Bright dual‐color electrochemiluminescence of a structurally determined Pt1Ag18 nanocluster

Metal nanoclusters possess excellent electrochemical, optical, and catalytic properties, but correlating these properties remains challenging, which is the foundation to generate electrochemiluminescence (ECL). Herein, we report for the first time that a structurally determined Pt1Ag18 nanocluster generates intense ECL and simultaneously enhances the ECL of carbon dots (CDs) via an electrocatalytic effect. Pt1Ag18 nanocluster show aggregation‐induced emission enhancement and aggregation‐induced ECL enhancement under light and electrochemical stimulation, respectively. In the presence of tripropylamine (TPrA) as a coreactant, solid Pt1Ag18 shows unprecedented ECL efficiency, which is more than nine times higher than that of 1 mM Ru(bpy)32+ with the same TPrA concentration. Potential‐resolved ECL spectra reveal two ECL emission bands in the presence of TPrA. The ECL emission centered at 650 nm is assigned to the solid Pt1Ag18 nanocluster, consistent with the peak wavelength in self‐annihilation ECL and photoluminescence of the solid state. The ECL emission centered at 820 nm is assigned to the CDs on the glassy carbon electrode. The electrocatalytic effect of the nanoclusters enhanced the ECL of the CDs by a factor of more than 180 in comparison to that without nanoclusters. Based on the combined optical and electrochemical results, the ECL generation pathways and mechanisms of Pt1Ag18 and CDs are proposed. These findings are extremely promising for designing multifunctional nanocluster luminophores with strong emissions and developing ratiometric sensing devices.


INTRODUCTION
Atomically precise metal nanoclusters have attracted much attention as materials due to their definite molecular compositions, atomic structures, and the rich electrochemical, optical, and catalytic properties, which inducing a broad range of applications and allowing for the structureproperty correlations. [1,2]Recently, metal nanoclusters have been observed as emerging electrochemiluminescence (ECL) luminophores.The studies of metal nanoclusters are developing.The ECL of gold nanoclusters [3] and the correlation between nanocluster structure and the ECL properties [4] have been demonstrated.The recent report by our group that the ECL signal of Au 12 Ag 13 is 400 times higher than that of the Ru(bpy) 3 2+ -tripropylamine (TPrA) standard system reveals the great potential of metal nanoclusters as novel ECL This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.© 2023 The Authors.Aggregate published by SCUT, AIEI, and John Wiley & Sons Australia, Ltd.
emitters. [5]Moreover, it has been demonstrated that the metal nanocluster geometry, electronic structure, and excited state have important effects on ECL.Although metal nanoclusters have versatile properties and their ECL has been investigated in solution, the combination of ECL with other properties is challenging [6] and ECL in aggregated states has rarely been reported. [7]n fact, ECL is a process where radicals of a luminophore are electrogenerated in the vicinity of an electrode to react and form excited species, which emit light upon relaxing to ground state. [8,9]Two pathways, annihilation and coreaction, have been discovered for ECL generation.[11] Coreaction has been extensively studied as an alternative ECL pathway that requires the introduction of secondary coreactants into the system. [8]As a coreactant, tripropylamine (TPrA) has been observed to enhance oxidative reduction ECL in many systems. [12]Fundamental research on the interactions between luminophores and coreactants can provide insights into the emission process and improve the mechanistic understanding. [13,14]The definite structure, unique electrochemical property, good luminescent property, and excellent catalytical property of metal nanoclusters provide good platform for ECL mechanism and development of high ECL lumiphores.
[31] To elucidate complicated ECL mechanisms, ECL spectra have been used to identify the luminescent species at the molecular level. [32]Furthermore, ECL spectroscopy has been successfully applied in multianalyte detection and ratiometric ECL biosensors. [33]erein, we report the synthesis, structural determination, optical properties, ECL performance, and electrocatalytic catalysis behavior of a bimetallic Pt 1 Ag 18 nanocluster (Pt 1 Ag 18 (S-Adm) 6 (DPPP) 4 Cl 4 , where S-Adm is 1-adamantanethiol and DPPP is bisdiphenylphosphinopropane).The Pt 1 Ag 18 nanocluster produces intense ECL and electrocatalytic dual functionality.For the first time, intense self-annihilation and coreactant ECL was observed for Pt 1 Ag 18 in the solid state and the mechanism was investigated.Unexpectedly, the Pt 1 Ag 18 nanoclusters promote the generation of excited-state carbon dots (CDs) at a glassy carbon electrode by electrocatalytic effect, which produce strong ECL at ∼820 nm, as revealed by a spectrum-resolution ECL technique.Property analysis and mechanistic study reveal that the rich electrochemical and catalytical features are responsible for the excellent ECL performance.This work opens an avenue to construct nanocluster ECL platform and ratiometric sensing devices.

Structure and composition of Pt 1 Ag 18 nanoclusters
Pt 1 Ag 18 nanoclusters were synthesized by a post-etching method (for experimental details, see the Supporting Information).The total structure of Pt 1 Ag 18 was determined by single-crystal X-ray diffraction (Figure 1), which revealed that Pt 1 Ag 18 crystallized in the monoclinic space group P21/c.As shown in Figure 1, an icosahedral Pt 1 Ag 12 kernel (Figure 1A) is wrapped with a Ag 3 (SR) 3 Cl motif at both ends (Figure 1B).Two DPPP ligands are pinned to the Ag 3 (SR) 3 Cl motif and the Pt 1 Ag 12 kernel (Figure 1C) to form a Pt 1 Ag 18 nanocluster (Figure 1D).Eight Pt 1 Ag 18 molecules pack at the eight vertices of the unit cell, and half of the two Pt 1 Ag 18 molecules sit inside the unit cell, so the entire unit cell contains two Pt 1 Ag 18 molecules (Figure 1E and Figure S1).The π⋯π interactions were observed in the neighboring nanocluster molecules (Figure 1F).
The composition of Pt 1 Ag 18 was further confirmed by electrospray ionization mass spectrometry, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS).As shown in Figure S2A, a peak was observed at m/z = 2579.24,corresponding to [Pt 1 Ag 18 (S-Adm) 6 (DPPP) 4 Cl 4 +Cl 2 +K 4 ] 2+ (calcd m/z = 2579.53),which indicates that Pt 1 Ag 18 is neutral with eight free electrons.All expected elements were detected by XPS, and the binding energy of Ag was between those of Ag(0) and Ag(I), indicating the presence of Ag(0) in the Pt 1 Ag 18 nanocluster (Figure S2C,D).TGA of Pt 1 Ag 18 showed a total weight loss of 49.84%, consistent with the theoretical weight loss of 50.63% (Figure S2B).

Optical and electrochemical properties of Pt 1 Ag 18 nanoclusters
The UV-vis absorption spectrum of Pt 1 Ag 18 showed two peaks at 375 and 400 nm, as well as two shoulder peaks at 465 and 515 nm (Figure 2A, orange line).The Pt 1 Ag 18 nanoclusters emitted bright red photoluminescence (PL) after excited by 400 nm (Figure S3), with emission bands centered at 635, 640, and 695 nm in dichloromethane (DCM) solution, amorphous powder, and crystalline states, respectively (Figure 2A).The red shift of 55 nm between the amorphous powder and crystalline states of Pt 1 Ag 18 differs from the blue shift reported for Au 4 Ag 13 nanoclusters. [34][37] The quantum yields of Pt 1 Ag 18 in solution, amorphous powder, and crystalline states were 1.6%, 23.3%, and 28.4%, respectively, with lifetimes of 0.24, 2.15, and 2.24 μs, respectively (Figure 2B).The PL characteristics of Pt 1 Ag 18 nanoclusters in both solution and solid states showed sensitivity to oxygen (O 2 ).Specifically, the PL intensity decreased upon O 2 purging but increased upon N 2 purging (Figure S4), indicating a phosphorescent behavior exhibited by the nanoclusters.The PL behavior of Pt 1 Ag 18 nanoclusters in a mixed solvent system consisting of dichloromethane (DCM) as the good solvent and n-hexane (Hex) as the poor solvent was investigated.Figure S5 demonstrates that the PL intensity of the nanoclusters exhibited a slight increase as the solvent ratio of DCM to Hex ranged from 10:0 to 2:8.However, a significant enhancement in PL intensity was observed when the solvent ratio reached 1:9.These results are consistent with the dynamic light scattering (DLS) analysis (Figure S6), which revealed a minor increase in the aggregation size for solvent ratios ranging from 10:0 to 2:8, but a pronounced increase at a solvent ratio of 1:9.The interactions among benzene rings made nanoclusters more rigid and thus more luminescent (Figure 1F).These results indicate that intense aggregation-induced emission enhancement (AIEE) and crystallization-induced emission enhancement effects occur in Pt 1 Ag 18 nanoclusters.
The redox behavior was analyzed using differential pulse voltammetry (DPV).As shown in Figure 2C, the DPV curve during anodic scanning showed four quasi-reversible oxidation peaks at potentials of 0.25 V (O1), 0.50 V (O2), 0.77 V (O3), and 1.03 V (O4), indicating the removal of four electrons from the Pt 1 Ag 18 nanocluster.One reduction peak was observed at a potential of −0.59 V (R1) during cathodic scanning.The relatively small onset potential of the first oxidation peak is highly beneficial for subsequent ECL and electrocatalysis processes.

Self-annihilation ECL of solid Pt 1 Ag 18 nanoclusters
Subsequently, the self-annihilation ECL of Pt 1 Ag 18 in solution and solid states was investigated.Pt 1 Ag 18 show weak self-annihilation ECL in DCM solution (Figure S7).Surprisingly, the ECL of amorphous solid Pt 1 Ag 18 was observed during potential scanning and step experiments, implying an aggregation-induced electrochemiluminescence enhancement (AIECLE) effect.As shown in Figure 3A, ECL from the self-annihilation of electrogenerated Pt 1 Ag 18 radicals is observed at potentials of 1.0-1.2V, which corresponds to the increasing current.The absence of multiple oxidation peaks in the solid state may be due to the diffusion of redox species being hindered in a solid, but it does not mean that the nanoclusters cannot be oxidized at the corresponding potentials.Although Pt 1 Ag 18 can be reduced at −0.41 V, no cathodic ECL signal was detected.In addition, no ECL was observed before 1.0 V, which may be due to the fact that insufficient electrolysis, a short radical lifetime or the excited state formed at this time does not emit light (or the light emission is too weak to be detected).The ECL spectra of Pt 1 Ag 18 in the solid state collected at different potentials were all similar.The averaged spectrum was centered at ∼650 nm (Figure 3B), which is slightly red-shifted compared to the PL spectrum of Pt 1 Ag 18 in the amorphous state.Such a red shift might be due to the low crystallinity on the electrode surface as the PL in crystalline state is more red-shifted than that in amorphous state (Figure 2A, green line vs. blue line).Similarly, anodic ECL was observed for Pt 1 Ag 18 in the potential-step experiment (Figure 3C).The averaged spectrum (Figure 3D) was similar to that obtained in the potential-scan experiment.

Coreactant ECL of solid Pt 1 Ag 18 nanoclusters
The rich electrochemical properties and self-annihilation ECL of Pt 1 Ag 18 in the amorphous solid state are encouraging for the generation of ECL in the presence of TPrA as a coreactant.The structural stability of Pt 1 Ag 18 nanoclusters in the presence of TPrA in solution was assessed.It was observed that the nanoclusters exhibited favorable stability in the presence of TPrA (Figure S8), which is advantageous for subsequent ECL investigations.The ECL of solid Pt 1 Ag 18 in the presence of 50 mM TPrA was detected over three potential scanning cycles (Figure S9). Figure 4A shows the coreactant ECL intensity of Pt 1 Ag 18 in the solid state.Intense ECL was observed in the presence of 50 mM TPrA as a coreactant, which allowed us to collect the potential-resolved ECL spectra.As shown in Figure 4A, the onset potential for the ECL of Pt 1 Ag 18 in the solid state (0.50 V) matched the onset oxidation potential of TPrA (Figure 4A, black line) and the onset potential of the second oxidation peak of the Pt 1 Ag 18 nanocluster (Figure 2C).The coreactant ECL intensity reached a maximum at 1.10 V during anodic scanning (Figure 4A, blue line).Surprisingly, the ECL spectra of solid Pt 1 Ag 18 in the presence of TPrA has two ECL emission bands centered at ∼650 and 820 nm, the intensities of which varied with the potential.Figures 4B,C shows the ECL spectra obtained by anodic scanning (from 0.55 to 1.20 V) and cathodic scanning (from 1.20 to 0.55 V), respectively, during the first cycle.As shown in Figure 4B, when the applied potential was 0.55 V, only one emission peak at ∼650 nm was observed, which is assigned to the emission of the Pt 1 Ag 18 nanocluster.The intensity of this emission band increased as the applied potential became more positive, reaching a maximum at 1.00 V (Figure 4B).During cathodic scanning, the emission intensity at ∼650 nm decreased as the potential decreased (Figure 4C).
To eliminate the influence of the ECL emission from Pt 1 Ag 18 (∼650 nm) and identify the emission band centered at ∼820 nm, the ECL spectra were fitted with Gaussian function (Figure S10). Figure 4E,F shows the ECL spectra centered at ∼650 nm during anodic and cathodic scanning, respectively.Figure 4H,I shows the ECL spectra centered at ∼820 nm during anodic and cathodic scanning, respectively.Figure 4D,G shows the ECL intensities of the two emission bands at corresponding potentials, respectively.As shown in Figure 4G, during anodic scanning, the intensity of the ECL emission at ∼820 nm increased during potential from 0.55 to 1.10 V and then decreased during potential from 1.10 to 1.20 V with the change in potential.In cathodic scanning, the emission intensity at ∼820 nm increased during potential from 1.15 to 1.05 V and then decreased during potential from 1.00 to 0.55 V.The emission intensity at ∼650 nm increased from 0.55 to 0.90 V during anodic scanning and decreased from 1.20 to 0.55 V during cathodic scanning (Figure 4D).
In addition, we studied the ECL of solid Pt 1 Ag 18 in the presence of 25 mM TPrA.As shown in Figure S11, two emission bands were observed during potential scanning.Similarly, the ECL spectra were fitted with Gaussian function (Figure S12).Two ECL emission bands centered at ∼650 and 820 nm were identified (Figure S13).Both emissions are weaker than that in the presence of 50 mM TPrA, meaning the coreactant has the same effect on the two ECL emissions.The ECL stability of solid Pt 1 Ag 18 over 10 cycles for sweeping potential ECL was studied.The relative standard deviation (RSD) of ECL intensity under 10 cycles of continuous potential sweep is 12.13% (Figure S14).
To assign the ECL emission centered at ∼820 nm, we explored factors that influenced this emission, including the state of Pt 1 Ag 18 nanocluster, the type of nanoclusters, electrode, and electrolytes.We studied the coreactant ECL of Pt 1 Ag 18 in solution state.Although the ECL in the solution state is much weaker than that in the solid state, two emission bands at ∼650 and 820 nm can still be resolved (Figure 5D-I, Figure S15), which is consistent with the ECL emissions in solid state.Such results imply that the emission band of ∼820 nm is not due to the state changes of the nanoclusters.Next, we studied the ECL of Pt 1 Ag 28 , the parent nanocluster of Pt 1 Ag 18 , and found only ECL emission band was observed at 670 nm, which is consistent with its PL emission (Figure 5A-C).Such results indicate that the double ECL emissions are highly dependent on the type of nanocluster.We investigated the ECL emission in the absence of Pt 1 Ag 18 nanoclusters on GCE.As shown in Figure S16, a bare GCE had an extremely weak ECL band centered at ∼820 nm, similar to the second emission band in coreactant ECL of Pt 1 Ag 18 .In addition, we studied ECL emission of solid Pt 1 Ag 18 on a Pt disk electrode and Pt mesh electrode.Only one emission band at ∼650 nm was observed (Figure S17).When PBS was replaced with 0.1 M sodium perchlorate as the electrolyte, the ECL spectrum also contained two emission bands (Figure S18), indicating that the emission at ∼820 nm does not originate from the phosphate electrolyte.
These results confirm that the ECL emission at ∼820 nm origin from the GCE and can be enhanced by Pt 1 Ag 18 nanoclusters.Recently, He et al. demonstrated the ECL activity of bare GCE in the presence of benzoyl peroxide as a coreactant, and the CDs on the GCE produced the ECL. [38]It can be conclude that the CDs on GCE produce the emission at ∼820 nm, where the Pt 1 Ag 18 nanoclusters significantly enhance this emission.This enhancement ability is strongly dependent on the species of the metal nanocluster.By integrating the ECL intensity spectra in the presence and absence of Pt 1 Ag 18 nanoclusters (blue line in Figure 4G and pink line in Figure S16A, respectively), we conclude that these nanoclusters enhance the ECL of CDs by a factor of more than 180 in comparison to that in absence of Pt 1 Ag 18 nanoclusters.

Electrochemiluminescence efficiency of solid Pt 1 Ag 18
The ECL efficiency of Pt 1 Ag 18 in the solid state was compared to that of the Ru(bpy) 3 2+ /TPrA system (Equa- b Determined relative to that of the Ru(bpy) 3 2+ /TPrA system with an absolute ECL efficiency (ϕECL) of 5%. [ 39]on S1). Figure S19 shows the coreactant ECL of 1 mM Ru(bpy) 3 2+ with 50 mM TPrA.  of Pt 1 Ag 18 and Pt 1 Ag 18 /CD were more than 9 and 11 times higher, respectively, than that of 1 mM Ru(bpy) 3 2+ with 50 mM TPrA. [39]Although the ECL of [Ru(bpy) 3 ] 2+ /TPrA on GCE was underestimated, since the ECL of the cluster was tested in the solid state, its actual ECL should also be underestimated due to the much lower electron transfer rate, ion migration rate and free radical reaction rate in the solid state in comparison to that in solution state.

Electrocatalytic effect of Pt 1 Ag 18 and ECL generation pathways
The results of the above-described photoelectrochemical and spectroscopic experiments showed that the AIEE effect of the Pt 1 Ag 18 nanoclusters remarkably promotes its ECL in the solid state, resulting in an AIECLE effect.The coreactant significantly enhances the ECL emission of the Pt 1 Ag 18 nanoclusters in the solid state.An ECL generation pathway is proposed in Figure 6.For the ECL emission band at ∼650 nm, the Pt 1 Ag 18 nanoclusters immobilized on the electrode are first oxidized to form cationic radicals (step 1).Since the coreactant ECL signal starts to appear after 0.6 V (Figure 4A), the nanoclusters generate ECL after being oxidized to +2 (Figure 2C).Then, the coreactants diffuse to the GCE surface, where they are oxidized and deprotonated to form radicals (steps 2 and 3).The generated Pt 1 Ag 18 radicals and TPrA rad-icals react to form excited Pt 1 Ag 18 species (step 4).A single luminescent excited state was proposed because the emission peak at ∼650 nm was not observed to shift with potential in potential sweeps, unlike the Au 21 nanocluster.Different valence excited states are proposed in the Au 21 nanoclusters as the spectra are shifted with the potential sweep. [4]The excited Pt 1 Ag 18 species relax to the ground state and release energy via photon emission (step 5).
Furthermore, the Pt 1 Ag 18 nanoclusters significantly enhance the ECL of the CDs on GCE.In early work, Wu et al. reported the ECL of bare GCE in basic media, and three ECL signals were observed at 1.36, 1.72, and 2.34 V, indicating a high over-potential in the generation of ECL from bare GCE. [40]In the system of bare GCE with TPrA as coreactant (Figure S16A), the onset potential of ECL for bare GCE is 0.80 V, indicating that CDs on the GCE are oxidized at 0.80 V.However, the onset potential of the ECL of CDs on GCE in the presence of Pt 1 Ag 18 nanoclusters is 0.60 V (Figure 4G-I), implying that the CDs were oxidized at 0.60 V and generate ECL.Pt 1 Ag 18 significantly reduces the overpotential of CDs to generate ECL.In addition, we compared the resistance of bare GCE and GCE coated with Pt 1 Ag 18 nanoclusters.As shown in Figure S20A, the resistance of GCE coated with Pt 1 Ag 18 is 3.5 times greater than that of bare GCE.While the current of GCE shows comparable value in the presence and absence of Pt 1 Ag 18 (Figure S20B), revealing a significant electrocatalytic effect of Pt 1 Ag 18 on CDs.DPV of Pt 1 Ag 18 shows that its first oxidation potential (Figure 2C) is lower than that of the CDs (Figure S16A), indicating that the Pt 1 Ag 18 nanoclusters are oxidized first during potential-scan experiments, and the CDs on GCE are subsequently oxidized as the potential goes higher.Considering these experiment results, we propose a generation pathway of the ECL of CDs on GCE (Figure 6).The oxidized Pt 1 Ag 18 nanoclusters can promote the generation of excited cation free radicals CD +• (step 6), and the excited state CD +• react with TPrA radicals to form an excited CD species (step 7), which relaxes to the ground state and releases energy via photon emission (step 8).

CONCLUSIONS
Here, we synthesized and determined the structure of Pt 1 Ag 18 nanoclusters and investigated their PL and ECL performance in solution and solid states.AIEE and AIECLE effects were observed for the PL and ECL of the Pt 1 Ag 18 nanocluster, respectively.The self-annihilation ECL spectrum of solid Pt 1 Ag 18 was collected using both potential scan and step experiments, and the ECL spectrum in the solid state was similar to the PL spectrum in the amorphous state.Potentialresolved ECL spectra reveal two ECL emission bands for Pt 1 Ag 18 in the presence of TPrA as coreactant.The emission centered at ∼650 nm belongs to the solid Pt 1 Ag 18 nanocluster, consistent with its self-annihilation ECL and PL spectra in the solid state.The ECL emission centered at ∼820 nm originates from the GCE.Investigation of the ECL mechanism revealed the unique electrocatalytic effect of the Pt 1 Ag 18 nanocluster that significantly enhanced the ECL of CDs on GCE by a factor of more than 180 in comparison to that in absence of Pt 1 Ag 18 nanoclusters.The rich electrochemical property endows Pt 1 Ag 18 with unique electrocatalytic

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I G U R E 2 (A) Absorption spectrum of Pt 1 Ag 18 in dichloromethane (DCM) and photoluminescence (PL) spectra of Pt 1 Ag 18 in DCM, amphous and crystal state.PL spectra were collected under irradiation of 400 nm.(B) Lifetimes of Pt 1 Ag 18 in DCM, amorphous powder, and crystalline states.(C) Differential pulse voltammetry (DPV) curve of ∼0.18 mM Pt 1 Ag 18 in DCM with 0.1 M TBAP.A 3 mm glassy carbon electrode (GCE) served as a working electrode.A pulse peak amplitude of 50 mV, width of 0.05 s, period of 0.2 s, and 4 mV increment per cycle were applied to obtain DPV.

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I G U R E 3 Self-annihilation electrochemiluminescence (ECL) of Pt 1 Ag 18 in the solid state.(A) Cyclic Voltammetry (CV, left axis) and ECL-potential (right axis) curves (scan rate of 0.1 V/s).(B) Self-annihilation ECL spectrum of Pt 1 Ag 18 in the solid state obtained from the potential scanning experiment.(C) Potential-step self-annihilation ECL of Pt 1 Ag 18 in the solid state.The electrode potential was held for 2.5 s at each potential from −1.2 to 1.2 V; no potential was applied during the first and final 2.5 s.The dotted line indicates the potential steps.(D) Self-annihilation ECL spectrum of Pt 1 Ag 18 in the solid state obtained from the potential-step experiment.All experiments were conducted using a glassy carbon electrode (GCE) modified with 50 μg of Pt 1 Ag 18 in 0.1 M phosphate buffer solution (PBS, pH 7.4).

F I G U R E 4
Coreactant electrochemiluminescence (ECL) of solid Pt 1 Ag 18 with TPrA as a coreactant.(A) Cyclic Voltammetry (CV, left axis) and ECLpotential (right axis) curves.(B and C) ECL spectra of solid Pt 1 Ag 18 with TPrA during (B) anodic scanning from 0.55 to 1.20 V and (C) cathodic scanning from 1.20 to 0.55 V. (D) ECL intensity versus potential for the emission band at ∼650 nm (the ECL intensity at each potential was obtained by integrating the corresponding ECL spectra from 450 to 850 nm).(E and F) ECL spectra for the emission band at ∼650 nm at potentials from (E) 0.55 to 1.20 V and (F) 1.20 to 0.55 V. (G) ECL intensity versus potential for the emission band at ∼820 nm (the ECL intensity at each potential was obtained by integrating the corresponding ECL spectra from 500 to 1100 nm).(H and I) ECL spectra for the emission band at ∼820 nm at potentials ranging from (H) 0.55 to 1.20 V and (I) 1.20 to 0.55 V.All experiments were conducted using a GCE modified with a 50 μg of Pt 1 Ag 18 in 0.1 M phosphate buffer solution (PBS, pH 7.4) with 50 mM TPrA.

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I G U R E 5 (A-C) Coreactant electrochemiluminescence (ECL) of the parent nanocluster Pt 1 Ag 28 in solid state with TPrA as a coreactant.(A) Cyclic Voltammetry (CV, left axis) and ECL-potential (right axis) curves.(B) ECL spectra of solid Pt 1 Ag 28 with TPrA in oxidation scanning at potentials from 0.70 to 1.20 V. (C) ECL spectra of solid Pt 1 Ag 28 with TPrA in reduction scanning at potentials from 1.20 to 0.70 V.The coreactant ECL of Pt 1 Ag 28 in solid state was collected with a 50 μg Pt 1 Ag 28 modified on GCE in 0.1 M phosphate buffer solution (PBS, pH 7.4) with 50 mM TPrA.The potential scan rate is 0.1 V/s, and the exposure time is 1.0 s. (D-I) Coreactant ECL of Pt 1 Ag 18 in solution state with TPrA as a coreactant.(D and G) ECL spectra of Pt 1 Ag 18 in solution with TPrA during (D) anodic scanning from 0.60 to 1.20 V and (G) cathodic scanning from 1.20 to 0.60 V. (E and F) ECL spectra for the emission band at ∼650 nm at potentials from (E) 0.60 to 1.20 V and (F) 1.20 to 0.60 V. (H and I) ECL spectra for the emission band at ∼820 nm at potentials ranging from (H) 0.60 to 1.20 V and (I) 1.20 to 0.60 V. ECL of Pt 1 Ag 18 in solution was detected in dichloromethane (DCM) with 0.1 M TBAP and 50 mM TPrA at a scan rate of 0.1 V/s.The concentration of Pt 1 Ag 18 is ∼1 mM.
) 3 2+ obtained by integrating the ECL intensity spectra (Figure 4D,A, and Figure S19), the ECL efficiencies F I G U R E 6 Proposed electrochemiluminescence (ECL) generation pathway and mechanism.(A) Electron transfer and reaction between Pt 1 Ag 18 nanocluster and CDs.(B) Schematic illustration of the enhanced ECL of Pt 1 Ag 18 and CDs by coreaction and electrocatalysis, respectively.
Table 1 lists ECL intensity ratio, charge ratio, and relative efficiency data for Pt 1 Ag 18 and Pt 1 Ag 18 /CD relative to the Ru(bpy) 3 2+ /TPrA system.Based on the ECL intensities of solid Pt 1 Ag 18 , Pt 1 Ag 18 /CD and Ru(bpy