Electroactive Metal–Organic Frameworks as Emitters for Self‐Enhanced Electrochemiluminescence in Aqueous Medium

Metal–organic frameworks (MOFs) have limited applications in electrochemistry owing to their poor conductivity. Now, an electroactive MOF (E‐MOF) is designed as a highly crystallized electrochemiluminescence (ECL) emitter in aqueous medium. The E‐MOF contains mixed ligands of hydroquinone and phenanthroline as oxidative and reductive couples, respectively. E‐MOFs demonstrate excellent performance with surface state model in both co‐reactant and annihilation ECL in aqueous medium. Compared with the individual components, E‐MOFs significantly improve the ECL emission due to the framework structure. The self‐enhanced ECL emission with high stability is realized by the accumulation of MOF cation radicals via pre‐reduction electrolysis. The self‐enhanced mechanism is theoretically identified by DFT. The mixed‐ligand E‐MOFs provide a proof of concept using molecular crystalline materials as new ECL emitters for fundamental mechanism studies.     

Electroactive Metal–Organic Frameworks as Emitters for Self-Enhanced Electrochemiluminescence in Aqueous Medium

Metal–organic frameworks (MOFs) have limited applications in electrochemistry owing to their poor conductivity. Now, an electroactive MOF (E-MOF) is designed as a highly crystallized electrochemiluminescence (ECL) emitter in aqueous medium. The E-MOF contains mixed ligands of hydroquinone and phenanthroline as oxidative and reductive couples, respectively. E-MOFs demonstrate excellent performance with surface state model in both co-reactant and annihilation ECL in aqueous medium. Compared with the individual components, E-MOFs significantly improve the ECL emission due to the framework structure. The self-enhanced ECL emission with high stability is realized by the accumulation of MOF cation radicals via pre-reduction electrolysis. The self-enhanced mechanism is theoretically identified by DFT. The mixed-ligand E-MOFs provide a proof of concept using molecular crystalline materials as new ECL emitters for fundamental mechanism studies.     

Spectroelectrochemistry for studying electrochemiluminescence mechanism

UV–Vis spectroelectrochemistry (SEC) was introduced for the first time into the study of electrochemiluminescence (ECL) mechanisms of nitrogen heterocyclic compounds. Uracil and its two derivatives, 5-fluorouracil and 1-methyl-uracil, were chosen as model molecules in the ECL mechanism study. SEC revealed that the substitution of hydrogen at N(1) and the destruction of conjugate heterocyclic ring were very important for ECL activities of uracils. On the basis, a new ECL mechanism was proposed for the uracils. The successful explanation of ECL mechanism for the model molecules by employing SEC indicates that SEC would play an important role in future ECL mechanism studies.     

Inhibition of Ru Complex Electrochemiluminescence by Phenols and Anilines

The effect of 30 phenols and anilines on typical Ru complex electrochemiluminescence (ECL) was systematically investigated under different conditions. It was found that all the tested compounds showed an ECL inhibiting signal. The magnitude of ECL inhibition was related to the position of the substituting group in the benzene ring and decreased in the following order: meta‐>ortho‐>para‐. The oxidation potential of the tested compounds, the ECL spectra and UV‐visible absorption spectra of Ru(bpy) /tripropylamine (TPrA) in the presence of phenols and anilines, and the direct ECL between Ru(bpy) and phenols/aniline were studied. The mechanism of ECL inhibition has been proposed due to energy transfer from the excited state Ru(bpy) to a quinone or ketone or their polymer formed by electro‐oxidation of phenols and anilines. The potential of analytical application was explored by use of the inhibited ECL. The results demonstrate that numerous compounds are detectable with the detection limits in the range of 10^?8–10^?9 mol/L for Ru(bpy) /TPrA system and in the range of 10^?6–10^?7 mol/L for Ru(bpy) /C₂O system, respectively.     

Synthesis,Characterization, and Thermal Behavior of Carboranyl–Styrene Decorated Octasilsesquioxanes: Influence of the Carborane Clusters on Photoluminescence

Novel polyhedral oligomeric silsesquioxanes (POSS) or octasilsesquioxanes with carboranyl–styrene fragments attached to each corner are described. These compounds have been synthesized by olefin‐metathesis reactions between octavinylsilsesquioxane and carboranyl–styrene compounds that possess different substituents (Ph, Me, or H). In all cases, these reactions, which were catalyzed by the Grubbs catalyst, are highly regioselective and yield exclusively the E isomers. The existence of the carborane cage in the POSS structure induces a remarkable thermal stability in these compounds. After combustion at 1000 °C, these carboranyl–POSS compounds exhibit a mass loss lower than 10 %. The UV/Vis absorption data of these carboranyl–POSS compounds shows a slight bathochromic shift with respect to the carboranyl–styrene monomers, with an absorption maximum around 262 nm. Nevertheless, important differences in the emission spectra of the carboranyl–POSS compounds with regard to their carboranyl–styrene precursors are observed; the phenyl‐o‐carborane‐containing POSS compound exhibits the highest fluorescence intensity (Φ_F=44 %), whereas for the POSS compound bearing the methyl substituent, and for the unsubstituted o‐carborane clusters, the fluorescence intensity is much lower (Φ_F=9 and 2 %, respectively). This is precisely the reverse of what occurs with the monomers, in which the unsubstituted o‐carboranyl–styrene compound exhibits the highest Φ_F, and a quenching of the fluorescence is observed in the phenyl‐o‐carboranyl–styrene compound. In addition, a large red shift of around 100 nm is observed for the POSS compounds with respect to their precursors. These experimental results can only be accounted for by the spatial ordering induced by the POSS core that eases interactions, which otherwise would not occur. These results have been confirmed by time‐dependent density functional theory (TDDFT) calculations that exclude a photoinduced electron transfer (PET) process in the POSS compounds.     

Efficient and Monochromatic Electrochemiluminescence of Aqueous‐Soluble Au Nanoclusters via Host–Guest Recognition

Inspired by the enhanced photoluminescence of Au nanoclusters (AuNCs) with a rigid shell, the formation of rigid host–guest assemblies on AuNC surfaces was employed to screen novel electrochemiluminophores with 6‐aza‐2‐thiothymine(ATT)‐protected AuNCs (ATT‐AuNCs) and l ‐arginine (ARG) as models for the first time. The rigid host–guest assemblies formed between ARG and ATT on the ATT‐AuNC surface enabled aqueous‐soluble ARG/ATT‐AuNCs with a dramatically enhanced electrochemiluminescence (ECL) compared to ATT‐AuNCs. This includes one cathodic ECL process (?1.30 V) and three anodic ECL processes (+0.78, 0.90, and 1.05 V) in a so‐called half‐scan experiment without a co‐reactant, as well as a 70‐fold enhanced oxidative‐reduction ECL at +0.78 V with tri‐n‐propylamine as a co‐reactant. Importantly, the ECL of the ARG/ATT‐AuNCs is highly monochromatic with an emission maximum around 532 nm and a full width at half‐maximum of 36 nm, which is of great interest for color‐selective ECL assays.     

Electrochemiluminescence Platforms Based on Small Water‐Insoluble Organic Molecules for Ultrasensitive Aqueous‐Phase Detection

Highly efficient detection in the aqueous phase for water‐insoluble organic molecule probes is challenging. The bright aggregated‐state electrochemiluminescence (ECL) of 1,1‐disubstituted 2,3,4,5‐tetraphenylsiloles by a co‐reactant approach was discovered, and a heterogeneous aggregation‐induced emission ECL (HAIE‐ECL) was constructed at the electrode surface, showing very high ECL efficiency (37.8 %) and selective recognition for industrially important DNBP plasticizer with a low detection limit of 0.15 nm in the water phase. A mechanistic study indicates that ECL is mainly generated due to the high electron affinity of siloles and restriction of the intramolecular motions caused by their propeller‐like noncoplanar structures. This system realizes the sensing of organic‐based ECL in the water phase by solving the crucial problems of water insolubility and aggregation‐caused quenching (ACQ), and demonstrates potential for further application because of its design and high efficiency.     

Understanding the Unconventional Effects of Halogenation on the Luminescent Properties of Oligo(Phenylene Vinylene) Molecules

It is commonly known that halogenation tends to decrease the luminescence quantum yield of an organic dye, owing to the high electronegativity and heavy‐atom effect of the halogen atom. However, based on an investigation of the effects of halogenation on the luminescence of the oligo(phenylene vinylene) (OPV) framework, we demonstrate that halogenation can have positive impact on the solid‐state fluorescence and electrochemiluminescence (ECL) properties of OPV derivatives. The chlorinated OPV exhibits a very high solid‐state fluorescence quantum yield (91 %), whilst the brominated analogue gives the highest ECL emission intensity. Time‐dependent density functional theory calculations, natural bond orbital analysis, and natural transition orbital analysis were performed to assist the understanding of the origin of these positive halogenation effects, which provide insight into the rational design of highly luminescent halogenated organic materials for solid‐state devices and ECL applications.     

Efficient electrochemiluminescent cyclometalated iridium(III) complexes: Synthesis,photophysical and electrochemiluminescent properties

A series of new cyclometalated iridium(III) complexes for electrochemiluminescence (ECL) system were synthesized and fully characterized. Using tri-n-propylamine (TPA) as an oxidative–reductive co-reactant, their ECL properties were studied in acetonitrile (CH₃CN) and mixed CH₃CN/H₂O (50:50, v/v) solutions, respectively. Meanwhile, the influencing factors of ECL efficiencies, including working electrode, pH, and surfactant were investigated. A remarkable ECL enhancement (up to about 13.5 times), in comparison with the commonly used Ru(bpy)₃²⁺ (2,2′-bipyridyl) ruthenium(II), is observed from Ir(FPP)₂(acac) (where FPP is 2-(4-fluorophenyl)-4-phenylpyridine, acac = acetylacetone) at Pt disk electrode. At the same time, an increase in ECL efficiency is also observed in surfactant media. This study provided a new method for further improving and tuning the ECL efficiency by designing new iridium complexes with the appropriate cyclometalated or ancillary ligands.     

磺酸基卟啉的电化学发光研究及应用

以四(4-磺酸基苯基)卟啉（TSPP）为发光体,过硫酸钾（K₂S₂O₈）为共反应剂,构建了一个新的电化学发光（ECL）体系. 在扫描范围为0~-1.5V时,该体系出现两个阴极ECL峰,分别为TSPP的还原峰（-0.8V）和K₂S₂O₈ 的还原峰 (-1.2V). 亚甲基蓝能有效猝灭四(4-磺酸基苯基)卟啉的电化学发光,根据猝灭效率与亚甲基蓝浓度的线性关系,建立了一种测定亚甲基蓝含量的新方法.     

Enhanced electrochemiluminescence of luminol-O2 system at gold–hydrophobic ionic liquid|water interface

A hydrophobic thiol-functionalized ionic liquid (IL) was synthesized and immobilized tightly on a gold electrode surface via Au–S bond to construct a stable Au–IL|water interface. At the Au–IL|water interface, the electrochemiluminescence (ECL) of luminol-O₂ system was investigated. The ECL intensity of luminol-O₂ system at the Au–IL|water interface was much larger and more stable than that at Au|water interface. The enhanced ECL mechanism at the Au–IL|water interface was studied and discussed in details.     

Paper‐Based Electrochemiluminescent 3D Immunodevice for Lab‐on‐Paper,Specific, and Sensitive Point‐of‐Care Testing

Recent research on microfluidic paper‐based analytical devices (μPADs) has shown that paper has great potential for the fabrication of low‐cost diagnostic devices for healthcare and environmental monitoring applications. Herein, electrochemiluminescence (ECL) was introduced for the first time into μPADs that were based on screen‐printed paper‐electrodes. To further perform high‐specificity, high‐performance, and high‐sensitivity ECL on μPADs for point‐of‐care testing (POCT), ECL immunoassay capabilities were introduced into a wax‐patterned 3D paper‐based ECL device, which was characterized by SEM, contact‐angle measurement, and electrochemical impedance spectroscopy. With the aid of a home‐made device‐holder, the ECL reaction was triggered at room temperature. By using a typical tris(bipyridine)ruthenium–tri‐n‐propylamine ECL system, this paper‐based ECL 3D immunodevice was applied to the diagnosis of carcinoembryonic antigens in real clinical serum samples. This contribution further expands the number of sensitive and specific detection modes of μPADs.     

Image‐Contrast Technology Based on the Electrochemiluminescence of Porous Silicon and Its Application in Fingerprint Visualization

The electrochemiluminescence (ECL) of porous silicon (pSi) has attracted great interest for its potential application in display technology and chemical sensors. In this study, we found that pSi with a different surface chemistry displayed an apparently different dynamic ECL process. An image‐contrast technology was established on the basis of the intrinsic mechanism of the ECL dynamic process. As a proof of principle, the visualization of latent fingerprints (LFPs) and in situ detection of TNT in fingerprints was demonstrated by using the ECL‐based image‐contrast technology.     

Electochemiluminescence of CdTe/CdS Quantum Dots with Triproprylamine as Coreactant in Aqueous Solution at a Lower Potential and Its Application for Highly Sensitive and Selective Detection of Cu2+

Anodic electrochemiluminescence (ECL) of 3‐mercaptopropionic acid (MPA)‐ capped CdTe/CdS core‐shell quantum dots (QDs) with tripropylamine (TPrA) as the co‐reactant were studied in aqueous (Tris buffer) solution for the first time. The results suggest that the oxidation of TPrA at a glassy carbon electrode (GCE) surface participated in the ECL of QDs, and the onset potential and the intensity of ECL of CdTe/CdS QDs were affected seriously by TPrA, as the co‐reactant, in Tris buffer solution. The onset potential of ECL in this new system was about +0.5 V (vs. Ag/AgCl) and the ECL intensity greatly enhanced when TPrA was present. Various influencing factors, such as the electrolyte, pH, QDs concentration, potential range and scan rates on the ECL were studied. Based on the selective quenching by Cu²⁺ to the light emission from CdTe/CdS QDs/TPrA system, a highly sensitive and selective method for the determination of Cu²⁺ was developed. At the optimal conditions, the relative ECL intensity, I₀/I, was proportional to the concentration of Cu²⁺ from 14 nM to 0.21 μM with the detection limit of 6.1 nM based on the signal‐to‐noise ratio of 3. The possible ECL mechanism of QDs and the quenching mechanism of ECL were proposed.     

Dual Intramolecular Electron Transfer for In Situ Coreactant‐Embedded Electrochemiluminescence Microimaging of Membrane Protein

The demand for transporting coreactant to emitter and short lifetime of the radicals in electrochemiluminescence (ECL) emission inhibit greatly its application in cytosensing and microscopic imaging. Herein we designed a dual intramolecular electron transfer strategy and tertiary amine conjugated polymer dots (TEA‐Pdots) to develop a coreactant‐embedded ECL mechanism and microimaging system. The TEA‐Pdots could produce ECL emission at +1.2 V without need of coreactant in test solution. The superstructure and intramolecular electron transfer led to unprecedented ECL strength, which was 132 and 45 times stronger than those from the mixture of Pdots with TEA at equivalent and 62.5 times higher amounts, respectively. The ECL efficiency was even higher than that of typical [Ru(bpy)₃]²⁺ system. Therefore, this strategy and coreactant‐embedded ECL system could be used for in situ ECL microimaging of membrane protein on single living cells without additional permeable treatment for transporting coreactant. The feasibility and validity were demonstrated by evaluating the specific protein expression on cell surface. This work opens new avenues for ECL applications in single cell analysis and dynamic study of biological events.     

Circularly‐Polarized Electrochemiluminescence from a Chiral Bispyrene Organic Macrocycle

The first observation of circular polarization of electrochemiluminescence (ECL) from a purely organic derivative is reported. A bispyrene scaffold mounted on a constrained polyether macrocycle displaying intense excimer fluorescence and highly circularly‐polarized (CP) photoluminescence has been selected for this purpose. The compound displays an ECL dissymmetry factor of about |8×10^?3|, which is in good agreement with the corresponding photoluminescence value. This observation is the first step towards the molecular engineering of tailored dyes that can act as both ECL and CP‐ECL reporters for (bio)analysis by bringing a new level of information when dealing with chiral environments. Additionally, it provides an extra dimension to the ECL phenomenon and opens the way to chiral detection and discrimination.     

Highly fluorescent N,N-dimethylaminophenylethynylarenes: synthesis, photophysical properties, and electrochemiluminescence

A new family of aryl-pi-donor-aryl molecules has been synthesized and studied with respect to their photophysical properties and electrogenerated chemiluminscence (ECL) for the first time. Anthracene, phenanthrene, naphthalene, biphenyl, and fluorene were coupled with N,N-dimethylanilino moiety via a C-C triple bond (1-7). Introduction of such a strong electron-donating moiety as N,N-dimethylanilino group through a triple bond imparts new properties to the resultant molecules that are not commonly observed for the parent arenes. All molecules show absorption in the near-visible region and emission totally in the visible region with high fluorescence quantum yields. Bright solid-state photoluminescence has also been noticed for all the compounds in the visible region. 9-Anthryl- and 1-naphthyl- derivatives exhibited blue-shifted electrochemiluminescence (ECL) relative to their photoluminescence because of aggregation. 9-Phenanthryl- and 2-naphthyl- derivatives did not show ECL. 2-Biphenyl derivative showed monomeric ECL while 4-biphenyl counterpart exhibited excimer ECL. No ECL was observed for 2-fluorenyl derivative. The observed electronic properties are discussed with regard to the structure of the molecules. The characteristics of the molecules chosen in the present study open up new prospects and promises for novel tunable organic materials, on the basis of simple extension of conjugation to promote intramolecular communication, for ECL, OLED, and other optoelectronic applications.     

Versatile electrochemiluminescent organic emitters

Organic luminophores for electrochemiluminescence (ECL), namely polycyclic aromatic hydrocarbons, have been the first molecules investigated since the beginning of ECL studies. Moving from organic solvents to water-based solutions in view of analytical applications, the attention on ECL emitters shifted to soluble inorganic complexes, which prevailed in both fundamental and applied research. However, the investigation of organic molecules has recently revived owing to new synthetic procedures and concepts. Polymeric nanoparticles, surface functionalisation, aggregation-induced emission (AIE), and thermally activated delayed fluorescence (TADF) sparked the research with renovated interest for organic molecules. Here, we introduce and summarise these new concepts behind organic emitters for ECL.     

苯酚和苯胺类化合物对鲁米诺电致化学发光的增强和抑制作用

系统研究了不同pH下的NaHCO₃-Na₂CO₃和NaOH缓冲介质中, 36种苯酚和苯胺类化合物对鲁米诺电致化学发光(Electrochemiluminescence, ECL)体系的影响. 发现苯酚和苯胺类化合物的抑制和增强作用与化合物的结构、氧化电位和介质的pH有直接的关系: 具有较高氧化电位的苯酚和苯胺类化合物对鲁米诺的ECL没有影响; 而具有较低的氧化电位、苯环上有两个处于对位的-OH(或-NH₂)或苯环上有多个相邻的-OH的化合物, 在较低的pH下有增强作用, 在较高的pH下具有抑制作用; 其它的化合物则呈现抑制作用, 抑制作用的大小与化合物的结构有关. 通过研究化合物的氧化半峰电位、ECL光谱、荧光光谱等, 提出了增强和抑制作用的可能机理: 各种有机物的电氧化产物如醌、酮及具有醌、酮结构的聚合物等能够淬灭激发态3-氨基邻苯二甲酸根阴离子(3-AP^2－*)的发射, 导致了鲁米诺的ECL的降低; 同时, 反应过程中生成的半醌自由基中间体或 会促进鲁米诺的发光反应, 呈现增强作用.     

Luminescence Amplification at BiVO4 Photoanodes by Photoinduced Electrochemiluminescence

Photoinduced electrochemiluminescence (PECL) combines semiconductor (SC) photoelectrochemistry with electrochemiluminescence (ECL). In PECL, the incident light is converted into a different wavelength by an electrochemical reaction at a SC photoelectrode and allows triggering of ECL at low potentials. This concept has been employed to design up‐conversion systems. However, PECL strongly suffers from the photoelectrochemical instability of these low band gap SCs. Reported here for the first time is an original light‐conversion strategy based on PECL of a luminol derivative (L‐012) at BiVO₄ photoanodes in water. Incident light photoexcites simultaneously the L‐012 fluorescence and the photoanode. However, the resulting signal is surpassed by the PECL emission. PECL can be induced at a potential as low as ?0.4 V for several hours and can be employed to finely tune L‐012 luminescence. This finding is promising for the design of new analytical strategies and light‐addressable systems.