Electrogenerated Chemiluminescence Efficiency Research Articles

Regulating highly photoelectrochemical activity of Zr-based mixed-linker metal-organic frameworks toward sensitive electrogenerated chemiluminescence sensing of α-glucosidase

The conductivity and emission efficiency of metal-organic frameworks (MOFs) remain challenging factors that limit their electrogenerated chemiluminescence (ECL) sensing applications. Herein, we report a facile approach to address these challenges by integrating an electroactive linker (H2-TCPP) with an ECL active electrogenerated chemiluminescence linker (H4-TBAPy) to construct a highly photoelectrochemical active mixed-linker MOFs (ML-MOFs). ECL results revealed a remarkable 15.4-fold enhancement for the top-performing ML-MOFs (M6-MOFs), surpassing the single linker MOFs. In addition, M6-MOFs also exhibit a remarkable 73-fold enhancement in ECL efficiency compared to commercial Ru (bpy)32+. This improvement should be attributed to the synergistic effects resulting from the combination of two linkers. Furthermore, M6-MOFs are found to be served as a model ECLphore for sensitive and selective detection of α-glucosidase for the first time with good potential practicability in human serum samples. This work represents a promising direction to guide for designing good conductivity and high ECL efficiency MOFs in terms of linker functionalization and thus bandgap modulation for advancing their ECL sensing applications.

Organic nanoparticles for electrogenerated chemiluminescence assay

Organic nanoparticles (ONPs) are one type of nanoparticles assembled by the organic compounds with one dimension smaller than 100 nm. ONPs are alternative nanomaterials in organic light-emitting diode and analytical applications due to their unique optical and electrochemical properties. In electrogenerated chemiluminescence (ECL) assays, ONPs are generally taken as signal reporters for chemical sensing and biosensing. In this opinion, we focus on recent developments of ONPs as ECL luminophores in analytical application. The types and ECL mechanisms of ONPs systems and the approaches of ONPs-based ECL methods are briefly introduced. New advances on the improvement of the ECL efficiency of ONPs are highlighted. The challenges and perspectives of ONPs-based ECL methods are discussed.

Near-infrared electrogenerated chemiluminescence of Au22(glutathione)18 nanoclusters in aqueous solution and its analytical application

Gold nanoclusters (AuNCs) have attracted great attention in analytical sciences because they have unique optical and electrochemical properties with low biological toxicity. However, the analytical application of Au NCs-based electrogenerated chemiluminescence (ECL) still remains relatively unexplored largely due to their low ECL efficiency in aqueous solution. Moreover, the precise information of molecular formula of Au NCs have not been determined in large number of reports. In the present study, the ECL behavior of atomically precise Au22(SG)18 NCs, where SG is glutathione, were characterized in the aqueous solution. The oxidation of Au22(SG)18 NCs together with coreactant tripropylamine (TPA) at the working electrode potential of 1.25 V vs Ag/AgCl (3 M NaCl) has led to strong ECL emission at ~767 nm in the near-infrared region. The ECL intensity of the Au22(SG)18 NCs was about 14-fold higher than the ECL intensity obtained with the [email protected] NCs, which is most commonly used Au NCs in aqueous solution. The ECL intensity is strongly dependent upon the concentrations of Au22(SG)18 NCs and TPA. However, the ECL intensity of Au22(SG)18 NCs with TPA is diminished in the presence of phenolic compounds depending upon their concentrations. Using catechol as a model analyte, the present ECL system can detect it in the linear range from 1.0 × 10−7 to 1.0 × 10−4 M with a detection limit of 3.3 × 10−9 M (S/N = 3). The present study has demonstrated the potential application of the Au NCs-based ECL in real analytical problems.

Electrogenerated Chemiluminescence and Spectroelectrochemistry Characteristics of Blue Photoluminescence Perovskite Quantum Dots.

Lead-based perovskite MAPbX3 (MA = CH3NH3, X = Cl and Br) has shown great potential benefits to advance modern optoelectronics and clean energy harvesting devices. Poor structural stability is one of the major challenges of MAPbX3 perovskite materials to overcome to achieve desired device performance. Here, we present the electrochemical stability study of CH3NH3PbCl1.08Br1.92 quantum dots (QDs) by electrogenerated chemiluminescence (ECL) and photoluminescence (PL) spectroelectrochemistry methods. Electrochemical anodization of pristine MAPbX3 QD film results in the disproportionate loss of methylammonium and halide ions (X = Cl and Br). ECL efficiency and stability of perovskite QDs in the presence of coreactant tripropyl amine (TPrA) can be greatly improved after being incorporated into a polystyrene (PS) matrix. Mass spectrum and X-ray photoelectron spectroscopy (XPS) measurements were used to provide chemical composition variation details of QDs, which are responsible for the ECL and PL characteristics (e.g., wavelength redshift) of perovskite QDs in an electrochemical cell.

Measuring nanoparticle-induced resonance energy transfer effect by electrogenerated chemiluminescent reactions

Electrogenerated chemiluminescence (ECL) efficiencies, redox potentials, photoluminescent (PL) (quenching and coupling) effects, and AFM images for the [Ru(bpy)3]2+/Au@tiopronin system were determined in aqueous solutions of the gold nanoparticles (NPs) at pH 7.0. The most remarkable finding was that ECL measurements can display the nanoparticle-induced resonance energy transfer (NP-RET) effect. Its effectiveness was quantified through a coefficient, K(NP-RET)ECL, which measures how much an ECL reaction has been enhanced. Moreover, the NP-RET effect was also checked using PL measurements, in such a way that a coefficient, K(NP-RET)PL, was determined; both constants, K(NP-RET)ECL and K(NP-RET)PL being in close agreement. It is important to highlight the fact that the NP-RET effect is only displayed in diluted solutions in which there is no NPs self-aggregation. The existence of the NPs self-aggregation behavior is revealed through AFM measurements.

Signal-Off Electrogenerated Chemiluminescence Biosensing Platform Based on the Quenching Effect between Ferrocene and Ru(bpy)32+-Functionalized Metal-Organic Frameworks for the Detection of Methylated RNA.

N6-methyladenine (m6A), one of the most common chemical modifications of eukaryotic RNA, participates in many important biological processes. An effective strategy for the quantitative determination of m6A is of great significance. Herein, we used methylated microRNA-21 (miRNA21) as the model target to propose a simple and sensitive electrogenerated chemiluminescence (ECL) biosensing platform to detect a specific m6A RNA sequence. This strategy is based on the fact that the anti-m6A-antibody can specifically recognize and bind to the m6A site in the RNA sequence, resulting in a quenching effect between Ru(bpy)32+-functionalized metal-organic frameworks and ferrocene. Luminescent metal-organic frameworks (Ru@MOFs) not only act as ECL indicators but also serve as nanoreactors for the relative ECL reactions owing to their porous or multichannel structure, which overcomes the fact that Ru(bpy)32+ is easily released when used for aqueous-phase detection, thus enhancing the ECL efficiency. Moreover, the ECL method has fewer modification steps and uses only one antibody to recognize the target RNA sequence, which simplifies the operation process and reduces the detection time, presenting a wide linear range (0.001-10 nM) for m6A RNA determination with a low detection limit (0.0003 nM). Additionally, this developed strategy was validated for m6A RNA detection in human serum. Thus, the ECL biosensing method provides a new method for m6A RNA determination that is simple, highly specific, and sensitive.

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.

Aqueous Gold Nanoparticle Solutions for Improved Efficiency in Electrogenerated Chemiluminescent Reactions

The efficiency of the high-energy electrogenerated chemiluminescence (ECL) tris(2,2′-bipyridine)ruthenium(II)/oxalate reaction was determined in the presence of citrate-coated gold nanoparticle (AuNPs) aqueous solutions. The ECL efficiency (ΦECL) for this reaction is enhanced by the addition of increasing amounts of AuNPs, followed by a sharp decrease when [AuNPs] is higher than 1.6 × 10–8 M. To explain this ΦECL/[AuNPs] trend, photoluminescent (PL) quenching, transmission electronic microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS) measurements were also performed as well as redox potentials for the [Ru(bpy)3]3+/2+ couple. Two facts were noteworthy: First, there is an increase in ΦECL, which accompanies an energy transfer effect by coupling between the Ru(II) complex ECL emission band and the AuNPs surface plasmon resonance (SPR)-induced band. This coupling, which we have called the ECL-SPR effect, enabled the quantifying of a coefficient (KECL-SPR, ECL-SPR effectiveness) for the improved ...

Precise mono-Cu+ ion doping enhanced electrogenerated chemiluminescence from Cd-In-S supertetrahedral chalcogenide nanoclusters for dopamine detection.

Herein, the ECL behaviors of precise mono-Cu+ ion doped Cd-In-S supertetrahedral chalcogenide nanoclusters (Cu@CdInS NCs) were investigated, and the effect of mono-Cu+ ions at the vacancy site of NCs on ECL emission performance was also elucidated. Precise mono-Cu+ ion doping not only induced new ECL emission at 596 nm with enhanced efficiency as high as 21.72% relative to [Ru(bpy)3]2+, but also improved acid tolerance of the ECL performances of NCs. In addition, a simple, fast and label-free dopamine ECL sensor with excellent selectivity was achieved.

Electrogenerated Chemiluminescence of a BODIPY Derivative with Extended Conjugation

AbstractThe electrochemical properties and electrogenerated chemiluminescence (ECL) of a borondipyrromethane (BODIPY) derivative, 2,8‐bis(4‐isopropylphenyl)‐difuro[2, 3‐b][3, 2‐g]‐5,5‐difluoro‐5‐bora‐3a,4a‐diaza‐s‐indacene (Derivative 1, Figure 1) are described. Derivative 1 emitted ECL in the range of 650∼800 nm by using tripropylamine (TPA) as a coreactant. In the cyclic voltammogram, Derivative 1 showed a reversible oxidation wave, whereas the reduction wave was irreversible. Energetically, it is likely that triplet‐triplet annihilation is the main pathway to emit ECL through the ion annihilation of the radical anions and cations of Derivative 1 whereas the lowest excited singlet state of Derivative 1 is directly produced with TPA. The maximum ECL wavelengths (670 nm at 0.01 mM) were red‐shifted with increasing the concentration of Derivative 1 because of the self‐absorption resulted from a small Stokes shift (∼10 nm). Relative ECL efficiency of Derivative 1 was 0.13 compared to that of a Ru(bpy)2+/TPA system.

Cyclometalated Iridium‐Complex‐Based Label‐Free Supersandwich Electrogenerated Chemiluminescence Biosensor for the Detection of Micro‐RNA

AbstractThe synthesis and characterization of compounds as electrogenerated chemiluminescence (ECL) reagents are crucial in fundamental research for ECL biosensors. In this work, a new cyclometalated iridium(III) complex, [(bt)2Ir(dmphen)](PF6), was synthesized by using 2‐phenylbenzothiazole (bt) as the main ligand and 5,6‐dimethyl‐1,10‐phenanthroline (dmphen) as the ancillary ligand. The photophysical, electrochemical, and ECL properties of this complex were extensively studied in acetonitrile solvent and aqueous solution. This complex displayed yellow‐green photoluminescence with a maximum wavelength at 522 nm, a reversible one‐electron oxidation wave at E1/2=+1.51 V (vs. SCE), and a reversible one‐electron reduction wave at −1.29 V (vs. SCE). Typically, in the annihilation process, the ECL efficiency of this complex was 12 times higher than that of Ru(bpy)32+. More importantly, a highly sensitive ECL method for the determination of micro‐RNA at the sub‐picomolar level was developed on basis of employing this complex as an ECL intercalator and signal amplification by using the supersandwich model. Compared with Ru(phen)3Cl2 and [(bt)2Ir(dcbpy)](PF6), this complex showed a relatively low background and the highest increased ratio as an ECL intercalator in the developed system. The increased ECL intensity was directly proportional to the concentration of the micro‐RNA in the range of 0.1 to 10 pM, with a detection limit of 13 fM. The developed method can effectively discriminate target micro‐RNA122 from two‐base mismatched micro‐RNA122. This work demonstrates that this cyclometalated iridium(III) complex is an effective alternative intercalator for ECL determination of the micro‐RNA. It is expected that this complex will be extended to design various analytical platforms for the detection of diverse analytes such as DNA/RNA, DNAzyme/target, and aptamer/targets.

A Grand Avenue to Au Nanocluster Electrochemiluminescence.

In most cases of semiconductor quantum dot nanocrystals, the inherent optical and electrochemical properties of these interesting nanomaterials do not translate into expected efficient electrochemiluminescence or electrogenerated chemiluminescence (ECL) because of the surface-state induction effect. Thus, their low ECL efficiencies, while very interesting to explore, limit their applications. As their electrochemistry is not well-defined, insight into their ECL mechanistic details is also limited. Alternatively, gold nanoclusters possess monodispersed sizes with atomic precision, low and well defined HOMO-LUMO energy gaps, and stable optical and electrochemical properties that make them suitable for potential ECL applications. In this Account, we demonstrate strong and sustainable ECL of gold nanoclusters Au25z (i.e., Au25(SR)18z, z = 1-, 0, 1+), Au38(SR)24, and Au144(SR)60, where the ligand SR is 2-phenylethanethiol. By correlation of the optical and electrochemical features of Au25 nanoclusters, a Latimer-type diagram can be constructed to reveal thermodynamic relationships of five oxidation states (Au252+, Au25+, Au250, Au25-, and Au252-) and three excited states (Au25-*, Au250*, and Au25+*). We describe ECL mechanisms and reaction kinetics by means of conventional ECL-voltage curves and novel spooling ECL spectroscopy. Notably, their ECL in the presence of tri-n-propylamine (TPrA), as a coreactant, is attributed to emissions from Au25-* (950 nm, strong), Au250* (890 nm, very strong), and Au25+* (890 nm, very strong), as confirmed by the photoluminescence (PL) spectra of the three Au25 clusters electrogenerated in situ. The ECL emissions are controllable by adjustment of the concentrations of TPrA· and Au25-, Au250, and Au25+ species in the vicinity of the working electrode and ultimately the applied potential. It was determined that the Au25-/TPrA coreactant system should have an ECL efficiency of >50% relative to the Ru(bpy)32+/TPrA, while those of Au250/TPrA and Au25+/TPrA reach 103% and 116%, respectively. Au25-* is the main light emission source for Au25z in the presence of benzoyl peroxide (BPO) as a coreactant, with a relative efficiency of up to 30%. For Au38, BPO leads to the Au38-* excited state, which emits light at 930 nm. In the Au38/TPrA coreactant system, we find that highly efficient light emission at 930 nm is mainly from Au38+* (and also Au383+*), with an efficiency 3.5 times that of the Ru(bpy)32+/TPrA reference. We show that the ECL and PL of the various Au38 charge states, namely, Au382-, Au38-, Au380, Au38+, Au382+, and Au384+, have the same peak wavelength of 930 nm. Finally, we demonstrate ECL with a peak wavelength of 930 nm from the Au144/TPrA coreactant system, which is released from the electrogenerated excited states Au144+* and Au1443+*. In our opinion, these gold nanoclusters represent a new class of effective near-IR ECL emitters, from which applications such as bioimaging, biological testing, and medical diagnosis are anticipated once they are made water-dispersible with hydrophilic capping ligands.

Electrogenerated chemiluminescence logic gate operations based on molecule-responsive organic microwires.

Complex logic gate operations using organic microwires as signal transducers based on electrogenerated chemiluminescence (ECL) intensity as the optical readout signal have been developed by taking advantage of the unique ECL reaction between organic semiconductor 9,10-bis(phenylethynyl)anthracene (BPEA) microwires and small molecules. The BPEA microwires, prepared on cleaned-ITO substrate using a simple physical vapor transport (PVT) method, were subsequently used for construction of the ECL sensors. The developed sensor exhibits high ECL efficiency and excellent stability in the presence of co-reactant tripropylamine. Based on the remarkable detection performance of BPEA MWs/TPrA system, the sensors manifested high sensitive ECL response in a wide linear range with low detection limit for the detection of dopamine, proline or methylene blue, which behaves on the basis of molecule-responsive ECL properties based on different ECL reaction mechanisms. Inspired by this, these sensing systems can be utilized to design OR, XOR and INHIBIT logic gates, which would be used for the determination of dopamine, proline and ethylene blue via logic outputs. Importantly, the individual logic gates can be easily brought together through three-input operations to function as integrated logic gates.

Electrogenerated chemiluminescence of Si quantum dots in neutral aqueous solution and its biosensing application

Electrogenerated chemiluminescence (ECL) of semiconductor quantum dots (QDs) has been considered as a powerful technique in the fabrication of biosensor, however, high-toxicity of heavy metal ion containing in QDs severely limits their further applications, and the search for the alternative benign nanomaterials with high ECL efficiency is urgent. Herein, ECL behavior of eco-friendly silicon quantum dots (SiQDs) was reported in neutral aqueous condition. Stable and intense cathodic ECL emission was obtained in phosphate buffer solution (PBS) with K2S2O8 as coreactant. ECL resonance energy transfer (ECL-RET) system was established with SiQDs ECL as energy donor and gold nanoparticles (AuNPs) as energy acceptor, based on which a novel ECL biosensor was fabricated. AuNPs was connected at the terminal of hairpin DNA to form a signal probe. When the probe was modified on SiQDs, ECL-RET occurred due to the short distance between AuNPs and SiQDs, resulting in the apparent decrease of ECL signal. Target DNA can open the loop of hairpin DNA, and move AuNPs away from the electrode surface. As a result, the ECL-RET process was hampered, and the ECL emission resumed. The increased ECL signals varied linearly with the target DNA concentrations in the range of 0.1fM to 1pM with the detection limit of 0.016fM (3σ). The proposed ECL sensor exhibited highly sensitivity and good selectivity in the detection of target DNA.

Electrochemiluminescent (ECL) [Ru(bpy)3](2+)/PAMAM dendrimer reactions: coreactant effect and 5-fluorouracil/dendrimer complex formation.

Electrogenerated chemiluminescence (ECL) reactions between tris(2,2'-bipyridine)ruthenium(II) and PAMAM dendrimers of the full (G1.0) and half (G1.5) generations were carried out in an aqueous medium at pH 6.1 and 10.0. In the absence of 5-fluoro-1H,3H-pyrimidine-2,4-dione (5-fluorouracil, 5-Fu) (coreactant effect study), the ECL efficiency trends as a function of [G1.0] and [G1.5] at pH 6.1 and 10.0 revealed that PAMAM dendrimers are about 100 (G1.5, pH 6.1), 60 (G1.5, pH 10.0), 26 (G1.0, pH 10.0) and 13 (G1.0, pH 6.1) times more efficient as ECL coreactants than oxalate anion is. Moreover, ECL reactions were done in the presence of several solutions of 5-Fu at a fixed concentration of the G1.0 and G1.5 dendrimers at pH 6.1 and 10.0 (binding study). The ECL efficiency trends as a function of [5-Fu] highlighted a dendrimer/5-Fu binding. Therefore, one of the most remarkable and novel findings of this work is the potential of PAMAM dendrimers to be used as both sensors and biosensors in an aqueous medium in the presence of a suitable sensitizer. Redox potentials of the [Ru(bpy)3](3+/2+) couple were also determined in the absence and presence of 5-Fu at both pHs. In the absence of 5-Fu the positive or negative shift of redox potentials showed the influence of the repulsive or attractive electrostatic long-range and short-range interactions between the charged dendrimer surface and the oxidized and reduced forms of the couple. In the presence of 5-Fu the trends of redox potentials highlighted the existence of a charged dendrimer/5-Fu species. Graphical Abstract ECL emission for the [Ru(bpy)3](2+)/ G1.0 dendrimer reaction in the presence of the 5-Fu at pH 6.1.

Electrogenerated chemiluminescence of cyclometalated iridium(III) complexes with derived β-acetylacetone as ancillary ligand

Two cyclometalated iridium(III) complexes, (pq)2Ir(sa) and (pq)2Ir(psa), with 2-phenylquinoline (pq) as the C^N main ligand and succinylacetone (sa) or 4,6-dioxo-6-phenylhexanoic acid (psa) as the O^O ancillary ligand, were synthesized at first time. The solubility was reached down to 0.1mM for (pq)2Ir(sa) and 10μM for (pq)2Ir(psa) in acetonitrile-water (v/v=5:95) solution. The photophysical, electrochemical and electrogenerated chemiluminescence (ECL) properties of (pq)2Ir(sa) and (pq)2Ir(psa) in acetonitrile were mainly investigated. The oxidation peak potential of (pq)2Ir(sa) and (pq)2Ir(psa) appears at +0.79V and +0.8V vs SCE. (pq)2Ir(sa) and (pq)2Ir(psa) display orange ECL emission with a maximum wavelength at 621nm and 610nm, respectively. ECL efficiencies of (pq)2Ir(sa) and (pq)2Ir(psa) in acetonitrile containing tripropylamine were calculated to be 21.3-folds and 35.4-folds higher than that of Ru(bpy)32+. It was surprised to find that small amount of water can greatly increase the ECL intensity of these two complexes in acetonitrile containing tripropylamine. The ECL methods for the determination of trace water in organic solvent were developed in the range from 0.02 to 4.0% (v/v) and 0.05 to 4.0% (v/v) with detection limit of 0.01% and 0.03% for (pq)2Ir(sa) and (pq)2Ir(psa), respectively. It was found that the O^O ancillary ligand played a key function in the water-enhanced ECL emission. A double coreactant ECL pathway is proposed for the water-enhanced ECL emission. This work demonstrates that (pq)2Ir(sa) and (pq)2Ir(psa) have lower potential and high ECL coefficient, which are promising for the effective use as ECL emitter in analytical application.

Near-Infrared Electrogenerated Chemiluminescence from Aqueous Soluble Lipoic Acid Au Nanoclusters.

Strong electrogenerated chemiluminescence (ECL) is detected from dithiolate Au nanoclusters (AuNCs) in aqueous solution under ambient conditions. A novel mechanism to drastically enhance the ECL is established by covalent attachment of coreactants N,N-diethylethylenediamine (DEDA) onto lipoic acid stabilized Au (Au-LA) clusters with matching redox activities. The materials design reduces the complication of mass transport between the reactants during the lifetime of radical intermediates involved in conventional ECL generation pathway. The intracluster reactions are highly advantageous for applications by eliminating additional and high excess coreactants otherwise needed. The enhanced ECL efficiency also benefits uniquely from the multiple energy states per Au cluster and multiple DEDA ligands in the monolayer. Potential step and sweeping experiments reveal an onset potential of 0.78 V for oxidative-reduction ECL generation. Multifolds higher efficiency is found for the Au clusters alone in reference to the standard Rubpy with high excess TPrA. The ECL in near-IR region (beyond 700 nm) is highly advantageous with drastically reduced interference signals over visible ones. The features of ECL intensity responsive to electrode potential and solution pH under ambient conditions make Au-LA-DEDA clusters promising ECL reagents for broad applications. The strategy to attach coreactants on Au clusters is generalizable for other nanomaterials.

Photophysical Properties and Efficient, Stable, Electrogenerated Chemiluminescence of Donor-Acceptor Molecules Exhibiting Thermal Spin Upconversion.

The photophysical properties and electrogenerated chemiluminescence (ECL) of three donor-acceptor molecules composed of dicyanobenzene and methyl-, tert-butyl-, and phenyl-substituted carbazolyl groups, 1,2,3,5-tetrakis(3,6-disubstituted-carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN-Me, 4CzIPN-tBu, and 4CzIPN-Ph, respectively) are described. These molecules show delayed fluorescence as a result of thermal spin upconversion from the lowest triplet state to the lowest singlet state at room temperature. The three molecules showed yellow to yellowish-red ECL. Remarkably, the ECL efficiencies of 4CzIPN-tBu in dichloromethane reached almost 40 %. Moreover, stable ECL was emitted from 4CzIPN-tBu and 4CzIPN-Ph. In case of 4CzIPN-Me, the ECL intensity decreased during voltage cycles because of polymerization. Quantum chemical calculations revealed that polymerization was inhibited by the steric hindrance of the bulky tert-butyl and phenyl groups on the carbazolyl moieties and lowered the spin density on the carbazolyl groups through electron conjugation for 4CzIPN-Ph.

Efficient green electrogenerated chemiluminescence from cyclometalated iridium(III) complex

A novel cyclometalated iridium(III) complex, (dfppy)2Ir(PyBiz), was synthesized by using 2-(2,4-difluorophenyl)pyridine (dfppy) as the C^N main ligand and 2-(2-pyridyl)benzimidazolato-N,N′ (PyBiz) as the N^N ancillary ligand. The photophysical, electrochemical and electrogenerated chemiluminescence (ECL) properties of (dfppy)2Ir(PyBiz) were investigated. (dfppy)2Ir(PyBiz) shows a green photoluminescence emission with a maximum wavelength at 527nm and quasi-reversible redox behaviors in acetonitrile solvent. Intense green ECL emissions that could be seen with the naked eyes were observed in annihilation and coreactant processes and the ECL spectra generated from three processes are identical to its photoluminescence spectrum, indicating that the same excited state is formed in these processes. The green ECL emission of (dfppy)2Ir(PyBiz) can be distinguished from the red emission of Ru(bpy)32+, which provides the possibility of the identification of (dfppy)2Ir(PyBiz) and Ru(bpy)32+ in a single solution containing both compounds. The green ECL emission of (dfppy)2Ir(PyBiz) with high ECL efficiency makes it promising to develop ECL luminophore for multiple wavelength and potential use in multichannel analytical applications.

Electrogenerated chemiluminescence from heteroleptic iridium(III) complexes with multicolor emission.

Electrogenerated chemiluminescence (ECL) with different emission colors is important in the development of multichannel analytical techniques. In this report, five new heteroleptic iridium(III) complexes were synthesized, and their photophysical, electrochemical, and ECL properties were studied. Here, 2-(2,4-difluorophenyl)pyridine (dfppy, complex 1), 2-phenylbenzo[d]thiazole (bt, complex 2), and 2-phenylpyridine (ppy, complex 3) were used as the main ligands to tune the emission color, while avobenzone (avo) was used as the ancillary ligand. For comparison, complexes 4 and 5 with 2-phenylpyridine and 2-phenylbenzo[d]thiazole as the main ligand, respectively, and acetyl acetone (acac) as the ancillary ligand were also synthesized. All five iridium(III) complexes had strong intraligand absorption bands (π–π*) in the UV region (below 350 nm) and a featureless MLCT (d−π*) transition in the visible 400–500 nm range. Multicolored emissions were observed for these five iridium(III) complexes, including green, orange, and red for complexes 4, 5, 2, 1, 3, respectively. Density functional theory calculations indicate that the electronic density of the highest occupied molecular orbital is entirely located on the C^N ligands and the iridium atom, while the formation of the lowest unoccupied molecular orbital (LUMO) is complicated. The LUMO is mainly assigned to the ancillary ligand for complexes 1 and 3 but to the C^N ligand for complexes 2, 4, and 5. Cyclic voltammetry studies showed that all these complexes have a reversible oxidation wave, but no reduction waves were found in the electrochemical windows of CH2Cl2. The E1/2(ox) values of these complexes ranged from 0.642 to 0.978 V for complexes 3, 4, 2, 5, 1, (in increasing order) and are all lower than that of Ru(bpy)3(2+). Most importantly, when using tripropylamine as a coreactant, complexes 1–5 exhibited intense ECL signals with an emission wavelength centered at 616, 580, 663, 536, and 569 nm, respectively. In addition, complexes 1, 2, and 5 displayed approximately 2, 11, and 214 times higher ECL efficiencies than Ru(bpy)3(2+) under identical conditions.