English

• Recently, light-harvesting materials using supramolecular assembly as an effective strategy have attracted widespread focuses [1–7], due to their numerous application in fields of optoelectronic devices [8,9], photocatalysis [10–13], and near-infrared bioimaging [14], sensor [5,15,16], and so on [17,18]. Benefiting from advantages of macrocyclic host effectively binding guests, supramolecular assembly enables to confine and induce luminescence of guest [19–21], further contributing to fluorescence resonance energy transfer (FRET) [22–29]. Thus, lots of works were investigated based on multivalent supramolecular assembly and cascade assembly to achieve multicolor luminescence [30]. For instance, Perrier and coworkers reported an artificial light-harvesting system based on supramolecular peptide nanotubes in water, with a two-step sequential Förster resonance energy transfer process and an energy transfer efficiency up to 95% [27]. Tang et al. used a conjugated polymeric supramolecular network, a crosslinked network obtained from the self-assembly of a pillar[5]arene based conjugated polymeric host and conjugated ditopic guests, to construct artificial light-harvesting systems with high antenna effect (35.9 in solution and 90.4 in solid film) [28]. However, the current researches are mainly based on one-step FRET and two-step cascade FRET [10,11,31], purely organic multipath sequential FRET for multicolor luminescence is barelyreported due to rigorous match and ordered microenvironment between donor and various acceptor [32]. Especially, using one donor to perform multiple cascade FRET with controlled paths through a free combination of acceptors faces a great challenge.

  In this work, a new AIEgen, 4-(anthracen-9-yl)−1-(6-(trimethylammonio)hexyl)pyridin-1-ium bromide (A1), is synthesized to assemble with amphiphilic sulfonatocalix[4]arene (SC4AD) or sulfobutyl-β-cyclodextrin (SBE-β-CD) containing a porous cavity. Benefiting from macrocyclic confinement, the almost invisible emission from A1 is greatly enhanced 67 times by SC4AD and SBE-β-CD, with robust yellow-green fluorescence at 535 nm. Notably, the nanoparticle afforded by A1 and SC4AD enables to induce molecule A1 to perform multipath fluorescence resonance energy transfer (FRET) with various dye acceptors (EY, NiR and Cy5.5), including one-step and two-step FRET, and even three-step cascade FRET behavior (Scheme 1). Compared to one-step FRET, the three-step FRET process possesses higher energy transfer efficiency (efficiency: 84.9% for FRET Ⅰ, 81.4% for FRET Ⅱ, 66.9% for FRET Ⅲ), accompanying with emission ranging from 535 nm to 570 nm, and then to 638 nm, and finally to 717 nm. The antenna effect is still retained, and is 2.3 even after going through three FRET processes. The donor/acceptor ratio of three-step FRET system A1/SC4AD+EY+NiR+Cy5.5 is 3000 (A1): 20 (EY): 8 (NiR): 5 (Cy5.5), corresponding to light-harvesting trait of a high donor/acceptor ratio. By tuning the composition of dye acceptors, different cascade light-harvesting systems can be designed, which provides a feasible pathway to construct diverse light-harvesting materials.

  Scheme 1

  

  Scheme 1.  Schematic illustration of multipath cascade light-harvesting based on macrocyclic sulfonatocalix[4]arene.

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  Molecule A1 was synthesized and characterized by nuclear magnetic resonance (NMR) spectra and high resolution mass spectra (Scheme S1, Figs. S1–S5 in Supporting information). As revealed by UV–vis absorption spectra and fluorescence spectra, A1 had two characteristic absorption bands, located at 247 nm and 392 nm, respectively, and the emission was almost invisible in aqueous solution (Figs. S6a and b in Supporting information). After introducing poor solvent dimethyl sulfoxide, intermolecular aggregation was formed, and the fluorescence at 560 nm was induced and enhanced gradually (Figs. S6c and d in Supporting information), demonstrating its property of aggregation-induced emission (AIE). To promote robust aqueous fluorescence, various negatively charged macrocyclic host, including amphiphilic SC4AD containing long hydrophobic alkyl chains and SBE-β-CD, were selected to assemble with the guest A1. According to Figs. 1a and c, the faint fluorescence of A1 was likely enhanced with increasing the molar ratio of SC4AD or SBE-β-CD. Distinctly, the fluorescence based on macrocyclic host was located at 535 nm. The obvious blue shift meant that the bright emissions induced by macrocyclic hosts originated from single molecule A1, but not from intermolecular aggregation of A1.

  Figure 1

  

  Figure 1.  Fluorescence spectra of A1 with adding different ratios of (a) SC4AD and (c) SBE-β-CD ([A1] = 2 × 10^–5 mol/L, λ_ex = 392 nm, ex/em slits: 5 nm/5 nm); UV–vis absorption spectra and characteristic absorbance at 247 nm of guest A1 with adding various molar ratio of (b, d) SC4AD ([A1] = 2 × 10^–5 mol/L).

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  Additionally, it was found that, as gradually adding the macrocyclic hosts, SBE-β-CD enhanced the fluorescence of A1 continuously, while the fluorescence induced by SC4AD first increased and then fell, exhibiting that the excess of SC4AD was harmful to the fluorescence emission (Figs. 1a and c). To explore the enhanced mechanism of SC4AD and SBE-β-CD, transmittance and UV–vis absorption spectra were recorded. The results suggested that transmittance of molecule A1 at 550 nm first remained constant and then decreased obviously when the concentration of A1 exceeded 1 × 10^–5 mol/L (critical aggregation concentration, CAC), with concentration of SC4AD fixed at 5 × 10^–6 mol/L (Fig. S7 in Supporting information). As a contrast, no any change in corresponding transmittance was observed when using SBE-β-CD as the macrocyclic host, although the concentration of A1 increased to 4 × 10^–5 mol/L (Fig. S8 in Supporting information). Moreover, Tyndall effect was activated in A1/SC4AD solution, but no similar effect in A1/SBE-β-CD solution after being irradiated by laser. These differences proved that molecule A1 formed supramolecular nanoassembly through electrostatic interaction with SC4AD. The morphology of nanoparticles was displayed in the transmission electron microscope (TEM) (Fig. S9 in Supporting information). With a fixed concentration of A1 at 2 × 10^–5 mol/L, an optimal molar ratio was tested as 0.25 for A1/SC4AD (Fig. S10 in Supporting information). The nanoassembly and its dissociation was further demonstrated by UV–vis titration spectra. Uninterruptedly adding SC4AD caused that the characteristic absorption of A1 first decreased and then rose, corresponding to formation and dissociation of the assembly (Figs. 1b and d). The difference in optimal ratios of SC4AD/A1 based on fluorescence (0.6), transmittance (0.25), and UV–vis titration spectra (0.7) is ascribed to the various testing principle. The transmittance spectrum reveals the number of large colloid particles, while fluorescence and UV–vis spectra reflect change in photophysical behavior, the latter of which can be observed clearly even for small nanoparticles. When the ratio of SC4AD/A1 exceeds 0.25, dissociation from large colloid particles to small nanoparticles still enables to improve the photophysical properties. Nevertheless, the characteristic absorption of A1 continuously decreased with increasing amounts of SBE-β-CD (Fig. S11 in Supporting information). Combining with the results of no sign in transmittance and Tyndall effect, it was assumed that molecule A1 was encapsulated in cavity of SBE-β-CD, which was responsible for bright emission through macrocyclic confinement effect. ¹H NMR spectra showed that there was obvious down-shifted signals in aromatic protons of molecule A1, indicating that the moiety of anthracene-pyridinium was located at outside of cavity of SBE-β-CD (Fig. S12 in Supporting information). With above results in mind, a possible binding mode was deduced and given in supporting information. We made an attempt to verify host-guest binding site through 2D ¹H-¹H Noesy NMR spectra, but the result was unsatisfactory (Fig. S13 in Supporting information). It was probably due to cavity of SBE-β-CD was too large to induce strong correlated signals with alkyl chain of A1. In addition, molecule A1 was unable to generate self-aggregation even though increasing concentration to 1.2 × 10^–4 mol/L (Fig. S14 in Supporting information).

  It is well known that an ordered array of chromophores in supramolecular nanoassembly has unique advantages in constructing artificial light-harvesting systems by promoting energy transfer from donor to acceptor, similar to a dense array of chlorophyll molecules in green plants [1,22,33–36]. These requirements can be well met for amphiphilic SC4AD, in addition to enhancing fluorescence of molecule A1 through electrostatic assembly, whose amphiphilic self-assembly and long hydrophobic alkyl chains enable to load hydrophobic molecules and provide match distance to induce fluorescence resonance energy transfer between A1 and acceptors [37]. Therefore, the abovementioned supramolecular assemblies were used to further assemble with various organic dyes to explore possible FRET properties. Based on a principle of FRET, dyes EY, NiR, and Cy5.5 were selected due to the different overlaps between their absorption and emission of molecule A1 (Figs. 2a–c). To better load the dye acceptor, the optimal ratio of 0.25 was chosen to afford as many large nanoparticles as possible. As shown in Figs. 2d–f and Table 1, fluorescence of A1 (donor) at 535 nm and corresponding quantum yields were obviously reduced by introducing and increasing the fraction of EY, NiR or Cy5.5 (acceptor). Meanwhile, the characteristic emissions and integral areas of dyes EY at 570 nm, NiR at 638 nm, and Cy5.5 at 717 nm were activated and enhanced gradually, all of which reached constant values when the molar ratios of donor/acceptor were 150:1 for A1: EY, 100:1 for A1: NiR, and 450:1 for A1: Cy5.5, respectively. As the concentration of acceptor was fixed and concentration of donor was increased, the fluorescence of acceptor was also ignited successfully. All these spectral characteristics proved FRET processes between A1 and the dyes, and the fluorescence of acceptor was indeed originated from molecule A1 (Fig. S15 in Supporting information). Varying degrees of emission shifts of dyes, especially EY and Cy5.5 with charge transfer properties (Fig. S16 in Supporting information), were mainly attributed to variety in environmental polarity before (water environment) and after (hydrophobic environment) assembling with A1/SC4AD, hinting that dye acceptors were capsulated into nanoparticles. The corresponding fluorescence colors were presented by the 1931 CIE chromaticity diagram (Fig. S17 in Supporting information). Transmission electron microscopy (TEM) revealed that these supramolecular assembly containing dyes still retained the morphology of nanoparticles (Fig. S18 in Supporting information). In addition, FRET was also strongly validated by the change in lifetime of the donor. Through the addition of various dyes, the fluorescence lifetime of A1/SC4AD (10.3 ns) at 535 nm decreased to 3.5 ns for A1/SC4AD+EY, 3.3 ns for A1/SC4AD+NiR, and 6.5 ns for A1/SC4AD+Cy5.5, respectively (Fig. S19 and Table S1 in Supporting information). The energy transfer efficiencies and antenna effects were calculated as 70.4% and 3.7 (A1/SC4AD+EY), 76.0% and 4.0 (A1/SC4AD+NiR), and 43.0% and no antenna effect (A1/SC4AD+Cy5.5), respectively (Fig. S20 in Supporting information). As controlled experiments, there was no any fluorescence signal for individual dyes or dyes+SC4AD under the same conditions (Fig. S21 in Supporting information). Notably, the fluorescence of A1/SBE-β-CD was almost unchanged even after adding EY, NiR, or Cy5.5, probably indicating the indispensable importance of supramolecular nanoassembly in inducing FRET (Fig. S22 in Supporting information)

  Figure 2

  

  Figure 2.  Normalized emission spectra of A1/SC4AD and UV–vis absorption spectra of (a) EY, (b) NiR, and (c) Cy5.5; Fluorescence spectra of A1/SC4AD with increasing molar ratio of (d) EY, (e) NiR, and (f) Cy5.5 (λ_ex = 392 nm, ex/em slits: 5 nm/5 nm, [A1] = 2 × 10^–5 mol/L, [SC4AD] = 5 × 10^–6 mol/L, insets: photographs under 365 nm portable UV light).

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  Table 1

  

  Table 1.  Quantum yields of A1/SC4AD, A1/SC4AD+EY, A1/SC4AD+NiR, A1/SC4AD+Cy5.5 solutions in various integral areas.^a

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  Quantum yield (%)	Integral area
  	430–542 (nm)	542–750 (nm)	430–575 (nm)	575–765 (nm)	430–700 (nm)	700–765 (nm)
  A1/SC4AD	7.9	13.6	12.4	8.9	20.6	0.6
  A1/SC4AD+EY	3.9	22.9	ND	ND	ND	ND
  A1/SC4AD+NiR	ND	ND	3.8	29.7	ND	ND
  A1/SC4AD+Cy5.5	ND	ND	ND	ND	18.8	1.0
  a A1: SC4AD = 4:1 forA1/SC4AD, A1: SC4AD: EY = 150:37.5:1 forA1/SC4AD+EY, A1: SC4AD: NiR = 100:25:1 forA1/SC4AD+NiR, A1: SC4AD: Cy5.5 = 450:112.5:1 forA1/SC4AD+ Cy5.5 ([ A1] = 2 × 10 –5 mol/L). ND = not determined. The excitation wavelength is 392 nm.

  Intriguingly, the close relationship among absorption and emission of the three dyes gave us an inspiration to design and construct possible cascade FRET pathways, particularly, rare multipath FRET behavior (Fig. 3a). On the basis of FRET system A1/SC4AD+EY, introducing NiR as the second acceptor caused that the fluorescence intensity at 570 nm and 638 nm decreased and increased, respectively, which was clearly recognized by fluorescent color (Fig. 3b and Fig. S23a in Supporting information), while intensity at 535 nm almost maintained constant. In the meantime, dye Cy5.5 as the third acceptor was added to the abovementioned solution to perform the tertiary FRET process. According to Fig. 3c and Fig. S23b (Supporting information), Cy5.5 selectively induced a decrease in fluorescence at 638 nm of the second acceptor NiR to activate emission of itself at 717 nm, with the fluorescence of the donor (535 nm) and the first acceptor (570 nm) unchanged. These specified emission changes hinted that the fluorescence of EY and NiR, but not molecule A1, played dominant roles as donors in the second FRET (A1/SC4AD+EY+NiR) and the third FRET (A1/SC4AD+EY+NiR+Cy5.5), respectively. The fluorescence lifetime also demonstrated that the lifetime at 570 nm was reduced from 3.8 ns to 2.7 ns in the second FRET A1/SC4AD+EY+NiR (Fig. S24a and Table S2 in Supporting information). Compared to the variety in the first FRET A1/SC4AD+EY (from 10.3 ns to 3.3 ns), the lifetime at 535 nm only decreased slightly from 3.5 ns to 2.9 ns (Fig. S24b and Table S3 in Supporting information). After adding the third acceptor Cy5.5, selectively reduced lifetime at 638 nm (from 5.4 ns to 3.7 ns) further proved the specified energy transfer process from NiR to Cy5.5, while lifetimes at 535 nm (from 2.9 ns to 2.4 ns) and 570 nm (from 2.7 ns to 2.3 ns) were almost unchanged (Figs. 4a–c, Tables S4–S6 in Supporting information). To observe process of selective FRET more clearly, quantitative experiments were carried out by controlling donor/acceptor ratio. With A1/SC4AD+EY+NiR as an example, molar ratio of A1: EY was fixed at 3000:10, where partial fluorescence of donor A1 was retained due to insufficient FRET between A1 and EY. Subsequently, a small amount of the second acceptor NiR was added to the above solution. The result showed that fluorescence intensity at 570 nm decreased in sequence and the surplus fluorescence of A1 was unchanged (Fig. S25a in Supporting information). It strongly validated the acceptor NiR selectively absorbing energy of EY, but not residual energy of A1 in the second FRET process. Similar phenomenon was also found in a A1/SC4AD+EY+NiR+Cy5.5 system. Targeted reduction at 638 nm (fluorescence emission for NiR) was displayed when fluorescence of A1, EY, and NiR existed simultaneously via controlling molar ratio of A1: EY: NiR at 6000:1500:20 (Fig. S25b in Supporting information). As a result, it was rationally concluded that a scarce three-step cascade FRET behavior was successfully achieved. The first and second energy transfer efficiencies were calculated as 84.3% and 74.0% for A1/SC4AD+EY+NiR, respectively, together with an antenna effect of 2.8 at 638 nm (Fig. S26 in Supporting information). In the three-step cascade FRET system A1/SC4AD+EY+NiR+Cy5.5, the energy transfer efficiencies were 84.9% for the first FRET, 81.4% for the second FRET, and 66.9% for the third FRET, respectively (Figs. 4d–f). It was worth noting that, different from the no light-harvesting property in one-step FRET (A1/SC4AD+Cy5.5), the three-step FRET successfully induced an antenna effect (2.3) of Cy5.5 at 717 nm (Fig. S27 in Supporting information). Additionally, various two-step cascade energy transfer systems (A1/SC4AD+EY+Cy5.5, A1/SC4AD+NiR+Cy5.5) were also constructed and exhibited diverse light-harvesting performance (Fig. 3d, Figs. S28–S30, and Tables S7–S10 in Supporting information). When Cy5.5 was introduced in various systems, transition of shorter emission with high energy to longer emission of low energy is in agreement with FRET characteristics. Nevertheless, the color change from orange to yellow is due to weak emission and small peak area of longer wavelength from acceptor (Cy5.5) are not enough to compensate the lost fluorescence of donor (A1/SC4AD+EY, A1/SC4AD+NiR, or A1/SC4AD+EY+NiR), meanwhile, the other peak areas of shorter wavelength were almost unchanged. Changing the order in which dye acceptors were added gave the same fluorescence spectra, suggesting that these multilevel FRET processes were performed spontaneously via a donor-acceptor recognition pathway from high energy (low emission band) to low energy (high emission band) in supramolecular assembly, providing a theoretical foundation for designing smart multilevel energy transfer systems (Fig. 3e and Fig. S31 in Supporting information).

  Figure 3

  

  Figure 3.  (a) Normalized absorption and emission spectra of EY, NiR, and Cy5.5. (b) Fluorescence spectra of A1/SC4AD+EY with gradually adding NiR (λ_ex = 392 nm, ex/em slits: 5 nm/5 nm, [A1] = 2 × 10^–5 mol/L, [SC4AD] = 5 × 10^–6 mol/L, [EY] = 1.3 × 10^–7 mol/L, inset: photographs under 365 nm portable UV light). (c) Fluorescence spectra of A1/SC4AD+EY+NiR with gradually adding Cy5.5 (λ_ex = 392 nm, ex/em slits: 5 nm/5 nm, [A1] = 2 × 10^–5 mol/L, [SC4AD] = 5 × 10^–6 mol/L, [EY] = 1.3 × 10^–7 mol/L, [NiR] = 5.3 × 10^–8 mol/L, inset: photographs under 365 nm portable UV light). (d) Multipath FRET with A1/SC4AD as donor and various dyes as acceptors. (e) Change in energy level during three-step FRET process.

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  Figure 4

  

  Figure 4.  The time-resolved photoluminescence decay spectra of A1/SC4AD+EY+NiR before and after adding the third acceptor Cy5.5 at (a) 535 nm, (b) 570 nm, and (c) 638 nm. (d-f) The energy transfer efficiency in the three-step FRET system A1/SC4AD+EY+NiR+Cy5.5. [A1] = 2 × 10^–5 mol/L, [SC4AD] = 5 × 10^–6 mol/L, [EY] = 1.3 × 10^–7 mol/L, [NiR] = 5.3 × 10^–8 mol/L, [Cy5.5] = 3.3 × 10^–8 mol/L.

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  The SC4AD enhanced fluorescence and excellent FRET performance were successfully applied in information encryption (Fig. S32 in Supporting information). With various solution as patterns and background in a 96-well plate, the letters N and U were "written" by NiR solution, and SC4AD+NiR solution afford the letter K. The other areas were filled with pure water. The encrypted information NKU without luminescent components (A1/SC4AD) could not be found neither under daylight nor UV light. When we added the luminescent unit A1 solution in all holes, the letter K was activated and the incomplete information was only shown under UV light due to supramolecular assembly among A1 and SC4AD, and FRET between A1 and NiR. The letters N and U were still dark due to absence of SC4AD. With introducing the "last key" SC4AD solution in the 96-well plate, the complete information NKU, different from the green fluorescence in surroundings, was finally presented by UV light. Thus, a triplet information encryption (A1, SC4AD, and UV responsiveness) was triumphantly achieved.

  In summary, weak emissive anthracene-centered alkylammonium derivative A1 is used to assemble with macrocyclic SC4AD, which not only triumphantly induces robust fluorescence emission, but also activates multipath cascade FRET behavior with various dye molecules (EY, NiR and Cy5.5), including diverse two-step cascade FRET and three-step cascade FRET systems containing light-harvesting traits. Compared to one-step FRET, the three-step cascade FRET process provides higher energy transfer efficiency and an unexpected antenna effect, showing spontaneous energy transfer characteristics from high energy (low emission band) to low energy (high emission band) step-by-step. By adjusting group of the acceptors, various two-step cascade FRET systems are successfully constructed. It is believed that these spontaneous and selective multilevel FRET performances will be conducive to our in-depth understanding of the principle of multilevel fluorescence resonance energy transfer and provide a guideline for designing multilevel artificial light-harvesting materials.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  CRediT authorship contribution statement

  Wen-Wen Xu: Writing – original draft, Validation, Software, Investigation, Formal analysis. Yue-Xiu Qin: Validation, Formal analysis. Xiao-Yong Yu: Software. Lin-Nan Jiang: Investigation. Heng-Yi Zhang: Formal analysis. Yong Chen: Formal analysis. Yu Liu: Writing – review & editing, Visualization, Supervision, Resources, Project administration, Methodology, Funding acquisition, Conceptualization.

  Acknowledgment

  This work was financially supported by the National Natural Science Foundation of China (No. 22131008).

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2025.111068.

  
  
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• 

  Scheme 1  Schematic illustration of multipath cascade light-harvesting based on macrocyclic sulfonatocalix[4]arene.

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  Figure 1  Fluorescence spectra of A1 with adding different ratios of (a) SC4AD and (c) SBE-β-CD ([A1] = 2 × 10^–5 mol/L, λ_ex = 392 nm, ex/em slits: 5 nm/5 nm); UV–vis absorption spectra and characteristic absorbance at 247 nm of guest A1 with adding various molar ratio of (b, d) SC4AD ([A1] = 2 × 10^–5 mol/L).

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  Figure 2  Normalized emission spectra of A1/SC4AD and UV–vis absorption spectra of (a) EY, (b) NiR, and (c) Cy5.5; Fluorescence spectra of A1/SC4AD with increasing molar ratio of (d) EY, (e) NiR, and (f) Cy5.5 (λ_ex = 392 nm, ex/em slits: 5 nm/5 nm, [A1] = 2 × 10^–5 mol/L, [SC4AD] = 5 × 10^–6 mol/L, insets: photographs under 365 nm portable UV light).

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  Figure 3  (a) Normalized absorption and emission spectra of EY, NiR, and Cy5.5. (b) Fluorescence spectra of A1/SC4AD+EY with gradually adding NiR (λ_ex = 392 nm, ex/em slits: 5 nm/5 nm, [A1] = 2 × 10^–5 mol/L, [SC4AD] = 5 × 10^–6 mol/L, [EY] = 1.3 × 10^–7 mol/L, inset: photographs under 365 nm portable UV light). (c) Fluorescence spectra of A1/SC4AD+EY+NiR with gradually adding Cy5.5 (λ_ex = 392 nm, ex/em slits: 5 nm/5 nm, [A1] = 2 × 10^–5 mol/L, [SC4AD] = 5 × 10^–6 mol/L, [EY] = 1.3 × 10^–7 mol/L, [NiR] = 5.3 × 10^–8 mol/L, inset: photographs under 365 nm portable UV light). (d) Multipath FRET with A1/SC4AD as donor and various dyes as acceptors. (e) Change in energy level during three-step FRET process.

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  Figure 4  The time-resolved photoluminescence decay spectra of A1/SC4AD+EY+NiR before and after adding the third acceptor Cy5.5 at (a) 535 nm, (b) 570 nm, and (c) 638 nm. (d-f) The energy transfer efficiency in the three-step FRET system A1/SC4AD+EY+NiR+Cy5.5. [A1] = 2 × 10^–5 mol/L, [SC4AD] = 5 × 10^–6 mol/L, [EY] = 1.3 × 10^–7 mol/L, [NiR] = 5.3 × 10^–8 mol/L, [Cy5.5] = 3.3 × 10^–8 mol/L.

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  Table 1.  Quantum yields of A1/SC4AD, A1/SC4AD+EY, A1/SC4AD+NiR, A1/SC4AD+Cy5.5 solutions in various integral areas.^a

  Quantum yield (%)	Integral area
  	430–542 (nm)	542–750 (nm)	430–575 (nm)	575–765 (nm)	430–700 (nm)	700–765 (nm)
  A1/SC4AD	7.9	13.6	12.4	8.9	20.6	0.6
  A1/SC4AD+EY	3.9	22.9	ND	ND	ND	ND
  A1/SC4AD+NiR	ND	ND	3.8	29.7	ND	ND
  A1/SC4AD+Cy5.5	ND	ND	ND	ND	18.8	1.0
  a A1: SC4AD = 4:1 forA1/SC4AD, A1: SC4AD: EY = 150:37.5:1 forA1/SC4AD+EY, A1: SC4AD: NiR = 100:25:1 forA1/SC4AD+NiR, A1: SC4AD: Cy5.5 = 450:112.5:1 forA1/SC4AD+ Cy5.5 ([ A1] = 2 × 10 –5 mol/L). ND = not determined. The excitation wavelength is 392 nm.

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