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Two new metal-free organic dyes, CR29 and CR52, with high extinction coefficients in the visible spectral region between 400–650 nm, have been synthesized. The donor–acceptor structure of the dyes feature benzodithiophene moieties BDT1 and BDT as rigid π-conjugated spacers, which have so far been very little studied for dye-sensitized solar cell (DSSC) applications. DFT/TDDFT calculations have been employed to guide the design of the chromophores as well as to shed light on their electronic and optical properties. Photophysical and electrochemical characterization studies have been carried out to gather information on the charge transfer processes occurring at the dye–semiconductor interfaces. Under standard AM 1.5 conditions, DSSC sensitized with CR29 showed good conversion efficiencies: 5.14 % in the liquid electrolyte cell setup and 2.47 % in the solid-state DSSC.

In this contribution we provide an overview of the preparation and of the properties of different classes of luminescent dinuclear tricarbonyl rhenium(I) complexes of general formula [Re 2 (μ-X) 2 (CO) 6 (μ-1,2-diazine)] (X = halide, hydride, alkoxide, and thiolate). Their electrochemical and photophysical properties in solution are presented, as well as combined density functional (DFT) and time-dependent density functional (TDDFT) studies of their geometry, relative stability and electronic structure. The relationships between the structure and the emission properties of the complexes are discussed in detail, showing a modulation effect of the bridging ancillary ligands as well as of the diazine substituents on energy, lifetime and quantum yield of the emission. Photoluminescent quantum yields ( Φ ) up to 0.53 have been measured in fluid solution for the dichloro complexes containing diazines bearing alkyl groups in both the β positions, designed to optimize all the parameters responsible for the radiative decay. The photophysical properties in the solid state are also briefly presented, showing in some cases an increase of the emission intensity, discussed in terms of restriction of intramolecular roto-vibrational motions. These properties, together with their good processability and high stability, allowed the successful use of some of these complexes as a phosphorescent dopant in OLEDs. The good performances of OLED devices prepared both by solution- and vacuum-processing are reported. The preliminary work exploring the potential of these complexes as luminescent labels for bioimaging is also presented.

Push-pull Zn(II)-porphyrinates have recently shown attracting performances as light harvesting systems in dye-sensitized solar cells (DSSCs). To fully exploit their intrinsically high efficiency it is important to finely tune their HOMO and LUMO levels, which can be achieved by proper choice of the push and pull substituents. Of course such target-oriented molecular design requires the availability of reliable relationships between molecular structure and electronic properties; therefore we have carried out a combined electrochemical, spectroscopic and computational investigation on a wide, systematic range of Zn(II)-porphyrinates 5,15 meso substituted with phenylethynyl linkers, including a first symmetric series carrying on the opposite terminals the same substituent (-N(CH3)2,-OCH3,-COOCH3,-COOH,-NO2); and a second push-pull one, with the terminal positions carrying one donor and one acceptor group belonging to the series above. Moreover, two suitably modified porphyrins allowed evaluation of the effects of (i) the presence or absence of the phenyl group in the linker between the porphyrin core and the acceptor group, and (ii) the effect of perfluorination on the same phenyl group. A rationalization scheme is proposed encompassing the whole porphyrin set, affording inter alia interesting clues on the different localization of the redox centres and effective conjugation between the porphyrin core and the side chains as a function of the molecular design.

Tetrathia[7]helicene ([7]TH)-based complexes substituted at the thienyl ring ends by a ferrocenyl group (Fc) or by a (η5-cyclohexadienyl)Mn(CO)3 derivative have been prepared by Sonogashira coupling reactions starting from the mono- or diiodo [7]TH compounds. The molecular structure of one of the diferrocenyl [7]TH complexes was established by X-ray analysis. Electrochemical investigation on the Fc-[7]TH systems show that the Fc groups are significantly electron poorer with respect to Fc (ΔE° ≈ 0.15 V), due to the effective conjugation of the Fc redox moiety with the triple bond + helicene system, as also confirmed by spectroscopic data. Potential cycling around the second oxidation peak, assigned to the thiahelicene moiety, affords fast, regular growth of electrodeposited conducting films, provided that one terminal α-thiophene position be available for coupling; on the other hand, long alkyl chains hamper film formation. The conducting films feature a broad oxidation wave resulting from the merging of s...

To achieve rationalization criteria for target-oriented molecular design of Th–X–Th (Th = thiophene) semiconductor building blocks, we have carried out an extensive investigation on the effects of the X core (X = fluorene, carbazole or phenothiazine) on the electronic properties and polymerization ability of Th–X–Th monomers and on the electronic and structural properties of the corresponding periodic conducting polymers –(Th–X–Th) n –, obtained by electropolymerization and, for comparison's sake, by FeCl 3 -catalyzed polymerization and/or Suzuki coupling. The effects of molecule bending and of solubilising bulky alkyl substituents have also been considered. The systematic, exhaustive template sequence combined with a rigorous, multitechnique investigation protocol affords a unique data library and a complete set of reliable interpretative/predictive guidelines.

A series of 4-X-1-methylpyridinium cationic nonlinear optical (NLO) chromophores (X = (E)-CH=CHC(6)H(5); (E)-CH=CHC(6)H(4)-4'-C(CH(3))(3); (E)-CH=CHC(6)H(4)-4'-N(CH(3))(2); (E)-CH=CHC(6)H(4)-4'-N(C(4)H(9))(2); (E,E)-(CH=CH)(2)C(6)H(4)-4'-N(CH(3))(2)) with various organic (CF(3)SO(3)(-), p-CH(3)C(6)H(4)SO(3)(-)), inorganic (I(-), ClO(4)(-), SCN(-), [Hg(2)I(6)](2-)) and organometallic (cis-[Ir(CO)(2)I(2)](-)) counter anions are studied with the aim of investigating the role of ion pairing and of ionic dissociation or aggregation of ion pairs in controlling their second-order NLO response in anhydrous chloroform solution. The combined use of electronic absorption spectra, conductimetric measurements and pulsed field gradient spin echo (PGSE) NMR experiments show that the second-order NLO response, investigated by the electric-field-induced second harmonic generation (EFISH) technique, of the salts of the cationic NLO chromophores strongly depends upon the nature of the counter anion and concentration. The ion pairs are the major species at concentration around 10(-3) M, and their dipole moments were determined. Generally, below 5x10(-4) M, ion pairs start to dissociate into ions with parallel increase of the second-order NLO response, due to the increased concentration of purely cationic NLO chromophores with improved NLO response. At concentration higher than 10(-3) M, some multipolar aggregates, probably of H type, are formed, with parallel slight decrease of the second-order NLO response. Ion pairing is dependent upon the nature of the counter anion and on the electronic structure of the cationic NLO chromophore. It is very strong for the thiocyanate anion in particular and, albeit to a lesser extent, for the sulfonated anions. The latter show increased tendency to self-aggregate.

Polyamidoamines (PAAs) represent a family of degradable polymers carrying tert-amine groups in the polymer backbone, which behave as polyelectrolytes in aqueous solutions. Many relevant properties of PAAs, including the ability to interact with components of the biological environments, such as nucleic acids, proteins, and living cells, are strongly dependent on their acid-base properties, hence on their ionization state in different biological districts. In this article, the protonation constants of a series of PAAs have been precisely determined by electrochemical techniques in order to build up a homogeneous library containing both the protonation constants and the average distribution of the charged species, hence the net average charge as a function of pH. Moreover, correlations between chemical and cytotoxicity, have been attempted. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009

The anionic rhodium carbonyl clusters [Rh 7 (CO) 16 ] 3− and [Rh 14 (CO) 25 ] 4− can be easily prepared by a new simple and high yield one-pot synthesis starting from RhCl 3 · n H 2 O dissolved in ethylene glycol and involving two steps: (i) treatment of RhCl 3 · n H 2 O under 1 atm of CO at 50 °C to give [Rh(CO) 2 Cl 2 ] − ; (ii) addition of a base (CH 3 CO 2 Na or Na 2 CO 3 ) followed by reductive carbonylation under 1 atm of CO at an adequate temperature (50 °C for [Rh 7 (CO) 16 ] 3− ; 150 °C for [Rh 14 (CO) 25 ] 4− ). These new syntheses are more convenient than those previously reported, especially since such clusters are not accessible via silica surface-mediated reactions. This different behavior is due to the particular stabilization on the silica surface and under 1 atm of CO of an anionic carbonyl cluster, called A, which does not allow the formation of a higher nuclearity carbonyl cluster, called B, which was shown to be the key-intermediate in the synthesis of [Rh 14 (CO) 25 ] 4− working in ethylene glycol solution. Although it was not possible to isolate crystals of A and B suitable for X-ray structural determination, a combination of cyclovoltammetry, one of the few examples so far available of the use of this technique for anionic rhodium carbonyl clusters, infrared spectroscopy and elemental analyses suggest that A and B are probably the never reported [Rh 7 (CO) 14 ] − and [Rh 15 (CO) 28 ] 3− clusters, respectively. In particular the tentative formulation of the two clusters was carried out by a non-conventional method based on the existence of a linear correlation between carbonyl frequencies of the main band and the [(charge/Rh atoms)/CO number] ratio.

A series of neutral, dinuclear, luminescent rhenium(I) complexes suitable for phosphorescent organic light emitting devices (OLEDs) is reported. These compounds, of general formula [Re2(m-Cl)2(CO)6(m-1,2-diazine)], contain diazines bearing alkyl groups in one or in both the b positions. Their electrochemical and photophysical properties are presented, as well as a combined density functional and time-dependent density functional study of their geometry, relative stability and electronic structure. The complexes show intense green/yellow emissions in toluene solution and in the solid state and some of the complexes possess high emission quantum yields (f=0.18–0.22 for the derivatives with disubstituted diazines). In butyronitrile glass, at 77K, due to the charge transfer character of the lowest (emitting) excited state, strong blue shift of the emission is observed, accompanied by a strong increase in the lifetime values. The highest-performing emitting complex, containing cyclopentapyridazine as ligand, is tested in a polymer-based lightemitting device, with poly(9-vinylcarbazole) as matrix, as well as in a device obtained by vacuum sublimation of the complex in the 2,7bis(diphenylphosphine oxide)-9-(9-phenylcarbazol-3-yl)-9-phenylfluorene (PCF) matrix. This represents the first example of devices obtained with a rhenium complex which can be sublimed and is solution processable. Furthermore, the emission is the bluest ever reported for electrogenerated luminescence for rhenium complexes.

This works investigates the mechanistic features related to the reactions between Fe II Salen and several organic halides used as initiators in Atom Transfer Radical Polymerization. Within the time scale of cyclic voltammetry, a fast reaction is observed between electrogenerated Fe II Salen and either ethyl 2-bromoisobutyrate, carbon tetrachloride or 1-chloro-1-phenylethane. Since no catalytic current is observed in cyclic voltammetry in the presence of RX, no fast mediated reductive cleavage of RX into R + X − occured. An intermediate [R··X··FeSalen] complex was formed which was either relatively stable (ethyl 2-bromoisobutyrate and 1-chloro-1-phenylethane) or underwent further reduction (CCl 4 ). In the presence of styrene and at 110 °C, polymerization is observed and the polydispersity of the resulting polystyrene appears to depend on the Fe III Salen/Fe II Salen initial ratio. The role of both Fe III Salen and Fe II Salen in the regulation of radical concentration provided a controlled character to the polymerization.

The electrochemical reduction of a series of aromatic bromides including substituted bromobenzenes and polycyclic bromoarenes has been investigated in acetonitrile at silver and glassy carbon (GC) electrodes. Whereas GC behaves as a noncatalytic electrode, Ag exhibits remarkable electrocatalytic activities for the reduction of all compounds. The electrocatalytic effects are strongly influenced by the molecular structure of the aromatic bromide, decreasing with increasing electron-withdrawing ability of the substituents as well as with extension of the polycyclic aromatic system. Dissociative electron transfer (ET) to an organic halide RX may occur either in a single step (concerted mechanism) or in two distinct steps with the formation of an intermediate radical anion (stepwise mechanism). The mechanism of the reduction process was analyzed at both catalytic and noncatalytic electrodes. Electroreduction of all compounds at GC occurs according to a stepwise mechanism, whereas at Ag both mechanisms were obs...

The three complexes [Re2(mu-X1)(mu-X2)(CO)6(mu-ppd-kappaN3:kappaN4)] (X1, X2 ) H, 1; X1 ) H, X2 ) Cl, 2; X1, X2 ) Cl, 3; ppd) 2,5-diphenyl-1,3,4-oxadiazole) have been synthesized by different routes, involving the reaction of [Re4(mu3-H)4(CO)12]with ppd for 1, the reaction of 1 with HCl for 2, and the reaction of [ReCl(CO)5] with ppd for 3. The three complexes possess a different number of valence electrons, so the formal Re-Re bond order varies from 2 to 1 to 0 in complexes 1, 2, and 3, respectively. This is reflected in the Re-Re bond distance (277.9, 297.9, and 358.5 pm in the same series)and in the stability of the complexes in the coordinating solvent acetonitrile (t1/2 for ppd displacement 13.6, 4.5, and 3.7 h,for 1, 2, and 3, respectively). Both experimental and calculated structures indicates that coordination induces a distortion from planarity of the diphenyloxadiazole moiety due to the interaction of the equatorial carbonyls with the bridging ppd,which increases on going from 1 to 2 to 3 (dihedral angle between the oxadiazole and the phenyl rings 18.4 degrees, 23.3 degrees, and 45.0 degrees, respectively). The UV spectra show pi-pi* transitions of the oxadiazole ligand (which shift to higher energy on increasing the distortion from the planarity, from 252 to 267 nm) and metal-to-ligand charge transfer absorptions (from 300 to 362 nm). Upon irradiation between 340 and 380 nm, complex 2 only features a weak broad emission at 527 nm(phi)0.02%), whereas upon excitation at 300 nm, the emission typical of free ppd is observed, suggesting photodissociation.Cyclic voltammetry investigations in acetonitrile showed that the three complexes exhibit ligand-centered irreversible reduction peaks (from -1.83 to -1.93 V vs Fc+|Fc), shifted to more positive values with respect to free ppd (-2.50 V). The shift however is smaller than in the analogous derivatives containing 1,2-diazines, suggesting a smaller electron depletion of the heterocycle ligand upon coordination. The complexes also show a metal-centered, bi-electronic, irreversible oxidation peak (from 1.05 to 1.37 V vs Fc+/Fc). A combined density functional and time-dependent density functional (TD DFT)study allowed us to understand the factors affecting the stability of the three complexes and to rationalize their electrochemical and photophysical properties in terms of their electronic structure.

The primary and the secondary standards for the pH measurements in solvent media Z = (glycerol [G] + water [W]) at glycerol mass fractions wG up to 0.4 and at temperatures from −10 °C to +40 °C have been determined in compliance with the IUPAC criteria. To this purpose, Harned’s reversible cell {Pt|H2|Primary Buffer + KCl in Z|AgCl|Ag|Pt} and Baucke’s nonreversible cell {Pt|H2|Buffer at pHPS in Z|Salt Bridge in Z|Buffer at pHSS in Z|H2|Pt} were used, respectively. As a result, three primary standards (based on the “carbonate”, the “equimolal phosphate”, and the “phthalate” buffers) and three secondary standards (based on the “tetroxalate”, the “tartrate”, and the “unequimolal phosphate” buffers) are now available. Their internal consistency was ascertained through the linear pH dependence of the voltage of the cell {Pt|H2 |Buffer at pHPS [or pHSS] in Z|NH4Cl Bridge in Z|Reference Electrode}. These acquisitions enable the user to perform routine pHX measurements by the regular operational cell {Reference E...

Appropriately dealing with real surface area evaluation in organic electrocatalysis implies working mostly in organic media, and, above all, adopting molecular probes. Their selection is not straightforward, implying preliminary knowledge of the structural and mechanistic effects possibly modulating the probe molecule’s perspective of the electrode surface. Taking the electrocatalytic reduction of organic bromides on polycrystalline silver as a model process, we propose a stepwise approach to the evaluation of catalytic active surface areas, relative to a non-catalytic reference one, particularly focusing on the modulating effects of the bulkiness and reactivity of the probe molecules.

The possible use of some dinuclear rhenium complexes as sensitizers for dye sensitized solar cells (DSSCs) has been investigated. They have general formula [Re2(μ-X)(μ-Y)(CO)6(μ-pyridazine-4-COOH)], with X = Y = Cl (1), X = H, Y = benzoato (2), and X = H, Y = 4-diphenylaminobenzoato (3). An original synthetic strategy has been set for preparing the hydrido-carboxylato derivatives 2 and 3. They have been indicated by DFT and TD-DFT computations as the most promising dyes, endowed with good light harvesting capability. The complexes have absorption maxima in the range of 405–443 nm, on TiO2 films, arising from metal-to-ligand-charge transfer transitions. Cyclic voltammetry experiments have been performed on the derivatives containing the methyl ester of the pyridazine-4-COOH acid, showing electrochemical band gaps in the range of 2.25–1.63 eV. The best DSSC results have been obtained using complex 3, with an overall solar-to-electric conversion efficiency of 1.0%. Noteworthy the presence of a hydrido ligand did not show any detrimental effect on the stability of the sensitizers under the operating conditions.

The introduction of alkoxy chains in the molecular architecture of meso push-pull porphyrins is of paramount importance aiming at high performing dye-sensitized solar cells (DSSCs) based on these specific sensitizers. Recently, we have demonstrated that the same approach is fruitful even if it is applied to tetraarylporphyrins with an acceptor/anchoring substituent in the [small beta]-pyrrolic position. In particular, among the ortho-ortho, the ortho-para and the ortho-functionalization of the aryl rings with an octyloxy chain, we identified the latter as the most performing in the series, showing a good balance between the dye loading and the reduction of [small pi]-[small pi] aggregation. Herein, focusing our attention on the mono-ortho-functionalized molecular structure, we have investigated the effect of the alkoxy chain length and nature on the reduction of dye-to-dye aggregation as well as on the enhancement of light harvesting capabilities, finding an almost linear relationship between the device photon conversion efficiency (PCE) and the alkoxy chain length both in the presence and in the absence of a co-disaggregating agent.

Following the IUPAC criteria, four primary standards (pHPS) and three secondary standards (pHSS) have been determined at various temperatures using Harned's reversible cell and Baucke's nonreversible cell, respectively, the solvent media Z studied being N-methylacetamide and its mixture with water at 0.50 mass fraction. Their internal consistency was ascertained by the linear pH dependence of the emf of the cell (Pt|H2|pH standards in Z||NH4Cl bridge in Z|AgCl|Ag|Pt). Essential thermodynamic functions (standard emfs E° of cell and ionization constants of orthophthalic acid) hitherto unknown in the pertinent solvent Z had also to be determined from the emfs of the appropriate reversible cells. These pHPS and pHSS acquisitions enable the user to perform routine pHX measurements by the regular operational cell. A supplementary systematic search has been performed according to the method of Helmholtz transference cells both in N-methylacetamide and in its w = 0.50 mixture with water, to single out appropriate...

Novel poly(amidoamine)s (PAAs) containing disulfide linkages regularly arranged along the polymer chain, namely BP−CY and BAC−CY, were synthesized by stepwise polyaddition of l-cystine to 1,4-bis(acryloyl)piperazine (BP) and 2,2-bis(acrylamido)acetic acid (BAC), respectively. Even if l-cystine contains four acid hydrogens, no evidence of cross-linking was found. All products were characterized by 1H and 13C NMR spectroscopy, and their average molecular weight determined by size exclusion chromatography. The polymerization rates were investigated by means of 1H NMR spectroscopy. In both cases, the experimental data were consistent with pseudo-second-order kinetics. The calculated kinetic constants were kc,BP = 8.10 × 10-3 min-1 L mol-1 and kc,BAC = 1.41 × 10-3 min-1 L mol-1 for the polyaddition of l-cystine to BP and BAC, respectively. A potentiometric study was carried out of BP−CY and BAC−CY speciation as a function of pH, and the electrochemical activity of their disulfide bonds as a function of pH was ...

Following the IUPAC-endorsed procedure, the primary pH standards offered by the equimolal phosphate buffer (Na2HPO4 (0.01 mol⋅kg−1) + KH2PO4 (0.01 mol⋅kg−1)) in the (N-methyl-2-pyrrolidinone + water) solvent mixture of 50 mass percent composition at various temperatures have been determined from potential difference measurements with the reversible Harned cell. Since the essential prerequisite of the above procedure is the knowledge of the (hitherto unknown) standard potential difference of Harned’s cell, a parallel supplementary series of potential difference measurements has been carried out with the reversible cell, Pt|H2|HCl(m)|AgCl|Ag|Pt according to the classical thermodynamic procedure. The problem of comparability of the pH scale in the (N-methyl-2-pyrrolidinone + water) solvent with that in the pure water solvent is duly discussed in terms of primary medium effects.

Carboxy-terminated polyvinylpyrrolidin-2-one (PVP) has been used as a new water-soluble and biocompatible polymeric support for a series of ferrocene labeled amino acid and peptide nucleic acid (PNA) monomer derivatives 4 – 7 . The organometallic polymer-conjugates thus obtained are new and potentially useful as water-soluble electrochemically active probes for biomolecules. In view of such application, their electrochemical activity has been evaluated and has proved very high notwithstanding the complexity and bulkiness of the molecule, affording detection limits down to 10 −8 M in the aqueous medium.

The total selenium content in white, black, red rice and white rice hull samples, grown in Northern Italy cultivars, has been determined using the differential pulse cathodic stripping voltammetry (DPCSV) on the hanging drop mercury electrode (HDME), in the presence of Cu(II). The digestion was performed in open vessel through a combination of wet acid/dry ashing with Mg(II) salts. The calibration curve was linear in the concentration range 0.15–8 ppb, the detection limit was estimated to be 0.07 ppb, and the recovery was in the range 85–102%. Reproducibility was from 1.9% to 9.0% (RSD, n = 4). Rice samples were analyzed by the standard addition method and the results were compared with those obtained by a spectroscopic technique (HG-ICP-AES). The proposed procedure, sensitive, inexpensive, easy-to-handle and precise can be successfully applied for the determination of selenium in nutritional products. The resulting selenium contents in different Italian rice varieties were: 20.1 ± 1.8 ppb (white), 53.0 ± 1.0 ppb (red), 26.7 ± 1.3 ppb (black), 45.3 ± 4.1 ppb (white rice hull).

Three NIR-emitting neutral Ir(III) complexes [Ir(iqbt)2 (dpm)] (1), [Ir(iqbt)2 (tta)] (2), and [Ir(iqbt)2 (dtdk)] (3) based on the 1-(benzo[b]thiophen-2-yl)-isoquinolinate (iqtb) were synthesized and characterized (dpm=2,2,6,6-tetramethyl-3,5-heptanedionate; tta=2-thienoyltrifluoroacetonate; dtdk=1,3-di(thiophen-2-yl)propane-1,3-dionate). The compounds emit between λ=680 and 850 nm with high luminescence quantum yields (up to 16 %). By combining electrochemistry, photophysical measurements, and computational modelling, the relationship between the structure, energy levels, and properties were investigated. NIR-emitting, solution-processed phosphorescent organic light-emitting devices (PHOLEDs) were fabricated using the complexes. The devices show remarkable external quantum efficiencies (above 3 % with 1) with negligible efficiency roll-off values, exceeding the highest reported values for solution-processible NIR emitters.

A systematic investigation was performed on the specific adsorption of bromide and iodide anions on controlled-surface polycrystalline silver electrodes, from three organic solvents (acetonitrile, propylene carbonate, and dimethylformamide), combining differential capacity and impedance experiments with a recently proposed “indirect” voltammetric method based on the monitoring of the negative shift of the reduction peak potential of a “probe” organic halide molecule induced by progressive additions of halide anions, resulting in increasing adsorption competition. Bromide and iodide ions are specifically adsorbed onto polycrystalline silver electrodes in the three organic solvents studied. The adsorption process, which is slow and it is characterised by a partial charge transfer and by a slow diffusion step, is modulated by the different coordination abilities of the solvents for the species involved in the adsorption. The three experimental methods provide consistent results. In particular, the strength of halide adsorption increases in the halide sequence Br−

The potential difference E of the amalgam cell {CsxHg1 − x|CsX (m)|AgX|Ag} (X = Cl, Br, I) has been measured as a function of the mole fraction xCs of Cs metal in amalgams and of the molality m of CsX in (methanol + water), (acetonitrile + water), and (1,4-dioxane + water) solvent mixtures containing up to 0.75 mass fraction of the organic component, at the temperature 298.15 K. The respective standard molal potential differences E m ∘ have been determined together with the relevant activity coefficients γ± as functions of the CsX molality. The found E m ∘ values show a parabolic decrease with increasing proportion of the organic component in the solvent mixture. Analysis of the relevant primary medium effects upon CsX shows that the CsX transfer from the standard state in water to the standard state in the (aqueous + organic) mixture is always unfavoured, and the acetonitrile is the least unfavoured co-solvent studied. Analysis of the primary medium effect upon CsI in terms of Feakins and French’s theory leads to a primary hydration number close to zero, which is consistent with the results of supplementary EXAFS experiments on Cs+ and I− in (acetonitrile + water) solvent mixtures.

We have designed and synthesised a new organometallic molecule containing three ferrocene groups for use as a highly sensitive electrochemical marker in biological assays. This trisferrocene derivative was conjugated to different PNA monomers, and the electrochemical activities of the conjugates were extensively investigated in organic solvents, in view of their potential diagnostic applications. The results showed that the introduction of a trisferrocene unit on the PNA monomer triples the current signal in comparison with the monoferrocene-labelled one. Despite their greater molecular molecular complexity, trisferrocene-conjugated PNA monomers are even more electrochemically active than the reference ferrocene. By using differential pulse voltammetry (DPV), the detection limit can reach 10-8 M in acetonitrile solution. These results are a good premise for the use of the trisferrocene unit as an effective electrochemical probe for biomolecules.

This work describes the synthesis and the electronic characterisation by electronic absorption spectroscopy, cyclic voltammetry and dipole moments of diphenyl porphyrins and their ZnII complexes substituted at the meso position by a pseudo-linear π-delocalised substituent carrying an electron-donor or an electron-withdrawing group. The second-order NLO response was investigated by the EFISH technique working with a nonresonant incident wavelength of 1.907 μm. This work confirms the ambivalent role of the polarisable porphyrin ring, which, already in the ground state, acts as a donor or acceptor depending on the nature (acceptor or donor) of the substituent in the meso position, as was pointed out in our previous work on tetraphenyl porphyrins substituted at the β-pyrrolic position. The second-order NLO response has been discussed by comparing the nature of the substituent (electron donor or acceptor) and the kind of substitution (β pyrrolic or meso). This comparison evidenced a significant increase of the electron-donor properties of NBu2 or NMe2 when they are connected to the meso position or to the β-pyrrolic position, probably because of an auxiliary donor effect of the electron-rich porphyrin ring. When the substituent is the electron-withdrawing NO2 group, the substituent position (meso or β pyrrolic) is influential, with the existance of a significant increase in the second order NLO response when substitution occurs at the meso position. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

An amphoteric polyamidoamine (PAA)-based hydrogel, named INT-PAA1, with a novel molecular architecture was prepared and studied as a Co 2+ -, Ni 2+ -, and Cu 2+ -sorbing material. This hydrogel was obtained by the synthesis of a PAA in the presence of a second presynthesized PAA carrying many primary amino groups as side substituents, which acted as a macromolecular crosslinking agent. Therefore, it had an intersegmented structure. INT-PAA1 exhibited a remarkable sorption capacity and sorption rate for Co 2+ , Ni 2+ , and Cu 2+ that were advantageously in situ monitored by cyclic voltammetry. An extended X-ray absorption fine structure spectroscopy characterization of the Co 2+ /INT-PAA1 complex was also performed. The very fast and quantitative metal-ion uptake, made apparent by an intense coloring of the hydrogel, showed remarkable potential for environmental applications such as heavy-metal detection, recovery, and elimination.

[structure: see text] The role played by the electronic properties and the steric features of bis(oxazoline) ligands in the Cu(I)-catalyzed cyclopropanation of styrene effected with ethyl diazoacetate was investigated. Two pairs of new bis(oxazolines) displaying flexible and atropisomeric 3,3'-bithiophene backbones were synthesized and structurally and electronically characterized. For the first time, the electrochemical oxidative potential was used as a reliable index of the electronic density on the nitrogen atom of the chelating groups of new and, for comparative purposes, of already known bis(oxazolines). The Cu(I) complexes of the new ligands were prepared, and their enantioselection ability and catalytic efficiency were tested. This investigation suggests that steric factors and catalyst geometrical features are clearly more important than any consideration of the electronic properties of the chiral ligands.

A wide investigation on the electrochemical activity of four model organic bromides has been carried out in acetonitrile on nine cathodes of widely different affinity for halide anions (Pt, Zn, Hg, Sn, Bi, Pb, Au, Cu, Ag), and the electrocatalytic activities of the latter have been evaluated with respect to three possible inert reference cathode materials, i.e. glassy carbon, boron-doped diamond, and fluorinated boron-doped diamond. A general electrocatalytic activity scale for the process is proposed, with a discussion on its modulation by the configuration of the reacting molecule, and its connection with thermodynamic parameters accounting for halide adsorption.

For the amalgam cell {MxHg1 − x|MCl2 (m)|AgCl |Ag} (with M = Sr, Ba) the potential difference E has been measured as a function of the mole fraction xM of the metal M in amalgams and of the molality m of MCl2 in {methanol + water} and {ethanol + water} solvent mixtures Z = {A + W} with mass fractions of alcohol wA ⩽ 0.50 of alcohol, at temperature 298.15 K. The respective molal-scale standard potential differences E m ∘ have been determined together with the relevant activity coefficients γ± as functions of the MCl2 molality. The E m ∘ dependence on the alcohol mole fraction in the solvent mixture within the ranges explored turns out to be linear for both of these two metals M in the amalgams studied. Of course, also the molal-scale standard Gibbs free energy change ( Δ G W → Z ∘ ) m = 2 F ( W E m ∘ - Z E m ∘ ) , which constitutes the “primary medium effect” upon transferring MCl2 from pure water to the (alcohol + water) mixture, is linear in xA. In the same context, following Feakins and French’s treatment, which implies volume fraction statistics, the relevant primary medium effects upon MCl2 on the mol · dm−3 scale have been analysed in terms of the expected linear relation of ( Δ G W → Z ∘ ) c = 2 F ( W E c ∘ - Z E c ∘ ) against the logarithm of water volume fraction, leading to primary hydration numbers for SrCl2 and BaCl2, respectively, in acceptable agreement with Bockris’ data based on different methods.

To evidentiate the role of the nature of sulfonate ancillary ligands on the value of the quadratic hyperpolarizability of Zn(II) complexes with stilbazole-like ligands, the second-order nonlinear optical (NLO) properties of [ZnY 2 (4,4'-trans-NC 5 H 4 CH=CHC 6 H 4 NMe 2 ) 2 ] complexes (Y = CF 3 SO 3 , CH 3 SO 3 , or p-CH 3 C 6 H 4 SO 3 ) are investigated. By working at relatively high concentrations (>3 x 10 - 4 M), the positive effect of the triflate ligand remains unique while, with nonfluorinated sulfonate ligands, the second-order NLO response is comparable to that of the related complexes with acetate or trifluoroacetate as ancillary ligands. However, at dilutions higher than 10 - 4 M, all of the sulfonate complexes reach huge quadratic hyperpolarizabilities because of solvolysis with the formation of cationic species such as [ZnY(4,4'-trans-NC 5 H 4 CH=CHC 6 H 4 NMe 2 ) 2 ] + , characterized by a large second-order NLO response. This view is supported by careful conductivity measurements. The same behavior occurs if 4,4'-trans-NC 5 H 4 CH=CHC 6 H 4 . NMe 2 is substituted by 4,4'-trans,trans-NC 5 H 4 (CH=CH) 2 C 6 H 4 NMe 2 .

A new chiral ferrocene-labelled tyrosine PNA monomer 1 has been synthesised in good yield in both racemic and enantiomerically pure forms. It is suitable for insertion in various positions of PNA oligomers, a possibility that has been preliminarily demonstrated by synthesising the dimer 16. Moreover, in view of possible applications to nucleic acid detection, a preliminary voltammetric investigation on the electrochemical activity of monomer 1 and its synthetic precursors has been carried out in DMF. It appears that, despite the bulkiness of the PNA monomer backbone, its insertion on the ferrocene group only moderately lowers the latter’s diffusion coefficients and peak currents, thus affording voltammetric detection limits in the order of 10 −6 –10 −7 M.

The electromotive forces EA of concentration cells with transference Ag|AgCl|HCl(m2,var), (S + H2O)||HCl(m1,fixed), (S + H2O)|AgCl|Ag, where m1,fixed and m2,var denote electrolyte molalities (fixed and variable, respectively), have been measured at T = 298.15 K in a wide range of aqueous organic solvents (S + H2O) with both protic (methanol, ethanol, propanol, ethylene glycol, and glycerol) and aprotic cosolvents (propylene carbonate, acetonitrile, and 1,4-dioxane) of low to high permittivities, allowing the determination of infinite dilution ionic transference numbers for HCl in such solvents. Appropriate combination of the latter with limiting molar conductivity data, determined in the same media, yielded the limiting ionic mobilities. The results provide an insight on the effect of the organic cosolvents on relative and absolute transport properties of HCl. They are compared with results obtained by our group for “viscous-motion” alkali halides MeCl, discussed in terms of dielectric friction parameters...

In the Atom Transfer Radical Polymerization (ATRP) technique, the suggested polymerization scheme is pivoted by a metal complex acting as a redox catalyst able to coordinate with the incipient radicals. The development of an a priori criterion of choice of the best (complex + solvent) combination is one of the current topics in this field. In this context we performed polarographic investigations on copper complexes with multidentate amino ligands (TMEDA and Me6TREN, plus acetonitrile as a reference) in water and in water + acetonitrile mixed solvents. In the latter case we took into account the competition between the co-solvent acetonitrile [a weaker ligand, but concentrated, selectively stabilizing Cu(I)], and the polyamine [a stronger ligand, but diluted, preferentially stabilizing Cu(II)], achieving further stabilization of the complexed copper, with a narrow potential range of stability as Cu(I), which is modulated through the acetonitrile/polyamine ratio. An interpretative scheme is presented.

The potential difference E of the amalgam cell {MxHg1 − x|MCl or MCl2 (m)| AgCl |Ag} (M=Rb, Cs, Sr, Ba) has been measured as a function of the mole fraction xM of M metal in amalgams and of the molality m of MCl (or MCl2) in (acetonitrile [A] + water [W]) solvent mixtures containing up to acetonitrile mass fraction wA=0.50, at T=298.15 K. The respective molal-scale standard potential differences E∘m have been determined together with the relevant activity coefficients γ± functions of the MCl (or MCl2) molality. The E∘m dependence on the mole fraction xA of acetonitrile in the solvent mixture within the range explored turns out to be linear for all the four metals M in the amalgams considered. Of course, also the difference ([E∘m]W−[E∘m]A), which is a measure of the primary medium effect upon transferring MCl (or MCl2) from pure water [W] to the acetonitrile [A] mixture, is linear in xA. In this context, following Feakins and French's scheme, which implies volume fraction statistics, analysis of the relevant mol · dm−3 scale primary medium effects, i.e., ([E∘c]W−[E∘c]A), upon MCl (or MCl2), as a linear function of the logarithm of water volume fraction, would lead to primary hydration numbers of 4.2 for RbCl, 4.0 for CsCl, 10.7 for SrCl2, and 10.3 for BaCl2, respectively, in acceptable agreement with literature data by Bockris based on different methods.

The synthesis of the new complex [Ru(Tetrazpy)(dcbpy)2]Cl is reported, along with its spectroscopical, electrochemical, and theoretical characterization. The first dye-sensitized solar cell device with this complex has been prepared, leading to a 3% of conversion efficiency, promising data considering the simplicity of the Tetrazpy ligand.

For the first time, the standardization for pH measurements is here implemented in the domain of superpermittive media. The nonaqueous solvent studied is formamide (epsilon = 109.5 at 298.15 K) for which three primary standards and two secondary standards have been determined, whose excellent internal consistency has also been demonstrated by specific cell measurements. A comparison of the pH scale in formamide with the aqueous scale has been duly tried by accounting for the primary medium effect on the H+ ion. Furthermore, as a result of an ad hoc supplementary systematic investigation, three salt bridges of appropriate level of equitransference in formamide, that is, NH(4)Cl, NH(4)Br, and NH(4)I, have been characterized for abating the liquid junction potentials intervening in the pH-measuring cell to enable the user to carry out regular pH measurements and related controls.

The electrocatalytic reduction of organic halides on silver, assumed to hinge on an attenuated radical intermediate R⋯X⋯Ag, is a reaction of great applicative interest that also provides an example of organic electrocatalytic process particularly convenient for a mechanistic study. The complexity of the problem requires to analyze separately the roles of the many actors involved. The present work focuses on the role of the silver surface morphology, contrasting the reactivity of a series of model halides in systematic CV experiments on (1 1 1), (1 1 0), and (1 0 0) silver monocrystals and on controlled polycrystalline silver surfaces of increasing roughness, in acetonitrile+tetraethylammonium perchlorate medium. The reduction potentials of the alkyl, glycosyl, and benzyl derivatives appear significantly shifted in the positive direction with increasing surface roughness (for polycrystals) or atomic densities and/or surface faceting (for monocrystals) by an extent linked with the molecular structure of the organic halide to be reduced. The addition of strongly specifically adsorbed iodide anions, resulting in surface screening, also results in a leveling effect of the catalytic properties of the different surfaces tested.

The silver surface screening effects by specifically adsorbed halide anions in the electrocatalytic reduction of a model organic bromide (acetobromoglucose) have been studied by cyclic voltammetry on controlled mono- and polycrystalline silver surfaces in acetonitrile+0.1 M tetraethylammonium perchlorate medium as a function of the concentration c X of added TEAX (X=Cl, Br, or I, TEA, tetraethylammonium). The reduction peak potentials, E p , are regularly shifted in the negative direction with increasing c X , typically tending to an asymptotic value for c X ≈0.1 M. Several literature models describing adsorption/desorption equilibria have been applied to justify the above experimental E p versus c X trends (being logarithmic in the iodide cases) for the three halides and the four silver surfaces tested.

The aqueous mixed (sodium chloride + sodium hydroxide) system has been studied using e.m.f. measurements at T=298.15 K of the combined cells Pt|Na–Hg|NaCl(m1)+NaOH(m2)|HgO|Hg|Pt and Pt|Tl–Hg|TlCl|NaCl(m1)+NaOH(m2)|HgO|Hg|Pt at constant total molalities (m1+m2) of (1, 2, 3, 4, 5, 6, 7, 9, and 11) mol·kg−1. The mean molal activity coefficients γ of each single component have been determined as a function of the respective molalities. For both components, the behaviour can, with reasonable approximation, be represented by Harned’s rule (linear dependence of lgγ on m), although a quadratic dependence is more appropriate. In terms of the mixing fraction X=m2/mTOT, the lgγ against X curves for NaCl and NaOH have slopes in opposite directions, contrary to (KCl+KOH)aq and most other (MX+MY)aq. The respective trace activity coefficients are unequal, and both of them are lower than the corresponding pure-component activity coefficients.

The thermodynamic behavior of the aqueous KCl + K2SO4 electrolyte has been studied on the basis of potential difference measurements on the reversible cell K-amalgam|KCl (mKCl) + K2SO4 (mK2SO4) |AgCl|Ag|Pt. The mean molal activity coefficients γKCl of KCl at molalities mKCl and γK2SO4 of K2SO4 at mK2SO4 in (KCl + K2SO4) mixtures have been determined at various constant values of total ionic strengths I of the mixed electrolyte studied. It has been found that log(γKCl) is a linear function of mKCl at each constant ionic strength studied, thus obeying Harned's rule. The corresponding trace activity coefficients, γ(0)KCl, vary linearly with log I. Using Pitzer's scheme of equations has allowed fair reproduction of the experimental activity coefficients γKCl for I values ≥ 0.5 mol·kg-1 and the evaluation of γK2SO4 in the same range.

An advantageous procedure is developed, allowing preparation of electrodeposited silver electrodes of highly controlled polycrystalline surface (characterized by both electrochemical techniques and SEM), to be employed as cathodes for interphase and electrocatalysis studies. Such electrodes, tested in halide adsorption experiments in parallel with the more demanding single-crystal and polycrystalline silver rod ones, acting as a reference, perform competitively in terms of both reproducibility and stability. The same experiments allow further evaluation of the surface roughness factors of the electrodeposited silver electrodes, based on (i) the Parsons–Zobel criterion and (ii) the comparison of their capacitance minima with those of the (110) single-crystal ones, both approaches resulting in very good agreement with the standard UPD and capacitive methods.

The state and problems of the electrochemical controls of oxidation-reduction systems in aqueous-organic and nonaqueous solvent media with particular emphasis on the rH index of the reducing power of such systems are discussed. In the frame of a generalized treatment of the rH-metric domain, the key definitions, the acquisition of primary rHS standards, the comparison of rH scales in different solvent media, and the recommended procedure of rHX determination are described. The most recent results here obtained in the studies of the behaviour of the quinhydrone electrode with respect to the hydrogen gas electrode, and of the key cell Pt|H2|H2O|HgO|Hg|Pt are reported, and the guidelines for further development are outlined.

Chloride impurities in ionic liquids (ILs), which can be present even in huge amounts depending on the IL synthetic route, are particularly critical for electrochemical processes; thus, their abatement is often mandatory. However, while their analytical quantification has been the subject of many studies involving a variety of techniques, the so far available processes for their abatement are still unsatisfactory, having low efficiency, and/or involving multiple steps, and/or being far from mild and easily scalable. In this context, like an “egg of Columbus”, a quite simple and safe process for chloride abatement in ILs is proposed, practically coinciding with the electrolytic preparation of a Ag|AgCl electrode. It proceeds in a single step, at room temperature, at very low potentials, with nearly ideal current efficiencies, and with negligible side effects on the electrolyzed IL. The chloride impurities are quantitatively captured and accumulated on the silver wire and eliminated by simply removing the resulting Ag|AgCl electrode from the solution, with no need of subsequent treatments. Keywords: Ionic liquids, Chloride removal, Electrodeposition, Silver electrode, Silver chloride

Artificial inherently chiral electrode surfaces perform clear enantiodiscrimination and enantiomeric ratio quantification, opening the way to chiral voltammetry., 2,2′-Bis[2-(5,2′-bithienyl)]-3,3′-bithianaphthene oligomers are a model case of electroactive films endowed with “inherent chirality”, originating from a stereogenic element coinciding with the whole electroactive backbone, thus resulting in impressive manifestations. This study highlights their applicative potentialities as low-cost and easy-to-prepare artificial enantiopure electrode surfaces, which display an unprecedented ability to pronouncedly separate voltammetry peaks of enantiomers of quite different chiral probes of applicative interest, concurrently with linear dynamic ranges for peak currents, affording enantiomer excess determination. Thus inherently chiral enantiopure electrodes can indeed be regarded as a key to chiral voltammetry.

In recent years it has been shown in detail how the electrocatalytic cleavage of carbon-halogen bonds is modulated by (a) the stepwise or concerted nature of the dissociative electron-transfer mechanism, which is influenced by the nature of the electrode surface, the type of halogen atom and the molecular structure of RX as a whole, and (b) the double-layer structure (as a function of the nature and bulkiness of the supporting electrolyte ions). In order to both complete and support the interpretative scheme thus developed, this work is focused on the solvent role. When one compares aprotic with protic organic solvents after appropriate intersolvental normalization, interesting peculiarities emerge, especially concerning protic media. Solvent proticity deeply affects both the reaction mechanism (on both non-catalytic and catalytic electrodes) and the extent of the catalytic effects. These items are discussed on the basis of a complete investigation carried out with a carefully controlled experimental protocol on two chloride and bromide couples, one aromatic and one aliphatic, representative of stepwise and concerted mechanisms, respectively, in four aprotic and four protic solvents, on both non−catalytic GC and catalytic Ag and Au electrodes. The results are discussed in the framework of a recently developed interpretative scheme of the carbon-halogen cleavage mechanism.

A novel molecular dyad, 1, made of a dinuclear {[Re2(μ-X)2(CO)6(μ-pyridazine)]} component covalently-linked to a fullerene unit by a carbocyclic molecular bridge has been prepared and its redox, spectroscopic, and photophysical properties - including pump-probe transient absorption spectroscopy in the visible and near-infrared region - have been investigated, along with those of its model species. Photoinduced, intercomponent electron transfer occurs in 1 from the thermally-equilibrated, triplet metal/ligand-to-ligand charge-transfer ((3)MLLCT) state of the dinuclear rhenium(I) subunit to the fullerene acceptor, with a time constant of about 100 ps. The so-formed triplet charge-separated state recombines in a few nanoseconds by a spin-selective process yielding, rather than the ground state, the locally-excited, triplet fullerene state, which finally decays to the ground state by intersystem crossing in about 290 ns.

A systematic study of {silver ∣ inorganic and/or organic halide} interphases is described, based on cyclovoltammetric and impedance experiments carried out on polycrystalline electrodes of high reproducibility (controlled by comparison with monocrystalline ones), in water and in acetonitrile. The adsorption competition is brought into focus (i) between the three inorganic halides Cl − , Br − , and I − , with the possible interference of ions from the supporting electrolyte, and (ii) between organic and inorganic halides, especially iodides. Actually adsorption competition proves to be a determining factor in the electrocatalytic mechanism (a remarkable threshold effect being observed for the reduction potentials of organic bromides in correspondence with the limiting negative potential for iodide anion adsorption). Vice versa, the variation of the reduction potentials of a given reacting molecule with the background electrolyte provides significant clues on the nature of the specifically adsorbed species.