Electrogenerated Chemiluminescence Intensity Research Articles

Electrogenerated Chemiluminescence of Perovskite Quantum Dots

Metal halide perovskites have attracted immense scientific interest owing to their unique optoelectronic properties, such as high absorption coefficient, band gap tunable in the entire visible range, and high photoluminescence quantum efficiency. Perovskites have been applied to applications in solar cells, photodetectors, nanolasers, and light emitting diodes (LED) because of these unique properties. Light emitting diodes are based on the luminescence of the material. Tunable photoluminescence (PL) and electrogenerated chemiluminescence (ECL) can be obtained from perovskite quantum dots (QDs) by varying their size and shapes because of quantum confinement effect. In this study, ligand assisted precipitation method is used to synthesize lead based mixed chloride and bromide perovskite quantum dots. The absorbance, fluorescence at 450nm, lifetime and quantum yield results will be presented. The average diameter of 3.5±1nm and the d-spacing of 0.3nm was determined using HR-TEM. ECL can be obtained from a transparent electrode coated with perovskite QDs using tripropylamine (TPrA) as the co-reactant in acetonitrile as solvent, although the ECL performance of dry-coated perovskite QDs suffers from decomposition and/or dissolution of the dots into electrolyte. The ECL stability issue can be partially addressed by coating the QDs along with polystyrene film accompanied with decrease in ECL intensity due to the sluggish charge transfer through polystyrene film. A dual ECL peak spectrum with emissions at 480 nm and 580 nm is observed over the period of ECL generation and collection. Further experiments need to be done to fully understand the mechanism behind this shift.

Electrogenerated chemiluminescence of cucurbit[n]urils modified electrode and its sensing application

In the present work, electrogenerated chemiluminescence (ECL) behaviors of Ru(bpy)32+ were investigated at cucurbit[n]urils (CB[n]s, n=5,6,7,8) modified electrodes in neutral condition, based on which a novel label-free strategy for lysozyme (Lyz) detection was proposed. Strong anodic Ru(bpy)32+ ECL could be generated at the modified electrodes in the absence of coreactant. The ECL intensity increased in the following order: CB[5]<CB[6]<CB[7]<CB[8], and the strongest ECL signal was obtained at the CB[8] modified electrode. The ECL mechanism was proposed based on the spectroscopic and the electrochemical results, and the excited state of Ru(bpy)32+ was proven as the luminophor. Lyz exhibited apparent inhibiting effect on the ECL emission, and could be sensitively detected without any labeling process. Under the optimal conditions, the decreased ECL intensity varied linearly with the logarithm of Lyz concentration in the range of 1.4×10−12-6.0×10−10mgmL−1, and the detection limit was calculated as 1.0×10−12mgmL−1 (3σ). Moreover, the modified electrode exhibited high sensitivity and good stability in the detection of Lyz. The results revealed a new role of cucurbit[n]urils in ECL sensing field, which will promote potential analytical application of macrocycle molecules.

Electrochemiluminescence sensing platform for ultrasensitive DNA analysis based on resonance energy transfer between graphitic carbon nitride quantum dots and gold nanoparticles

Electrogenerated chemiluminescence (ECL) of semiconductor quantum dots (QDs) is considered as a powerful technique in the fabrication of biosensor, however, the inherent toxicity of the heavy metal ion containing in QDs limits their further applications. Thus, searching for environment-friendly luminescent nanomaterials with high electrochemiluminescence (ECL) efficiency is an urgent goal. In this work, a solid-state method under low temperature was adopted to prepare graphitic carbon nitride quantum dots (g-CNQDs). By using coreactant K2S2O8, a strong cathodic ECL signal of g-CNQDs could be observed in phosphate buffer. A novel ECL resonance energy transfer procedure was constructed between g-CNQDs (emitter) and gold nanoparticles (acceptor). A signal probe was formed by connecting gold nanoparticles at the hairpin DNA (Hai-DNA) terminal. When the signal probe was anchored on g-CNQDs, ECL resonance energy transfer occurred due to the ECL quenching of gold nanoparticles to g-CNQDs. This phenomenon decreased the ECL signal. In the presence of target DNA (T-DNA), the looped structure of Hai-DNA could be destroyed by T-DNA, and gold nanoparticles were separated from g-CNQDs. Accordingly, the ECL resonance energy transfer procedure was hindered, and the ECL signal was recovered again. The ECL intensities exhibited linear correlation with the logarithm of T-DNA concentration from 0.02 fM to 0.1 pM, and the limit of detection was 0.01 fM (3σ). With the developed ECL resonance energy transfer system, good selectivity and high sensitivity were achieved in T-DNA detection.

Synthesis and electrochemiluminescence of a new iridium(III) complex

A new water-soluble iridium(III) diimine complex with appended glucose was synthesized and characterized. The photophysical properties and electrogenerated chemiluminescence (ECL) behavior of the complex were studied. The new iridium(III) complex displayed good emission under the UV-light excitation in aqueous solution and gave out the strongest ECL signals on the glass carbon electrode in the presence of high concentration of tri-n-propylamine (TPA, 20 mM) compared to that on Au and Pt electrodes in phosphate buffer (pH = 7.5). But at low concentration of TPA (1.0 mM), the ECL intensity of the complex was close on the GC, Au and Pt electrodes. The ECL of the system had a good linearity with the TPA concentration from 0.1 μM to 1 mM with a limit of determination of 50 nM (S/N = 3).

Electrogenerated Chemiluminescence of Phosphate-Modified Polymeric Carbon Nitride for Sensing of NADH: Role of Luminophore–Coreactant Interactions in Enhancing the Signal

Graphitic carbon nitride (GCN) is a potential material that has attracted a large attention for its application in electrogenerated chemiluminescence (ECL) due to its unique optical and electronic properties. Nanostructured and modified forms of GCN shows highly stable and intense ECL signals than the bulk counterpart. We report here that introducing phosphate species with different amounts during the synthesis of bulk GCN alters its morphology, surface area, bandgap and ECL properties. Interestingly, the phosphate (0.125%)-modified polymeric carbon nitride on glassy carbon electrode (PCN-0.125/GCE) showed an enhanced ECL intensity which is four times higher than that of the bulk GCN. Also, the ECL intensity shows a dependence on the phosphate content. Among the different coreactants tested, use of tri-propylamine (TPrA) resulted in the higher ECL intensity. The interaction between PCN-0.125 and TPrA could play an important role by forming an ion-pair that was revealed from 1H MAS-NMR spectroscopic results. The significance of this work lies in the gradual increase in the ECL intensity of PCN-0.125/GCE with each addition of nicotinamide adenine dinucleotide (NADH) in the range of 10 to 70 nM with 5.2 nM as the limit of detection (LOD). Our work demonstrates a new ECL sensing platform using an earth-abundant, easy-to-synthesize material, PCN, to detect NADH at lower level and this will be more useful in clinical diagnostics.

A conceptual framework for the development of iridium(iii) complex-based electrogenerated chemiluminescence labels.

Translation of the highly promising electrogenerated chemiluminescence (ECL) properties of Ir(iii) complexes (with tri-n-propylamine (TPrA) as a co-reactant) into a new generation of ECL labels for ligand binding assays necessitates the introduction of functionality suitable for bioconjugation. Modification of the ligands, however, can affect not only the photophysical and electrochemical properties of the complex, but also the reaction pathways available to generate light. Through a combined theoretical and experimental study, we reveal the limitations of conventional approaches to the design of electrochemiluminophores and introduce a new class of ECL label, [Ir(C^N)2(pt-TOxT-Sq)]+ (where C^N is a range of possible cyclometalating ligands, and pt-TOxT-Sq is a pyridyltriazole ligand with trioxatridecane chain and squarate amide ethyl ester), which outperformed commercial Ir(iii) complex labels in two commonly used assay formats. Predicted limits on the redox potentials and emission wavelengths of Ir(iii) complexes capable of generating ECL via the dominant pathway applicable in microbead supported ECL assays were experimentally verified by measuring the ECL intensities of the parent luminophores at different applied potentials, and comparing the ECL responses for the corresponding labels under assay conditions. This study provides a framework to tailor ECL labels for specific assay conditions and a fundamental understanding of the ECL pathways that will underpin exploration of new luminophores and co-reactants.

Electrogenerated Chemiluminescence of ZnO/MoS2 Nanocomposite and Its Application for Cysteine Detection

ZnO/MoS2 nanocomposite was synthesized by hydrothermal method, and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy, respectively. The morphology of ZnO nanoparticles changed from rod-like to cubic shape when they were deposited onto MoS2 nanosheets, revealing that the MoS2 layer could limit the growth of ZnO. Electrogenerated chemiluminescence (ECL) of ZnO/MoS2 nanocomposite was investigated in neutral condition with S2O82− as coreactant, and strong cathodic ECL signal was obtained, which is stronger than that of pure ZnO nanomaterials. Cysteine exhibited apparent inhibiting effect on ECL signal, and could be sensitively detected. In the range of 1.0 × 10−8 to 1.0 × 10−6 mol L−1, the decreased ECL intensities linearly varied with the logarithm of cysteine concentration, and the detection limit was calculated as 6.5 × 10−9 mol L−1 (3σ). The proposed ECL sensor exhibited high sensitivity and good stability, which revealed the potential application of 2D nanocomposite in ECL sensing field.

A convenient electrogenerated chemiluminescence biosensing method for selective detection of 5-hydroxymethylcytosine in genomic DNA

Herein, a novel and convenient electrogenerated chemiluminescence (ECL) biosensing method for the quantitative detection of 5-hydroxymethylcytosine (5-hmC) in genomic DNA was developed by employing thiolated anchor probe DNA to immobilize 5-hydroxymethylcytosine double-stranded DNA (5-hmC-dsDNA) and a ruthenium(II) complex-tagged reporter probe as an ECL probe. Briefly, the 5-hmC-dsDNA was firstly oxidized to 5-formylcytosine dsDNA (5-fC-dsDNA) by KRuO4 in high yields. Subsequently, the thiolated anchor probe DNA is employed to help immobilize the 5-fC-dsDNA onto the gold electrode surface via the Au-S bond. An ECL probe DNA, labeled with a signal transducer − Ru(bpy)2(cbpy)NHS, hybridized with the anchor probe DNA on the electrode, resulting in an intensive ECL emission. The obtained ECL intensity was linearly proportional to the content of 5-hmC in the range from 0.0090% to 0.5761%, with the limit of detection calculated to be 0.0036% (S/N = 3). Finally, we applied the developed 5-hmC detection strategy in various mice tissues. It demonstrates that the content of 5-hmC measured by this method in different mice tissues vary significantly: 5-hmC is highest in brain and lowest in spleen. The success in assaying the mice tissues samples signifies its great promise in a broad range of practical applications for the quantitative detection of 5-hmC in genomic DNA.

Anti-Site Defects-Assisted Enhancement of Electrogenerated Chemiluminescence from in Situ Mn2+-Doped Supertetrahedral Chalcogenide Nanoclusters.

Understanding and revealing the connection between defects and dopant for improving electrogenerated chemiluminescence (ECL) efficiency remain a constant challenge. In this work, the in situ Mn2+-doped Mn1.36Zn5.64In28S56 supertetrahedral chalcogenide semiconductor nanoclusters (NCs) with an ECL efficiency as high as 27.1% was obtained, the corresponding ECL behaviors were investigated, and the vital role of more anti-site defects (ADs) introduced in situ on the ECL emission was elucidated. The ADs can not only give rise to the ECL emission peak at 494 nm but also assist transfer of electrons to induce and enhance the ECL emission at 627 nm from doped Mn2+ in the NCs. Furthermore, based on the fact that dissolved oxygen can enhance the ECL intensity, a highly sensitive ECL sensor for the determination of dissolved oxygen was developed. This insight into the fundamental interactions between Mn2+ dopants and defects in NC host may open new opportunities for the design of novel ECL materials to promote their application potential in electrochemical analysis and imaging.

Homoleptic cyclometalated iridium(III) complex nanowires electrogenerated chemiluminescence sensors for high-performance discrimination of proline enantiomers based on the difference of electron-transfer capability

Chiral molecules can generally exhibit different physiological and biological activities, thus triggering wide interest in chiral discrimination. Herein, we demonstrate a sensitive homoleptic cyclometalated iridium(III) complexes nanowires (Ir(piq)3 NWs) electrogenerated chemiluminescence (ECL) sensor for high-performance discrimination of chiral molecules based on the difference in electron-transfer ability between different radicals. The developed Ir(piq)3 NWs/ITO sensor exhibits high ECL signal and satisfying stability without the presence of co-reactant based on hot electron-induced ECL, which would spur its further application in detecting proline enantiomers. Obvious difference on the ECL intensity towards L-Pro and D-Pro is observed under the presence of high concentration of proline enantiomers, which attributes to the different electron-transfer capability between Ir+(piq)3 and L-pro•/D-pro•. In order to attain high-performance discrimination, we construct the Ir(piq)3 NWs/TPrA sensor to achieve chiral discrimination for trace amounts of proline enantiomers (1.0 × 10−9 M), which attributes to the strong molecular interactions enhanced by introduction of active radical TPrA•.

A novel electrogenerated chemiluminescence biosensor for histone acetyltransferases activity analysis and inhibition based on mimetic superoxide dismutase of tannic acid assembled nanoprobes

A simple and sensitive turn-off electrogenerated chemiluminescence (ECL) biosensor was designed for the analysis of histone acetyltransferases (HATs) activity and inhibitor evaluation based on the anti-hydrolysis ability of acetylated peptide and mimetic superoxide dismutase (SOD) features of tannic acid (TA) assembled gold nanoparticles (AuNPs) nanoprobes. In this strategy, after the acetylated reaction in the presence of HATs, the acetylated peptide on electrode was resistance to the hydrolysis of trypsin, and can absorb AuNPs@TA-Fe probe onto the electrode by the hydrophobic interaction and hydrogen bonding interaction. Thus, the ECL signal of the modified electrode in luminol solution decreased significantly owing to the mimetic SOD features of the TA assembled nanoprobe that can eliminate the reactive oxygen species. The ECL intensity changes can be utilized for sensitive HATs activities detection and inhibitor screening. The detection limit of the as-prepared ECL biosensor was 0.074 nM (S/N = 3). Moreover, the as designed ECL biosensor was also applied in MCF-7 cell lysates for HATs activity analysis and drug inhibition, which is feasible to HATs activity analysis and inhibitor screening, and presents highly promise in HAT-related clinical diagnostics.

Sensitive electrogenerated chemiluminescence biosensing method for the determination of DNA hydroxymethylation based on Ru(bpy)32+-doped silica nanoparticles labeling and MoS2-poly(acrylic acid) nanosheets modified electrode

5-Hydroxymethylcytosine (5-hmC), an oxidation product of 5-mC (5-methylcytosine), is presented in DNA of most mammalian cells and play an important role in the alteration of cancer-related genes. Herein, a sensitive electrogenerated chemiluminescence (ECL) biosensing method for the determination of 5-hmC in DNA (5-hmC DNA) was established on the basis of chemical modification and nanomaterial amplification. First, electrochemically reduced molybdenum disulfide-poly(acrylic acid) (rMoS2-PAA) nanosheets were used to modify glassy carbon electrode (GCE) to form an ECL biosensing electrode (rMoS2-PAA/GCE) which has large accessible surface area to immobilize more DNA. Then, a capture probe with amino group was hybridized with the target 5-hmC DNA and immobilized on the surface of rMoS2-PAA/GCE via amido bond. When cysteamine was introduced, the M.HhaI methyltransferase (M.HhaI) was used as specific recognition element to replace the hydroxyl group of 5-hmC by thiol and generated the amine-derivated DNA. Finally, surface chemically activated Ru(bpy)32+-doped silica (Ru@SiO2) nanoparticles, carriers of ECL reagents, were employed as signal amplification unit which covalently bonded to the amine-derivated DNA resulting in an increased ECL intensity. The increased ECL intensity was linearity to the 5-hmC DNA concentration in a range from 5.0 × 10−14 M to 1.0 × 10−11 M, with a lower detection limit of 1.2 × 10−14 M. Besides, the proposed method also displayed a good selectivity to 5-hmC in the presence of 5-C and 5-mC. Moreover, the developed biosensing method was successfully employed to monitor human urine sample.

A novel and sensitive electrogenerated chemiluminescence biosensor for detection of p16INK4a gene based on the functional paste-like nanofibers composites-modified screen-printed carbon electrode

In this work, we offered a novel and sensitive electrogenerated chemiluminescence (ECL) biosensing system for detection of p16INK4a gene using the functional paste-like nanofibers composites-modified screen-printed carbon electrode (SPCE). The paste-like nanofibers composites (PG/GR/CS) which were comprised of the electrospun nanofibers (PG, the graphene (GR) doped polycaprolactam 6 (PA6) were prepared via one-step electrospinning), graphene (GR) and chitosan (CS) were served as the nanosized backbones for pyrrole (Py) electropolymerization. The functional paste-like nanofibers composites (PG/GR/CS/PPy) used as a substrate for dsDNA (hybridization reaction of ssDNA1, p16INK4a gene and the Ru(bpy)32+/silver nanoparticles (AgNPs) doped gold (Au) core-shell luminescent composite nanoparticles labeled ssDNA2 (RuAg@AuNPs-ssDNA2)) immobilization. Under optimal conditions, a linear relationship between ECL intensity and p16INK4a gene concentration was found in a range of 0.1 pM–1 nM with the detection limit of 0.05 pM (S/N = 3). This ECL biosensor based on the PG/GR/CS/PPy-modified SPCE demonstrated excellent electrochemical performance for the detection of p16INK4a gene and this platform can be used for the determination of various analytes.

Tris(2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence ethanol biosensor based on ionic liquid doped titania-Nafion composite film

A highly sensitive tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy)32+] electrogenerated chemiluminescence (ECL) biosensor for the detection of ethanol based on ADH and NAD+ cofactor with ionic liquid (IL) doped sol-gel titania-Nafion composite film has been developed. Regardless of the type of the ILs, the incorporation of IL in the composite resulted in the enhancement in both the electron transfer and diffusion rates in the composite modified electrode, thus leading to dramatic increase in ECL intensity. Among several ILs tested, 1-butyl-3-methylimidazolium with chloride counter anion was most effective for the construction of the Ru(bpy)32+ ECL biosensor. Two-layer system with the inner layer of Ru(bpy)32+ immobilized in IL-titania-Nafion composite film and the outer layer of ADH immobilized in titania-Nafion composite film has been used to maintain the activity of the enzyme and the overall stability of the ECL biosensor. The present biosensor exhibited linear response towards ethanol with a linear dynamic range of 1.2 × 10−5 M–2.5 × 10−1 M and a detection limit of 5.0 × 10−6 M (S/N = 3). The outstanding dynamic range showed the applicability of the present biosensor for ethanol detection not only in human blood but also in a variety of different fields such as alcoholic beverages or other commercially available products.

Electrogenerated Chemiluminescence Imaging of Electrocatalysis at a Single Au‐Pt Janus Nanoparticle

Noble metal nanoparticles are promising catalysts in electrochemical reactions, while understanding the relationship between the structure and reactivity of the particles is important to achieve higher efficiency of electrocatalysis, and promote the development of single-molecule electrochemistry. Electrogenerated chemiluminescence (ECL) was employed to image the catalytic oxidation of luminophore at single Au, Pt, and Au-Pt Janus nanoparticles. Compared to the monometal nanoparticles, the Janus particle structure exhibited enhanced ECL intensity and stability, indicating better catalytic efficiency. On the basis of the experimental results and digital simulation, it was concluded that a concentration difference arose at the asymmetric bimetallic interface according to different heterogeneous electron-transfer rate constants at Au and Pt. The fluid slip around the Janus particle enhanced local redox reactions and protected the particle surface from passivation.

Electrogenerated Chemiluminescence Imaging of Electrocatalysis at a Single Au‐Pt Janus Nanoparticle

AbstractNoble metal nanoparticles are promising catalysts in electrochemical reactions, while understanding the relationship between the structure and reactivity of the particles is important to achieve higher efficiency of electrocatalysis, and promote the development of single‐molecule electrochemistry. Electrogenerated chemiluminescence (ECL) was employed to image the catalytic oxidation of luminophore at single Au, Pt, and Au‐Pt Janus nanoparticles. Compared to the monometal nanoparticles, the Janus particle structure exhibited enhanced ECL intensity and stability, indicating better catalytic efficiency. On the basis of the experimental results and digital simulation, it was concluded that a concentration difference arose at the asymmetric bimetallic interface according to different heterogeneous electron‐transfer rate constants at Au and Pt. The fluid slip around the Janus particle enhanced local redox reactions and protected the particle surface from passivation.

Electrogenerated chemiluminescence of ZnO nanorods and its sensitive detection of cytochrome C

Various kinds of ZnO nanoparticles have been successfully used in gas sensing applications, however, these nanomaterials have been rarely investigated in electrogenerated chemiluminescence (ECL). In the present work, ZnO nanorods (ZnONRs) were synthesized by hydrothermal method, and characterized by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). ECL behaviors of ZnONRs were investigated in neutral aqueous condition in the presence of K2S2O8. Cyclic voltammetry (CV) results revealed that ZnONRs can react with K2S2O8 to generate strong light emission, revealing that K2S2O8 can act as coreactant of ZnONRs ECL. ZnONRs synthesized under different pH conditions exhibited different ECL intensities, and the most intense ECL signal was obtained at pH 7.0. Cytochrome C could compete with ZnONRs to react with K2S2O8, and exhibited apparent inhibiting effect on ZnONRs ECL, which can be sensitively detected in the range of 1.0 × 10–11–5.0 × 10−9molL−1, with a detection limit of 4.7 × 10−12molL−1 (3σ). The present ECL system exhibited high sensitivity and good stability, which is suitable for the fabrication of novel ECL sensors.

Stainless Steel Electrode for Sensitive Luminol Electrochemiluminescent Detection of H2O2, Glucose, and Glucose Oxidase Activity.

Electrogenerated chemiluminescence (ECL) application of stainless steel, a robust and cost-effective material, has been developed for the first time. Type 304 stainless steel electrode shows appealing ECL performance in the luminol-H2O2 system. It enables the detection of H2O2 with a linear range from 1 to 1000 nM and a limit of detection of 0.456 nM [signal-to-noise ratio (S/N) = 3]. The ECL method based on type 304 stainless steel electrode is more sensitive, more cost-effective, and much simpler than other ECL methods reported before. Because the stainless steel electrode has excellent performance for H2O2 detection and H2O2 participates in many important enzymatic reactions, applications of stainless steel electrode-based ECL for detection of enzyme activities and enzyme substrates were further investigated by use of glucose oxidase (GODx) and glucose as representative enzyme and substrate. The concentrations of glucose and the activity of GODx were directly proportional to ECL intensities over a range of 0.1-1000 μM and 0.001-0.7 units/mL with limits of detection of 0.076 μM and 0.00087 unit/mL (S/N = 3), respectively. This method was successfully used for determining glucose in honey. Because of their remarkable performance and user-friendly features, stainless steel electrodes hold great promise in various electroanalytical applications, such as biosensing, disposable sensors, and wearable sensors.

Iridium (III)‐Doped Core–Shell Silica Nanoparticles: Near‐IR Electrogenerated Chemiluminescence in Water

AbstractThe front cover artwork is provided by Dr. Francesco Paolucci and Dr. Luca Prodi, University of Bologna (Italy). The image illustrates the electrogenerated chemiluminescence (ECL) of metal complexes encapsulated in core–shell PEGylated silica (Plus) nanoparticles emitting light in aqueous medium in the presence of a co‐reactant. Read the full text of the Article at 10.1002/celc.201700071.

Co‐reactant Electrogenerated Chemiluminescence of Iridium(III) Complexes Containing an Acetylacetonate Ligand

AbstractWe examine the electrogenerated chemiluminescence (ECL) of three Ir( )2(acac) complexes, where acac=acetylacetonate anion and =2‐phenylpyridine (ppy), 2‐phenylbenzothiazole (bt), or 2‐phenylquinoline (pq) anions, with tri‐n‐propylamine co‐reactant in acetonitrile under a range of chemical and instrumental conditions; this follows somewhat conflicting recent claims of the ECL intensities from complexes of this type. Relevant electrochemical, spectroscopic, and ECL properties are evaluated in direct comparison with those of Ir(ppy)3 and [Ru(bpy)3](PF6)2, as well as data from previous publications. DFT calculations on the Ir( )2(acac) complexes show the HOMOs to be composed of both the metal and the ligand, and the LUMOs almost exclusively on the ligand. The ECL intensities of the Ir( )2(acac) complexes (relative to [Ru(bpy)3](PF6)2) were dependent on experimental conditions and, in some cases, the ECL intensities reported for iridium complexes may have been derived using conditions that unintentionally disadvantaged the reference electrochemiluminophore.