Aggregation-Induced Emission: A Simple Strategy to Improve

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Aggregation-Induced Emission: A Simple Strategy to Improve Chemiluminescence Resonance Energy Transfer Lijuan Zhang, Nan He, and Chao Lu Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/ac5041605 • Publication Date (Web): 19 Dec 2014 Downloaded from http://pubs.acs.org on January 2, 2015

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Analytical Chemistry

Aggregation−Induced Emission: A Simple Strategy to Improve Chemiluminescence Resonance Energy Transfer

Lijuan Zhang, Nan He, and Chao Lu*

State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China.

Fax/Tel.: +86 10 64411957. E−mail: [email protected].

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ABSTRACT: The emergence of aggregation−induced emission (AIE) has opened up a new avenue for scientists. There is a great demand for the development of a new generation chemiluminescence resonance energy transfer (CRET) acceptors with AIE characteristics due to the aggregation−caused chemiluminescence (CL) quenching effect commonly observed in the conventional fluorophore CL acceptors at high concentrations. However, the systematical studies involving in AIE−amplified CL are still scarce. Herein, it is the first report that the gold nanocluster aggregates (a type of well-defined AIE molecules) are used to study their influence on bis(2,4,6−trichlorophenyl) oxalate (TCPO)−H2O2 CL reaction. Interestingly, the AIE molecules in the diluted solution are unable to boost the CL signal of TCPO−H2O2 system, but their aggregates display a strongly enhanced CL emission compared to their counterparts of fluorophore molecules, thanks to the unique AIE effect of gold nanoclusters. In comparison to rhodamine B with the aid of an imidazole catalyst, the detection limit of gold nanocluster aggregate-amplified CL probe for H2O2 (S/N=3) is low in the absence of any catalyst. Finally, the other two typical AIE molecules, Au(I)−thiolate complexes

and

9,10–bis[4–(3–sulfonatopropoxyl)–styryl]anthracene

(BSPSA),

are

investigated to verify the generality of the AIE molecule−amplified CL emissions. These results demonstrate effective access to highly fluorescent AIE molecules with practical applications in avoiding the aggregation–induced CL quenching at high concentrations, which can be expected to provide a novel and sensitive platform for the CL amplified detection.

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INTRODUCTION Chemiluminescence resonance energy transfer (CRET) involves a nonradiative dipole−dipole energy transfer from a chemiluminescence (CL) donor to a suitable acceptor. It occurs via the specific oxidation of a luminescent substrate during CL reaction without the need for an external excitation source, and thus it can minimize nonspecific signals observed in fluorescence resonance energy transfer by utilizing simultaneous external excitation of both donor and acceptor.1-4 Currently, fluorescent dyes are widely employed as CL energy acceptors.5-8 However, the concentration of fluorescent dyes in solution during CRET is limited to a low level to prevent the typical aggregation−caused quenching (ACQ) at high concentrations. The aggregation−caused CL quenching becomes an intractable obstacle for an efficient CRET. Recently, various approaches and processes have been developed to mitigate these barriers.9-11 For example, peroxalate polymers and fluorescent dyes composed of CL nanoparticles to sequester peroxalate fuels and fluorophore in a close proximity in order to generate the intense CL emissions;9 highly efficient CRET can be achieved by assembling fluorescent dyes on the surface of layered double hydroxides as a result of the suppression of the intermolecular π–π stacking interactions among aromatic rings and the improvement of molecular orientation and planarity in the layered double hydroxide matrix.12 However, these attempts have met with only limited success. Such the problems can be absolutely avoided by the removal of ACQ characteristics. In 2001, Tang group observed a novel phenomenon of aggregation–induced emission (AIE), which is exactly opposite to the above–mentioned ACQ system.13 A group of nonemissive propeller–shaped luminescent molecules are non–emissive in diluted solutions but are induced to emit intensely when aggregated in concentrated solutions through a mechanism of the restriction of intramolecular rotation.14,15 The emergence of AIE can 3



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sweep away the shortcomings of ACQ. Such an intriguing AIE effect can boost the fluorescent quantum yields of the molecules up to two orders of magnitude. To date, a variety of fluorogens with AIE characteristics have attracted widespread interest as a multifunctional platform for various applications in chemical sensors, biological imaging, and optoelectronic devices.16-18 However, to the best of our knowledge, systematical studies focusing on the applications of AIE effects in the CL field are still scarce. Therefore, it is our primary interest to investigate the influence of AIE on the CL emissions. Metal nanoclusters (e.g., Au, Ag, and Cu) have received a great deal of interest due to their unique size–dependent optical properties that differ substantially from those of either the corresponding atoms and the traditional nanoparticle counterpart,19-22 and thus exhibited great potentials as unique functional building blocks in a wide range of applications such as biosensors, optoelectronic materials, and catalysts.23-27 Recently, scientists observed an AIE phenomenon of metal nanoclusters: the aqueous metal nanocluster colloidal solution can emit a faint fluorescence intensity, but generate a striking photoluminescence upon solvent−induced aggregation.28-30 In this contribution, we selected gold nanoclusters as a model AIE molecule to reveal the role of AIE molecules on bis(2,4,6−trichlorophenyl) oxalate (TCPO)−H2O2 CL system. Our preliminary research indicated that gold nanocluster aggregates exhibited a remarkable enhancement on TCPO−H2O2 CL reaction (Figure 1). To gain further insight in AIE structure–property relationships in CRET behavior, we have comprehensively explored the structural, optical and CL properties. In addition, the other two

typical

AIE

molecules,

Au(I)−thiolate

complexes31

and

9,10–bis[4–(3–sulfonatopropoxyl)–styryl]anthracene (BSPSA),32 were also used as CRET acceptors to couple with TCPO CL system. With respect to the experimental observations, we concluded unambiguously that the common nature of these AIE molecules are pivotal to

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improve the current CRET efficiency. Our success should inspire more exciting research in the development of other CL systems–based AIE molecules.

Figure 1. Schematic illustration of gold nanocluster aggregate–amplified TCPO–H2O2 CL.

EXPERIMENTAL SECTION Chemicals and Solutions. All chemicals used were of analytical grade without any further purification. All solutions were prepared with deionized water (18.2 MU cm, Milli Q,

Millipore,

Barnstead,

CA,

USA).

Hydrogen

tetrachloroaurate(III)

trihydrate

(HAuCl4·3H2O), L–glutathione in the reduced form (GSH), TCPO and imidazole were obtained from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). NaOH, MgSO4, H2O2, ethanol, petroleum ether, acetone, acetonitrile, dichloromethane, tetrahydrofuran (THF) and ethyl acetate were purchased from Beijing Chemical Reagent Company (Beijing, China). Rhodamine B was purchased from Tianjin Fuchen Chemical Reagent Factory (Tianjin, China). N,N−dimethylacetamide (DMAc) was purchased from Sigma–Aldrich Chemical Co. (St. Louis, MO, USA). K3PO4, 9,10−Dibromoanthracene, 4−methoxystryrene, palladium(II) acetate, boron tribromide, sodium ethoxide (NaOEt) and 1,3−propanesultone were purchased from Alfa Aesar (Ward Hill, MA, USA). A working solution of TCPO was 5



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prepared by dissolving the solids in ethyl acetate freshly. The working solutions of H2O2 were prepared by diluting 30% (v/v) H2O2 in acetonitrile before use. Apparatus. The photoluminescence spectra were obtained using a F−7000 fluorescence spectrophotometer (Hitachi, Japan) at a slit of 5.0 nm with a scanning rate of 1500 nm/min. The UV–visible spectra were acquired on a Shimadzu UV−2401 PC spectrophotometer (Tokyo, Japan). Transmission electron microscopy (TEM) photographs, high resolution transmission electron microscopy (HRTEM) were measured on a Tecnai G220 TEM (FEI Company, USA). CL spectra were detected with a Hitachi F−7000 fluorescence spectrophotometer (Tokyo, Japan). The excitation lamp was off and the emission slit was maintained at 20 nm. The scan rate of the monochromators was maintained at 3000 nm/min. X−ray photoelectron spectroscopy (XPS) measurements were performed using an ESCALAB−MKII 250 photo electron spectrometer (Thermo, USA). The lifetime was obtained by an Edinburgh FLS 980 Lifetime and Steady State Spectrometer. The quantum yield was performed from the reconvolution fit analysis (Edinburgh F980 analysis software) on an Edinburgh instrument spectrometer using Xe lamp. 1H–nuclear magnetic resonance (1H–NMR) spectra were recorded at room temperature with a 600 MHz Bruker (Germany) spectrometer. Mass spectrum (MS) was carried out with Quattro microtriple quadrupole mass spectrometer (Waters, USA). The CL detection was conducted on a biophysics chemiluminescence (BPCL) luminescence analyzer (Institute of Biophysics, Chinese Academy of Science, Beijing, China). Synthesis of Gold Nanoclusters. Gold nanoclusters were synthesized following a literature procedures with minor modifications.31 Briefly, the fresh prepared aqueous solutions of HAuCl4 (20 mM, 1.0 mL) and GSH (100 mM, 0.3 mL) were added into 8.7 mL of deionized water under gentle stirring at room temperature. And then, the formed mixture was heated to 70 °C under gentle stirring for 24 h. A yellow−colored and orange−emitting 6


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gold nanoclusters were obtained. The as−prepared gold nanocluster solution was purified by the dialysis membrane with a molecular weight cutoff of 2000 for 12 h. The obtained gold nanoclusters (0.4 mg/mL) were stored at 4 °C for further use. The pH value of gold nanocluster colloidal solution was adjusted to pH 7.0 with 0.5 M NaOH before use. Synthesis of Au(I)−Thiolate Complexes. Au(I)−thiolate complexes were synthesized according to literature procedures with little modification.31 In brief, Au(I)−thiolate complexes were synthesized by chemical reduction of HAuCl4 with GSH. The fresh prepared aqueous solutions of HAuCl4 (20 mM, 1.0 mL) and GSH (100 mM, 0.4 mL) were added into 8.6 mL of deionized water under gentle stirring for 0.5 h at room temperature. The generated white precipitation was purified by centrifugation (12000 rpm for 5min) and washed with deionized water for three times. The precipitation was then dispersed in 10 mL of deionized water, and then its pH was adjusted to pH 7.0 with 0.5 M NaOH. The obtained colorless solution was aged for 0.5 h. The as−prepared Au(I)−thiolate complexes (0.8 mg/mL) were stable for several months when they were stored at 4 °C. Synthesis of BSPSA. According to our previous paper,32 an aqueous solution of BSPSA

was

prepared

by

the

following

three

steps:

(1)

synthesis

of

9,10−Bis(4−methoxystyryl)anthracene. A 100 mL round−bottom flask was charged with 9,10−Dibromoanthracene (1.02 g), 4−methoxystryrene (0.96 g), K3PO4 (1.92 g), palladium(II) acetate (60 mg) and 30 mL of anhydrous DMAc. The reaction mixture was heated to 110 °C in an oil bath and stirred for 24 h under nitrogen atmosphere. And then, the mixture was allowed to cool to room temperature and poured into 50 mL water to quench the reaction completely. Dichloromethane (50 mL) was used to extract the crude for six times. The product was washed with saturation salt and dried over anhydrous MgSO4. Finally, the crude product was chromatographed over silica gel column chromatography using petroleum ether/dichloromethane (4:1, v/v) as an eluent to yield 1.25 g (94 %) of a 7



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yellow powder; (2) synthesis of 9,10−Bis(4−hydroxystyryl)anthracene. Adding 0.67 g 9,10−Bis(4−methoxystyryl)anthracene and 20 mL anhydrous dichloromethane into a 100 mL flask. The reaction took place under liquid nitrogen−ethanol at −78 °C. A solution of 1.51 g of 6 mM boron tribromide in 10 mL anhydrous dichloromethane was added carefully to the mixture with gentle stirring. The reaction mixture was stirred for 12 h and then allowed to warm to room temperature slowly. After that, 15 mL water was added carefully to the reaction mixture to make the product and unreacted boron tribromide hydrolyze. The organic layers were dried over anhydrous MgSO4 and concentrated to dryness under vacuum. The crude product was further purified by silica gel column chromatography using petroleum ether/acetone (3:1, v/v) as an eluent to yield 0.50 g (80%) of a yellow powder; (3) synthesis of BSPSA. Adding 0.54 g 9,10−Bis(4−hydroxystyryl)anthracene and 20 mL anhydrous dichloromethane into a 100 mL flask under nitrogen. A solution of NaOEt (0.20 g) which was dissolved in anhydrous ethanol (20 mL) was added dropwise under continuous stirring for 1 h until the color of the solution turned to orange−red. And then, 0.37 g 1,3−propanesultone in 20 mL ethanol was added to this solution. The reaction mixture was stirred continuously for 12 h at room temperature and then a yellow product was precipitated out. At last, the product was filtrated and then washed with ethanol and acetone two times to give 0.75 g (82%) of a yellow powder. Note that the structures of the obtained products in each step were confirmed by an analysis using NMR spectra and BSPSA product (its chemical structure was shown in Figure S1) was confimed by MS (data were shown in Supporting Information of reference 32). CL Measurements. As shown in Figure S2, the aggregates of Au(I)−thiolate complexes/gold nanoclusters/BSPSA controlled by varying the volume fraction of solvent (i.e., ethanol or THF) and water. Rhodamine B was dissolved in ethanol. 100 µL of 5.0 mM TCPO was mixed with 100 µL of the aggregates or rhodamine B solution in a CL quartz 8


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vial adjacent to photomultiplier tube (PMT). Then 100 µL of 5 mM H2O2 solution was injected to the mixture, and the CL signal was detected by the PMT. The signals were imported to the computer for data acquisition.

RESULTS AND DISCUSSION AIE Characteristics of Gold Nanoclusters. The typical adsorption and fluorescence profiles of the as–prepared gold nanoclusters were recorded. As shown in Figure 2a, a well-defined peak in the UV region can be observed with the gold nanoclusters, which was clearly different from characteristic surface plasmon resonance band of large gold nanoparticles at around 520 nm, illustrating that the formed gold nanoclusters are smaller than 2 nm.25 This speculation was further confirmed by TEM/HRTEM images of the as–prepared gold nanoclusters, indicating the typical structural lattices spacing of 0.234 nm corresponding to the (111) planes of the face−centered cubic gold crystal (Figure 2c).33 Additionally, under excitation at 365 nm, the gold nanoclusters in the aqueous solution exhibited an emission maximum at 565 nm, and the excitation spectrum displayed a peak at around 400 nm (Figure 2a). The inset photograph of Figure 2a showed that a bright yellow luminescence from the as–prepared gold nanoclusters was clearly observed under UV light (365 nm), indicating that highly fluorescent gold nanoclusters were obtained. Figure 2b showed the changes of the fluorescence (FL) intensity of the diluted solution of as–prepared gold nanoclusters after the addition of different amounts of ethanol. Interestingly, under excitation at 365 nm, a weak fluorescence emission for the diluted solution of gold nanoclusters in water was observed at 565 nm; however, the fluorescence intensity of the gold nanoclusters kept rising when the volumetric fraction of ethanol in water–ethanol mixtures was increased from 30% to 90%. This phenomenon may be attributed to the AIE characteristics of gold nanoclusters in poor solvents (ethanol) as a 9



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result of the enhanced aurophilic gold–gold interactions and the restricted intramolecular motions.29,31 Note Figure S3 demonstrated that the fluorescence intensities were not quenched at high concentrations of gold nanoclusters, further confirming the AIE characteristics of gold nanoclusters. Such the AIE feature of gold nanoclusters in 90% ethanol–10% water mixture can be visually manifested under UV light at 365 nm (inset of Fig. 2b), which was in accordance with that of the TEM image of the gold nanocluster aggregates (Figure 2d). The fluorescence quantum yield of the gold nanoclusters was increased from 9.8% to 42.7% after aggregation. Similarly, the fluorescence lifetime of gold nanoclusters was increased from 2.58 to 3.63 µs when gold nanoclusters were aggregated in 90% ethanol−10% water mixture (Figure S4).

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Figure 2. (a) UV−vis absorption (blue line), photoexcitation (dotted red line, λem= 565 nm), and photoemission (solid red line, λex= 365 nm) spectra of gold nanoclusters. Inset: digital photographs of gold nanoclusters under (left) daylight and (right) UV light. (b) Fluorescence spectra of the diluted solution of gold nanoclusters after the addition of different amounts of ethanol. Inset: digital photographs of the diluted gold nanoclusters in water (left) and in 90% ethanol−10% water mixture (right) under UV light. (c) TEM images of gold nanoclusters in water and (d) in 90% ethanol−10% water mixture. Inset: HRTEM image of gold nanoclusters.

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Luminescent Gold Nanocluster Aggregate−Improved CRET. The influence of gold nanoclusters in variable volume fractions of ethanol on the TCPO−H2O2 system was discussed. The concentration of TCPO was investigated and the results showed that the optimum concentration of TCPO was 5 mM (Figure S5). Figure 3a showed that the CL intensity of the TCPO−H2O2 system was gradually increased with an increase of ethanol fractions in water–ethanol mixtures. These interesting results were in good agreement with those of ethanol−induced fluorescence changes of gold nanoclusters (please see Figure 2b), indicating that AIE nature of the gold nanoclusters led to the CL enhancement of the TCPO−H2O2 system. Figure 3b showed that the CL spectrum of TCPO−H2O2 system overlapped well with the absorption of the gold nanoclusters in 90% ethanol−10% water mixture, meaning the efficient occurrence of CRET between TCPO energy donors and gold nanocluster aggregate acceptors.3 From the CL spectrum of TCPO−H2O2 system in the presence of gold nanoclusters in 90% ethanol−10% water mixture (inset of Figure 3b), we calculated that the CRET efficiency was about 47.9% by dividing area integral of aggregates emission spectrum by the integral area of the whole spectrum of the aggregate− TCPO−H2O2 system.1 Furthermore, the UV−vis absorption and fluorescence spectra of gold nanocluster aggregates kept constant before and after the CL reactions (Figures S6 and S7), further confirming that the gold nanocluster aggregates acted as CRET acceptors in the present system.

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Figure 3. (a) Influence of gold nanoclusters in variable volume fractions of ethanol on the TCPO−H2O2 system. The concentrations of TCPO, gold nanoclusters and H2O2 were 5 mM, 20 µg/mL and 5 mM, respectively. (b) CL spectrum of TCPO−H2O2 system (red line) and absorption spectrum of the gold nanoclusters in 90% ethanol−10% water mixture (blue line). Inset: CL spectrum of the TCPO−H2O2 system in presence of gold nanoclusters in 90% ethanol−10% water mixture.

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Advantages of Luminescent Gold Nanocluster Aggregates as CRET Acceptors. Fluorescent dyes are usually used as CRET acceptors by harmful imidazole–accelerated reaction.34,35 Here, rhodamine B was employed as the model CRET acceptors to highlight the superior properties of gold nanocluster aggregates (Figure 4). The kinetic profile of rhodamine B−TCPO−H2O2 system indicated that the peak of the CL curve appeared at 20 min with a decay time of 4 h, but the maximum value of the CL signal was 30 s with a decay time of 4 min in the presence of imidazole catalyst. Interestingly, the CL signal reached its maximum value at 3 s with a decay time of 2.5 min when the gold nanocluster aggregates were injected into the TCPO−H2O2 system in the absence of any catalyst. In addition, Figures S8 and S9 demonstrated ACQ characteristics of rhodamine B at high concentrations as CRET acceptors. Figures S10 and S11 showed that the CL intensity of the rhodamine B−TCPO−H2O2 system was lower than that of gold nanocluster aggregate−TCPO−H2O2 system, although the CRET efficiency of the rhodamine B−TCPO−H2O2 system was almost 100%. Finally, the analytical performances of rhodamine B CRET acceptors were compared with those of the gold nanocluster aggregates. For rhodamine B, a linear response in the concentration range from 10 µM to 300 µM was obtained with a detection limit of 6.0 µM (S/N=3) for the determination of H2O2 (Figure S12); for gold nanocluster aggregates, it was found that the CL intensity was proportional to H2O2 concentration in the range of 5.0–400 µM, and the detection limit for H2O2 (S/N=3) was 2.0 µM (Figure S13). In conclusion, these results demonstrated that the gold nanocluster aggregates could act as an ideal CRET acceptor.

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Figure 4. Kinetic CL intensity−time profile for the rhodamine B−TCPO−H2O2 system. Inset: kinetic CL intensity−time profiles for the gold nanocluster aggregate−TCPO−H2O2 system (red line) and imidazole−rhodamine B−TCPO−H2O2 system (blue line). The concentrations of TCPO, imidazole, rhodamine B, gold nanoclusters and H2O2 were 5 mM, 2 mM, 0.5 mM, 20 µg/mL and 5 mM, respectively. Gold nanoclusters were aggregated in 90% ethanol−10% water mixture.

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Universality of AIE Molecule−Amplified CL. The other two typical AIE molecules, Au(I)−thiolate complexes and BSPSA,31,32 were investigated to verify the generality of the AIE molecule−amplified CL emissions. Figure 5a demonstrated the AIE characteristics of the Au(I)−thiolate complexes, which was reported by Xie and his co-workers.31 The fluorescence quantum yield of Au(I)−thiolate complexes in 95% ethanol−5% water mixture was 16.8%. When the aggregates of the Au(I)−thiolate complexes were added into the TCPO−H2O2 system, an obvious CL enhancement was observed as a result of the occurrence of an efficient CRET (34.6% CRET efficiency) between TCPO donors and Au(I)−thiolate complex aggregate acceptors (Figure 5b and Figures S14−S18). In addition, the kinetic CL intensity-time profile for Au(I)−thiolate complex aggregate−TCPO−H2O2 system (Figure 19) indicated a relative faster reaction rate were (a decay time of 2.5 min). On the other hand, the AIE characteristics of BSPSA with the fluorescence quantum yield of 18.4% in 98% THF−2% water mixture were certified according to our previous paper (Figure 5c).32 Figure 5d and Figure S20−S22 indicated that BSPSA also could act as an efficient CRET acceptor with 72.9% transfer efficiency for the TCPO−H2O2 system. Figures S23 showed that the CL kinetic rate of BSPSA aggregate−TCPO−H2O2 system was relatively slow (a decay time of 70 min). These results showed that AIE molecules exhibited the generality as CRET acceptors to amplify CL emissions.

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Figure 5. (a) Fluorescence spectra (λex= 365 nm) of the Au(I)−thiolate complexes in water (red line) and in 95% ethanol−5% water mixture (blue line). Insets: relationship between the fluorescence intensity and volumetric fraction of ethanol. Digital photographs of the Au(I)−thiolate complexes in water (left) and in 95% ethanol−5% water mixture (right) under UV light at 365 nm. (b) Influence of Au(I)−thiolate complexes in water and in 95% ethanol−5% water mixture on the CL intensity of the TCPO−H2O2 system. Inset: CL spectrum of the TCPO−H2O2 system in presence of Au(I)−thiolate complexes in 95% ethanol−5% water mixture. (c) Fluorescence spectra (λex = 410 nm) of BSPSA in water (red line) and in 98% THF−2% water mixture (blue line). Insets: relationship between the fluorescence intensity and volumetric fraction of THF. Digital photographs of BSPSA in water (left) and in 98% THF−2% water mixture (right) under UV light at 365 nm. (d) Influence of BSPSA in water and in 98% THF−2% water mixture on the CL intensity of the TCPO−H2O2 system. Inset: CL spectrum of the TCPO−H2O2 system in presence of BSPSA in 98% THF−2% water mixture. The concentrations of TCPO, Au(I)−thiolate complexes, BSPSA and H2O2 were 5 mM, 40 µg/mL, 0.5 mM, 25 µM and 5 mM, respectively.

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CONCLUSIONS In summary, the AIE molecules are used as the new type of CRET acceptors. It is found that these AIE molecules with an increase in the degree of aggregation exhibit remarkably enhanced performances toward the CL signals of the TCPO–H2O2 system due to a high CRET efficiency between TCPO donors and AIE acceptors. In contrast to their conventional counterparts (e.g., rhodamine B), the AIE molecules (e.g., gold nanocluster aggregates) have much faster reaction rate in the absence of any catalyst, and mitigate the aggregation−caused CL quenching at high concentrations. Additionally, this study achieves a significant breakthrough in improving the CRET efficiency by utilizing AIE molecules. Our strategy can be generalized to perform other CL systems by simply tuning the emission spectrum of AIE molecules for the development of specific CL probes. We are working on expanding the scope of AIE potential applications in analytical chemistry.

ASSOCIATED CONTENT Supporting Information Chemical structure of BSPSA, schematic diagram of the static CL analysis system, fluorescence spectra of gold nanoclusters with different concentrations, fluorescence decay profiles of gold nanoclusters in water and in 90% ethanol−10% water mixture, effects of the concentration of TCPO on the gold nanocluster aggregate−TCPO−H2O2, UV−vis absorption spectra of gold nanocluster aggregates in 90% ethanol−10% water mixture before and after reaction, fluorescence spectra of gold nanocluster aggregates in 90% ethanol−10% water mixture before and after reaction, fluorescence spectra of different concentrations of rhodamine B, CL intensity of TCPO−H2O2 system mixed with different concentrations of rhodamine B, CL spectrum of rhodamine B−TCPO−H2O2 system, CL intensity of TCPO−H2O2 system mixed with gold nanoclusters and rhodamine B, CL 18


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intensity of the imidazole−rhodamine B−TCPO−H2O2 system by adding different concentrations of H2O2, CL intensity of the gold nanocluster aggregate−TCPO−H2O2 system by adding different concentrations of H2O2, UV−vis absorption spectra of Au(I)−thiolate complexes in water and in 95% ethanol−5% water mixture, TEM image of Au(I)−thiolate complexes in 95% ethanol−5% water mixture, UV−vis absorption spectra of Au(I)−thiolate complexes in 90% ethanol−10% water mixture before and after the CL reaction, fluorescence spectra of Au(I)−thiolate complexes in 95% ethanol−5% water mixture before and after the CL reaction, XPS of Au(I)−thiolate complexes before and after the CL reaction, kinetic CL intensity−time profile for the Au(I)−thiolate complex aggregate−TCPO−H2O2 system, UV−vis absorption spectra of BSPSA in water and in 98% THF−2% water mixture, UV−vis absorption spectra of BSPSA in 98% THF−2% water mixture before and after the CL reaction, fluorescence spectra of BSPSA in 98% THF−2% water mixture before and after the CL reaction, and kinetic CL intensity−time profile for the BSPSA aggregate−TCPO−H2O2 system. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * E−mail: [email protected]. Fax/Tel.: +86 10 64411957. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by National Basic Research Program of China (973 Program, 2014CB932103), the National Natural Foundation of China (21375006), the 973 Program 19



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(2011CBA00503), and the Fundamental Research Funds for the Central Universities (YS1406 and JD1311). We also thank Prof. Xue Duan, Beijing University of Chemical Technology, for his valuable discussion.

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For TOC only

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