Gregory J. Barbante

A potential-controlled switch on/off mechanism for selective excitation in mixed electrochemiluminescent systems

We demonstrate the complete, rapid, and reversible switching between the emissions from two electrogenerated chemiluminescence (ECL) systems contained within the same solution, controlled by simple modification of the applied potential. The fundamental bases of the approach are the ability to selectively ‘switch on’ luminophores at distinct oxidation potentials, and an intriguing observation that the emission from the well-known electrochemiluminescent complex, fac-Ir(ppy)3, (where ppy is 2-phenylpyridinato), can be selectively ‘switched-off’ at high overpotentials. The dependence of this phenomenon on high concentrations of the co-reactant implicates quenching of the excited [Ir(ppy)3]* state by electron transfer. Rapid spectral scanning during modulation of the applied potential reveals well resolved maxima for mixtures comprising either green and red or green and blue luminophores, illustrating the vast potential of this approach for multiplexed ECL detection.

Red–Green–Blue Electrogenerated Chemiluminescence Utilizing a Digital Camera as Detector

Exploiting the distinct excitation and emission properties of concomitant electrochemiluminophores in conjunction with the inherent color selectivity of a conventional digital camera, we create a new strategy for multiplexed electrogenerated chemiluminescence detection, suitable for the development of low-cost, portable clinical diagnostic devices. Red, green and blue emitters can be efficiently resolved over the three-dimensional space of ECL intensity versus applied potential and emission wavelength. As the relative contribution ratio of each emitter to the photographic RGB channels is constant, the RGB ECL intensity versus applied-potential curves could be effectively isolated to a single emitter at each potential.

Selective Excitation of Concomitant Electrochemiluminophores: Tuning Emission Color by Electrode Potential†

ECL in 3D: Selective electrogenerated chemiluminescence (ECL) of several ruthenium and iridium complexes simultaneously in solution can be controlled by electrode potential (see picture; λem=emission wavelength). These luminescent redox systems create a range of new possibilities for multi-analyte ECL detection, assessment of interdependent electrochemical/spectroscopic properties, and color tuning in light-emitting devices.

Understanding electrogenerated chemiluminescence efficiency in blue-shifted iridium(III)-complexes: an experimental and theoretical study.

Compared to tris(2-phenylpyridine)iridium(III) ([Ir(ppy)3 ]), iridium(III) complexes containing difluorophenylpyridine (df-ppy) and/or an ancillary triazolylpyridine ligand [3-phenyl-1,2,4-triazol-5-ylpyridinato (ptp) or 1-benzyl-1,2,3-triazol-4-ylpyridine (ptb)] exhibit considerable hypsochromic shifts (ca. 25-60 nm), due to the significant stabilising effect of these ligands on the HOMO energy, whilst having relatively little effect on the LUMO. Despite their lower photoluminescence quantum yields compared with [Ir(ppy)3 ] and [Ir(df-ppy)3 ], the iridium(III) complexes containing triazolylpyridine ligands gave greater electrogenerated chemiluminescence (ECL) intensities (using tri-n-propylamine (TPA) as a co-reactant), which can in part be ascribed to the more energetically favourable reactions of the oxidised complex (M(+) ) with both TPA and its neutral radical oxidation product. The calculated iridium(III) complex LUMO energies were shown to be a good predictor of the corresponding M(+) LUMO energies, and both HOMO and LUMO levels are related to ECL efficiency. The theoretical and experimental data together show that the best strategy for the design of efficient new blue-shifted electrochemiluminophores is to aim to stabilise the HOMO, while only moderately stabilising the LUMO, thereby increasing the energy gap but ensuring favourable thermodynamics and kinetics for the ECL reaction. Of the iridium(III) complexes examined, [Ir(df-ppy)2 (ptb)](+) was most attractive as a blue-emitter for ECL detection, featuring a large hypsochromic shift (λmax =454 and 484 nm), superior co-reactant ECL intensity than the archetypal homoleptic green and blue emitters: [Ir(ppy)3 ] and [Ir(df-ppy)3 ] (by over 16-fold and threefold, respectively), and greater solubility in polar solvents.

Simultaneous control of spectroscopic and electrochemical properties in functionalised electrochemiluminescent tris(2,2′-bipyridine)ruthenium(II) complexes

Using a combination of electrochemical, spectroscopic and computational techniques, we have explored the fundamental properties of a series of ruthenium diimine complexes designed for coupling with other molecules or surfaces for electrochemiluminescence (ECL) sensing applications. With appropriate choice of ligand functionality, it is possible to manipulate emission wavelengths while keeping the redox ability of the complex relatively constant. DFT calculations show that in the case of electron withdrawing substituents such as ester or amide, the excited state is located on the substituted bipyridine ligand whereas in the case of alkyl functionality it is localised on a bipyridine. The factors that dictate annihilation ECL efficiency are interrelated. For example, the same factors that determine ΔG for the annihilation reaction (i.e. the relative energies of the HOMO and LUMO) have a corresponding effect on the energy of the excited state product. As a result, most of the complexes populate the excited state with an efficiency (Φ(ex)) of close to 80% despite the relatively wide range of emission maxima. The quantum yield of emission (Φ(p)) and the possibility of competing side reactions are found to be the main determinants of ECL intensity.

Electrochemiluminescence of surface bound microparticles of ruthenium complexes

The ability to study electrochemiluminescence (ECL) and related phenomena in solids is crucial to practical applications such as novel analytical and light-emitting devices. In this study we have used electrochemical, spectroscopic and surface techniques to explore the solid-state electrochemistry and electrochemiluminescence properties of two ruthenium complexes: [Ru(dpp)3](PF6)2 and [Ru(tmp)3](PF6)2 (where dpp is 4,7-diphenyl-1,10-phenanthroline and tmp is 3,4,7,8-tetramethyl-1,10-phenanthroline). We employed a novel method for the characterization of solid-state ECL properties by using surface bound microparticles of these compounds. For light-emitting devices and other solid-state applications it is essential to determine the mobility of charged species; electrons and ions, and thus emphasis has been given to the measurements of transport properties. In the solid-state, stable voltammetric responses have been observed for both materials, characterized by semi-infinite linear diffusional charge transport at relatively fast scan rates. The deposits can be also exhaustively oxidized at longer experimental timescales, exhibiting finite diffusional type voltammetric behaviour. We show that the oxidation and reduction rate depend not only on the structure of the phenanthroline ligand but also on the identity and concentration of the anion of the supporting electrolyte. This suggests that ion insertion/desertion into the solid is rate limiting rather than electron self-exchange. In situ electrochemical AFM reveals that initial redox cycling, necessary to “break-in” the system, is accompanied by subtle morphological changes, implying that the cycling promotes an electrochemical change in the solid phase. Electrochemiluminescence was observed from the microparticle films when oxidized in the presence of a suitable coreactant. The intensity of ECL is lower compared to the solution phase system because the reaction with the coreactant occurs only at the surface of each particle. Annihilation between the sequentially oxidized and reduced forms of the material, which likely occurs in the bulk of the solid rather than at the surface, produces ECL which is notably more intense.

3D-printed and CNC milled flow-cells for chemiluminescence detection

Herein we explore modern fabrication techniques for the development of chemiluminescence detection flow-cells with features not attainable using the traditional coiled tubing approach. This includes the first 3D-printed chemiluminescence flow-cells, and a milled flow-cell designed to split the analyte stream into two separate detection zones within the same polymer chip. The flow-cells are compared to conventional detection systems using flow injection analysis (FIA) and high performance liquid chromatography (HPLC), with the fast chemiluminescence reactions of an acidic potassium permanganate reagent with morphine and a series of adrenergic phenolic amines.

Photoredox Catalysis of Intramolecular Cyclizations with a Reusable Silica‐Bound Ruthenium Complex

Photoredox catalysis with the use of a stable, reusable silica‐bound chromophore was applied to the intramolecular cyclization of a series of 2‐benzylidenehydrazinecarbothioamides to give 5‐phenyl‐1,3,4‐thiadiazol‐2‐amines. The catalyst was readily prepared by carbodiimide‐mediated coupling of commercially available amine‐functionalized silica beads to a carboxylic acid functionalized ruthenium complex. The immobilized catalyst was readily removed from the reaction product by filtration and was used eight times without loss of catalytic activity. This simple, safe, and practical method is an attractive alternative to conventional procedures.