examined using the Brookhaven BI-9000AT system (New York, United States) with a polarized laser source (200 mW, λ = 514 nm). The absolute fluorescence quantum yield was recorded by Edinburg FLS-980 fluorescence spectrophotometer (Livingston, United Kingdom) with a calibrated integrating sphere. The fluorescence lifetime measurements were also observed on the same spectrophotometer. Fluorescence imaging was analyzed on confocal laser scanning microscopy (CLSM; Wetzlar, Germany). A spot of the composite aqueous solution was dropped into glass capillaries by an ultraviolet-curing epoxy glue and conducted experiments in Leica TCS SP8 STED 3X (Wetzlar, Germany). Synthesis and characterization Synthesis and relevant characterization details are provided in the Supporting Information. Results and Discussion Host–guest interactions between WP5 and GR in water Alanine-derived copolymeric guests (L-1/D-1) were prepared by polymerization of vinylbenzoyl-alaninate (L-4/D-4) and thermo-sensitive N-isopropylacrylamide monomers through reversible addition-fragmentation chain transfer polymerization35,36 with a low PDI [number average molecular weight (Mn,SEC) = 11.4 kDa, Polydispersity (Đ) = 1.13]. The detailed synthetic routes of chiral copolymeric guest (L-1/D-1) and water-soluble pillar[5]arene ( WP5) are shown in Supporting Information Figures S1–S5 and Schemes S1–S4. To investigate the host–guest interactions, water-soluble ammonium benzoyl-l-alaninate ( GR) was taken as a model guest. First, the interactions between WP5 and GR (1∶1) were examined by 1H NMR titrations (D2O), as shown in Figures 1a–1c. For GR, the aromatic protons of He and Hf showed apparent upfield shifts (Δδ = −1.76 and −1.02 ppm) due to the shielding effects induced by the quaternary ammonium groups attached on the electron-rich cavity of WP5. However, the alkyl protons of Hg and Hh did not show obvious changes in the NMR scale.37 Moreover, the signals of Hc, Hc′ broadened into a single peak, revealing that the activity of those protons was not restricted. These results suggested that the guest GR threaded into the cavity of WP5. To prove this phenomenon, two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY) by NMR was carried out using the above sample with an equimolar solution in D2O. Strong NOE correlations were observed between GR proton of Hg and WP5 protons of Hb-d, as well as between WP5 protons of Ha and GR protons of Hg and Hh ( Supporting Information Figure S6), indicating that the alanine pendant in the guest molecule was threaded into the pillar[5]arene cavity. Figure 1 | 1H NMR spectra (400 MHz, D2O, 298 K): (a) Ammonium benzoyl-l-alaninate (GR); (b) mixture of WP5 (1 equiv) and GR (1 equiv); (c) WP5. Download figure Download PowerPoint The binding stoichiometry between WP5 and L-1 was confirmed by fluorescence titration experiments. Based on Job’s plot method,38 the maximum molar fraction of L-1 attained was ∼0.5 ( Supporting Information Figure S7), which implied 1:1 binding stoichiometry of the formed WP5⊃L-1 complex. In addition, the titration result showed two distinct observations: first, upon increasing the concentration of copolymeric guest (L-1) (0–1 equiv) to WP5, the fluorescent intensity of WP5 was decreased gradually at 318 nm, accompanied by enhanced emission of the guest at 391 nm ( Supporting Information Figure S8). This ratiometric spectrum was attributed to the involvement of WP5 and L-1 binding to form a charge-transfer complex called exciplex.39–41 With further additions of L-1, there was no appreciable change in the spectra. From this titration experiment, the binding constant (Ka)42–44 of the host–guest complex ( WP5⊃L-1) (1∶1) was calculated to be 1.53 × 104 M−1 in the aqueous medium ( Supporting Information Figure S9). This strong binding ability was responsible for the following chiral amplification and chirality transfer process. Chirality amplification via host–guest complex Amino acid-containing copolymers have intrinsic chirality at a lower wavelength and could hardly be observed at a higher wavelength (<270 nm) due to the lack of conjugations. Therefore, we analyzed the chiral amplification16 of WP5 and amino acids containing copolymeric guest (L-1 or D-1) based on their host–guest complexation. In general, alkyl-substituted pillararenes existed as a racemic mixture, that is, two enantiomers (pS and pR) with a 1∶1 ratio (Scheme 2). This led to undetectable chiroptical activity due to the fast interconversion of the enantiomers via phenyl ring rotation. When a chiral guest was encapsulated by pillararene, the chirality of pillararene was induced and stabilized by a selection of one stable enantiomer, thereby could produce a CD signal at pillararene wavelength.16 Scheme 2 | Schematic diagrams of the plausible mechanism of chirality amplification. Download figure Download PowerPoint Hence, WP5⊃(L-1 or D-1) complexation-assisted chiral amplification was analyzed by UV–vis and CD experiments. Upon the addition of L-1 (1 equiv) to WP5 solution, the absorption band of WP5 (300 nm) was enhanced with a small redshift (304 nm) (Figure 2). This spectral shift indicated that the J-aggregation of WP5 took place in the WP5⊃L-1 self-assembled system.45,46 At the same concentration, the CD signals of L-1 or D-1 were amplified after the complexation of L-1 or D-1 by WP5. In Figure 2, both WP5 (black line) and L-1 (sky blue line) showed negligible CD signal in the testing wavelength. In contrast, with the addition of WP5 into L-1 (1 equiv of each), a negative Cotton effect (green line) was observed at ∼304 nm; a similar phenomenon was observed in the case of WP5 with D-1 (blue line) (dissymmetry factor (gabs) = ±1.04 × 10−3 at 304 nm).16,42–44 These amplified CD signals with different cotton effects induced by different enantiomers of WP5 (Scheme 2) could be utilized to detect the unknown configuration of the amino acid-containing copolymers. As expected, the host–guest interaction was responsible for chiral amplification, which was analyzed further by heating the WP5⊃(L-1 or D-1) complex to 60 °C and monitoring their CD signals. Indeed, the amplified CD signal of WP5⊃(L-1 or D-1) complex was decreased (red line) at 60 °C. It further revealed that the host–guest complex was destabilized at high temperatures, resulting in decreased chiral signals. Figure 2 | UV–vis and CD spectra of WP5 (black line) (1.2 × 10−4 M = 1 equiv), L-1 (sky blue) (4 μM = 1 equiv), and WP5+L-1 (green line) (1 equiv of each). WP5+D-1 (blue line) and WP5+(L-1 or D-1) at 60 °C (red line) (1 equiv of each) in aqueous solution. Download figure Download PowerPoint Moreover, the effect of the guest concentration in chiral amplification was also investigated. Upon gradually increasing the amount of L-1 or D-1 to WP5 (1 equiv), the CD signals increased progressively with redshift (negative or positive CD band at 304 nm concerning absorption band of WP5) and reached a steady-state at 1 equiv of L-1 or D-1 (Figure 3). This significant redshift provided further evidence that the J-aggregation of WP5 assisted a robust chiral amplification in the WP5⊃L-1 self-assembled system.45,46 Upon further increasing the L-1 or D-1 concentration (1.1 equiv), there were no significant changes in the intensity of CD signals. These results suggested that the 1∶1 stoichiometric ratio of WP5⊃(L-1 or D-1) was optimum for chiral amplification. Figure 3 | CD titrations of WP5 (1 equiv) with the gradual addition of L-1 or D-1 (0–1.1 equiv) in an aqueous solution. Download figure Download PowerPoint Chirality transfer in composite nanohelixes For further understanding of the induced chirality by the WP5⊃(L-1 or D-1) complex, CD spectra of different dye-doped systems were measured, such as cationic dyes (Rhodamine B (RhB) and Thioflavin T (ThT), and anionic dyes (EsY and FL). It was anticipated that the anionic EsY or FL could associate with the WP5⊃(L-1 or D-1) complex via strong electrostatic interactions between the negatively charged EsY or FL and positively charged WP5. The WP5⊃(L-1 or D-1)/EsY system displayed a strong induced CD signal at a longer wavelength (518 nm), corresponding to the absorption band of EsY. Meanwhile, the CD signal of WP5 at a lower wavelength (304 nm) was decreased, caused by the efficient transfer of chiral information from the chiral pillararene to achiral dye via electrostatic interaction (Figures 4a–4d). Notably, during this interaction, the electron-withdrawing substituents contained in EsY might have partially reduced the electron densities of WP5, leading to the lower intensity band of WP5 at 304 nm.47 In addition, when higher amounts of EsY was loaded into WP5⊃(L-1 or D-1), the long fibers formed by WP5⊃(L-1 or D-1) partially dissociated into short fibers in the resulting WP5⊃(L-1 or D-1)/EsY system via chromophoric dye stacking (evidenced by AFM and TEM results in the morphological section). This is another possible reason for the decreased CD signal of pillararene. Similarly, WP5⊃(L-1 or D-1)/FL system also showed a strongly induced CD peak at a longer wavelength (475 nm) relating to the absorption wavelength of FL, while the CD signal of pillararene (304 nm) was reduced accordingly (Figure 4). Figure 4 | (a) UV–vis and CD spectra of WP5⊃L-1 (1 equiv), EsY (3 equiv = 3.6 × 10−4 M with respect to WP5), WP5⊃L-1+EsY, WP5⊃D-1+EsY, and WP5⊃(L-1 or D-1)+EsY at 60 °C in aqueous solution; (b) UV–vis and CD spectra of WP5⊃L-1 (1 equiv), FL (3 equiv = 3.6 × 10−4 M with respect to WP5), WP5⊃L-1+FL, WP5⊃D-1+FL and WP5⊃(L-1 or D-1)+FL at 60 °C in aqueous solution. Download figure Download PowerPoint On the contrary, no CD signals could be observed at the longer wavelength for both WP5⊃(L-1 or D-1)/RhB and WP5⊃(L-1 or D-1)/ThT systems ( Supporting Information Figure S10) due to the repulsion between similarly charged species of WP5 and RhB/ThT dye. Subsequently, the thermo-responsive/reversible properties of WP5⊃(L-1 or D-1)/EsY and WP5⊃(L-1 or D-1)/FL self-assembled supramolecular systems were verified by temperature-dependent CD studies. When the WP5⊃(L-1 or D-1)/EsY and WP5⊃(L-1 or D-1)/FL solutions were heated to 60 °C, the CD signals disappeared completely at the longer wavelength, indicating that a disassembly process had occurred. To confirm the thermo-responsiveness, temperature-dependent CD spectrometry was performed for these supramolecular systems, which displayed typical signal changes with respect to the testing temperature range ( Supporting Information Figure S11). Subsequently, CD titrations of WP5⊃L-1 and WP5⊃D-1 were performed carefully at varying EsY and FL concentrations, respectively (Figures 5a and 5b). Upon increasing the concentration of EsY gradually into WP5⊃L-1, a negative Cotton effect with significant redshift (518 nm) was observed, and the intensity of CD signal was saturated at 3 equiv of EsY. Meanwhile, the CD signal (304 nm) of pillararene was gradually decreased by increasing the EsY concentration in WP5⊃L-1. A similar phenomenon was observed in the titration experiments when adding EsY into the WP5⊃D-1 complex and FL into WP5⊃(L-1 or D-1) system. These considerable shifts suggested that the J-aggregation of negatively charged chromophoric dyes (EsY/FL) took place in WP5⊃(L-1 or D-1)/EsY and WP5⊃(L-1 or D-1)/FL systems.48 These stacking modes further contribute to the effective chiral transfer process that occurred in the above supramolecular systems. To understand the role of WP5 in the self-assembled composite systems, control CD experiments were carried out in the absence and post-addition of WP5 into the mixture of L-1 or D-1 with dyes (EsY and ThT). Both systems did not show CD signals in a wide range of spectral wavelengths ( Supporting Information Figure S12). These results evidenced that WP5 acted as a potential bridge in the chirality amplification and transfer processes in the supramolecular self-assembled composite systems. Figure 5 | CD titrations of WP5⊃(L-1 or D-1) (1 equiv) with the gradual addition of (a) EsY (0–3 equiv); (b) FL (0–3 equiv) in aqueous solution. Download figure Download PowerPoint To understand the chiral transfer mechanism, the energy-transfer efficiency of the host–guest complex to different dyes was calculated using WP5⊃L-1 as an ideal donor and EsY, FL, RhB, and ThT as acceptors. The absorption bands of EsY, FL, RhB, and ThT overlapped with the emission peak of the WP5⊃L-1 ( Supporting Information Figure S13). The fluorescence responses of the dyes-loaded systems were examined. Upon increasing the concentrations of EsY, FL, RhB, and ThT (0–3 equiv) to WP5⊃L-1, the emission intensity of the donor decreased gradually, while emission intensities of EsY, FL, RhB, and ThT increased progressively (Figures 6a–6d). Interestingly, the energy transfer efficiency49,50 of the WP5⊃L-1/EsY and WP5⊃L-1/FL (1:1:3) systems was calculated to be 96.3% and 92.7%, respectively, which were much higher than that of the WP5⊃L-1/RhB (1:1:3) (6.4%) system. In contrast, the distance between the donor ( WP5⊃L-1) and acceptor (RhB) could be farthest compared with WP5⊃L-1/EsY and WP5⊃L-1/FL systems due to the repulsive forces between similarly charged WP5 and RhB, resulting in weak or almost no FRET effect. Although the cationic ThT loaded WP5⊃L-1 system showed high energy transfer efficiency (95.5%) via an efficient FRET process, no chiral transfer process occurred in this system. From the above results, we inferred that electrostatic interactions assisted by the FRET process played a significant role in the chiral transfer process. When there was no electrostatic interaction between the same charged chiral and achiral units containing supramolecular system, chirality transfer from chiral to an achiral molecule was not feasible even for an efficient FRET system. Furthermore, 1H NMR titrations and 2D NOESY NMR measurements were carried out to confirm the electrostatic interactions between WP5⊃ GR assembly and dyes (EsY and RhB), as shown in Supporting Information Figures S15–S17. Figure 6 | Fluorescence titrations of WP5⊃L-1 (1 equiv) assembly with different concentrations of (a) EsY (0–3 equiv), (b) FL (0–3 equiv), (c) ThT (0–3 equiv), and (d) RhB (0–3 equiv) (λex. = 300 nm, excitation/emission slit width = 5/5 nm) in aqueous solution. Download figure Download PowerPoint Fluorescence lifetime decay experiments were performed to confirm the energy transfer process and understand the possible mechanism. The WP5⊃L-1 complex showed a fluorescence lifetime of τ = 12.35 ns, which decreased to 2.62 and 4.27 ns for WP5⊃L-1/EsY and WP5⊃L-1/FL systems, respectively ( Supporting Information Figure S14 and Table S1). These results revealed that the energy decay time of WP5⊃L-1 was shortened in the presence of EsY and FL acceptors, indicating that the FRET process might have performed as the key mechanism for energy transfer. More importantly, the fluorescence quantum yield of WP5⊃L-1 (1∶1) was calculated to be 0.12%, which increased drastically to 14.80% and 16.26% in the WP5⊃L-1/EsY (1∶1∶3) and WP5⊃L-1/FL (1∶1∶3) systems, respectively. These results further highlighted the excellent energy transfer efficiency from the donor to the acceptor. Therefore, these supramolecular WP5⊃L-1/EsY and WP5⊃L-1/FL composite systems could perform as a potential chiral transfer system with higher energy transfer efficiency and reasonable fluorescence quantum yield. FRET-assisted amplified CPL of supramolecular composite To further investigate the supramolecular chirality at an excited state, CPL measurement was carried out for WP5⊃(L-1 or D-1)/EsY and WP5⊃(L-1 or D-1)/FL supramolecular composite systems in an aqueous solution. Interestingly, both WP5⊃(L-1 or D-1)/EsY and WP5⊃(L-1 or D-1)/FL systems displayed strong CPL signals with an emission maximum at 544 and 509 nm, respectively (Figures 7a and 7b). The signs of the CDs were almost similar to CPL signals, which revealed that ground- and excited-state supramolecular chiralities showed a similar phenomenon. Another possible reason is that the packing of acceptor dyes is in the same direction within the supramolecular WP5⊃(L-1 or D-1) helix system; thus, similar helical orientations were observed in both supramolecular systems. Similar molecular packing models between chiral donors and achiral acceptors in the supramolecular chiral systems have also been reported using an exciton-coupled CD theory.51 The luminescence dissymmetry factor (glum = 2 × (IL − IR)/(IL + IR)) was calculated from the magnitude of CPL (where IL and IR denote the intensity of left- and right-handed CPL, respectively). An ideal left- or right-handed CPL system had a maximum glum value (glum = ±2), while the glum value was equal to zero without chirality. In the present WP5⊃(L-1 or D-1)/EsY and WP5⊃(L-1 or D-1)/FL supramolecular systems, the glum values were calculated to be 1.32 × 10−2 and 1.24 × 10−2, respectively ( Supporting Information Figure S18), which were larger than those reported in water-soluble supramolecular systems.52–55 Figure 7 | (a) CPL spectra of WP5⊃L-1/EsY (1:1:3) (green line) and WP5⊃D-1/EsY (1∶1∶3) (b
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