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Metallo-supramolecular polyelectrolytes (MEPE) have a variety of attractive properties concerning electrochromism, spin-crossover, rheology, and cell differentiation. Previous studies suggest that these polynuclear structures can be regarded as an assembly of individual subunits and mononuclear complexes can act as models. In this study, we synthesize a monotopic and a ditopic terpyridine ligand with pyridinium units as well as the corresponding iron and ruthenium MEPEs and their mononuclear counterparts. UV-vis studies show that the mononuclear complexes have similar absorption properties to MEPEs. Furthermore, all complexes and MEPEs exhibit electrochromic behavior. Yet only the MEPEs can be deposited on different substrates using a layer-by-layer approach which makes them attractive for applications as electrochromic devices. However, the low solubility particularly of the ruthenium MEPE, renders characterization in solution impractical. Hence, the use of mononuclear complexes with similar monotopic ligands as presented herein can act as a first instance to evaluate the properties of corresponding MEPEs, facilitating the development of metallo-supramolecular materials. [ABSTRACT FROM AUTHOR]

Three Pt(II)-bis(quinolinyl) complexes with varying electron densities were synthesized, structurally characterized and used for photocatalytic hydrogen production under different conditions. All the complexes were found to be active for hydrogen production giving a maximum turnover number (TON) of 1230 surpassing the conventionally used Pt-terpyridyl complexes. [ABSTRACT FROM AUTHOR]

A series of new π-conjugated donor (D) and acceptor (A) dyad comonomers were prepared using Suzuki coupling protocols. The D-A comonomers consisling of thiophene/bilhiophene as donors and pyridine/pyrimidine as acceptors were prepared 10 investigate their photophysical and electrochemical properties. The dyads were spectroscopically confirmed to be highly conjugated. This was further supported by the X-ray crystal structure of the bithophene-pyridine dyad that showed all the heterocycles to be coplanar. It was further found that the fluorescence yields (On) of the dyads were highly dependent on the number of thiophenes. The bithiophene derivatives exhibited [Φ.sub.n] values ≥ 0.3 while the thiophene derivatives did not fluoresce. The suppressed fluorescence observed for the thiophene derivatives was due to their higher triplet energy resulting in efficient intersystem crossing (ISC) to the triplet state with [Φ.sub.ISC] ≥ 0.8. This was confirmed both by time-resolved and steady-state measurements. The singlet excited state of both thiophene and bithiophene dyads was deactivated solely by either fluorescence and (or) ISC. Owing to their donor and acceptor character, the dyads could be oxidized and reduced both electrochemically and photochemitally to afford the radical cation and anion, respectively. Key words: comonomer, thiophene, pyridine, pyrimidine. photophysics, fluorescence. A l'aide d'un couplage de Suzuki, une serie de comonomeres conjugues contenant une fonction donneur d'electrons (D) et une fonction accepteur d'electrons (A) out ete prepares. Ces comonomeres, dits D-A, qui utilisent le thiophene/bithiophene comme donneurs d'electrons et la pyridine/pyrimidine comme accepteurs d'electrons, ont ete synthetises dans le but d'analyser leurs proprietes photophysiques et electrochimiques. 11 a ete lvalue spectroscopiquement que les dimeres sont grandement conjugues. Ceci est d'ailleurs soutenu par la structure rayons-X du compose bithiophenepyridine qui montre que tons les heterocycles sont coplanaires. II a ete determine que les rendements quantiques de fluorescence ([Φ.sub.n]) des composes dependent du nombre de thiophenes presents dans la molecule. En effet, les derives du bithiophene ont des [Φ.sub.n] ≥ 0,3 tandis que les derives du thiophene ne fluorescent pas. Cette absence de fluorescence est causee par la formation d'un etat triplet de haute energie par croisement iutersysteme (ISC pour << intersystem crossing >>) avec un [Φ.sub.ISC] ≥ 0,8. L'etat singulet excite des dimeres de thiophene et de bithiophene est uniquement desactive par la fluorescence ou le ISC. Grace a leur caracterislique donneur/accepteur, les comonomeres ont pu etre oxydes el reduits electrochimiquement et chimiquement aim de former le radical cation et le radical anion. Mots-cles: comonomere, thiophene, pyridine, pyrimidine, photophysique, fluorescence. [Traduit par la Redaction], Introduction Conjugated materials have attracted much attention because of their electrochemical and photophysical properties that are ideally suited for plastic electronics, including organic field effect transistor, (1-4) photovoltaics, (5,6) emitting [...]

A family made of four bis(pyridyl)triazine ligands with appended aryl rings, including three fused aromatic rings, have been synthesized, and their corresponding homoleptic RU(II) and Zn(II) complexes have been prepared and characterized by several means. The free ligands 2,4-di(2-pyridyl)-6-phenyl-1,3,5-triazine (L1); 2,4-di(2-pyridyl)-6-(1-naphthyl)-1,3,5-triazine (L2); 2,4-di(2-pyridyl)-6-(9-phenanthryl)-1,3,5-triazine (L3); and 2,4-di(2-pyridyl)-6-(1-pyrenyl)-1,3,5-triazine (L4) were formed in triazine ring-forming reactions from the reactions of the cyano-functionalized aromatic rings with LiN[Me.sub.2] followed by the addition of 2 equiv. of 2-cyanopyridine. The metal complexes examined in this study are the homoleptic Ru(II) complexes Ru[(L1).sub.2.sup.2+] (2a), Ru[(L2).sub.2.sup.2+] (2b), Ru[(L3).sub.2.sup.2+] (2c), and Ru[(L4).sub.2.sup.2+] (2d) and Zn(II) complexes Zn[(L1).sub.2.sup.2+] (3a), Zn[(L2).sub.2.sup.2+] (3b), Zn[(L3).sub.2.sup.2+] (3c), and Zn[(L4).sub.2.sup.2+] (3d). Also, crystallographic data for the free ligands and Zn(II) and Ru(II) complexes have been obtained in some cases. The redox behaviour and absorption spectra of all the species have been investigated, together with the luminescence properties of the free ligands at room temperature in fluid solution and of the RU(II) complexes both at room temperature in fluid solution and at 77 K in rigid matrix. The redox data indicate that the free ligands are reduced twice at relatively mild potentials (< -2.30 V vs. SCE), with the first reduction almost independent of the nature of the substituted aryl group. The UV absorption spectra of all the compounds are dominated by intense spin-allowed π-π* transitions mainly centered on the bis(pyridyl)triazine moiety; however, in L2-L4, moderately intense intraligand charge-transfer (ILCT) bands are also present. Such bands are red-shifted in the Zn(II) compounds, while they are obscured in the Ru(II) species by the more intense spin-allowed metal-to-ligand charge-transfer (MLCT) bands. The free ligands exhibit interesting emission properties, ranging from fluorescence from π-π* states to excimeric (in L4) and ILCT (in L2 and L3) emission. In the RU(II) complexes, strong emission is found at 77 K from triplet MLCT states. For 2c and 2d, the emissive MLCT states are mixed with low-lying triplet ligand-centered states. Key words: triazine ligands, ruthenium complexes, zinc complexes, ILCT emission. Resume : On a effectue la synthese d'une famille formee de quatre ligands bis(pyridyl)triazine portant des noyaux aromatiques, y compris trois noyaux aromatiques dont on a prepare et caracterise les complexes homoleptiques correspondants du Ru(IO) et du Zn(II). Les ligands libres 2,4-di(2-pyridyl)-6-phenyl-1,3,5-triazine (L1), 2,4-di(2-pyridyl)-6-(1-naphtyl)-1,3,5-triazine (L2), 2,4-di(2-pyridyl)-6-(9-phenanthryl)-1,3,5-triazine (L3) et 2,4-di(2-pyridyl)-6-(1-pyrenyl)1,3,5-triazine (L4) ont ete obtenus par des reactions conduisant a des triazines et impliquant l'action du LiN[Me.sub.2] sur des cyano portes par noyaux aromatiques fonctionnalises, suivie par l'addition de deux equivalents de 2-cyanopyridine. Les complexes metalliques examines dans cette etude sont les complexes homoleptiques du Ru(II), Ru[(L1).sub.2.sup.2+] (2a), Ru[(L2).sub.2.sup.2+] (2b), Ru[(L3).sub.2.sup.2+] (2c) et Ru[(L4).sub.2.sup.2+] (2d) et du Zn(II), Zn[(L1).sub.2.sup.2+] (3a), Zn[(L2).sub.2.sup.2+] (3b), Zn[(L3).sub.2.sup.2+] (3c) et Zn[(L4).sub.2.sup.2+] (3d). Dans certains cas, on a aussi obtenu des donnees cristallographiques pour les ligands libres et des complexes du Zn(II) et du Ru(II). On a etudie le comportement redox et les spectres d'absorption de toutes les especes, de meme que les proprietes de luminescence des ligands libres, a la temperature ambiante et en solution fluide ainsi que celles des complexes du Ru(II) tant a la temperature ambiante, en solution fluide, que celles a 77 K, dans une matrice solide. Les donnees redox indiquent que les ligands libres sont reduits deux fois a des potentiels relativement faibles (< -2,30 V vs SCE) et que la premiere reduction est pratiquement independante de la nature du substituant aryle. La region UV des spectres d'absorption de tous les composes est dominee par d'intenses transitions π-π* permises par les spins et centres principalement sur la portion bis (pyridyl)triazine; toutefois, dans les ligands L2-L4, on observe aussi la presence de bandes de transfert de charge intraligand (TCIL) d'intensite moyenne. Ces bandes sont deplacees vers le rouge dans les composes du Zn(II) alors que dans les especes Ru(II) elles sont obscurcies par les bandes de transfert de charge metal a ligand (TCML) permises par les spins et de grande intensite. Les ligands libres possedent des proprietes d'emission interessantes allant de la fluorescence des etats π-π* aux emissions excimeres (dans L4) et aux bandes de transfert de charge intraligand (dans L2 et L3). Dans les complexes du Ru(II), a 77 K, on observe une emission intense de transfert de charge metal a ligand a partir des etats triplets. Pour les composes 2c et 2d, les etats d'emission TCML sont mixtes avec des etats triplets de basse energie centres sur le ligand. Mots-cles : ligands de triazine, complexes du ruthenium, complexes du zinc, emission de transfert de charge intraligand (TCIL). [Traduit par la Redaction], Introduction Complexes of polypyridine ligands have been the subject of intense research because of their promising photophysical properties and potential applications in areas of light-harvesting devices, luminescent sensors, and photocatalysis. [...]

A new family of tetracarbonyl molybdenum(0) and tungsten(0) complexes based on new 6,6'-disubstituted-4,4'-bipyrimidine ligands was synthesized and characterized. The visible region of the absorption spectrum of each complex is dominated by a metal-to-ligand charge transfer band significantly lower in energy than the corresponding transition in 2,2'-bipyridine tetracarbonyl metal complexes. The 6,6'-substituents create a larger n-electronic system in the substituted bipyrimidines and are consequently better [pi] acceptors than even the parent 4,4'-bipyrimidine. The absorption bands are shifted bathochromically with a decrease in solvent polarity. Key words: molybdenum and tungsten, nitrogen ligands, tetracarbonyl metal complexes, absorption spectroscopy, electrochemistry. Resume : Une nouvelle famille de complexes de type tetracarbonyle de molybdbne(0) et tungstene(0), a base des 4,4'-bipyrimidine substituees dans les positions-6,6', a ete synthdtisde et caractdrisee. Le spectre d'absorption dans la region du visible de chaque compose indique un deplacement vers le rouge pour la bande de transfert de charge metal-ligand compare a celui du complexe tetracarbonyle de 2,2'-bipyridine. Ceci demontre une meilleure delocalisation du systeme [pi]-electronique darts la bipyrimidine substitude qui rend ces ligands des meilleurs accepteurs [pi]. Cette bande d'absorption est deplacee bathochromiquement avec la diminution de la polarite du solvant. Mots cles : molybdenum et tungsten, ligands azotes, complexes metal-tetracarbonyle, spectroscopie d'absorption, electrochimie.

A series of tetranuclear metal complexes of grid-type consisting of four bis-tridentate ligands and four divalent transition metal ions were synthesized and characterized. The [sup.1]H NMR spectra of diamagnetic complexes containing Zn(II), Cd(II), Fe(II), and Ru(II) was correlated to the radius of the metal ion. The UV--vis and electrochemical results indicated that the bridging ligand [pi] *orbital and the [d.sub.[pi]] metal orbital are stabilized by complexation of more than one metal ion. Furthermore, the Co(II) and Fe(II) grids exhibit metal--metal interaction mediated by the bistridentate ligands as indicated by electrochemical and spectroscopic methods. These results provide guidelines for the design of larger grids bearing several metal centres in a square arrangement, which also represent potential components of molecular electronic devices. Key words: complexes with nitrogen ligands, octahedral metal ions, self-assembly, supramolecular chemistry.

In this study, we report two dinuclear Ru(II) complexes C1 and C2 and compare them to their mononuclear analogues Ref1 and Ref2. The dinuclear species exhibit a much stronger absorption, longer excited-state lifetimes and higher luminescence quantum yields than the mononuclear complexes. In addition, C1 and C2 are easier to reduce. An estimation of the driving forces for the electron transfer processes relevant to photocatalytic hydrogen evolution suggests that C1 and Ref2 possess similar activity as photosensitizer (PS). Yet, the improved photophysical properties of C1 make it a more promising candidate for hydrogen evolution. In hydrogen evolution experiments, C1 indeed exhibits increased activity as PS, however, the catalytic system loses its activity after only a few hours. C2 is less active than the mononuclear complexes despite its superior photophysical properties. This observation is attributed to a lack of driving force for the electron transfer towards the catalyst. Further studies of the dinuclear complex C1 show that it is indeed the PS, which decomposes under the catalytic conditions, presumably due to the electron transfer towards the catalyst being the rate-limiting step. [ABSTRACT FROM AUTHOR]

The thiocyclophanes 2,6, 10-trithia(11)-ortho-cyclophane (TT 11 OC) and 2,6, 10-trithia(11)-meta-cyclophane (TT 11 MC) which contain the -S(CH2)3S(CH2)3S- linkage were synthesized through a one-pot reaction involving the Cs1+-mediated cyclization method of Buter and Kellogg. The reactions of both complexes with PdCl2(PhCN)2 in acetonitrile generated the square planar adducts PdCl2(TT 11 MC) and PdCl2(TT 11 OC). The reaction of PdCl2(TT 11 MC) with AgBF4 resulted in the palladation at the 2-position of the thiacyclophane to produce (Pd TT 11 MC)(BF4).