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The reaction between a series of non mesogenic tetradentate salen-like Schiff bases and Zn(II) acetate gives rise to the formation of liquid cristalline complexes showing nematic and smectic phases stable over a quite large temperature range. A dimeric structural arrangement could favour the appearance of such type of mesophase in the case of 1,3-diaminopropane and 1,3-diamino-2,2-dimethylpropane bridges containing ligands while for the salen derivatives a monomeric solvent-induced pentacoordinated arrengement observed in solution and in the crystalline molecular structure, probably prevent the liquid crystalline behaviour.

Luminescent complexes with general formula [(C^N)2Ir(N^N)]OCOCH3, where C^N = 2-phenylpyridine (ppy) and N^N = 2,2ʹ-bipyridine (bpy), self-assemble into ordered ‘soft’ viscous mesophases of chromonic type. By changing the ancillary ligand with 1,10-phenanthroline (phen), a new mesomorphic complex was obtained. The self-assembly into ordered liquid crystalline phases of chromonic type in water was investigated by comprehensive rheological and photophysical studies. By changing the ancillary ligand bpy with phen, assembly into smaller, more symetric aggregates is favoured, resulting in lower viscosity and more dynamic mesophase.

Three homologous series of luminescent octahedral ionic Ir(III) complexes (1–12) with a dual stereogenic center of general formula Δ,Λ (R,S)[(ppy)2Ir(R-campy)]X, where ppy=2-phenylpyridine, R-campy=2-methyl-5,6,7,8-tetrahydroquinolin-8-amine (Me-campy) or 8-amino-5,6,7,8-tetrahydroquinolines (H-campy) and as counterions X−=Cl− or CH3COO− have been synthesized and characterized. The NMR characterization of each complex highlighted the diastereoisomeric purity and the absolute configuration has been confirmed by Electronic Circular Dichroism spectroscopy. The absorption and the luminescence properties of the compounds in solution and in solid state have been investigated by UV–vis, steady-state emission and time-correlated single-photon counting spectroscopy. The obtained results from the 12 compounds highlight the difficult to correlate photophysical properties in solution to the stereochemistry, while excited states decay studies of the solid state samples indicate a correlation between photophysics and packing mode which is affected by the different stereochemistry.

The low fluorescence quantum yield of 8-hydroxyquinoline cannot be correctly interpreted without knowing the form that such a compound assumes in different environments. The commonly accepted emission-quenching excited-state proton transfer can follow different reaction paths if 8-hydroxyquinoline is dimeric or monomeric or if it exists in the form of cis and trans conformers; in this light, the knowledge of the compound form in a particular environment is basic. We have performed a spectroscopic and computational investigation aimed at the determination of the form of 8-hydroxyquinoline in different solvents. UV-vis, fluorescence, and IR spectral features have been assigned by ab initio computations based on the density functional theory and time-dependent density functional theory; the density functional theory and MP2 computations have been applied to the determination of the relative stability of the dimeric and monomeric cis and trans forms of 8-hydroxyquinoline in different solvents. Molecular dynamics computations have been used to determine the compound behavior in water solutions. According to our results, 8-hydroxyquinoline shows a clear preference for the cis conformation (as dimer or monomer), but, in water solutions, a small fraction of the trans conformation is also present.

Cyclometallated chloridoplatinum complexes containing neutral monodentate ligands such as 2-phenylpyridine (1a), 2-(2′-thienyl)pyridine (1c) or 4-methoxypyridine (1d), as well as the cyclometallated benzo[h]quinoline chlorido complex with 4-methoxypyridine (2d), can be synthesised in a few minutes by irradiating the reaction mixture with microwaves. The single-crystal X-ray molecular structures of the solvato complexes 1·dmso and 2·dmso as well as 1c, 1d and 2d are reported. The availability of this class of complexes in a few minutes offers the possibility of a combinatorial approach for the preparation of libraries of homologous compounds of potential interest for applicative purposes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

2-Benzoylpyridine and 2-acetylpyridine N-methyl-N-phenylhydrazones (HL1 and HL2) in cyclopalladation reactions with Pd-3(OAc)(6) behave as N(py)N(im)C tridentate ligands and form the neutral mononuclear complexes [Pd(k(3)-N,N,C-L-1,L-2)(k(1)-OAc)] (1 and 2). The labile OAc ligand can be replaced by pyridine (py) and, in the presence of NH4PF6, a compound of the general formula [Pd(k(3)-N,N,C-L-1,L-2)(py)]PF6 (3 and 4) can be obtained. Reacting 1 or 2 with the poly(4-vinylpyridine) polymer (PVP, (M) over bar (w) = 160000) adducts of the general formula x[Pd(k(3)-N,N,C-L-1,L-2)(PF6)]center dot y[PVP] gives (5a-c and 6a-c, a-c: x/y = 80/20, 50150, 25/75 w/w) containing the laterally appended cyclopalladated 'Pd(k(3)-N,N,C-L-1,L-2)' fragments. These metallorganic polymers show high glass transition temperatures, high thermal stability and good solubility, and are optimal for obtaining transparent thin films by the spin coating method. (c) 2007 Elsevier B.V. All rights reserved.

A new red emitting ( λ em = 610 nm) discotic metal containing liquid crystal, NIRPAC, exhibiting a columnar phase over a broad temperature range (35–173 °C) has been successfully synthesised by an appropriate functionalisation of the cyclopalladated nile red molecular fragment.

Historically, many useful drugs have been developed from natural sources and their mechanisms of action deeply investigated for therapeutic applications. Recently, the interaction between pharmacologically active biomolecules and transition metal ions has opened the way to the construction of new drugs, where the unique properties of metal complexes are combined with the specific mechanisms of action of the coordinated bioligands of natural extraction. In this context, this perspective summarizes some recent research studies devoted to the development of new metal-based drugs containing Zn(II) or Cu(II) metal ions. Both metals have a strong tendency to form highly stable complexes with N,N- and O,O-donor ligands bound through chelation, giving rise, particularly when the bound organic molecules are drug candidates of natural extraction, to drug delivery systems, new biologically active complexes and potential diagnostic agents due to their intrinsic spectroscopic properties.

International audience; The complete characterization of novel electro-polymerizable organometallic complexes is presented. These are newly synthesized cyclometalated complexes of general formula (PPy)M(O∧N) n (H(PPy) = 2-phenylpyridine, M = Pd(II) or Pt(II), H(O∧N) n = Schiff base). Polymeric thin films have been obtained from these complexes by electro-polymerization of the triphenylamino group grafted onto the H(O∧N) n ancillary ligand. The redox behavior and the photoconductivity of both of the monomers (PPy)M(O∧N) n and the electropolymerized species have been investigated. The polymeric films of (PPy)M(O∧N) n have shown a very significant enhancement of photoconductivity when compared to their monomeric amorphous counterparts. The high stability of the obtained films strongly suggests that electropolymerization of cyclometalated complexes represents a viable deposition technique of quality thin films with improved photoconduction properties, hence opening the door to a new class of materials with suitable properties for optoelectronic applications.

The five-membered “(C,N)Pd” metallacycle is a structural feature common to a number of stable photoactive molecular materials. This review is centred on the connection among molecular geometries, types of ligand and photophysical, optical, thermal and electrooptical properties of several series of dinuclear and mononuclear cyclopalladated species, based on HC,N ligands (HC,N = azobenzenes or nitrogen containing heteroaromatic ligands). In the discussion, some representative examples of complexes featuring an useful set of physical properties, were selected and divided into different classes, depending on the nature of the ancillary ligands bonded to the “(C,N)Pd” fragment.

This paper reports the synthesis, characterisation and photophysical investigation of the homologous series of blue-emitting pentacoordinated AlQ'(2)L complexes 1-6, where Q' is 2-methylquinolin-8-olate and L is a phenolate substituted in para to the oxygen donor atom. Both electron attracting and electron releasing substituents have been considered. Also binuclear complexes of formula Q'(2)Al-L'-AlQ'(2), where L' = OC(6)H(4)C(6)H(4)O, OC(6)H(4)(CH(2))(3)C(6)H(4)O and OC(6)H(4)C(CH(3))(2)C(6)H(4)C(CH(3))(2)C(6)H(4)O have been synthesised and characterised. These are interesting blue-emitting materials for OLED (organic light emitting diode) fabrication. A comparison between computational and experimental results allowed the description of the absorption and fluorescence processes. A study of the frontier orbitals involved in the electric conduction and fluorescence emission has been performed. Influences of the phenolate-based ligands on the compounds spectroscopy have been particularly taken into account.

New Ni(II) and UO2(II) metallomesogens obtained from mesomorphic N,N′‐salicyliden(3,3′‐diamine‐N‐methyldipropylamine) ligands containing a pentadentate N3O2 chelating cavity and bearing two or four lateral substituents, are isolated and fully characterized. Some of the synthesized nickel and dioxouranium complexes show a SmC mesophase. To the best of our knowledge, these species are the first pentacoordinated Ni(II) and heptacoordinated UO2(II) metallomesogens to be reported.

The Nile Red dye, H(NR), forms cyclometalated R2-disubstituted-acetylacetonato square planar Pd(II) complexes (1–3; R = CH3, CF3, C6H5 respectively) whose photophysical properties were tested in cyclohexane, dichloromethane or methanol solutions. In cyclohexane 1–3 emit in the range 580–650 nm with a quantum yield ranging from 0.12 (R = CH3) to 0.50 (R = CF3) and lifetimes between 0.88 and 4.46 ns. These complexes form a new family of notably efficient red emitting organometallic dyes which could be of interest for practical applications.

This communication reports the synthesis of polymetallic species formed by a zinc-tetraphenolporphyrinate core (ZnTPP(OH) 4 , 1 ) and peripheral gallium-quinaldinate ( Q 2 ′ Ga ) fragments. The photophysical analysis of 1 and of the model compound Q 2 ′ GaOPh , R , shows an appreciable overlap between the absorption spectra of 1 and the emission spectra of R , suggesting the presence of a donor–acceptor energy-transfer process. Contrarily, the obtained results indicated that energy transfer does not occur, hence these polymetallic complexes work as double emitting species, for which the colour of luminescence depends on the excitation energy.

2,7-Dimethoxynaphthalene (DMN) is proposed as matrix to investigate the structure of polymetallic porphyrins through matrix-assisted laser desorption/ionization tandem time-of-flight experiments. The peculiarity of DMN is represented by the formation of molecular radical cations and of some diagnostic fragments only. The traditional matrixes do not afford the expected molecular species. The experiments have been performed on extremely labile species such as zinc porphyirinate complexes with aluminum and gallium quinolinate to prove the softness of the methodology.

The spectroscopic characterization of the metal complexes the 5-amidopyridine-8-hydroxyquinoline (HQ'NHCOC 5 H 4 N) form with M = Be, Zn, Cd, Al, Ga and In is reported. These compounds, M(Q'NHCOC 5 H 4 N) 2 (M = Be, Zn, Cd) and M(Q'NHCOC 5 H 4 N) 3 (M = Al, Ga, In), are highly soluble in DMSO and, in addition, the gallium and indium products dissolve in methyl or ethyl alcohol. These species are very stable in solution and emit in the range 520 (Be)-590 (Ga and In) nm with photoluminescent quantum yields ranging from 0.010 (Al) to 0.001 (In). Processability and color emission suggest that some of these new materials can be of interest for practical applications in optoelectronic devices.

A homologous series of isostructural and isoelectronic palladium acetylacetonato complexes containing different cyclometalated ligands HL (HL=2-phenylpyridine H(PhPy), benzo[h]quinoline H(BhQ), 9-diethylamino-benzo[a]phenoxazin-5-one H(NR), azobenzene H(Azo), 5-[(4′-methyl)-phenylazo]-8-methoxyquinoline H(QAzo), 2-benzoylpyridine H(BKPy), phenyl-2-pyridylketone-2,4-dinitrophenylhydrazone, H(BHPy)) has been prepared. The photophysical characterization of the newly synthesized products shows that many of them are luminescent in solution at room temperature. The best performances are exhibited by the H(NR) derivative (Φem=0.23, λem=660, in dichloromethane solution), which improves the emission features displayed by the unmetalated ligand (Φem=0.13, λem=602, in dichloromethane solution). H(NR) is a well known laser dye commonly named nile red and to the best of our knowledge [(NR)Pd(acac)] is the first example reported up to now of its incorporation in a transition metal complex. Interestingly, the results of the present investigation prove that “[(NR)Pd]” can be an useful building block for the preparation of luminescent organometallic complexes.

New mononuclear palladium(II) complexes formed by with 2-hydroxy-4-(n-hexyloxybenzylidene)-4′-n-hexyaniline (HL) and 2-phenylpyridine (I), benzo[h]quinoline (II), azobenzene (III), 2-benzoylpyridine (IV) or phenyl-2-pyridylketone-2,4-dinitrophenylhydrazone (V) have been synthesized and characterized by analytical and spectroscopic methods and the single-crystal structures of [(IVa)Pd(L)] and [(Va)Pd(L)] have been established. The spectroscopic and diffractrometric data account for molecular structures wherein the palladium(II) center is part of two chelate rings involving HL and one of the I–V ligands which form a five-member N,C{[(Ia)PdL], [(IIa)Pd(L)] and [(IIIa)Pd(L)]}, a six-member N,C{[(IVa)Pd(L)]}, or a six-member N,N′{[(Va)Pd(L)]} metallacycle. The electronic spectra of [(IIIa)Pd(L)] and [(Va)Pd(L)] show an absorption maxima, at 495 (e∼3×103 M−1 cm−1) and 531 nm (e∼2×104 M−1 cm−1), respectively, which results are significantly affected by the polarity of the solvent. These chromophores should therefore be of interest for the preparation of nonlinear optical materials.

Two new dinuclear Pd(II) cyclometalated complexes of formula [L2Pd2(μ-1,2-sq)(C5H11N)2] (1) and [L2Pd2(μ-1,3-sq)(C5H11N)2]·2[(C5H12N)BF4] (1a) [HL=2,6-dimethylazobenzene], have been synthetized from a reaction of the mononuclear [LPd(acetone)2][BF4] with the piperidinium salt of squaric acid, [C5H12N]2[sq]. The single crystal X-ray analysis of complexes 1 and 1a shows that the sq ligand is found to bridge in both μ-1,2- and μ-1,3-coordination modes. These are the first examples of squarato Pd(II) complexes characterized structurally up to now.

A luminescent zinc complex was successfully incorporated to mesostructured porous titania films through a grafting process. The resulting films show an intense blue-emission increasing with functionalization time. The emission quantum yield of these newly synthesized films was quantitatively and accurately determined by measurements carried by an integrating sphere.

The series of dinuclear 4,4′-bis(hexyloxy)azobenzene, [H(Azo-6)], cyclopalladated complexes of general formula [Azo-6)Pd(µ-X)]2, (X = Cl, Br, I, N3, SCN, OAc) and [Azo-6)2Pd2(µ-Ox)] (Ox = oxalate) have been synthesized and investigated for mesomorphism and spectroscopic properties. Single-crystal X-ray analysis of the dinuclear bromo- and iodo-bridged complexes has been performed. The structural data, compared with those of the known homologous chloro compound, show that all the [Azo-6)Pd(µ-X)]2)] (X = Cl, Br, I) molecules crystallize in the monoclinic space group P21/c and are isomorphous. They are arranged in slipped pairs with intermolecular non-bonding Pd–Pd contacts ranging from 3.668(1) A(X = Cl) to 3.758(3) A(X = I). The different nature of the bridging group allows variation of the distance between the palladium atoms and the bond environment experienced by the metal centers. Thus, this comparative study reveals that the effectiveness of the bridging group in promoting thermotropic mesophases is greater for chloride, bromide, azide or oxalate than for iodide, thiocyanate or acetate. The greatest range of liquid-crystal behavior was displayed by [Azo−6)2Pd2(µ−Ox)]. Remarkably, this compound is the first example of a metallomesogen containing the bridging oxalate group. The bimetallic complexes exhibit different absorption spectra (i.e. colors) depending, in general terms, on the nature of the bridge connecting the two cyclometalated [H(Azo-6)] moieties, which can be varied so as to tune the optical properties. Blocking the azo group in the trans position results in several cases in weakly luminescent complexes, with luminescence efficiencies ϕ ≈10−4 and luminescence lifetimes of the order of nanoseconds. Using the data obtained from the 4,4′-bis(hexyloxy)azoxybenzene [H(Azoxy-6)] derivative, [Azoxy-6)Pd(µ -Cl)]2, from the mononuclear acetylacetonate (acac) complexes [(Azo-6)Pd(acac)] and [(Azoxy-6)Pd(acac)], and from the uncomplexed [H(Azo-6)] and [H(Azoxy-6)] ligands, the nature of the excited states relevant to the photophysical behavior are discussed. Copyright © 1999 John Wiley & Sons, Ltd.

A series of new cationic ortho-metalated Pd(II) complexes of general formula [(C ∧ N)Pd(N ∧ N)]X (HC ∧ N = 2-phenylpyridine, H(PhPy) or benzo[ h ]quinoline, H(BhQ); N ∧ N = ethylenediamine, 2,2′-bipyridine, 1,10-phenanthroline, N , N , N ′, N ′-tetramethylethylenediamine, 4,4′-dimethyl-2,2′-bipyridine, 4,7-dimethyl-1,10-phenanthroline, or 4,4′-dinonyl-2,2′-bipyridine; X = CF 3 SO 3 ) are reported. Photophysical characterization of these species indicates that electronic transitions are prominently cyclometalating ligand-localized in character and nearly unaffected by the polarity of solvent in which the spectra are recorded.

An acrylate monomer was obtained by the reaction of the azobenzene ligand C 6 H 13 OPhN=NPhO(CH 2 ) 6 OCOCH=CH 2 with [Pd(PhCN) 2 Cl 2 ] followed by treatment of the chloro-bridged dinuclear cyclopalladated derivative with the stoichiometric amount of potassium acetylacetonate. The polymer was obtained by free radical polymerization

The electrochemistry and the optical absorption properties of a series of cyclopalladated complexes are reported. Variation of the cyclometallated ligand has been performed (azobenzene, 2-phenylpyridine and benzo[h]quinoline) as well as variation of the ancillary ligand (acetylacetone and hexafluoroacetylacetone). Results have confirmed that the LUMO energy levels of these complexes is mainly distributed on the cyclometallated ligand. High electronegativity of the fluorinated groups has a weak influence on the electrochemical and absorption properties of the complexes, except for the benzo[h]quinoline for which its planar and comparatively more aromatic character lead to a partial delocalisation of the LUMO energy level.

Synthesis, crystal structural determination and photophysical properties of a series of heteroleptic cationic cyclometalated iridium(III) derivatives of general formula [(ppy)(2)Ir(en)]X (X = ClO(4)(-) (1), PF(6)(-) (2), Cl(-) (3), BPh(4)(-) (4)), are described. The assembly of the common molecular building block allows to get highly luminescent crystalline materials or to assemble poorly luminescent supramolecular channelled architectures, for which the additional contribution of oxygen quenching effects has been observed. Moreover, the high reproducibility of the preparations of the crystalline materials in their specific crystalline phases, makes the control of the supramolecular organization of photo-active iridium(III) complexes within the crystalline structures a useful synthetic procedure for the construction of highly luminescent materials.

The analysis of the crystal structures of two new mononuclear Pd(II) compounds, containing 3,5-disubstituted-2-(2′-pyridyl)pyrrole ligands, reveals that the use of fluoroaliphatic (1) versus aliphatic (2) substituting groups on the HLn ligand induces substantial changes in their supramolecular architectures. Despite the common molecular geometry suitable for the formation of mixed “aryl embraces”, “tetris-like” columnar heterochiral (1) and helicoidal chiral (2) organizations are formed. The resulting supramolecular packing affects their solid state photophysical properties.

Four cyclometalated Pt(IV) compounds, 1a,b and 2a,b, were successfully obtained by oxidative addition of I(2) to 2-phenylpyridinate (PhPy) and Nile Red (NR) derived Pt(II) complexes with acetylacetonate (acac) or hexafluoroacetylacetonate (hacac) ancillary ligands. Single crystal X-ray diffraction, electrochemical, photophysical and computational studies have been performed in comparison with the analogues Pt(II) compounds, shedding new light on the role of the oxidation state of the metal centre towards both the luminescence properties and the dioxygen quenching.

The neutral luminescent tris-cyclometallated 2-phenylpyridine iridium(III) complex, (fac-Ir(ppy)3, [Ir]) following a self-assembling procedure, has been successfully located in the cavities of mesostructured silica materials through a surfactant-mediated process. Two different structure-directing agents, the cationic cetyltrimethyl ammonium bromide (CTAB) and the non-ionic poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) were tested. The structural features induced by the metal complex incorporation can be explained by comparing the newly synthesized hybrid mesostructured materials with the corresponding undoped samples which were similarly prepared. X-Ray powder diffraction (XRD), nitrogen sorption, scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and UV-Vis spectroscopy were used to characterize the investigated materials. Medium-sized spherical particles of 800 nm were obtained using CTAB as a structure-directing agent whereas larger monolithic aggregates with a minimum dimension of 5–8 μm were obtained using P123. The new hybrids showed the typical hexagonal symmetry of analogously prepared materials. Moreover high luminescence quantum yield values were obtained for both hybrids as a result of a very good dispersion of the chromophore in the mesostructured matrices, thereby avoiding dramatic self-quenching phenomena. The approach described in this paper provides a simple synthetic way to prepare new luminescent silica-based materials by the inclusion of neutral metal-containing luminophores into the pores of a mesoporous hosting skeleton.

The first cyclopalladation of 3,5-disubstituted-2-(2′-pyridyl)pyrroles leads to columnar metallomesogens of non-conventional molecular shape.

The incorporation of a rigid core, formed by a cyclopalladated azobenzene fragment bonded to an ancillary Schiff base ligand, into molecules with 12 or 11 peripheral alkyl chains has been successfully achieved. These new complexes, 1 and 2, respectively, are columnar liquid crystals between room temperature and about 50 degrees C. Both cyclometallated and ancillary ligands have been polyalkylated through either aryl ester (electron-withdrawing group) or aryl ether (electron-releasing group) linkages, in order to tune the HOMO/LUMO energy levels. The photoconductive properties of 1 and 2 have been studied as a function of their absorption properties before and after annealing, from the UV/Vis to NIR region. Compared with the reference compounds, tris-alkynyl benzene discotics, these new materials gave similar performances (sigma/I approximately 8x10(-13) S cm W(-1) with E = 10 V microm(-1) at lambda = 370 nm). Moreover, complex 2 shows a normalized photoconductivity sigma/I = 8.5x10(-13) S cm W(-1) at lambda = 760 nm. Organic photoconductors in such a high wavelength spectral range are not common and are usually assembled by mixing dyes with organic semiconductors.

The synthesis of the first gallium(III)-based liquid crystal has been achieved grafting around the metal centre two chelating 2-methylquinolin-8-olate anions and one monodentate 3,4,5-tris(hexadecyloxy)benzoyloxy ligand, allowing the resulting complex to be a soft luminescent material with the typical high quantum yield of pentacordinated gallium species.

The coordination of the N,N ligands 2,2-bipyridine (bipy) and 1,10-phenanthroline (phen) to Ga(III) has been investigated via the formation of new ionic hexacoordinated complexes of general formula [Q'(2)Ga(N,N)][X], where HQ' stands for 2-methyl-8-hydroxyquinoline and the counter anion X(-) is nitrate (NO(3)(-)) or hexafluorophosphate (PF(6)(-)). All synthesized complexes were characterized by single-crystal X-ray diffraction analysis. The geometry of the Ga(III) cations is octahedral and a single geometric isomer (all N, N trans conformation) has been obtained in all cases. The role of both the N,N ligand and the counter anion has been investigated in the formation of the crystal supramolecular motifs occurring in the 3D-crystal networks of these new class of ionic Ga(III) derivatives. A full investigation of the photophysical properties of the new synthesized ionic species is reported and discussed in relation to their crystalline packing and the degree of crystallinity of thin solid films as well as the nature of the N,N ligand and the counter anion.

This paper reports the synthesis, characterization, photophysical and structural properties of the homologous series of good emitting pentacoordinated GaQ'2L complexes 1-3, where Q' is 2-methyl-quinolin-8-olate and L is a phenolate substituted in para position with respect to the oxygen donor atom. A combined approach between the experimental structural analysis (i.e. the molecular fragments involved in intermolecular pi-pi interactions) and the computational study (i.e. the nature of the molecular orbitals residing therein) is discussed in order to compare the charge transport aptitude of complexes 1-3, in relation to the facing of their LUMO/LUMO, HOMO/HOMO and HOMO/LUMO arising from the molecular packing. The different phenolate ligands significantly change the packing characteristics of 1-3, with indirect effects on the electron hopping kinetics responsible for conduction in amorphous thin films. The observed preference for pyridyl-pyridyl stacking proves a faster electron conduction in comparison to hole conduction in the three complexes studied.

We present results on the photorefractive performance of cyclometalated complexes in which a central metal atom (Pd or Pt) coordinates two different molecular sub-units in a single species. Depending on the details of their structure, these molecules aggregate in crystals, glasses or liquid crystalline phases. The photorefractive properties of the complexes are discussed by treating separately results obtained in different phases. Crystalline compounds can be dissolved in suitable polymers and we show how phase separation in polymeric composites, which is usually detrimental for sample stability, can be controlled and used to increase photorefractive performance parameters by orders of magnitude. In addition, we present a method for estimating the itensity of the space-charge field in chiral smectic phases without using any of the standard models developed for crystalline or amorphous materials.

A new series of 5-(4'-substituted)phenylazo-8-hydroxyquinolines (H[L-R]; R = N(CH(3))(2), C(2)H(5), n-C(4)H(9), C(CH(3))(3), H, and F, ) has been prepared and the corresponding Zn[L-R](2) (1a-6a) and Al[L-R](3) (1b-6b) complexes successfully synthesized. These compounds have been studied in order to design new molecular materials with enhanced electron transport properties. The obtained species have been extensively characterized by absorption and emission spectra and by cyclic voltammetric measurements. Experimental and computational results show that the Zn[L-N(CH(3))(2)].2H(2)O (1a) and Al[L-N(CH(3))(2)](1b) complexes only feature luminescence (at 620 and 600 nm), respectively. The unique effects, which are induced by the N=N-C(6)H(4)-N(CH(3))(2) group, are further proved by a reversible electron transfer process detected by cyclic voltammetry. These outcomes, discussed on the basis of theoretical calculations performed on the (H[L-N(CH3)2])-, H[L-N(CH3)2] and (H[L-N(CH3)(2)])+ species, suggest that metal complexes formed by 5-(4'-N,N-dimethylamino)phenylazo-8-hydroxyquinoline should be considered as electron transport materials suitable for applications in photonic devices.

Photorefractivity is of considerable interest in the development of a variety of optical devices.1 Among the most important applications of photorefractive materials are image amplification, novelty filtering and memories for optical processing.2 Photorefractivity is a property exhibited by some materials in which the spatial redistribution of photogenerated charges induces a non-uniform electric space-charge field which can, in turn, affect the refractive index of the material. The net effect is a refractive index replica of the illumination pattern (figure 1).

Three organometallic homopolymers and three copolymers have been obtained, by reacting, respectively, cyclopalladated dinuclear complexes with a polymeric backbone, and by radical copolymerization of cyclopalladated acrylic monomers and methyl methacrylate. Taking into account thermal behaviour and solubility, the copolymers, which display good second order nonlinear optical activity, seem to be the most promising for applications within the new metallated macromolecules. Macroscopic nonlinear optical coefficients d 33 have been determined on spin-coated corona-poled thin films by means of Second Harmonic Generation (SHG) measurements at the wavelength of 1064 nm.

We present results on the photorefractive performance of two different classes of organic materials. One of them is based on the space-charge field induced reorientation of the optical axis of chiral smectic A phases. In this case the orientational effect is linear in the field and it is due to the so-called electroclinic effect, in contrast with the quadratic effect present in nematics and associated with dielectric anisotropy. Besides presenting data on the photorefractive properties of these new mesophases, we will consider a simple model which describes their performance as a function of several material and geometrical parameters. In the second part of the paper we introduce cyclopalladated complexes as a new class of multifunctional photorefractive materials. Such molecules form amorphous phases which are photoconducting and exhibit a field dependent refractive index. Their efficiency is among the best known to date for organic materials and the simple synthetic route makes us foresee a fast optimization of cyclometallated compounds for photorefractive applications.

Thin film morphology of tris-(8-hydroxyquinolate) aluminium (III) (Al q3 ) and bis-(8-hydroxyquinolate) oxovanadium (IV) (VO q2 ) are compared. Al q3 films deposited onto mica at 300K look almost featureless, but dendrimers or randomly distributed needleshaped crystallites appear as a consequence of crystallization in time. We show that a possible origin of this process is exposure to solvent vapors. On the other hand, VO q2 films retain their textured morphology as thickness increases because of stabilizing intermolecular interactions between vanadyl groups.

Interest in materials for optical storage effect has been intense in the last years. In this paper we report the observation of permanent gratings in a new liquid crystalline side-chain polymer containing a mononuclear cyclopalladated azobenzene complex. Two-beam coupling experiments indicate photorefractive properties. A gain of 900 cm−1, without applied electric field, was determined by two beam coupling measurements. A significant feature of this high gain material is that this effect occurs in an easily processable pure compound.

A new salen-like compound, H2L, bearing a 12-carbon atom length aliphatic chain bridging iminic nitrogen atoms, was successfully synthesized and characterized. Interestingly, its zinc complex, ZnL,...

The synthesis and a comprehensive experimental study of molecular structure, electrochemical properties, photoconductivity, absorption and emission properties of two homologous series of square planar cyclometallated Pd(II) and Pt(II) complexes are described. In these complexes, a five member (C,N) metallacycle is formed by either azobenzene, 2-phenylpyridine or benzo[h]quinoline, while the ancillary (O,N) ligand required to complete the metal coordination sphere is the Schiff base resulting from the condensation of 4-n-hexylaniline with 2-hydroxy-4-n-hexyloxybenzaldehyde. The study is complemented by Density Functional Theory calculations of molecular structure in the ground state, frontier orbitals distribution and energies. Absorption energies, intensities for the transitions and composition of the excited states are characterized by Time Dependent Density Functional Theory computations. Results show that for these complexes the HOMO is located on the Schiff base and the LUMO on the cyclometalated ligand. As also indicated by spectroscopic and photoconductivity results, the photogeneration of charge carriers might be associated with the spatial separation of HOMO and LUMO, while an additional contribution could derive from a conformational variation in the excited state. The separation of the frontier orbitals on different ligands provides simple synthetic routes towards band-gap tuning and energy matching with other molecular species and electrodes, both important features for several applications of molecular semiconductors. The results of the present investigation suggest that these square planar cyclometalated Pd(II) and Pt(II) complexes actually form a new class of photoconductors.