Search

A new crown ether bearing two hydrophobic lateral chains was synthesized and its complexation properties toward divalent metal ions were studied experimentally and theoretically in water and in non-aqueous environment. Electrochemistry and Langmuir film technique were used to evaluate the stability of complexes formed by the ligand with Cu(II), Zn(II) or Ni(II). Molecular modeling allowed unveiling the structure of the complexes. The results obtained show that all three cations form complexes with the crown ether. However, the stability of the complexes is different depending on the cation and on the environment in which they are formed. This observation suggests that cation complexation can be controlled by adjusting solvent properties; it can be useful in view of possible technological and/or medical applications.

International audience; A series of homo- and heteroleptic Ru(II) complexes [Ru(phen)3−n(phen-X)n](PF6)2 (n = 0–3, X = CN, epoxy, H, NH2) were prepared and characterized. The influence of electron-withdrawing or electron-releasing substituents of the 1,10-phenanthroline ligands on the photo-physical properties was evaluated. It reveals fundamental interests in the fine tuning of redox potentials and photo-physical characteristics, depending both on the nature of the substitution of the ligand, and on the symmetry of the related homo- or heteroleptic complex. These complexes exhibit linear absorption and two-photon absorption (2PA) cross-sections over a broad range of wavelength (700–900 nm) due to absorption in the intra-ligand charge transfer (ILCT) and the metal-to-ligand charge transfer (MLCT) bands. These 2PA properties were more particularly investigated in the 700–1000 spectral range for a family of complexes bearing electro-donating ligands (phen-NH2).

The possibility of achieving luminescent and photophysically active metal-organic compounds relies on the stabilization of charge transfer states and kinetically and thermodynamically blocking non-...

Attempts to prepare a supramolecular M4L2 box involving two tetra-bipyridyl calix[4]arene units and four copper(I) cations afforded, in fact, complex 2 for which, in the solid state, X-ray diffraction analysis showed that the stoichiometry is indeed M4L2, with the two calixarene subunits associated in a “hand-to-hand” mode by complexation via two adjacent bipyridine units to two copper(I) cations, and each group of two residual, adjacent, bipyridine arms is complexed to one copper(I) centre. Mass spectrometry, UV spectroscopy and preliminary 1H-NMR analysis are in preliminary accordance with a monocalixarenic right/left handed M2L structure. Nevertheless, some particularities of the NMR spectrum related to Ar-CH2-Ar and O-CH2bpy resonance signals, the possible generation of the M2L species during the mass spectrometry experiment and the lack of sensitivity of the UV-visible titration caused us to proceed to deeper investigations, looking for other associations, notably the M4L2 “hand-to-hand” systems. This involved 1D and 2D-NMR spectroscopies, among them 1H–15N HMBC, for the reconstruction of the molecule, but also the measurement of self-diffusion coefficients by NMR and electrochemistry. The 2D-NMR analysis and NMR self-diffusion evaluation were in accordance with the M2L structure, but the electrochemical self-diffusion experiment indicated a M4L2 structure.

We demonstrate the implementation of a broadband fluorescence up-conversion set-up with high signal-to-noise ratio and dynamic range allowing for the detection of weak luminescence from triplet states in Fe(II) NHC complexes. Based on the experimentally determined radiative rates and the emission spectra, these states have dominant MLCT character.

The control of photophysical properties of iron complexes and especially of their excited states decay is a great challenge in the search for sustainable alternatives to noble metals in photochemical applications. Herein we report the synthesis and investigations of the photophysics of mer and fac iron complexes bearing bidentate pyridyl-NHC ligands, coordinating the iron with three ligand-field-enhancing carbene bonds. Ultrafast transient absorption spectroscopy reveals two distinct excited state populations for both mer and fac forms, ascribed to the populations of the T1 and the T2 states, respectively, which decay to the ground state via parallel pathways. We find 3-4 ps and 15-20 ps excited-state lifetimes, with respective amplitudes depending on the isomer. The longer lifetime exceeds the one reported for iron complexes with tridentate ligands analogues involving four iron-carbene bonds. By combining experimental and computational results, a mechanism based on the differential trapping of the triplet states in spin-crossover regions is proposed for the first time to explain the impact of the fac/ mer isomerism on the overall excited-state lifetimes. Our results clearly highlight the impact of bidentate pyridyl-NHC ligands on the photophysics of iron complexes, especially the paramount role of fac/ mer isomerism in modulating the overall decay process, which can be potentially exploited in the design of new Fe(II)-based photoactive compounds.

International audience; Ligand field enhancing N-heterocyclic carbene (NHC) ligands were recently shown to prevent photo-induced spin crossover in Fe(II) complexes due to their intricate effects on the electronic excited state structure. Due to their pico- to nanosecond lifetimes, these complexes are now good candidates for photo-sensitizing applications. Herein we report the synthesis and photophysical characterization of a new family of homoleptic Fe(II) complexes with C^N^C ligands involving diazines as the central N-heteroaromatic ligand. For these four carbene bond complexes, ultrafast transient absorption spectroscopy revealed a significant improvement of the excited-state lifetime. A record 32 ps lifetime was measured for a complex bearing a ligand combining a π-deficient pyrazine nucleus and a benzimidazolylidene as NHC. When compared to other azine-based ligands investigated, we argue that the lifetimes are modulated by a small excited state barrier expressing the ability of the ligand to reach the Fe–N distance needed for internal conversion to the ground state

International audience

The development of renewable energy sources is one of the biggest challenges in the 21st century. Within this context, great efforts are spent to develop new materials for cheaper and sustainable solar energy conversion schemes. Commercial dye-sensitized solar cells (DSSCs) are based on Ru(II) transition metal complexes as photo-sensitizers. But, ruthenium is rare and expensive, hence iron, abundant and cheap, is a good candidate to replace it. However, Fe(II) complexes are notorious for their ultrafast excited state spin crossover (SCO) into low-energy quintuplet states (5T2), cutting short on their use for light-harvesting applications relying on photo-sensitization. Very recently, it was shown that SCO can be avoided in Fe(II) complexes featuring N-heterocyclic carbene (NHC) ligands [1], and excited state lifetimes up to 26 ps were reported [2], making these complexes promising photo-sensitizers in DSSCs or photo-catalytic applications. In this work, the effect of structural parameters and variations of the proto-typical octahedric Fe(II)-NHC complexes and up to ten different variants thereof were investigated by femtosecond transient absorption and picosecond fluorescence spectroscopy at room temperature in order to understand which structural and electronic factors contribute to increasing the excited state metal-to-ligand charge transfer state (3MLCT) lifetime. From an energetic perspective, the aim of the chemical design is to increase the ligand field splitting so as to have the 5T2 state higher in energy than 3MLCT. The use of the strong -donating character of the carbene ligands led to a breakthrough in this respect. The experiments show that at minimum three carbene bonds are required to prevent SCO. Their hybridization with the metal-centered orbitals is optimal when the octahedral symmetry of the six coordinating Fe(II) bonds is respected. Bidentate ligands preserving the octahedral geometry are thus expected to induce a larger ligand field per carbene bond than tridentate ones, with smaller bite angles. We show indeed that three carbene bonds in bidentate ligands lead to the same 3MLCT lifetime as four carbene bonds in tridentate moieties. An increased conjugation across the organic ligands is also beneficial since it lowers the 3MLCT energy. We made use of this effect in several complexes with increasing electron accepting character of the ligands, leading for the record lifetime complex (26 ps) to the theoretical prediction of the 3MLCT state being lower in energy than 5T2 [3]. However, since the 5T2 requires a significant bond lengthening [4], a possible effect of the ligand substitutions on the structural rigidity of Fe-C bonds cannot be excluded. Despite the successful development of these complexes displaying sufficiently long excited state lifetimes, DSSCs turn out to have very low power conversion efficiency (

International audience; For two decades, DSSC's have shown promising performance for high yielding conversion of solar energy to electricity under mild conditions. However, the related investigation techniques rely either on pure electrochemical techniques regardless of the light source wavelength either on photochemical processes with a poor electrochemical description. The present study aims at bridging together these two domains using electrochemical impedance spectroscopy (EIS) through wavelength scanning using a monochromator. The main electrochemical features of the DSSC and parameters of the EIS model were examined depending on light wavelength. The technique has been developed at open circuit voltage, using the Ru-based N719 sensitizer impregnating a thin mesoscopic TiO2 layer, with I-2/I mediating redox couple. Tests were carried out with and without mediator, thus resulting in precise interpretation of the various electron transfers occurring at the photo-anode. The time constants of the various processes involved could be obtained without the use of transient absorption or emission spectroscopy: comparison of the data with formerly published results could validate the original method. Moreover interpretation of the wavelength-dependent spectra revealed the existence of two deactivation processes in the cell - which have been identified and quantified - depending on the density of excited states generated at the SC-electrolyte interface. Finally, in relation to IPCE measurements and absorption spectra, the exchange current density of the cathode for I regeneration was also found affected by wavelength. The approach could be applied to non-zero currents and to other sensitizer-semiconductor systems.

The synthesis and the steady-state absorption spectrum of a new pyridine-imidazolylidene Fe(II) complex (Fe-NHC) are presented. A detailed mechanism of the triplet metal-to-ligand charge-transfer states decay is provided on the basis of minimum energy path (MEP) calculations used to connect the lowest-lying singlet, triplet, and quintet state minima. The competition between the different decay pathways involved in the photoresponse is assessed by analyzing the shapes of the obtained potential energy surfaces. A qualitative difference between facial (fac) and meridional (mer) isomers’ potential energy surface (PES) topologies is evidenced for the first time in iron-based complexes. Indeed, the mer complex shows a steeper triplet path toward the corresponding 3MC minimum, which lies at a lower energy as compared to the fac isomer, thus pointing to a faster triplet decay of the former. Furthermore, while a major role of the metal-centered quintet state population from the triplet 3MC region is excluded, we i...

International audience; A set of homoleptic ruthenium polypyridine (bipyridine and terpyridine) complexes flanked with several electron-donating pyrrolidine moieties has been characterized and the anticancer activity was evaluated toward human lung adenocarcinoma epithelial (A549) and murine colon carcinoma (CT26). Good antiproliferative effects were observed with an IC50 ranging from ca. 4 to 21 mu M against both cell lines. Dependence was found between the cytotoxicity, the lipophilicity and the Ru-II/Ru-III oxidation potential. All the studied compounds interacted quite well with albumin while the interaction with DNA was marginal. The biological studies revealed that the ruthenium complexes induced the ROS overproduction which might be one but not the only way of cell death induction.

The new compound 3-((2,5-dimethoxyphenyl)ethynyl)thiophene has been synthesised by Sonogashira coupling. A modified electrode coated with a polythiophene film bearing a quinone moiety was obtained by electropolymerisation of the thienyl group followed by anodic oxidation of para-dimethoxyphenyl group. The cyclovoltammetric response resulting from the reaction of glutathione with the benzoquinone moiety was investigated. The responses of the modified electrode as a new potentiometric sensor of reduced thiols are proposed.

Depending on the strength of oxidative stress, cells exhibit proliferative, apoptotic or necrotic responses. We have investigated whether the severity of glutathione (GSH) depletion could determine the type of cell death using 1,4-benzoquinone (BQ) and H(2)O(2) in two different tumor cell lines (human mammary gland carcinoma MCF-7 and rat hepatoma H5-6). BQ-treated surviving cells showed an increase in GSH, but no detectable oxidized glutathione (GSSG) nor reactive oxygen species (ROS) augmentation. Alternatively, H(2)O(2) depressed GSH. BQ induced mostly apoptosis, up to 90% cell elimination, while necrosis was prominent in H(2)O(2)-treated cultures. The resistance of BQ-treated cells to necrosis could be due to increased cellular GSH and formation of BQ-GSH conjugates which are less toxic than free BQ, minimal toxicity being provided by GS4-BHQ. This ability of certain cancer cells to tightly keep the apoptotic pathway may have therapeutic applications for oxidation-based drugs.

[RuL3](PF6)2 complexes containing 4-alkoxycarbonyl-substituted unsymmetrical bipyridine ligands (L) have been obtained exclusively as the fac isomers by simple reaction of L with ruthenium(III) chloride in ethylene glycol under microwave irradiation. The position of the alkoxycarbonyl group on the pyridine ring and its transesterification by ethylene glycol were found critical for stereocontrol during ruthenium coordination. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Dye-sensitized photo-electrochemical cells based on a solid poly-(3,4-(ethylenedioxy)pyrrole) (PEDOP) electron mediating matrix were assembled and photo-electrochemically characterized. The conductive polymer was directly grown on the sensitized TiO2 surface exploiting a photo-assisted electropolymerization promoted by a properly designed ruthenium dye bearing pyrrole functionalities. J-V characteristics and photoaction spectra indicated very low efficiencies mainly determined by an efficient recombination of photo-injected electrons with both PEDOP acceptor states and oxidized sensitizers. (c) 2007 Elsevier B.V. All rights reserved.

International audience; Herein we report the synthesis and time-resolved spectroscopic characterization of an homoleptic Fe(II) complex exhibiting a record 26 ps 3 MLCT lifetime promoted by benzimidazolylidene-based ligands. Time Dependent Density Functional molecular modeling of the triplet excited state manifold clearly reveals that, at equilibrium geometries, the lowest 3 MC state lies higher in energy than the lowest 3 MLCT one. This unprecedented energetic reversal in iron complexes series, with the stabilization of the charge-transfer state, opens new perspectives towards iron made excitonic and photonic devices, hampering the deactivation of the excitation via metal centered channels.

In this study we report a detailed exploration of the use of two different co-adsorbents - namely bis-methoxyphenylphosphinic acid (BMPP) and chenodeoxycholic acid (CDCA) - known to increase photoconversion efficiency (PCE) of DSSCs sensitized with N719. We have explored the variation of their abilities with the [co-ads]/[D] ratio of the sensitization bath in order to lower the intermolecular deactivations (anti-π-stacking effect) and recombinations between photo-injected electrons and the oxidized mediator (shield effect). EIS-λ technique has been used for this purpose, allowing the two effects considered here to be accurately quantified. DSSC containing BMPP allowed to improve the cell PCE by 60% with a ratio [co-ads]/[D] = 1, exhibiting a strong shield effect, while the maximum PCE obtained with CDCA was slightly over 7% (corresponding to 30% improvement) with a ratio [co-ads]/[D] = 10 and exhibiting a strong anti-π-stacking effect.

International audience; Three ruthenium complexes bearing glycol chains of varied length and number have been prepared and evaluated as hydrophilic sensitizers in aqueous dye-sensitized solar cell (DSSC) devices. The new complexes performed better than N719 in a 100% aqueous electrolyte. The use of co-adsorbents and particularly bis(4-methoxyphenyl)phosphinic acid (BMPP) improved the efficiency and short-circuit photocurrent.

The effect of pyrrole- and pyrrolidine-containing ligands (L) on the properties of heteroleptic [RuL2dcbpy]2+ complexes has been investigated. TiO2 electrodes modified with the new complexes exhibited extended absorption domains and high absorbances. Providing that a cobalt-based mediator was used for regeneration of the RuII state, good incident photon-to-current efficiency (near 80%) values were obtained in the pyrrole series.

International audience; Herein, we report a homoleptic iron complex bearing tridentate bis-carbene (CNC) ligands designed for sensitization of TiO2 photoanodes. Its excited state has been characterized by ultra-fast transient spectroscopy and time-dependent density functional theory (TD-DFT) computations, which reveal a record triplet metal-to-ligand charge-transfer ((MLCT)-M-3) excited-state lifetime (16 ps). The new dye was efficiently chemisorbed on TiO2 and promoted electron injection and photocurrent generation in a dye-sensitized solar cell upon solar irradiation.

Two ligands whose general formula is R-terpy with terpy = 2,2′:6′,2″-terpyridine bearing at the 4′-position a substituent R = 2-thenyloxy and 3-thenyloxy were synthesised. The electronic spectra and the electrochemical behaviour of the corresponding Ru(II) complexes were investigated. The donor effect of the grafted groups as the non-conjugation between the Π* ligand orbitals of the terpyridine and the thienyl groups induce an increase of the energy level of the LUMO.

Trans-[FMo{NN=CH(5´-R-thienyl)}(dppe)2][BF4] (R = OMe and OEt) and trans[FMo{NN=CH(5’-R-2,2’-bithienyl)}(dppe)2][BF4] (R = OMe, OEt and O(iPr)) were synthesised in good yields by reacting 2-formyl-5-alkoxylthiophenes and 5-formyl-5’-alkoxy-2,2-’bithiophenes respectively, with hydrazido(2-) complex, trans-[MoF(NNH2)(dppe)2][BF4]. The electrochemical, spectroscopic and solvatochromic properties of these compounds were studied. These results suggest that efficient π conjugated systems were obtained due to the low energy charge transfer between the metal and the heterocyclic moieties., Fundação para a Ciência e a Tecnologia (FCT)

The preparation of terpyridine ligands under solventless conditions is presented. A new procedure using alumina as the base is described. This new procedure was applied to the preparation of new terpyridines.

A new terpyridinyl ruthenium(II) complex functionalised with a carboxylic acid moiety was synthesised. This complex was prepared according to two different pathways. The first one successively involves protection of the carboxylic group on the ligand before formation of the complex followed by hydrolysis. The second one is a new route based on oxidation of a furan ring directly on the complex.

Organic dyes have been prepared to evaluate the ability of 2,5-dithienylpyrrole (DTP) to act as a donor substituent in D-π-A sensitizers for DSSCs. Using a styryl π-bridge the dyes were found to be excellent sunlight harvesters when adsorbed on TiO2 photoanodes with absorbances >3 in the 300-550 nm region. Calculations as well as transient absorption spectroscopy in both solution and on a TiO2 surface revealed that they were favourable for efficient injection and regeneration.

This personal account gives an overview of our research efforts dedicated to the chemistry of ruthenium polypyridine complexes, with a special focus on the effect of pyrrole substituents and their π-extended analogues. The synthesis of the complexes and their characterization will be presented, as well as their photovoltaic applications when applicable.

International audience; This personal account gives an overview of our research efforts dedicated to the chemistry of ruthenium polypyridine complexes, with a special focus on the effect of pyrrole substituents and their pi-extended analogues. The synthesis of the complexes and their characterization will be presented, as well as their photovoltaic applications when applicable.

Unsymmetrical bisterpyridinyl ruthenium complexes carrying vicinal carboxylic acids are prepared. They show room temperature luminescence and efficient sensitisation of nanocrystalline TiO 2 films, with conversion yields (IPCE) of 70%.

For the first time arv unsymmetrical 2,2′-6′2″-terpyridine carry two carboxylic acids has been prepared using Hantzsch's method for pyridine ring formation and furan as a latent carboxylic group.

A novel C2-symmetric lariat ether containing two [1,2,3]triazolo-ligands as sidearms was prepared via a click chemistry approach from known N,N′-dipropargyl-4,13-diaza-18-crown-6 (1). The ligand (2) readily forms a stable 1:1-complex with cupric perchlorate. A single crystal structure of the centro-symmetric mononuclear complex (3) could be determined. The CuII center displays a distorted six-coordinated octahedral geometry where two triazoles and two pivot nitrogens constitute the basal plane. The axial positions are occupied by two oxygens of the crown ether part. The cyclic voltammograms of a DMF solution of the complex showed two redox processes in our experimental conditions.

Symmetrical and unsymmetrical ligands containing terpyridyl coordinating units (N, N, N) or a cyclometalating equivalent (N, C, N), connected back-to-back either directly or via a p-terphenylene or 1,3-phenylene spacer, have been used to construct new diruthenium complexes. These compounds incorporate various terdentate chelates as capping ligands, to allow a double control of the electronic properties of each subcomplex and of the ensemble: via the terminal ligand or through the bridging fragment. Electronic coupling was studied from the intervalence transitions observed in several bimetallic ruthenium complexes of the bis(cyclometalated) type differing by the substitution of a nitrogen atom by carbon in the terminal terpyridyl unit. The largest metal−metal interaction was found in complexes for which the terminal complexing unit is of the 1,3-di-2-pyridylbenzene type, i.e., with the carbon atom located on the metal−metal C2 axis of the molecule. Investigations of the mechanism of interaction by extende...

International audience; Eight novel ligands were prepared from a known symmetric diaza-18-crown-6 (cyclic ligand) and two commercial N,N'-dimethyl-alkyl diamines (acyclic ligands) via the Cu(I)-catalyzed Huisgen dipolar cycloaddition, All C-2-symmetric isolated ligands readily formed stable crystalline 1:1-copper(II) complexes with cupric perchlorate. Their structural, electrochemical and physico-chemical properties were fully investigated with the help of X-ray diffraction, cyclic voltammetry, FT-IR, UV-visible, and electron paramagnetic resonance (EPR) spectroscopies. Planar - or nearly planar - arrangement of the two N3-triazole nitrogens and the two tertiary amine pivot nitrogens was found in one single four-coordinated species, in four five-coordinated species, and three six-coordinated species, with one or two solvent molecule(s), or two oxygen atoms of the crown ether, occupying the axial position(s) in the solid sate. The electron-donating or electron-withdrawing effect of the N1-substituent on the triazol was found to influence the Cu(II)/Cu(I) redox potential of all studied complexes in DMF. The EPR-spectrum of cyclic complexes in frozen DMF at 100 K exhibited two mononuclear species, one of them likely promoting the formation of dinuclear species as a minor component, whereas most acyclic complex spectra were quite similar.

Bipyridine bearing pi-delocalized dithienypyrrole moieties (DTP) have been involved as ligands (L) in the preparation of RuL2(dcbpy)(2+) and RuL(dcbpy)(NCS)(2) dyes. These dyes exhibited wide absorption domains in solution and when adsorbed on TiO2 photoanodes, light harvesting was found to be excellent (absorbance>1 in the 350-600 nm range). Careful investigations, combining transient spectroscopy and ab initio computations evidenced the capture of the photoexcited electron by low lying orbitals centred on the DTP moiety thus limiting the efficiency in DSSC despite favourable redox potentials for both injection and ground state regeneration. (C) 2013 Elsevier Ltd. All rights reserved.

Two dinuclear ruthenium complexes have been prepared using funtionalized mononuclear complexes as building block in a classical aromatic cross coupling reaction (Suzuki's procedure) with a difunctionalized aromatic spacer.

We have prepared rodlike cyclometalated Ru(II)/Os(II) dinuclear complexes, (ttp)Ru(dpb-(ph)(n)()-dpb)Os(ttp)(2+), where the biscyclometalating bridging ligands contain dipyridylbenzene fragments, dbp, separated by a variable number, n, of phenylene spacers, and the terminal ligand is a terpyridine derivative [dpbH is di-2-pyridyl-1,3-benzene, ttp is 4'-p-tolyl-2,2':6',2"-terpyridine, and n = 0-2]. The rigid bridging ligands keep the metal centers at a distance r(MM) = 11, 15.5, and 20 Å, depending on n. Photoinduced energy transfer has been investigated by luminescence spectroscopy in nitrile solvents at room temperature and at 77 K (i.e., in frozen medium). According to a classical description of the process, the energy transfer occurs in a nearly activationless regime, is governed by electronic factors, and can be described in terms of the Dexter-type mechanism. The obtained energy transfer rates roughly span 3 orders of magnitude and indicate (i) that the temperature (i.e., the state of the solvent) has a small influence on the process and (ii) that the interposed phenylene spacers are weak attenuators of intercenter electronic coupling, H [H = H(0) exp(-betar(MM)), with beta approximately 0.33 Å(-)(1)].

Three new pyrrole-containing ligands and their ruthenium complexes have been prepared. The pyrrole ring bound by nitrogen to pyridine was found to significantly modify photophysical and electrochemical properties compared to parent bi- and terpyridines. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The properties of the ground and excited states of several porphyrins appended with external chelates coordinated to ruthenium-bisbipyridine units are reported. The important modification of the absorption spectrum upon coordination with the ruthenium complex showed that a significant electronic communication between the two subunits was present in the ground state. Experimental results were compared with quantum chemistry calculations performed at density functional theory and time-dependent density functional theory level. The influence of the exchange-correlation functional on the quality of the computed absorption spectrum is shown, and the better behavior of hybrid functionals over long-range corrected ones was rationalized. The excited states topology analysis, performed using natural transition orbitals, gave a more evident confirmation of the communication between the subunits and showed that these new compounds can be promising as dyes in dye-sensitized solar cells.

Porphyrins bearing enaminoketones at their periphery have been used as ancillary ligands in ruthenium complexes. Free base, nickel and zinc porphyrins were successfully coordinated to Ru(bpy)(2)Cl(2) under microwave irradiation. The positive contribution of the ruthenium complex was demonstrated by the complexes' wide absorption domains that covered the 500-600 nm region where the parent porphyrins did not absorb. Electrochemical as well as computational data revealed an efficient electronic communication between the porphyrins and the ruthenium cation in the dyads.

The first dithienylpyrrole (DTP)-based bipyridine ligands has been prepared and coordinated with ruthenium to give the corresponding homoleptic complexes. Bipyridine was bound at pyrrole (DTP(1)) or thiophene (DTP(2)) ring. A strong bathochromic effect was obtained by switching from pyrrole to thiophene for ligands and complexes. Interestingly the DTP(2) series offered a wide absorption window from UV to visible domain with an almost constant absorbance. These effects are due to a larger extent of delocalization as supported by DFT calculations and photophysical measurements.

Two novel organometallic diruthenium complexes, [Ru 2 II,II ] 2+ and [Ru 2 III,III ] 4+ , containing a di-anionic biphenyl grouping that linearly bridges the two ruthenium centres, have been synthesized. In the solid state (X-ray structures) the biphenyl grouping of [Ru 2 III,III ] 4+ is essentially planar indicating extensive π-conjugation whereas in [Ru 2 II,II ] 2+ the phenyl rings make and angle of 22.2° with respect to each other. The complexes can also exist in the mixed valences state [Ru 2 II,III ] and have a K C of 600 and 1250, respectively; the presence of strongly communicating metal centres is indicated by huge intervalence charge transfer bands at λ 1820 nm (e 27000 M −1 cm −1 ) and 1875 nm (e 33000 M −1 cm −1 ), respectively

The spectroscopic properties (UV-vis absorption and luminescence) of Ru(II)- and Os(II)-based mononuclear and dinuclear complexes containing terdentate terpyridine-type (ttp) and related cyclometalating (dpb - , and tpbp 2- ) ligands are reported [ttp is 4'-p-tolyl-2,2':6',2''-terpyridine, dpbH is di-o-pyridyl-1,3-benzene, tpbpH 2 is 3,3',5,5'-tetrapyridylbiphenyl]. For the dinuclear species, [(ttp)M(tpbp)M'(ttp)] 2+ , the biscyclometalating dianionic tpbp 2- ligand bridges the two metal centers, which are held at a fixed distance of 11 A [M, M'=Ru, Os]

Two relevant, recently reported, ruthenium-based complexes to be used as sensitizers in Grätzel photovoltaic cells are theoretically studied. The UV/vis absorption spectra have been computed within the time-dependent density functional theory formalism. The obtained excitation energies are compared with the experimental results, and the nature of the transition is analyzed in terms of the electronic density. A preliminary study on the performance of different functionals against the equation of motion coupled cluster is performed on a smaller model system.

The dinuclear complexes (tterpy)M(tbtp)M(tterpy) 2+ (M=Ru(II) or Os(II)), tterpy=4',-p-tolyl-2,2':6',2''-terpyridine, tpbpH 2 =3,3',5,5'-tetrapyridylbiphenyl) have been prepared by oxidative coupling of the corresponding monomers M(tterpy)(dpb) + (dpbH=1,3-di-o-pyridylbenzene). Spectrochemical and electrochemical properties of the monomers and dimers in different oxidation states are described. Chemical or electrochemical oxidation of the M(II)-M(II) species leads to the mixed-valence M(II)-M(III) dimer

By combining palladium catalyzed C-C coupling procedures either based on aromatic stannanes or utilizing boronic acids or esters (Suzuki's reaction), various bis-cyclometallating N-C-N ligands could be prepared. Their di-ruthenium(II) complexes have also been synthesized.

A rhodium (III) bis-terpyridine complex covalently linked to two pyrrole groups has been electropolymerized on a reticulated vitreous carbon electrode. The resulting modified electrode has been used in the electrocatalytic reduction of nicotinamide adenine dinucleotide into 1,4-NADH. The efficiency of a system incorporating cyclohexanone as substrate and liver alcohol dehydrogenase as enzyme has demonstrated the feasibility of bioreactors with electrochemical regeneration of NADH cofactor.