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The classic and most widely used co-reactant electrochemiluminescence (ECL) reaction of tris(2,2′-bipyridine)ruthenium(ii) ([Ru(bpy)3]2+) and tri-n-propylamine is enhanced by an order of magnitude by fac-[Ir(sppy)3]3− (where sppy = 5′-sulfo-2-phenylpyridinato-C2,N), through a novel ‘redox mediator’ pathway. Moreover, the concomitant green emission of [Ir(sppy)3]3−* enables internal standardisation of the co-reactant ECL of [Ru(bpy)3]2+. This can be applied using a digital camera as the photodetector by exploiting the ratio of R and B values of the RGB colour data, providing superior sensitivity and precision for the development of low-cost, portable ECL-based analytical devices., A water-soluble Ir(iii) complex is shown to enhance the ‘remote’ mechanism of the most widely used co-reactant ECL reaction of tris(2,2′-bipyridine)ruthenium(ii) with tripropylamine.

Preliminary explorations of the annihilation electrogenerated chemiluminescence (ECL) of mixed metal complexes have revealed opportunities to enhance emission intensities and control the relative intensities from multiple luminophores through the applied potentials. However, the mechanisms of these systems are only poorly understood. Herein, we present a comprehensive characterisation of the annihilation ECL of mixtures of tris(2,2'-bipyridine) ruthenium(II) hexafluorophosphate ([Ru(bpy)(3)](PF6)(2)) and fac-tris(2-phenylpyridine)iridium(III) ([Ir(ppy)(3)]). This includes a detailed investigation of the change in emission intensity from each luminophore as a function of both the applied electrochemical potentials and the relative concentrations of the two complexes, and a direct comparison with two mixed (Ru/Ir) ECL systems for which emission from only the ruthenium-complex was previously reported. Concomitant emission from both luminophores was observed in all three systems, but only when: (1) the applied potentials were sufficient to generate the intermediates required to form the electronically excited state of both complexes; and (2) the concentration of the iridium complex (relative to the ruthenium complex) was sufficient to overcome quenching processes. Both enhancement and quenching of the ECL of the ruthenium complex was observed, depending on the experimental conditions. The observations were rationalised through several complementary mechanisms, including resonance energy transfer and various energetically favourable electron-transfer pathways. Refereed/Peer-reviewed

A family of four Ir(iii) complexes of the form [Ir(ppy)2(L)]Cl (where ppy = 2-phenyl-pyridine and L = a pyridyl-1,2,4-triazole or pyridyl-1,3,4-oxadiazole ligand bearing a boronic acid group) have been prepared as potential luminescent sensors for carbohydrates. A modular eight step procedure was developed to synthesise the complexes, and this was initiated with the preparation of two benzhydrazide and three S-ethylated pyridine-2-thiocarboxamides precursors. Reaction of these precursors produced three new 1,2,4-triazole- and one 1,3,4-oxadiazole-based ligands substituted with boronic acid pinacol ester groups. The boronic acid pinacol esters were then converted to boronic acids in two steps via potassium trifluoroborate intermediates. The boronic acid substituted ligands and their Ir(iii) complexes were fully characterised using a range of techniques including X-ray crystallography in the case of the pyridyl-1,3,4-oxadiazole ligand and two of the Ir(iii) complexes. The capacity of the synthesised Ir(iii) complexes to form boronic acid cyclic esters with the simple sugars glucose and fructose was evaluated using high-resolution mass spectrometry (HRMS) and photoluminescence titration studies. These studies confirm that the Ir(iii) complexes form adducts with both glucose and fructose, with increased levels of boronic acid cyclic esters being formed with fructose at higher pHs. Theoretical calculations were used to gain insight into the nature of the electronic transitions involved in the electronic absorption and emission spectra.

We present a new approach to explore the potential-dependent multi-colour co-reactant electrochemiluminescence (ECL) from multiple luminophores. The potentials at both the working and counter electrodes, the current between these electrodes, and the emission over cyclic voltammetric scans were simultaneously measured for the ECL reaction of Ir(ppy)3 and either [Ru(bpy)3]2+ or [Ir(df-ppy)2(ptb)]+, with tri-n-propylamine as the co-reactant. The counter electrode potential was monitored by adding a differential electrometer module to the potentiostat. Plotting the data against the applied working electrode potential and against time provided complementary depictions of their relationships. Photographs of the ECL at the surface of the two electrodes were taken to confirm the source of the emissions. This provided a new understanding of these multifaceted ECL systems, including the nature of the counter electrode potential and the possibility of eliciting ECL at this electrode, a mechanism-based rationalisation of the interactions of different metal-complex luminophores, and a previously unknown ECL pathway for the Ir(ppy)3 complex at negative potentials that was observed even in the absence of the co-reactant., Exploration of potential-dependent, multi-colour co-reactant electrochemiluminescence from multiple luminophores at the working and counter electrodes reveals new pathways to emission.

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.

Energy transfer in a redox metallopolymer containing both fluorinated and non-fluorinated cyclometalated iridium (II) centres is explored. These materials are readily prepared by mixing two different iridium dimers and a backbone chain containing pendant groups (e.g. poly-vinylpyridine/poly-styrene), which can coordinate to the metal centres. Their easy synthesis together with their ability to self-assemble into polymeric nanoparticles in aqueous media render them a unique emitting material with nanoscale dimensions. We report the photophysical, electrochemical and electrochemiluminescence (ECL) properties of these polymeric nanoparticles in solution and immobilised as a thin layer. We demonstrate Dexter-type Energy Transfer (ET) and ECL-ET phenomena resulting in ECL enhancement by up to 505% compared with metallopolymers containing only one type of iridium centre. These results demonstrate the possibility of synthesising new materials with tailored and enhanced emission wavelengths by careful selection of the emitting centres for any opto-electronic and sensing-related applications.

A new strategy to create iridium(iii)-based ECL labels reveals limitations of conventional approaches., Translation of the highly promising electrogenerated chemiluminescence (ECL) properties of Ir(iii) complexes (with tri-n-propylamine (TPrA) as a co-reactant) into a new generation of ECL labels for ligand binding assays necessitates the introduction of functionality suitable for bioconjugation. Modification of the ligands, however, can affect not only the photophysical and electrochemical properties of the complex, but also the reaction pathways available to generate light. Through a combined theoretical and experimental study, we reveal the limitations of conventional approaches to the design of electrochemiluminophores and introduce a new class of ECL label, [Ir(C^N)2(pt-TOxT-Sq)]+ (where C^N is a range of possible cyclometalating ligands, and pt-TOxT-Sq is a pyridyltriazole ligand with trioxatridecane chain and squarate amide ethyl ester), which outperformed commercial Ir(iii) complex labels in two commonly used assay formats. Predicted limits on the redox potentials and emission wavelengths of Ir(iii) complexes capable of generating ECL via the dominant pathway applicable in microbead supported ECL assays were experimentally verified by measuring the ECL intensities of the parent luminophores at different applied potentials, and comparing the ECL responses for the corresponding labels under assay conditions. This study provides a framework to tailor ECL labels for specific assay conditions and a fundamental understanding of the ECL pathways that will underpin exploration of new luminophores and co-reactants.

A powerful, yet low-cost and semi-portable electrochemiluminescence (ECL) biosensing device is described. It is constructed around a Raspberry Pi single-board computer, which serves as the controller and user interface. The Pi is interfaced with an expansion board that controls the potential applied to a disposable screen-printed electrode and facilitates data acquisition from a photomultiplier tube (PMT), which detects the ECL emission from the sensor surface. As proof-of-concept, we demonstrate that this arrangement can quantitate tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)

Funding: C.L. thanks the Prof. & Mrs Purdie Bequests Scholarship and AstraZeneca for a PhD Studentship. The St Andrews researchers thank the Engineering and Physical Sciences Research Council (EP/M02105X/1 and EP/R035164/1) for financial support. A.K.P. acknowledges the Leverhulme Trust and the University of St Andrews for an Early Career Fellowship (ECF-2017-326). H.J.B. and M.S. acknowledge funding from the Spanish Ministry of Science, Innovation and Universities (MAT2017‐88821‐R and RYC-2016-21316, respectively). C.F.H. acknowledges the support of the Australian Research Council (ARC) Discovery grant scheme (DP200102947). 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. Postprint

In this paper we report the outcome of the reduction of NHC stabilized acetylenic dications, [NHC-Cn-NHC]2+ for n=2 and 4. The target compounds were NHC stabilized di- and tetracarbon in the form of NHC-Cn-NHC. However, upon chemical reduction, decomposition ensues with release of the free NHC. This effect is also observed in electrochemical studies. This lends credence to Bestman’s hypothesis that two donor ligands cannot stabilize Cn for n=even numbers.

The reaction between trans-[AuF2(pyridine)2]+ and [PhI(pyridine)2]2+ results in the formation of PhIF2 and [Au(pyridine)4]3+. Investigation of the reaction pathway using model Pd and Pt analogues of the gold complex indicate that the most likely mechanism is attack by the Au–F onto the I(III), rather than a redox process. This demonstrates that the Au(III)–F fragment can behave in a nucleophilic manner even in a relatively electron-poor cationic complex.

Previously reported annihilation ECL of mixtures of metal complexes have generally comprised Ir(ppy)3 or a close analogue as a higher energy donor/emitter (green/blue light) and [Ru(bpy)3]2+ or its derivative as a lower energy acceptor/emitter (red light). In contrast, here we examine Ir(ppy)3 as the lower energy acceptor/emitter, by combining it with a second Ir(iii) complex: [Ir(df-ppy)2(ptb)]+ (where ptb = 1-benzyl-1,2,3-triazol-4-ylpyridine). The application of potentials sufficient to attain the first single-electron oxidation and reduction products can be exploited to detect Ir(ppy)3 at orders of magnitude lower concentration, or enhance its maximum emission intensity at high concentration far beyond that achievable through conventional annihilation ECL of Ir(ppy)3 involving comproportionation. Moreover, under certain conditions, the colour of the emission can be selected through the applied electrochemical potentials. We have also prepared a novel Ir(iii) complex with a sufficiently low reduction potential that the reaction between its reduced form and Ir(ppy)3+ cannot populate the excited state of either luminophore. This enabled, for the first time, the exclusive formation of either excited state through the application of higher cathodic or anodic potentials, but in both cases, the ECL was greatly diminished by parasitic dark reactions.

Summary The advent of highly emissive cyclometalated iridium complexes has injected new vigour into the field of electrochemiluminescence (ECL), with these materials now beginning to challenge the dominance of ruthenium diimine complexes for ECL applications. The promise of iridium-based electrochemiluminophores lies not only in their enhanced photophysical properties but in the relative ease with which their emission wavelengths and redox potentials can be tailored. However, innovative approaches and better understanding are required to tackle the challenges which sometimes arise associated with their susceptibility to quenching, especially in aqueous media.

Impairment of the protein quality control network leads to the accumulation of unfolded and aggregated proteins. Direct detection of unfolded protein accumulation in the cells may provide the possibility for early diagnosis of neurodegenerative diseases. Here a new platform based on a peptide-conjugated thiol-reactive aggregation-induced emission fluorogen (AIEgen), named MI-BTD-P (or D1), for labeling and tracking unfolded proteins in cells is reported. In vitro experiments with model proteins show that the non-fluorescent D1 only becomes highly fluorescent when reacted with the thiol group of free cysteine (Cys) residues on unfolded proteins but not glutathione or folded proteins with buried or surface exposed Cys. When the labeled unfolded proteins form aggregates, D1 fluorescence intensity is further increased, and fluorescence lifetime is prolonged. D1 is then used to measure unfolded protein loads in cells by flow cytometry and track the aggregate formation of the D1 labeled unfolded proteins using confocal microscopy. In combination with fluorescence lifetime imaging technique, the proteome at different folding statuses can be better differentiated, demonstrating the versatility of this new platform. The rational design of D1 demonstrates the outlook of incorporation of diverse functional groups to achieve maximal sensitivity and selectivity in biological samples.

A new class of electrochemiluminescent (ECL) system is reported in which a heterobimetallic array is used to facilitate electrochemically initiated lanthanide emission, following energy transfer from an ECL-active donor. Spectroscopic measurements are used to probe the efficiency, rate and mechanism of the energy-transfer process in two bimetallic systems with differing donor energies. Non-optical sensitization of the luminescence from lanthanide ions opens up exciting new possibilities for the development of ECL probes with sharper emission peaks and a greater variety of emission colours.

We report the electrochemiluminescence properties of square-planar Pt(II) complexes that result from the formation of supramolecular nanostructures. We define this new phenomenon as aggregation-induced electrochemiluminescence (AIECL). In this system, self-assembly changes the HOMO and LUMO energies, making their population accessible via ECL pathways and leading to the generation of the luminescent excited state. Significantly, the emission from the self-assembled system is the first example of electrochemiluminescence (ECL) of Pt(II) complexes in aqueous solution having higher efficiency than the standard, Ru(bpy)32+.The finding can lead to a new generation of bright emitters that can be used as ECL labels.

We examine the electrogenerated chemiluminescence (ECL) of three Ir(C∧N )2(acac) complexes, where acac=acetylacetonate anion and C∧N =2-phenylpyridine (ppy), 2-phenylbenzothiazole (bt), or 2-phenylquinoline (pq) anions, with tri-n-propylamine co-reactant in acetonitrile under a range of chemical and instrumental conditions; this follows somewhat conflicting recent claims of the ECL intensities from complexes of this type. Relevant electrochemical, spectroscopic, and ECL properties are evaluated in direct comparison with those of Ir(ppy)3 and [Ru(bpy)3](PF6)2, as well as data from previous publications. DFT calculations on the Ir(C∧N )2(acac) complexes show the HOMOs to be composed of both the metal and the C∧N ligand, and the LUMOs almost exclusively on the C∧N ligand. The ECL intensities of the Ir(C∧N )2(acac) complexes (relative to [Ru(bpy)3](PF6)2) were dependent on experimental conditions and, in some cases, the ECL intensities reported for iridium complexes may have been derived using conditions that unintentionally disadvantaged the reference electrochemiluminophore.

Here we describe a new aspect of multicolor potential-resolved electrochemiluminescence (ECL) based on bipolar electrochemistry (BPE). BPE involves a potential gradient established along a polarized conducting object which thus acts as a bipolar electrode (BE). The resulting driving force can induce electron-transfer reactions, necessary for processes such as ECL occurring at different longitudinal locations along the same BE. In this work, we exploit the entire spatial domain where anodic polarization occurs to demonstrate, for the first time, how the potential gradient along a BE may be used to simultaneously resolve the emissions of ECL-active luminophores with differing oxidation potentials. The control of both size and position of the ECL-emitting domains was achieved by tuning the applied electric field. Multicolor light-emission was analyzed in detail to demonstrate spatial and spectral resolution of a solution containing different emitters. Keywords: Electrochemiluminescence, Bipolar electrochemistry, Iridium/ruthenium complexes, Multicolor emission, Potential gradient

We report the synthesis, photophysics, electrochemistry and electrochemiluminescence (ECL) of two dqp (dqp=2,6-di(quinoline-8-yl)pyridine) based ruthenium(II) complexes, bearing either a n-butyl ester (1) or the corresponding carboxylic acid functionality (2). The complexes were prepared from [Ru(dqp)(MeCN)3 ][PF6 ]2 by reaction with the dqp precursor using microwave irradiation. In both cases, photoluminescence spectra present strong 3 MLCT-based red/near-infrared (NIR) emissions centred at about 710 nm. The photoluminescence quantum yields were 6.1 % and 1.8 % for 1 and 2 respectively while the excited state lifetimes were 3.60 μs and 2.37 μs. Both complexes are ECL active, although ECL efficiency (ΦECL ) of 1 was substantially higher than 2, due to its more favourable electrochemical properties. Importantly, 1 also gave strong ECL in aqueous media, which is rare for near-infrared emitters. The results suggest the possibility of very interesting ECL sensing applications for this class of emitter in biological media.

Parent isoquinoline diimide (IQDI) and phthalazine diimide (PTDI), as two new heterocyclic analogues of naphthalene diimides (NDIs), have been synthesized through an oxidative strategy in 35-79 % yield. X-ray crystallography has been used to support the formation of IQDI, which also show fluorescence quantum yields of 3.5 %. The electrochemical and electrical properties of these molecules have been studied. The electrochemical results show an interesting trend in first reduction potential PTDI

Electrochemiluminescence (ECL) as a basis for chemical and biochemical measurement has risen to prominence in the last two decades, and is now firmly established as one of the most important means of achieving ultrasensitive bioanalytical detection. Until recently, it seemed that ECL was approaching the limits of its development as a technique, with the vast majority of applications being limited to derivatives of Ru(bpy)32+, the red-emitting standard ECL emitter. Recently, however, with the advent of new classes of electrochemiluminophores, notably cyclometalated iridium complexes, and various types of nanomaterials, new possibilities have arisen, which have stimulated new developments. Chief among these advances has been the ability to simultaneously detect more than one luminophore in the same solution, by exploiting differences in colour and/or redox potential. Combined with the emergence of new electrochemical methodologies, such as bipolar electrochemistry (BPE), and advances in spectroscopic, electrochemical and data acquisition hardware, this has resulted in a surge of research activity in recent years, related to multicolour ECL for potential multiplex detection applications. Here, we summarise and critically analyse the most important developments in the area, provide practical information related to instrumental aspects of potential-resolved and wavelength-resolved measurements and offer insights related to future directions in this field.

Fluorescent sensors have proved invaluable in elucidating the regulation and dysregulation of redox processes in biology, but understanding of the breadth of biological redox reactions requires development of new sensors based on a range of sensing groups with varied reduction potentials. The aim of this work was to investigate the use of nicotinamide as a redox switch when conjugated to two classes of amino-fluorophores. We prepared four fluorophore conjugates based on 7-aminocoumarins and 4-amino-1,8-naphthalimides via the nicotinamide Zincke salt. These conjugates all showed clear fluorescence changes in response to chemical reduction, but this reduction was irreversible both chemically and electrochemically. The reduction behaviour of the 1,8-naphthalimides was investigated further by spectroelectrochemistry, revealing that conjugate NNpR1 showed the clearest spectral changes upon both chemical and electrochemical reduction. Cells dosed with NNpR1 and maintained under hypoxic conditions exhibited a significantly higher green:blue fluorescence ratio than cells cultivated under normoxia, confirming the potential of this molecule as a sensor for reductive biological environments.

The facile synthesis of a bimetallic polymer is demonstrated by a single-step modification of [Ru(bpy)2PVP10]2+ (bpy = bipyridine, PVP = poly-4-vinylpyridine), which has been partially photolyzed, with an iridium precursor. This bimetallic polymer possesses three emissive centres: Ir, Ru(N)6, and Ru(N)5. The photophysical, electrochemical and electrochemiluminescent properties of this bimetallic and corresponding monometallic polymers in solution-phase, and when immobilised as a thin layer, are reported. The perceived emission colour can be readily tuned from near-infrared through to green, by varying the ratio of iridium to ruthenium centres in the polymer. Energy transfer from the iridium centre to the Ru(N)5 and Ru(N)6 centres is observed on photoexcitation of the polymers in solution-phase. When the materials are immobilised as a thin layer, energy transfer can be observed following excitation via electrochemiluminescent (ECL) pathways. Mechanistic studies were performed and further investigated through 3D ECL. Dexter-type energy transfer enhances the electrochemiluminescence properties of the bimetallic polymer versus the monometallic polymer, improving the limit of detection of the co-reactant oxalate from 20 to 5 μM.

Electrochemical measurements are attractive for continuous or long-term monitoring of chemical species in a range of analytical applications including health, environmental and agricultural monitoring, as well as food analysis and industrial process control. A significant barrier to long-term electrochemical measurements in continuous online monitoring applications is the requirement for stable and durable reference electrodes. Most reference electrodes require regular maintenance in such situations to maintain the concentration of the internal electrolyte reservoir and prevent fouling of the electrode. Solid state reference electrodes (SSREs) are well suited to these long-term monitoring applications, but most only have their short-term performance reported or are designed for disposable applications. Additionally, polymer crosslinking has been demonstrated as an effective way to slow leakage of suspended solutes, improve chemical resistance, and control a polymer's physical properties; but application of this technique in SSRE materials is yet to be reported. This work describes the construction and performance of a novel SSRE with exceptional long-term stability, using an ethylene glycol dimethacrylate (EGDMA) crosslinked PVAc/KCl composite material. Open circuit potentiometry and electrochemical impedance spectroscopy were used to study the electrochemical performance. Conductivity measurements and micro X-ray fluorescence mapping were used to examine the effect of EGDMA crosslinking on electrolyte leakage and electrode lifetime. A SSRE with a 1% molar ratio of EGDMA/vinyl acetate proved to be exceptionally stable and provided a reliable reference potential for at least 175 days in a 1 M Na2SO4 solution. PVAc/KCl composites without crosslinker were found to leak electrolyte ca. 30% faster than those with 1% EGDMA. EGDMA crosslinking also was shown to improve electrochemical performance and SSRE lifetime in both highly acidic and strongly alkaline solutions, suggesting a broad range of applications. Additionally, a 1% crosslinked SSRE demonstrated comparable performance to a commercial reference electrode in potentiometric and voltammetric measurements. The results demonstrate that crosslinked polymer-electrolyte composites provide a promising new approach for improving reference electrode performance in electrochemical measurements, particularly in continuous long-term online monitoring applications.

In this paper we report on the use of [NO][BF4] to access tricationic tetrakis(pyridine)gold(III) from Au powder, a species inaccessible using the more traditional (tetrahydrothiophene)AuCl route. It is then demonstrated that this family of compounds can be used to access new terminal Au(III) hydroxides, a challenging class of compounds, and the first crystallographically characterized examples employing bidentate ligands. Finally, preliminary biological studies indicate good activity for derivatives featuring polydentate ligands against the HeLa and PC3 cell lines but also strong inhibition of primary HUVEC cells.

A single component electrochemiluminescence system from which red, green, blue or white emission can be obtained, depending on the applied potential or the mode of the ECL experiment, is described., A single starting component electrochemiluminescence system from which red, green, blue or white emission can be obtained, depending on the applied potential or the mode of the ECL experiment, is described. The convoluted ECL spectral responses observed at different potentials are readily explained using a 3D-ECL technique, where the ECL spectral profile is continuously monitored as a function of potential during voltammetric scanning. The 3D plots obtained using this technique implicate cross-annihilation ECL reactions involving the complex itself and stable products resulting from its electrolysis. Combining this information with knowledge of the energetic requirements of the various reactions involved, suggests a mechanism involving traces of two emissive products, related to the loss of a methyl group from the triazole moiety. These products, while barely detectable electrochemically, are sufficiently emissive to influence and even dominate the ECL emission under some conditions.

A series of five heteroleptic Ir(III) complexes of the general form Ir(dfppy)2(C^C) have been prepared (where dfppy represents 2-(2,4-difluorophenyl)pyridine and C^C represents a bidentate cyclometalated phenyl substituted imidazolylidene ligand). The cyclometalated phenyl ring of the imidazolylidene ligand was either unsubstituted or substituted with electron donating (OMe and Me) or electron withdrawing (Cl and F) groups in the 2 and 4 positions. The synthesised Ir(III) complexes have been characterised by elemental analysis, NMR spectroscopy, cyclic voltammetry and electronic absorption and emission spectroscopy. The molecular structures for four Ir(III) complexes were determined by single crystal X-ray diffraction. Each of the Ir(III) complexes exhibited intense photoluminescence in acetonitrile solution at room temperature with quantum yields (ΦPL) ranging from 58% to 86%. Cyclic voltammetry experiments revealed one oxidation process (formally ascribed to the metal centre), and two ligand-based reductions for each complex. Complexes 1–5 gave moderate to intense annihilation and co-reactant electrochemiluminescence (ECL). Consideration of the electrochemical, spectroscopic and theoretical investigations provide insights into the electrochemiluminescence behaviour.

The attempted synthesis of NHC-stabilized dicarbon (NHC=C=C=NHC) through deprotonation of a doubly protonated precursor ([NHC-CH=CH-NHC](2+) ) is reported. Rather than deprotonation, a clean reduction to NHC=CH-CH=NHC is observed with a variety of bases. The apparent resistance towards deprotonation to the target compound led to a reinvestigation of the electronic structure of NHC→CC←NHC, which showed that the highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) gap is likely too small to allow for isolation of this species. This is in contrast to the recent isolation of the cyclic alkylaminocarbene analogue (cAAC=C=C=cAAC), which has a large HOMO-LUMO gap. A detailed theoretical study illuminates the differences in electronic structures between these molecules, highlighting another case of the potential advantages of using cAAC rather than NHC as a ligand. The bonding analysis suggests that the dicarbon compounds are well represented in terms of donor-acceptor interactions L→C2 ←L (L=NHC, cAAC).

Four cationic heteroleptic iridium(III) complexes have been prepared from methyl- or benzyl-substituted chelating imidazolylidene or benzimidazolylidene ligands using a Ag(I) transmetallation protocol. The synthesised iridium(III) complexes were characterised by elemental analysis, ᴵH and ᶦᶟC NMR spectroscopy and the molecular structures for three complexes were determined by single crystal X-ray diffraction. A combined theoretical and experimental investigation into the spectroscopic and electrochemical properties of the series was performed in order to gain understanding into the factors influencing photoluminescence and electrochemiluminescence efficiency for these complexes, with the results compared with those of similar NHC complexes of iridium and ruthenium. The N^C coordination mode in these complexes is thought to stabilise thermally accessible non-emissive states relative to the case with analogous complexes with C^C coordinated NHC ligands, resulting in low quantum yields. As a result of this and the instability of the oxidised and reduced forms of the complexes, the electrogenerated chemiluminescence intensities for the compounds are also low, despite favourable energetics. These studies provide valuable insights into the factors that must be considered when designing new NHC-based luminescent complexes. Refereed/Peer-reviewed

We report the first example of an alkene with two carbon-bound substituents (imidazole and imidazolium rings) where the Z-isomer has a greater thermodynamic stability than the E-isomer which persists in both the gas phase and in solution. Theoretical calculations, solution fluorescence spectroscopy and gas-phase ion mobility mass spectrometry studies confirm the preference for the Z-isomer, the stability of which is traced to a non-covalent interaction between the imidazole lone pair and the imidazolium ring.

A series of six dinuclear AuI complexes bearing arene-bridged bidentate imidazolylidene (N-heterocyclic carbene, NHC) ligands have been synthesized and characterized. The ligand arene linkers (benzene, pyridine, pyrazine) and NHC-wingtip R-groups (methyl, benzyl) were modified to investigate the influence of these groups on the preference for two distinct conformational isomeric forms. These two conformations differ in their Au···Au distances; an open form with an Au···Au separation of ca. 7 A and a twisted conformation with a short Au···Au distance of ca. 3 A. Five of the complexes were structurally characterized using X-ray crystallography. Photophysical studies on the complex with a pyridyl linker group and benzyl wingtip groups showed that the twisted conformation resulted in a low-energy (LE) photoluminescence emission that is associated with the intermolecular aurophilic interaction. In contrast, no room temperature (r.t.) photoluminescence was observed for the open conformation in the solid state, while a high-energy (HE) emission was observed at 77 K. The pyridyl linked complexes were non-emissive in solution at room temp., but upon freezing to form a glassy matrix at 77 K, dual HE and LE emissions were observed that closely match the solid-state spectra for open and twisted complexes, respectively. These observations, in combination with a thorough theoretical investigation, provide important insights into the conformational behavior of complexes of this type. The use of low temperature frozen glasses to trap individual components of conformationally diverse samples for photoluminescence investigations represents a novel approach to study the dynamic and conformational behavior of dinuclear AuI complexes in solution.

Lipid-mimetic metallosurfactant based luminophores are promising candidates for labeling phospholipid membranes without altering their biophysical characteristics. The metallosurfactants studied exhibit high structural and physicochemical similarity to phospholipid molecules, designed to incorporate into the membrane structure without the need for covalent attachment to a lipid molecule. In this work, two lipid-mimetic phosphorescent metal complexes are described: [Ru(bpy)2(dn-bpy)]2 + and [Ir(ppy)2(dn-bpy)]+ where bpy is 2,2′-bipyridine, dn-bpy is 4,4′-dinonyl-2,2′-bipyridine and ppy is 2-phenylpyridine. Apart from being lipid-mimetic in size, shape and physical properties, both complexes exhibit intense photoluminescence and enhanced photostability compared with conventional organic fluorophores, allowing for prolonged observation. Moreover, the large Stokes shift and long luminescence lifetime associated with these complexes make them more suitable for spectroscopic studies. The complexes are easily incorporated into dimyristoil-phosphatidyl-choline (DMPC) liposomes by mixing in the organic solvent phase. DLS reveals the labeled membranes form liposomes of similar size to that of neat DMPC membrane. Synchrotron Small-Angle X-ray Scattering (SAXS) measurements confirmed that up to 5% of either complex could be incorporated into DMPC membranes without producing any structural changes in the membrane. Fluorescence microscopy reveals that 0.5% label content is sufficient for imaging. Atomic Force Microscopic imaging confirms that liposomes of the labeled bilayers on a mica surface can fuse into a flat lamellar membrane that is morphologically identical to neat lipid membranes. These results demonstrate the potential of such lipid-mimetic luminescent metal complexes as a new class of labels for imaging lipid membranes.

A series of five heteroleptic Ir(III) complexes of the general form Ir(ppy)2(C∧C:) have been prepared (C∧C represents a bidentate cyclometalated phenyl-substituted imidazolylidene ligand). The five complexes arise from the cyclometalated phenyl ring of the NHC ligand being unsubstituted or having electron-donating (OMe and Me) or electron-withdrawing (Cl and F) groups at the 2- and 4-positions of the ring. The synthesized phenyl-substituted imidazole precursors, imidazolium salts, and Ir(III) complexes have been characterized by elemental analysis, NMR spectroscopy, cyclic voltammetry, and electronic absorption and emission spectroscopy. The molecular structures for two imidazolium salts and two Ir(III) complexes were determined by single-crystal X-ray diffraction. Each of the Ir(III) complexes exhibited intense photoluminescence in acetonitrile solution at room temperature with quantum yields (ϕp) ranging from 42% to 68% and excited-state lifetimes on the order of 2 μs. Voltammetric experiments revealed ...

A versatile and straightforward synthetic approach is described for the preparation of triamide bearing analogues of sarcophagine hexaazamacrobicyclic cage ligands without the need for a templating metal ion. Reaction of 1,1,1-tris(aminoethyl)ethane (tame) with 3 equiv of 2-chloroacetyl chloride, yields the tris(α-chloroamide) synthetic intermediate 6, which when treated with either 1,1,1-tris(aminoethyl)ethane or 1,4,7-triazacyclononane furnished two novel triamidetriamine cryptand ligands (7 and 8 respectively). The Co(III) and Cu(II) complexes of cryptand 7 were prepared; however, cryptand 8 could not be metalated. The cryptands and the Co(III) complex 9 have been characterized by elemental analysis, (1)H and (13)C NMR spectroscopy, and X-ray crystallography. These studies confirm that the Co(III) complex 9 adopts an octahedral geometry with three facial deprotonated amido-donors and three facial amine donor groups. The Cu(II) complex 10 was characterized by elemental analysis, single crystal X-ray crystallography, cyclic voltammetry, and UV-visible absorption spectroscopy. In contrast to the Co(III) complex (9), the Cu(II) center adopts a square planar coordination geometry, with two amine and two deprotonated amido donor groups. Compound 10 exhibited a quasi-reversible, one-electron oxidation, which is assigned to the Cu(2+/3+) redox couple. These cryptands represent interesting ligands for radiopharmaceutical applications, and 7 has been labeled with (64)Cu to give (64)Cu-10. This complex showed good stability when subjected to L-cysteine challenge whereas low levels of decomplexation were evident in the presence of L-histidine.

The photophysical and related properties of platinum(II) Schiff base complexes can be finely and predictably tuned over a wide range of wavelengths by small and easily implemented changes to ligand structure. A series of such complexes, differing only in the number and positioning of methoxy substituents on the phenoxy ring, were synthesised and their photophysical, electrochemical and electrochemiluminescent (ECL) properties investigated. Theoretical calculations were performed in order to gain further insight into the relationship between structure and properties in these materials. By positioning methoxy groups para and/or ortho to either the imine or the oxygen group on the ligand, electron density could be directed selectively toward the LUMO or HOMO as required. This allowed the emission colour (both photoluminescent and electrochemiluminescent) to be tuned over a wide range between 587 and 739 nm. The variation in orbital energies was also manifested in the positions of the absorption bands and the redox properties of the complexes, as well as in the NMR shifts for the uncoordinated ligands. All reported complexes displayed intense electrochemiluminescence (ECL), which could be initiated either by annihilation or co-reactant pathways. The relationship between the electrochemical and photophysical properties and the efficiency of the ECL is discussed. For two of the complexes solid-state ECL could be generated from electrodeposited layers of the complex.

By exploiting its ability to play sounds, a mobile phone with suitable software installed can serve the basic functions of a potentiostat in controlling an applied potential to oxidise ECL-active molecules, while the resultant photonic signal is monitored using the camera in video mode. In combination with paper microfluidic sensors this opens significant new possibilities for low-cost, instrument-free sensing.

The solution phase and solid-state electrochemistry and electrochemiluminescence (ECL) of an iridium(III) complex-cored dendrimeric analogue of Ir(ppy)3, (G1pIr), are reported. The solid-state electrochemistry and solid-state ECL of Ir(ppy)3 itself is also described for the first time. In solution phase, the dendrimer displays greater immunity to oxygen quenching in photoluminescence (PL) experiments and exhibits greater ECL efficiency compared to the parent Ir(ppy)3 core under the same conditions, despite a lower photoluminescence quantum yield. It is proposed that the dendrons which effectively shield the core from PL quenching interactions in the solid-state counteract the effects of parasitic side-reactions during the solution ECL experiments. Electroactive and ECL-active solid-state films of both Ir(ppy)3 and G1pIr were produced by drop-coating on boron doped diamond electrodes. Films of Ir(ppy)3 produced stable co-reactant ECL. However, films of G1pIr produced lower than expected ECL intensity. This was attributed to poorer charge transport and the lipophilicity of the film limiting the rate of interaction with the co-reactant required for formation of the excited state.

In contrast to most common electrochemiluminescence (ECL) techniques that require either an additional reagent or continuous pulsing between oxidative and reductive potentials, here a fluorescent polymer of intrinsic microporosity (PIM-1) is shown to exhibit intrinsic ECL without the need for a co-reactant at positive applied potentials and as a function of pH. PIM-1 is known to possess high microporosity (based on its rigid and contorted molecular structure) and excellent fluorescence properties. By depositing a nanoparticulate form of the PIM-1 material onto tin-doped indium oxide, we achieve a hierarchically porous deposit with good sustained ECL activity in aqueous media. The mechanism for this reagentless ECL is suggested to be linked to reactive oxygen species produced at positive potentials and discussed in terms of potential analytical applications.

A chemosensor bearing dipyrrolyl motifs as recognition sites and a tetrathiafulvalene redox tag has been evaluated as an optical and redox sensor for a series of anions (F(-), Cl(-), Br(-), HSO(4)(-), CH(3)COO(-), and H(2)PO(4)(-)) in DCM solution. The receptor shows specific optical signaling for fluoride but little electrochemical effect in solution. The solid-state performance of the sensor leads to measurable changes in water. Design implications towards better systems based on these results and other examples are discussed.

A series of Ru(II)-peptide nucleic acid (PNA)-like monomers, [Ru(bpy) 2(dpq-L-PNA-OH)] 2+ (M1), [Ru(phen) 2(dpq-L-PNA- OH)] 2+ (M2), [Ru(bpy) 2(dppz-L-PNA-OH)] 2+ (M3), and [Ru(phen) 2(dppz-L-PNA-OH)] 2+ (M4) (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, dpq-L-PNA-OH = 2-(N-(2-(((9H-fluoren-9-yl)methoxy)carbonylamino)ethyl)-6-(dipyrido[3,2-a: 2′,3′-c]phenazine-11-carboxamido)hexanamido)acetic acid, dppz-L-PNA-OH = 2-(N-(2-(((9H-fluoren-9-yl) methoxy)carbonylamino)ethyl)-6- (dipyrido[3,2-f:2′,3′-h]quinoxaline-2-carboxamido)acetic acid) have been synthesized and characterized by IR and 1H NMR spectroscopy, mass spectrometry, and elemental analysis. As is typical for Ru(II)-tris(diimine) complexes, acetonitrile solutions of these complexes (M1-M4) show MLCT transitions in the 443-455 nm region and emission maxima at 618, 613, 658, and 660 nm, respectively, upon photoexcitation at 450 nm. Changes in the ligand environment around the Ru(II) center are reflected in the luminescence and electrochemical response obtained from these monomers. The emission intensity and quantum yield for M1 and M2 were found to be higher than for M3 and M4. Electrochemical studies in acetonitrile show the Ru(II)-PNA monomers to undergo a one-electron redox process associated with Ru II to Ru III oxidation. A positive shift was observed in the reversible redox potentials for M1-M4 (962, 951, 936, and 938 mV, respectively, vs Fc 0/+ (Fc = ferrocene)) in comparison with [Ru(bpy) 3] 2+ (888 mV vs Fc 0/+). The ability of the Ru(II)-PNA monomers to generate electrochemiluminescence (ECL) was assessed in acetonitrile solutions containing tripropylamine (TPA) as a coreactant. Intense ECL signals were observed with emission maxima for M1-M4 at 622, 616, 673, and 675 nm, respectively. At an applied potential sufficiently positive to oxidize the ruthenium center, the integrated intensity for ECL from the PNA monomers was found to vary in the order M1 (62%) > M3 (60%) > M4 (46%) > M2 (44%) with respect to [Ru(bpy) 3] 2+ (100%). These findings indicate that such Ru(II)-PNA bioconjugates could be investigated as multimodal labels for biosensing applications. Refereed/Peer-reviewed

The electrochemical and photophysical properties of biscyclometallated iridium(III) complexes containing phenanthroline-based ligands have been investigated and compared in organic and aqueous media. Complexes having general formula [Ir(ppy)2(N∩N)]+/– were synthesized, where ppy is the cyclometallating ligand, 2-phenylpyridine, and N∩N represents one of the following phenanthroline based ligands: 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (dpp) and 4,7-diphenyl-1,10-phenanthrolinedisulfonate (BPS). In the case of [Ir(ppy)2(BPS)]–, the SO3– group located on the phenyl ring of BPS dramatically increases the aqueous solubility of the complex compared to the dpp complex, which is only soluble in organic media. The chloride salt of the underivatized phen complex, though not as soluble as the BPS chelated complex, is sufficiently soluble (> 1 mM) for sensing and other applications in aqueous media. The electrochemical response depends markedly on the medium; all the complexes showed reversible behaviour in organic media, whereas the oxidative electrochemistry of [Ir(ppy)2BPS]– and [Ir(ppy)2phen]+ was irreversible. Results from spectroelectrochemical experiments indicate that electrolysis produces significant changes to the UV region of the spectrum associated with the ppy moieties. Significantly, this demonstrates that the highest occupied molecular orbital (HOMO) is not entirely metal based but is also associated with the cyclometallating ligand. The variation in emission maxima between the iridium complexes was small in organic and aqueous media, but the colour of the emission depends on solvent polarity and strongly on temperature. Most significantly, the quantum yields for these species are also strongly influenced by the solvent: high quantum yields, ranging from 14.0 to 28.6 %, are observed in CH2Cl2. However, in aqueous media the water-soluble complexes, [Ir(ppy)2BPS]– and [Ir(ppy)2phen]+, exhibited significantly diminished quantum yields of 2.5 and 2.6 %, respectively. Theoretical calculations confirm the spectroscopic assignments and that the HOMO is significantly delocalized over the metal and cyclometallating ligands. The relationship between the electrochemical, spectroscopic and theoretical results is discussed.

A series of platinum (II) complexes with Schiff base ligands were synthesized and compared in terms of their photoluminescence, electrochemical and electrochemiluminescence (ECL) properties. Photochemical and electrochemical techniques were used to establish the relationship between the photophysical and redox properties. The emission wavelengths (λem) of theses complexes were found to be highly tuneable with shifts of up to 150 nm in the emission resulting from very minor changes in the ligand structure. All reported complexes exhibit intense ECL via both annihilation and co-reactant pathways. The ECL properties are considered in the light of the photochemical and electrochemical properties of each complex as well as the thermodynamics of the ECL reaction in each case. The findings provide useful insights into the favorable characteristics required for efficient ECL and the directions which should be explored in the search for new ECL luminophores.