Annihilation Electrochemiluminescence Research Articles

Annihilation Electrochemiluminescence Triggered by Bipolar Electrochemistry

AbstractBipolar electrochemistry (BE) combined with electrochemiluminescence (ECL) has gained considerable attention as a versatile and powerful analytical technique operating in a wireless manner. However, only co‐reactant ECL has been reported so far when using a BE setup. In this work, the generation of annihilation ECL at the anodic extremity of a bipolar electrode (BPE) is demonstrated in two different spatial arrangements of the electrodes. The reported approach is based on a synergetic effect between the asymmetric electroactivity induced across the BPE, which produces different redox states of [Ru(bpy)3]2+, and the electro‐migration mechanism of the formed ionic species, allowing the localization and concentration of the ECL emission. The presented approach demonstrating annihilation ECL via BE, paves the way for the design of easy and straightforward light‐emitting platforms for multiple applications.

Dual-Ligand Europium-Organic Gels as a Highly Efficient Anodic Annihilation Electrochemiluminescence Emitter for Ultrasensitive Detection of MicroRNA.

In this study, a novel europium dual-ligand metal-organic gel (Eu-D-MOGs) with high-efficient anodic annihilation electrochemiluminescence (ECL) was synthesized as an ECL emitter to construct a biosensor for ultrasensitive detection of microRNA-221 (miR-221). Impressively, compared to the ECL signal of europium single-ligand metal-organic gels (Eu-S-MOGs), the ECL signal of Eu-D-MOGs was significantly improved since the two organic ligands could jointly replace the H2O and coordinate with Eu3+, which could remarkably reduce the nonradiative vibrational energy transfer caused by the coordination between H2O and Eu3+ with a high coordination demand. In addition, Eu-D-MOGs could be electrochemically oxidized to Eu-D-MOGs•+ at 1.45 V and reduced to Eu-D-MOGs•- at 0.65 V to achieve effective annihilation of ECL, which overcame the side reaction brought by the remaining emitters at negative potential. This benefited from the annihilation ECL performance of the central ion Eu3+ caused by its redox in the electrochemical process. Furthermore, the annihilation ECL signal of Eu3+ could be improved by sensitizing Eu3+ via the antenna effect. In addition, combined with the improved rolling circle amplification-assisted strand displacement amplification strategy (RCA-SDA), a sensitive biosensor was constructed for the sensitive detection of miR-221 with a low detection limit of 5.12 aM and could be successfully applied for the detection of miR-221 in the lysate of cancer cells. This strategy offered a unique approach to synthesizing metal-organic gels as ECL emitters without a coreactant for the construction of ECL biosensing platforms in biomarker detection and disease diagnosis.

Electrochemiluminescence of a First-Row d6 Transition Metal Complex.

We report the electrochemiluminescence (ECL) of a 3d6 Cr(0) complex ([Cr(LMes)3]; λem=735 nm) with comparable photophysical properties to those of ECL-active complexes of 4d6 or 5d6 precious metal ions. The electrochemical potentials of [Cr(LMes)3] are more negative than those of [Ir(ppy)3] and render the [Cr(LMes)3]* excited state inaccessible through conventional co-reactant ECL with tri-n-propylamine or oxalate. ECL can be obtained, however, through the annihilation route in which potentials sufficient to oxidise and reduce the luminophore are alternately applied. When combined with [Ir(ppy)3] (λem=520 nm), the annihilation ECL of [Cr(LMes)3] was greatly enhanced whereas that of [Ir(ppy)3] was diminished. Under appropriate conditions, the relative intensities of the two spectrally distinct emissions can be controlled through the applied potentials. From this starting point for ECL with 3d6 metal complexes, we discuss some directions for future development.

Electrochemiluminescence of a First‐Row d6 Transition Metal Complex

AbstractWe report the electrochemiluminescence (ECL) of a 3d6 Cr(0) complex ([Cr(LMes)3]; λem=735 nm) with comparable photophysical properties to those of ECL‐active complexes of 4d6 or 5d6 precious metal ions. The electrochemical potentials of [Cr(LMes)3] are more negative than those of [Ir(ppy)3] and render the [Cr(LMes)3]* excited state inaccessible through conventional co‐reactant ECL with tri‐n‐propylamine or oxalate. ECL can be obtained, however, through the annihilation route in which potentials sufficient to oxidise and reduce the luminophore are alternately applied. When combined with [Ir(ppy)3] (λem=520 nm), the annihilation ECL of [Cr(LMes)3] was greatly enhanced whereas that of [Ir(ppy)3] was diminished. Under appropriate conditions, the relative intensities of the two spectrally distinct emissions can be controlled through the applied potentials. From this starting point for ECL with 3d6 metal complexes, we discuss some directions for future development.

Electrochemiluminescence of hot exciton nanomaterial with boosted efficiency for visual bioanalysis

The electrochemiluminescence (ECL) efficiency (ΦECL) of organic ECL emitters is greatly influenced by the excited state property and component. Here we design a hot exciton molecule (BCzP-BT) with hybridized local and charge-transfer (HLCT) excited state property to prepare the first hot exciton organic nanorods (BB NRs). The BB NRs exhibit both sensitive annihilation and intense coreactant ECL emissions with a band gap emission model. Due to the reverse intersystem crossing among high-lying excited states (hRISC), the HLCT excited state property leads to highly efficient utilization of triplet excitons and thus high photoluminescence quantum yields (ΦPL) of more than 80% at 554 nm, which is demonstrated by solvatochromic experiments and quantum chemical calculations. The high ΦPL endows BB NRs with superior ΦECL over other nanoemitters, even the thermally activated delayed fluorescence materials, and thus offers highly-efficient nanoemitters for the design of ECL imaging strategy. As a proof of concept, an ECL probe is constructed by assembling BHQ2-ssDNA on BB NRs to integrate CRISPR/Cas12a system for target recognition, which produces a rapid and high-throughput ECL imaging platform. The proposed imaging method for HPV16 DNA detection shows excellent performance with a detection limit of 0.6 fM. This work broadens the application of hot exciton materials in ECL field, and opens a new avenue for developing next-generation ECL devices.

Tuning Dimensionality of Benzimidazole Aggregates by Using Tetraoctylammonium Bromide: Enhanced Electrochemiluminescence Studies

Exploring the depolymerization strategy of liposoluble luminophores in the aqueous phase is vital for the development of electrochemiluminescence (ECL). In this work, tetraoctylammonium bromide (TOAB) with four long hydrophobic chains and short hydrophilic ends is used as a template to limit the aggregation of benzimidazole (BIM). By adjusting the loading of BIM on the hydrophobic chains of TOAB, a two-dimensional lamellar BIM/TOAB is formed, the ECL intensity of which is 6.4 times higher than that of the aggregated BIM (H2O2 as the coreactant). In terms of ECL spectroscopies, cyclic voltammetry , ECL transients, and the adjustment of the scanning potential range, the ECL mechanism is thoroughly studied. This work provides a new way to depolymerize organic luminophores and reveals a possible pathway in the annihilation ECL mechanism.

Efficient annihilation electrochemiluminescence of [Ru(bpy)3]2+ within a deep eutectic solvent as green electrolyte

The generation of annihilation electrochemiluminescence (ECL) is typically limited to highly purified organic solvent-supporting electrolyte solutions or ionic liquids. Herein, we have prepared a deep eutectic solvent (DES) based on choline chloride (ChCl) and lactic acid (LA), which was directly used to investigate the annihilation ECL of [Ru(bpy)3]2+ for the first time. [Ru(bpy)3]2+ could be oxidized to stable [Ru(bpy)3]3+ radicals, while reduced to unstable [Ru(bpy)3]+ radicals in ChCl-LA DES. Moreover, [Ru(bpy)3]3+ was sufficiently stable on the time scale to react with [Ru(bpy)3]+ in ChCl-LA DES, resulting in the generation of intense annihilation ECL by a potential scanning or pulsing. This annihilation ECL system was further integrated into chitosan (CS) for the formation of homogenous and microporous ChCl-LA DES/CS/[Ru(bpy)3]2+ ionic gel, which was used as the emitting layer in ECL devices (ECLDs). The display performances for the ECLDs were demonstrated based on the efficient annihilation ECL in the ionic gel, giving bright light-emission visible to naked eye. Hence, this work confirmed the possibilities for studying annihilation ECL and its application in ECLDs using green DESs and CS materials.

Electrochemiluminescence of Polymer Dots Featuring Thermally Activated Delayed Fluorescence for Sensitive DNA Methylation Detection.

Polymer dots (Pdots) as electrochemiluminescence (ECL) emitters have drawn intensive attention for expanding the application of ECL analytical technology. Here we used a donor-acceptor polymer with thermally activated delayed fluorescence (TADF) property as a precursor to design and synthesize a kind of highly efficient Pdots with desirable annihilation and co-reactant ECL behaviors. The TADF Pdots possessed a highly stable negative-charged state in the ECL process, and their ECL emission followed the "S-route", thus achieving theoretically 100% excitons harvesting for radiative decay. With S2O82- or tripropylamine as the co-reactant, the TADF Pdots exhibited intensive bandgap ECL emission and possessed ultrahigh ECL efficiency, which were superior to conventional fluorescent Pdots due to the TADF property and the shielding of oxygen quenching effect toward triplet excitons. By combining the stable cathodic ECL property of TADF Pdots with rolling circle amplification reaction, a sensitive ECL biosensor was designed for DNA methylation detection with RASSF1A gene fragment as a target model, which showed detection limits down to the fM level and realized the localization of the methylation site on target DNA based on steric hindrance effect. This work revealed the great potential of TADF emitters in ECL efficiency elevation and offered a new idea for the development of detection kits to quantitatively detect gene methylation.

Zinc-Metal Organic Frameworks: A Coreactant-free Electrochemiluminescence Luminophore for Ratiometric Detection of miRNA-133a.

Developing a coreactant-free ratiometric electrochemiluminescence (ECL) strategy based on a single luminophore to achieve more accurate and sensitive microRNA (miRNA) detection is highly desired. Herein, utilizing zinc-metal organic frameworks (Zn-MOFs) as the single luminophore, a novel dual-potential ratiometric ECL biosensor was constructed for ultrasensitive detection of miRNA-133a. The as-prepared Zn-MOFs exhibited simultaneous cathode and anode ECL emission. Furthermore, the Zn-MOFs were confirmed to be a multichannel ECL sensing platform with excellent annihilation and coreactant ECL emission. The corresponding ECL behaviors were investigated in detail. Benefiting from the hybridization chain reaction (HCR) amplification technology, N,N-diethylethylenediamine (DEAEA) was modified on hairpin DNA, and the gained products loaded with quantities of DEAEA enhanced the anodic ECL intensity of Zn-MOFs. In the presence of miRNA-133a, the ECL intensity ratio of anode to cathode (Ia/Ic) was significantly increased, which realized the ultrasensitive ratiometric detection of miRNA-133a. In addition, without an exogenous coreactant, the biosensor revealed superb accuracy and stability. Under optimal conditions, the detection linearity of miRNA-133a was from 50 aM to 50 fM with a low detection limit of 35.8 aM (S/N = 3). This is the first work to use Zn-MOFs as a single emitter for reliable ratiometric ECL bioanalysis, which provides a new perspective for fabricating a ratiometric ECL biosensor platform.

Surface-Engineering Enhanced Charge Injection and Recombination of Silver Nanoclusters in an Aqueous Medium

An effective way to enhance the charge injection and the radiative recombination within atomically precise nanoclusters (NCs) is proposed with Ag29(BDT)12 (BDT = 1,3-benzenedithiol) and Ag29(BDT)12(TPP)4 (TPP = triphenylphosphine) as models. Surface-engineering Ag29(BDT)12 with phosphine ligands can passivate the four naked Ag atom sites on the surface of Ag29(BDT)12 and circumvent the geometric packing limitation induced by the wide footprint of BDT, which endows Ag29(BDT)12(TPP)4 with enhanced electrochemical redox for improved charge injection as well as boosted photoluminescence (PL) and electrochemiluminescence (ECL) for enhanced radiative charge recombination. The surface-engineering process demonstrates a negligible effect on the charge-injection potentials as well as the excited state emission for PL and ECL. Ag29(BDT)12 and Ag29(BDT)12(TPP)4 can be injected with holes and electrons via similar electrochemical redox processes; both annihilation ECL and co-reactant ECL of Ag29(BDT)12 and Ag29(BDT)12(TPP)4 match well with their valence (VB) hole/conduction (CB) electron injection-related oxidative/reductive processes and are of similar wavebands with a maximum emission wavelength around 795 nm.

Label-free immunosensor for cardiac troponin I detection based on aggregation-induced electrochemiluminescence of a distyrylarylene derivative

Herein, the aggregation-induced electrochemiluminescence (AIECL) of a distyrylarylene derivative, 4,4′-bis(2,2-diphenylvinyl)-1,1′-biphenyl (DPVBi), was investigated for the first time. This luminophore exhibits significantly enhanced photoluminescence (PL) and electrochemiluminescence (ECL) emission with the increases of water content in organic/water mixtures. This high luminescence efficiency of DPVBi in aggregate state is due to the fact that the aggregates can reduce the energy loss by restricting the intramolecular motions. The ECL behavior of DPVBi in acetonitrile was investigated by ECL transients and so-called “half-scan” technology, where singlet-singlet annihilation ECL was generated under continuous potential switching. The DPVBi nanobulks (DPVBi NBs) were prepared to improve its application in aqueous media, which could be conveniently cast on electrode surface for developing sensing platform due to its good film-forming nature. The constructed heterogeneous AIECL platform can produce reductive-oxidative and oxidative-reductive ECL by using trimethylamine (TEA) and potassium peroxodisulfate (K2S2O8) as coreactant. On the basis of the higher ECL efficiency of DPVBi NBs/TEA system, a label free immunosensor for cardiac troponin I (cTnI) was developed with the assistance of electrodeposited gold nanoparticles, and it showed a wide linear range of 20 ng/mL~100 fg/mL and low detection limit of 43 fg/mL. Moreover, the constructed immunosensor also exhibited good specificity, stability and satisfied performance in practical sample analysis.

Wide-Bite-Angle Diphosphine Ligands in Thermally Activated Delayed Fluorescent Copper(I) Complexes: Impact on the Performance of Electroluminescence Applications.

We report a series of seven cationic heteroleptic copper(I) complexes of the form [Cu(P^P)(dmphen)]BF4, where dmphen is 2,9-dimethyl-1,10-phenanthroline and P^P is a diphosphine chelate, in which the effect of the bite angle of the diphosphine ligand on the photophysical properties of the complexes was studied. Several of the complexes exhibit moderately high photoluminescence quantum yields in the solid state, with ΦPL of up to 35%, and in solution, with ΦPL of up to 98%. We were able to correlate the powder photoluminescence quantum yields with the % Vbur of the P^P ligand. The most emissive complexes were used to fabricate both organic light-emitting diodes and light-emitting electrochemical cells (LECs), both of which showed moderate performance. Compared to the benchmark copper(I)-based LECs, [Cu(dnbp)(DPEPhos)]+ (maximum external quantum efficiency, EQEmax = 16%), complex 3 (EQEmax = 1.85%) showed a much longer device lifetime (t1/2 = 1.25 h and >16.5 h for [Cu(dnbp)(DPEPhos)]+ and complex 3, respectively). The electrochemiluminescence (ECL) properties of several complexes were also studied, which, to the best of our knowledge, constitutes the first ECL study for heteroleptic copper(I) complexes. Notably, complexes exhibiting more reversible electrochemistry were associated with higher annihilation ECL as well as better performance in a LEC.

Ultrasensitive Nucleic Acid Assay Based on AIE-Active Polymer Dots with Excellent Electrochemiluminescence Stability.

Aggregation-induced emission (AIE) active Pdots are attractive nanomaterials applied in electrochemiluminescence (ECL) fields, while the irreversible redox reaction of these Pdots is a prevailing problem, resulting in instability of ECL emission. Herein, we first designed and synthesized an AIE-active Pdot with reversible redox property, which contains a tetraphenylethene derivate and benzothiadiazole (BT) to achieve stable ECL emission. BT has a good rigid structure with excellent electrochemical behaviors, which is beneficial for avoiding the destruction of the conjugated structure as much as possible during the preparation of Pdots, thus maintaining good redox property. The tetraphenylethene derivate, as a typical AIE-active moiety, provides a channel for highly efficient luminescence in the aggregated states. The Pdots exhibited reversible and quasi-reversible electrochemical behaviors during cathodic and anodic scanning, respectively. The stable annihilation, reductive-oxidative, and oxidative-reductive ECL signals were observed. Subsequently, we constructed an ultrasensitive ECL biosensor based on the oxidative-reductive ECL mode for the detection of miRNA-21 with a detection limit of 32 aM. This work provides some inspiration for the future design of ECL materials featuring AIE-active property and stable ECL emission.

Three kinds of porphyrin dots as near-infrared electrochemiluminescence luminophores: Facile synthesis and biosensing

Three kinds of porphyrin dots, including TCPP dots, ZnTCPP dots and TCPP-based metal organic framework (pMOF) dots, have been subtly synthesized for the first time by a universal straightforward exfoliation of bulk porphyrin aggregates or pMOF. To explore their ECL application, a novel label free “signal-on” ECL biosensor for ultrasensitive detection of Pb 2+ was developed based on TCPP dots as DNA intercalators and DNAzyme-based hybridization chain reaction signal amplification. • Three kinds of porphyrin dots are subtly prepared by a simple and universal exfoliation. • The novel porphyrin dots show excellent annihilation ECL activity. • They all exhibit stable and robust near-infrared co-reactant ECL performance. • A label free ECL biosensor is established for trace Pb 2+ detection based on TCPP dots. • The porphyrin dots as ECL emitters give a new proof of concept. Exploring novel near-infrared (NIR) luminophore with highly efficient and benign is strongly anticipated for electrochemiluminescence (ECL) evolution. Here, three kinds of porphyrin dots including 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin (TCPP) dots, ZnTCPP dots and TCPP-based metal organic framework (pMOF) dots have been subtly synthesized for the first time by a universal straightforward exfoliation of bulk porphyrin aggregates or pMOF. These as-designed porphyrin dots perform excellent annihilation ECL activity, also exhibit stable and robust cathodic or anodic NIR ECL properties with different coreactants (potassium peroxydisulfate, hydrogen peroxide or tri-n-propylamine) in aqueous phase. Especially, the ECL efficiency of three kinds of porphyrin dots in S 2 O 8 2− cathodic system are 56, 44, 39-fold higher than that of the Ru(bpy) 3 2+ standard, respectively. As a new type of ECL luminophores, TCPP dots coupled with a lead ion-dependent DNAzyme and hybridization chain reaction cycle amplification are used to fabricate a label free “signal-on” ECL biosensor for ultrasensitive detection of Pb 2+ . A dynamic range from 10 pmol·L −1 to 1 μmol·L −1 with a low limit of detection (1.2 pmol·L −1 ) is obtained. These porphyrin dots provide evidence for the use of organics-based dots as new NIR ECL luminophores for fundamental ECL research, and highlight the significance of small-sized organic nanomaterials in ECL sensing applications.

Electrochemiluminescence Based on a Dual Carbon Ultramicroelectrode with Confined Steady-State Annihilation.

Developing novel microelectronic devices for electrochemical measurements and electrochemiluminescence (ECL) study is of great importance. Herein, we fabricated a submicrometer-sized dual carbon electrode (DCE) and investigated its annihilation ECL behavior under steady-state conditions for the first time. The oxidation and reduction of the model luminophore, [Ru(bpy)3]2+, occurred separately at the two sides of the DCE, and the electrogenerated ions then diffused to the gap between the two electrodes to generate the excited-state intermediate [Ru(bpy)3]2+* and ECL emission. Compared with other types of two-electrode systems, the prepared DCE possesses a smaller total size and an ultrasmall interelectrode distance of 60 nm or less, which could result in a shorter diffusion time and an amplified ECL signal without the purification of the solvent and supporting electrolytes. On the basis of the constructed ECL microscopic platform, we successfully obtained a stable and confined ECL signal in the vicinity of the electrode tip. Furthermore, a two-dimensional finite element method simulation of this model system was performed to quantitively analyze the concentration profiles of the electrogenerated species around the tip of the DCE and predict the concentrations of [Ru(bpy)3]2+* with various gap distances. The simulation results also proved that the higher concentrations of [Ru(bpy)3]2+* could be achieved with a smaller distance with a possible amplification factor of 6 (compared with the concentration when the gap distance is greater than 300 nm). This work provides an experimental model for further improvement of ECL efficiency and broadens the availability for annihilation ECL applications in small confined spaces.

Ultrasensitive Nucleic Acid Assay Based on Cyclometalated Iridium(III) Complex with High Electrochemiluminescence Efficiency.

This work developed a sensitive electrochemiluminescence (ECL) biosensor based on a cyclometalated iridium(III) complex ((bt)2Irbza), which was synthesized for the first time. Annihilation, reductive-oxidative, and oxidative-reductive ECL behaviors of (bt)2Irbza were investigated, respectively. The oxidative-reductive ECL intensity was the strongest compared with the other two, which showed 16.7 times relative ECL efficiency compared with commercial [Ru(bpy)3]2+ under the same experimental conditions. Therefore, an ECL biosensing system with (bt)2Irbza as the anodic luminophore was established for miRNA detection based on a closed bipolar electrode (BPE). Combined with both steric hindrance and catalytic effects induced by hemin/G-quadruplex in the cathodic reservoir of BPE that changed the Faraday current of the cathode and thus mediated the ECL intensity of (bt)2Irbza in the anode of BPE, the ECL sensor stated an ultrahigh sensitivity for microRNA (miRNA-122) analysis with a detection limit of 82 aM.

Enhancing electrochemiluminescence of FAPbBr3 nanocrystals by using carbon nanotubes and TiO2 nanoparticles as conductivity and co-reaction accelerator for dopamine determination

Perovskite nanocrystals (NCs) are regarded as potential candidates as electrochemiluminescence (ECL) emitters due to their excellent photoluminescence ability. Herein, we report the ECL behavior of FAPbBr3 NCs (FA stands for CH(NH2)2) in the aqueous media. It was shown that the ECL of FAPbBr3 NCs can be obtained by hole-injection to oxidize their reduced states, with the emission peak centered around 534±1 nm and the full width at half maximum of 31±0.5 nm. The annihilation ECL of FAPbBr3 NCs was 4.3± 0.4 folds enhanced by adding 8% (w/w) CNTs. In the presence of tripropanolamine (TPrA) as the co-reactant, the anodic ECL intensity of FAPbBr3 was enhanced by a factor of 29 in compared with its annihilation ECL. The ECL intensity of FAPbBr3 NCs was enhanced 4.8 and 10.6 folds by using TiO2 nanoparticles (NPs) as the co-reaction accelerator and CNTs as the conductivity enhancer, respectively. In the mixture of TiO2 NPs @FAPbBr3 NCs @CNTs, the enhancement in ECL intensity of FAPbBr3 NCs by a factor of 21.6 was obtained. The anodic ECL of TiO2 NP @FAPbBr3 NCs @CNTs/GCE was applied to determination dopamine in the linear range of 0.01–10 μM, with the detection limit of 2.9 nM.

Electrochemiluminescence reaction pathways in nanofluidic devices.

Nanofluidic electrochemical devices confine the volume of chemical reactions to femtoliters. When employed for light generation by electrochemiluminescence (ECL), nanofluidic confinement yields enhanced intensity and robust luminescence. Here, we investigate different ECL pathways, namely coreactant and annihilation ECL in a single nanochannel and compare light emission profiles. By high-resolution imaging of electrode areas, we show that different reaction schemes produce very different emission profiles in the unique confined geometry ofa nanochannel. The confrontation of experimental results with finite element simulation gives further insight into the exact reaction ECL pathways. We find that emission strongly depends on depletion, geometric exclusion, and recycling of reactants in the nanofluidic device.

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

AbstractMetal–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.