Green and blue electrochemically generated chemiluminescence from click chemistry--customizable iridium complexes.

Cationic cyclometalated iridium complexes containing two anionic phenylpyridine (ppy) ligands and the neutral bidentate triazole-pyridine ligand, 2-(1-substituted-1H-1,2,3-triazol-4-yl)pyridine (pytl), were investigated. The complexes display a rich and reversible electrochemical behavior, upon investigations by cyclic voltammetry in strictly aprotic conditions, that couples with excellent emission quantum yields and long lifetimes of the excited states. Therefore, in organic media, all complexes have generated intense green electrochemiluminescence (ECL) through the so-called annihilation procedure and, importantly, a modulation of the emission energy (to blue) has been easily obtained by simple fluorination of the ppy ligand. Finally, taking advantage of their remarkable solubility in water, intense ECL was also obtained from aqueous buffer solutions using the co-reactant method, thus making all the investigated complexes highly promising for their effective use as ECL labels in bioanalytical applications.

Ru(bpy)(3) covalently doped silica nanoparticles as multicenter tunable structures for electrochemiluminescence amplification.

The electrochemiluminescence (ECL) of doped silica nanoparticles (DSNPs), prepared by a reverse microemulsion method that leads to covalent incorporation of the Ru(bpy)(3)(2+), was investigated in acetonitrile and aqueous buffers. The emission was produced for the first time by cation-anion direct annihilation, and the position of ECL maxima indirectly allowed estimation of the E(1/2,IOx) and E(1/2,IRed) potentials for Ru(bpy)(3) inside DSNPs. The weak ECL emission is most likely generated by an intrananoparticle ruthenium unit annihilation rather than by the electron transfer between a reduced and oxidized DSNP due to the very low diffusivities of the nanoparticles. Thiol-terminated DSNPs were self-assembled on gold substrates, forming compact and stable monolayers which mimic probe-target assays with DSNPs as labels. The ECL intensity obtained by such functionalized substrates in aqueous media, using tripropylamine (TPrA) as coreactant, was surprisingly increased with respect to direct electrochemical oxidation because of the ability of oxidized TPrA to diffuse within the DSNPs structure and reach a higher number of emitting units with respect to direct electron tunneling. The experimental results have been explained by proposing a basic physical-chemical model which supports evaluation of the number of redox-active centers per nanoparticle. In the model the contrasting effects of increased luminescence quantum yield and decreased diffusion coefficient with respect to free (i.e., not bound within the silica structure) emitting molecules were taken into account. This allows, in principle, optimizing the ECL emission intensity as a function of DSNP size, doping material, charge, doping level, supporting electrolyte, electrode material, and solvent. Finally, it is worth noting that this study has provided a more than 1000-fold increase of the ECL signal of a chemically and electrochemically stable DSNP compared to that of a single dye, suggesting that use of this kind of nanostructures as luminescent labels represents a very promising system for ultrasensitive bioanalysis.

Iridium doped silica-PEG nanoparticles: enabling electrochemiluminescence of neutral complexes in aqueous media.

We report for the first time the stable electrochemiluminescence of a completely insoluble neutral Ir(III) complex in aqueous media. The strategy adopted is the encapsulation of emitting dye into silica-PEG nanoparticles. This nanoassembly by limiting water and oxygen quenching and allowing solubilization makes the electrogeneration of the excited state feasible under typical bioassay conditions.

Development of a new device for ultrasensitive electrochemiluminescence microscopy imaging.

Electrochemiluminescence (ECL) is widely used in biosensors and immunoassays thanks to the high sensitivity and specificity of the electrochemically triggered luminescence signal. So far, no applications have been reported on the use of ECL as a probe for ultrasensitive low-light microscope imaging. This work reports the development of a new transparent electrochemical cell for ECL imaging suitable for single cell analysis. The system is based on the use of a microscope placed in a dark box equipped with a CCD camera and a potentiostat. Transparent conducting glass coated with fluorine-doped tin oxide (FTO) has been used, and a three electrode configuration has been designed. The electrochemical cell was optimized using 8 microm diameter polystyrene beads coated with a Ru(bpy)(3)(2+) complex in order to simulate living cells. The Ru(bpy)(3)(2+) immobilized on the microbeads can be imaged and quantified at a concentration as low as 1 x 10(-19) mol/microm(2). Microscope imaging showed that the ECL signal was detected only in correspondence to the beads present on the electrode surface, and the probe could be accurately localized with a spatial resolution of 0.4 microm. The new ECL imaging device can be used in conjunction with other chemiluminescence-based imaging methods for ultrasensitive multiplex imaging on cells and tissues.

Electrochemistry and electrochemiluminescence of [Ru(II)-tris(bathophenanthroline-disulfonate)]4- in aprotic conditions and aqueous buffers.

In this work, the electrochemical and ECL properties of tris[1,10-phenanthrolinediyl-4,7-di(benzenesulfonate)]Ru(II) ([Ru(BPS)3]4-) have been addressed in both strictly aprotic conditions and aqueous buffers. A combined theoretical and experimental approach is presented to focus thermodynamics and kinetic effects of electro-generated species possessing highly negative charge. The complex, prepared as the sodium salt by using a newly developed procedure, was subsequently converted to the tetrabutylammonium salt by ion exchange, thus making it soluble in organic media and allowing, for the first time, its thorough electrochemical investigation in ultra-dry aprotic media. The electrochemically induced luminescence (ECL) of Na 4[Ru(BPS)3] in phosphate buffer, using the co-reactant method (tripropylamine), was investigated as a function of the electrode material and halide addition, and ECL intensities six times higher than that of [Ru(bpy)3]2+ were found. In addition, the ECL behavior of this promising dye for biomolecule recognition was investigated in aprotic media and, for the first time, the direct radical anion-radical cation annihilation ECL was obtained.

Ruthenium(II) complexes containing tetrazolate group: electrochemiluminescence in solution and solid state.

In this work, we report the results about the solution and solid-state phosphorescence emission properties of six Ru(II) complexes containing various 5-substituted tetrazolate ligands. The photo- and electrochemiluminescence spectra of all compounds revealed a red shifted emission with respect to the Ru(bpy)(3)(2+). Significant changes to the light emission energy and to the efficiency and sensitivity to oxygen were also determined by varying the nature of the substituent ring of the tetrazolate ligand. Light-emitting solid devices with active layers containing solid films of the same complexes were prepared, and preliminary studies of their electroinduced emission properties were performed. The electrochemiluminescence (ECL) emission intensity of two of the six complexes was of the same order of magnitude as the reference Ru(bpy)(3)(2+).

CoAPO5 as a water oxidation catalyst and a light sensitizer.

We report the first use of cobalt aluminophosphate (CoAPO5) as a water oxidation catalyst. A decrease in the overvoltage by about 0.2 V with respect to catalyst free FTO has been observed. Additionally, we show that CoAPO5, deposited on ITO or Pt, can also act as a photo-electro-catalyst, as it generates enhanced oxidation currents in the presence of light starting from a bias of +0.8 V vs. Ag/AgCl.

Improvements in the characterization of the crystalline structure of acid-terminated alkanethiol self-assembled monolayers on Au(111).

We report a study of acid-terminated self-assembled monolayers of alkanethiols of different length, 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHDA), on Au(111). Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and contact angle techniques were used for characterization, and the results were compared with those obtained from n-alkanethiols of similar chain length, providing a detailed description of the two-dimensional crystalline structure. Molecular resolution STM images show that 11-MUA forms a dense-packed monolayer arranged in a (square root 3 x square root 3)R30 degrees structure with a c(2 x 4) superlattice, where the simple hexagonal phase, the c(2 x 4) superlattice, and nonordered areas coexist. 16-MHDA assembles in a uniform monolayer with similar morphology to that of 11-MUA, but molecular resolution could not be reached in STM due to both the hydrophilicity of the acid groups and the poor conductivity of the thick monolayer. Nevertheless, the monolayer thicknesses estimated by XPS and electrochemistry and the highly blocking character of the film observed by electrochemistry as well as the low water contact angle are consistent with 16-MHDA molecules forming a compact monolayer on the Au(111) substrate with fully extended alkyl chains and acid groups pointing away from the surface. The results obtained for 16-MHDA were reproducible under different preparation conditions such as the addition or omission of acetic acid to the ethanolic solution. Contrary to other reports, we demonstrate that ordered acid-terminated self-assembled monolayers are obtained with the same preparation conditions as those of the methyl-terminated ones, without any additional treatment.

Polypyridyl ruthenium(II) complexes with tetrazolate-based chelating ligands. Synthesis, reactivity, and electrochemical and photophysical properties.

In this contribution, we report the synthesis, the chemical and photophysical characterization, and the study of the reactivity toward electrophiles of two mononuclear complexes of the type [Ru(bpy)2L]+ (bpy is 2,2'-bipyridyl), in which L is represented by the deprotonated form of 2-(1,H-tetrazol-5-yl)pyridine (L1) or 2-(1,H-tetrazol-5-yl)pyrazine (L2). The 1H and 13C NMR experiments that were performed on complexes RuL1 and RuL2 allowed us to establish that the tetrazolate moiety is bonded to the metal center via the N-1 nitrogen, while the coplanar arrangement adopted by the coordinated ligand upon coordination and the consequent interannular conjugation effect accounts for the unexpectedly low field resonance of the tetrazole carbon. The 13C NMR spectroscopy is also of fundamental importance to determine the chemo- and regioselectivity of the addition of a methyl group to RuL1 and RuL2, which takes place at the N-3 nitrogen of the five-membered ring. All these features were confirmed by the X-ray diffraction structures of RuL1 and of the methylated compounds RuL1Me and RuL2Me. Relative to these latter complexes, the presence of a methyl moiety does not cause any distortion from coplanarity of the coordinated tetrazolates. The redox properties of the complexes were investigated by cyclic voltammetry and indicated a quite different behavior between the pyrazinyl-tetrazolate and the pyridyl-tetrazolate complexes as the consequence of the higher electron-withdrawing character of the pyrazine ring. The study of the photophysical properties of the complexes also shows a significant diversity between the luminescent RuL1 and the rather poorly emissive RuL2. Interestingly, the methylated compounds RuL1Me and RuL2Me display radiative excited-state decays with longer lifetimes than their precursors; this feature indicates that methylation is a useful reaction for the tuning of the light emission performances of similar tetrazolate complexes. The synthesis and the characterization of a novel dinuclear complex of type [(bpy)2Ru-L3-Ru(bpy)2]2+, Ru(L3)Ru, where L3 is the bis-anion derived from bis-2,3-(1,H-tetrazol-5-yl)pyrazine, is also reported.