Search

The design and syntheses of new transition metal complexes are still of particular interest both for the investigation of intramolecular electron transfer processes, under carefully controlled geometry, and for the potential applications of such systems in the rapidly expanding field of new materials for molecular electronics and electrochemical and luminescent sensors. Ruthenium complexes with heterocycles ligands have proved to be of interest for applications as sensing materials for substrates ranging from molecular and ionic species to DNA, to probe both structural and functional aspects of nucleic acid chemistry.[1,2]In this respect, the electronic properties of the metal complex must be properly tuned in order to obtain a positive interaction between the probe and substrate for getting an efficient trasducing signal. In this communication we report the electrochemical, UV-Vis-NIR spectroelectrochemical and electrochemiluminescence behaviour of a class of new polypyridyl ruthenium species containing tetrazole-based ligands which appear to be very promising for the development of electrochemical sensors and biosensors. [1] T. G. Drummond, M. G. Hill, J. K. Barton, Nature Biotech., 21, 2003, 1192. [2] K. E. Erkkila, D. T. Odom, J. K. Barton, Chem. Rev., 99, 1999, 2777.

The anthryl-substituted rhodium(III) and iridium(III) heteroleptic â-ketoenolato derivatives of general formula [M(acac)2- (anCOacac)] [acac ) pentane-2,4-dionate; anCOacac ) 3-(9-anthroyl)pentane-2,4-dionate], 3 (M ) Rh) and 4 (M ) Ir), and [M(acac)2(anCH2acac)] [anCH2acac ) 3-(9-anthrylmethyl)pentane-2,4-dionate], 5 (M ) Rh) and 6 (M ) Ir), were prepared by reacting the corresponding tris(pentane-2,4-dionate)metal complexes, [M(acac)3], with 9-anthroyl chloride and 9-chloromethylanthracene, respectively, under Friedel-Crafts conditions. 3-6 were characterized by elemental analysis, ion spray mass spectrometry (IS-MS), 1H NMR, and UV-vis spectroscopy. The structure of 3 was also elucidated by single-crystal X-ray analysis. When excited at 365 nm, 3-6 result to be poorly luminescent compounds; while the free diketone, i.e., 3-(9-anthrylmethyl)pentane-2,4-dione 1, whose structure was established also by single-crystal X-ray analysis, results to be a strongly light emitting molecule. The study of the electrochemical behavior of 3-6 as well as of the corresponding tris-acetylacetonates of rhodium(III) and iridium(III) allows a satisfactory interpretation of their electrode process mechanism, and gives information about the location of the redox sites along with the thermodynamic and kinetic characterization of the corresponding redox processes. All data are in agreement with the hypothesis that the quenching of the anthracene fluorescence, observed for compounds 3-6, can be due to an intramolecular electron transfer process between the anthryl moiety and the metal-â-ketoenolato component. Moreover, a study was carried out of the redox behavior of the dyads 3-6 under chemical activation. The one-electron oxidation of compounds 3-6 by thallium(III) trifluoroacetate leads to the formation of the corresponding cation radicals, 3+-6+, whose highly resolved X-band EPR spectra were fully interpreted by computer simulation as well as by semiempirical and DFT calculations of spin density distribu

The study of the electrochemical behavior (CV) of 9- anthrylmethylcyclopentadienyl(AnCH2C5H4) derivatives of rhodium(I) and iridium(I) of formula [M(è 5 -AnCH2C5H4)L2](M) Rh or Ir; L ) è 2 -C2H4, è 1 -CO, è 2 -C8H14, PPh3;L2 ) è 4 -C8H12), 1-8, in strictly aprotic conditions, allows a satisfactory interpretation of the observed electrode processes and gives information about the location of the redox sites along with the thermodynamic characteriza-tion of the corresponding redox processes. These data show that the occurrence of an intramolecular charge- transfer process between the photoexcited 9-anthryl group and the cyclopentadienylmetal unit is a possible route for the observed anthracenic fluorescence quenching in the compounds 1-8. Moreover, a study was carried out on the redox behavior of these complexes under chemical activation. The one-electron oxidation of compounds 1-8 by thallium(III) trifluoroacetate leads to the formation of the corresponding cation radicals, whose highly resolved X-band EPR spectra were fully interpreted by computer simulation as well as by semiempirical and DFT calculations of spin density distribution.

A novel fullerene–Ru–porphyrin conjugate (3b) for Langmuir–Blodgett (LB) film deposition has been synthesized. The side polar chain that characterizes the complex is necessary to introduce enough amphiphilicity in these otherwise non-polar moieties. The complex can be deposited on solid substrates via the LB technique and the films obtained show charge separation upon light irradiation. In addition, a careful cyclic voltammetry study of the complex is reported.

Il contributo

Il tema viene affrontato in una prospettiva rigorosa , con attenzione agli aspetti normativi e pratici fondamentali.

Uno contributo scientificamente rigoroso con un ampio richiamo alle necessità della pratica .

Two fullerene-peralkylated ferrocene derivatives were synthesized: (1) a liquid-crystalline dyad (compound 1) was obtained by introduction of nonamethyl ferrocene into a liquid-crystalline fullerene derivative and (2) a reference compound (compound 2) was synthesized by attachment of nonamethyl ferrocene to a fulleropyrrolidine. The liquid-crystalline dyad displayed an enantiotropic smectic A phase from 57 to 155 degrees C. Oxidation and reduction processes were investigated by cyclic voltammetry, and were in agreement with the electrochemical characteristics of the redox-active units (peralkylated ferrocene, fullerene, dendrimer). Photoinduced electron transfer from ferrocene derivative to fullerene was identified.

An overview of the electrochemistry of C60, C70 and higher fullerenes, and of their derivatives and relatives is given together with highlights on possible future studies and applications. A general introduction gives the idea of the size and importance of this field that embraces classic solution and surface electrochemistry, materials chemistry, interlocked molecular architectures, biosensors and solar-energy conversion. A description of the general electrochemical behaviour for several fullerene derivatives is given together with insights on possible applications.

The electrochemistry of two new 1,7-diaryl C(60) phenylated derivatives is explored in THF at various temperatures (from 25 to -90 degrees C). While at room temperature their voltammetric response is that typically shown by fairly stable species, when the temperature drops a very high electrochemically induced reactivity is evidenced. The investigation of the voltammetric patterns supported by an extensive use of digital simulation techniques finally led to the formulation of a reaction mechanism that includes electrochemically-induced migration of the phenyl groups as a possible explanation of the observed behavior.

A new family of mono- and dinuclear ruthenium polypyridyl complexes containing 5-aryltetrazolate ligands such as the deprotonated form of 4-(1H-tetrazol-5-yl)benzonitrile (4-TBNH) and bis(1H-tetrazol-5-yl)benzene (BTBH(2)) have been synthesized and thoroughly characterized. The reactivity of the mononuclear species toward different electrophiles such as H(+) and CH(3)(+) has been investigated, and the effects of the resulting regioselective electrophilic attacks on the electronic and structural properties of the tetrazolate ligand have been studied by NMR ((1)H, (13)C) spectroscopy and X-ray crystal structures. Absorption and emission spectroscopy, together with an electrochemical and UV-vis-NIR spectroelectrochemical investigation of the uncoordinated ligand and complexes, has been performed, highlighting a rather good luminescence efficiency and a poor bridge-mediated electronic communication between the metal centers of the dinuclear complexes. The electrogenerated chemiluminescence (ECL) of the dinuclear species has been explored, and for one of these, an exceptionally high ECL efficiency has been observed, comparable to that of [Ru(bpy)(3)](2+), which is considered a standard in ECL studies.

A cyclopropanation reaction has been used to prepare two methanofullerenes bearing a 2,2'-bipyridine () or pyridine () ligand separated from the fullerene through an oxyethylene macrocyclic spacer. Derivatives and were, in turn, employed to synthesize two fullerene-based ruthenium(ii) and rhenium(i) donor-acceptor dyads whose molecular structure was confirmed by (1)H NMR, (13)C NMR and exact mass determination. The UV-Vis spectrum of the dyads is the superimposition of those of appropriate model systems, indicating that ground-state electronic interactions between the constituent chromophores, in solution, are negligible, in line also with the electrochemical results. The complex voltammetric pattern was characterized by the superimposition of signals attributed to one moiety or another without significant shifts with respect to their models. Furthermore, both species undergo partial chemical degradation in the time scale of cyclic voltammetry upon their multiple reduction. Photophysical properties of and , namely, excited state interactions between the ruthenium(ii) or rhenium(i) complexes and [60]fullerene have been investigated by steady-state and time-resolved UV-Vis-NIR luminescence spectroscopy that was complemented by nanosecond laser flash photolysis in CH(2)Cl(2) solutions. All experimental findings were set into relation with the corresponding reference compounds. More precisely, excitation of the metal complexes in and gives rise to a notable steady-state and time-resolved luminescence quenching of both metal to ligand charge transfer states (i.e., [Ru(bpy)(3)](2+) and [(bpy)Re(CO)(3)(py)](+)). Conclusive evidence about the nature of the photoproducts came from nanosecond laser flash photolysis. In these experiments, only the long-lived and oxygen-sensitive [60]fullerene triplets were detected. Two pathways are envisioned for this [60]fullerene triplet formation. Firstly, intramolecular transduction of the triplet excited state energy evolving from the photoexcited metal complexes. Secondly, intersystem crossing of directly excited [60]fullerene.

The structurally similar T , C 1 and C 3 isomers of C 60 F 36 show significant differences in electrochemical behaviour, the reduction potentials (vs. SCE) being 0.04, 0.07, and 0.12 V, respectively. The relative addend positions influence both the energetics of the first one-electron reduction of C 60 F 36 and the stability of electrochemically generated C 60 F 36 - . Thus whereas full reversibility of the first reduction is observed at scan rates as low as 0.5 V/s for C 3 -C 60 F 36 , reversible peaks were obtained for T - and C 1 -C 60 F 36 only at scan rates ⩾50 V/s. The subsequent multi-electron reductions of C 60 F 36 occur at more negative potentials, and are accompanied by irreversible loss of fluorides, analogous to the behaviour of other perfluorinated fullerenes.

The design and investigation of new transition metal complexes are still of particular interest both for the investigation of intramolecular electron transfer processes, under carefully controlled geometry, and their potential applications as molecular devices.1 Mono and polynuclear complexes are appealing as systems for optoelectronic molecular devices, conversion of light into electricity or chemical energy and electrochemical and luminescent molecular recognition. Ruthenium complexes with heterocycles ligands, bearing uncoordinated nitrogen atoms, have proved to be particularly interesting for applications as sensing materials towards substrates ranging from molecular and ionic species to DNA, to probe both structural and functional aspects of nucleic acid chemistry.2,3 In this respect, the electronic properties of the metal complex must be properly tuned in order to obtain a positive interaction between the probe and substrate, for getting an efficient trasducing signal. In this communication we report the electrochemical, UV-Vis-NIR spectroelectrochemical and electrochemiluminescence behaviour of a class of new polypyridyl ruthenium species containing tetrazole-based ligands which appear to be very promising for the development of electrochemical sensors and biosensors. References: 1) V. Balzani, A. Juris, M. Venturi, S. Campagna, S. Serroni, Chem. Rev. 96, 1996, 759. 2) T. G. Drummond, M. G. Hill, J. K. Barton, Nature Biotech., 21, 2003, 1192. 3)K. E. Erkkila, D. T. Odom, J. K. Barton, Chem. Rev., 99, 1999, 2777.

A family of N-methylpyrrolidinium fullerene iodide salts, possessing one (or two) solubilizing chain- (s), has been synthesized. As evidenced by CV and steady-state voltammetry experiments, carried out in tetrahydrofuran (THF) solutions, these species show enhanced electron-accepting properties with respect to both the parent fulleropyrrolidines and C60. CV measurements performed at -60 °C and scan rates of 50 V/s, made possible by the use of ultramicroelectrodes, have allowed the observation, for the first time in fullerene derivatives, of six fullerene-centered reductions. Bulk electrolysis of these novel compounds, performed at the stage of the first reduction potential, generates a stable zwitterion, with both anion and cation located on the fullerene derivative.

Scanning Electrochemical Microscopy (SECM) is used in combination with copper labeling to visualize roteins on surfaces. Proteins are adsorbed on a poly(vinylidene difluoride) (PVDF) membrane and stained using a standard protocol involving copper salts. The latter are then reduced to copper metal and further detected by SECM with ferrocene methanol as a redox mediator in aqueous solution. During the SECM scan, the potential is held at a value at which the oxidation of the redox mediator occurs and a positive feedback current is detected when scanning over copper clusters. A negative feedback is observed elsewhere.