On the mechanism of the bipolar reference electrode

Commercial silver/silver chloride (Ag/AgCl) reference electrodes are some of the most commonly used reference electrodes, but they suffer from a number of issues due to their porous frits. Such issues include difficulty miniaturizing, silver and chloride ion leakage, charge screening effects at low ionic strength, frit drying if left unattended in air, and incompatibility with organic solvents. To solve these issues, we recently designed a reference electrode that is leakless in principle by replacing the porous frit with a sealed, conductive wire, where the ends of the wire are exposed to the reference electrode solution and the working electrode solution. We hypothesized that the reference electrode operated like a closed, bipolar electrochemical cell, and we termed the name bipolar reference electrode (BPRE). Here, we provide evidence that the BPRE can either act as a reference electrode by operating through an ion transfer mechanism via leakage through the imperfect seal, or it can act as a highly stable quasi-reference electrode through a bipolar electron transfer mechanism (BPQRE). Finally, we demonstrate the effectiveness of the BPRE in other types of common electrochemical studies, including chronoamperometry, linear sweep voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy.

Enhanced Electrochemiluminescence of A Macrocyclic Tetradentate Chelate Pt(II) Molecule via Its Collisional Interactions with the Electrode

A macrocyclic tetradentate chelate Pt(II) molecule (Pt1) served as an excellent luminophore in electrochemiluminescence (ECL) processes. The blue ECL of Pt1/S2O82- coreactant system in N,N'-dimethylformamide was found to be 46 times higher than that of the Ru(bpy)2+/S2O82- system or 30 times higher than that of the 9,10-diphenylanthracene/S2O82- system. The unprecedented high ECL quantum efficiencies were caused by the cyclic generation of monomer excited states through collisional interactions of Pt1 molecules with the electrode at an elevated frequency. The ECL is tunable from bright blue to pure white by simply changing the solvent from N,N'-dimethylformamide to dichloromethane. The white ECL of Pt(II) molecule was reported for the first time and the mechanism was proposed to be the simultaneous emissions from the monomer excited state (blue) and excimer (red).

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.

Cyclometalated Ir(III) complexes as potential electron acceptors for organic solar cells

Cyclometalated iridium(iii) complexes have been investigated as promising electron donor (D) materials in organic solar cells (OSCs) due to their unique octahedral configuration for optimized morphology and their significantly long lifetimes potentially for enhanced exciton dissociation. However, the application as electron acceptor (A) materials has never been reported. In order to fill this blank, herein, two cyclometalated heteroleptic Ir complexes, TRIr and 2TRIr, based on electron donating-accepting type organic ligands with different π-conjugation lengths are reported as electron acceptor materials in comparison with their corresponding main organic ligands. The two Ir complexes exhibit suitable HOMO/LUMO energy levels of -5.55/-3.47 eV and -5.44/-3.48 eV, which are ∼0.1 eV higher in the HOMO and ∼0.15 eV deeper in the LUMO than the TR and 2TR ligands, respectively. 2TRIr with extended ligand π-conjugation displays a poor triplet feature, while TRIr demonstrates obvious metal-to-ligand charge transfer (MLCT) transition absorption, with a triplet component photoluminescence (PL) lifetime of 85 ns in neat films. When blended with PBDB-T in bulk heterojunction (BHJ) OSCs, the power conversion efficiencies (PCEs) are 2-3 times higher than their relevant ligands, with values of 1.20% and 1.62% for TRIr and 2TRIr, and 0.58% and 0.47% for the TR and 2TR ligand-based devices, respectively. TRIr and 2TRIr based active layer blends exhibit poorer hole and electron mobilities, whereas compared with their relatively linear planar ligands, both of the two octahedral Ir complexes exhibit an optimized surface morphology for less bimolecular recombination and more efficient exciton dissociation, thus contributing to improved photovoltaic performance.

‘Cathodic’ electrochemiluminescence of [Ru(bpy)3]2+ and tri-n-propylamine confirmed as emission at the counter electrode

Monitoring emission and potentials at both the working and counter electrodes provides new insight into a proposed cathodic electrochemiluminescence system.

Synthesis, coordination chemistry and photophysical properties of naphtho-fused pyrazole ligands

The synthesis of two π-extended pyrazole ligands is reported, and their zinc(ii) and copper(ii) complexes are studied spectroscopically and crystallographically, revealing the influence of the fused naphthyl substituent.