Role of the Environment Polarity on the Photophysical Properties of Mesogenic Hetero-Polymetallic Complexes.

New hetero-polynuclear coordination complexes based on a pentacoordinated Zn(II) metal center with tridentate terpyridine-based ligands and monoanionic gallates functionalized with long alkyl chains containing ferrocene units were designed, synthesized and characterized using spectroscopic and analytical methods. The complexes are mesomorphic, exhibiting columnar hexagonal mesophases. The photophysical properties in a solution and in an ordered condensed state were accurately investigated and the influence of the polarity of the solvent was evidenced.

Bimetallic liquid crystal blends based on structurally related 3d-metal coordination complexes.

Hetero-bimetallic liquid crystalline materials, exhibiting a single Colhex mesophase, were obtained by simple chemical blending between two structurally-related Cu(II) and Zn(II) metallomesogens based on 1,10-phenanthroline and two chelating gallate ligands. Mesomorphous and optical properties were modified upon their relative respective proportions. This study highlights the numerous possibilities for the fabrication of new multifunctional polymetallic materials, with the possibility of tuning the properties and controlling supramolecular interactions between metal centres and corresponding synergistic effects.

Hetero-Bimetallic Ferrocene-Containing Zinc(II)-Terpyridyl-Based Metallomesogen: Structural and Electrochemical Characterization.

The synthesis, as well as the mesomorphic and electrochemical properties, of a hetero-bimetallic coordination complex able to self-assemble into a columnar liquid crystalline phase is reported herein. The mesomorphic properties were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and Powder X-ray diffraction (PXRD) analysis. Electrochemical properties were explored by cyclic voltammetry (CV), relating the hetero-bimetallic complex behaviour to previously reported analogous monometallic Zn(II) compounds. The obtained results highlight how the presence of the second metal centre and the supramolecular arrangement in the condensed state pilot the function and properties of the new hetero-bimetallic Zn/Fe coordination complex.

Design of Nanostructured Hybrid Electrodes Based on a Liquid Crystalline Zn(II) Coordination Complex-Carbon Nanotubes Composition for the Specific Electrochemical Sensing of Uric Acid.

A metallomesogen based on an Zn(II) coordination complex was employed as precursor to obtain a complex matrix nanoplatform for the fabrication of a high-performance electrochemical hybrid sensor. Three representative paste electrodes, which differ by the weight ratio between Zn(II) metallomesogen and carbon nanotubes (CNT), i.e., PE_01, PE_02 and PE_03, were obtained by mixing the materials in different amounts. The composition with the largest amount of CNT with respect to Zn complex, i.e., PE_03, gives the best electrochemical signal for uric acid detection by cyclic voltammetry in an alkaline medium. The amphiphilic structure of the Zn(II) coordination complex likely induces a regular separation between the metal centers favoring the redox system through their reduction, followed by stripping, and is characterized by enhanced electrocatalytic activity towards uric acid oxidation. The comparative detection of uric acid between the PE_03 paste electrode and the commercial zinc electrode demonstrated the superiority of the former, and its great potential for the development of advanced electrochemical detection of uric acid. Advanced electrochemical techniques, such as differential-pulsed voltammetry (DPV) and square-wave voltammetry (SWV), allowed for the highly sensitive detection of uric acid in aqueous alkaline solutions. In addition, a good and fast amperometric signal for uric acid detection was achieved by multiple-pulsed amperometry, which was validated by urine analysis.

Graphene Quantum Dots and Cu(I) Liquid Crystal for Advanced Electrochemical Detection of Doxorubicine in Aqueous Solutions.

Two paste electrodes based on graphene quantum dots and carbon nanotubes (GRQD/CNT) and one modified with a homoleptic liquid crystalline Cu(I) based coordination complex (Cu/GRQD/CNT) were obtained and morphostructurally and electrochemically characterized in comparison with simple CNT electrode (CNT) for doxorubicine (DOX) detection in aqueous solutions. GRQD/CNT showed the best electroanalytical performance by differential pulse voltammetry technique (DPV). Moreover, applying a preconcentration step prior to detection stage, the lowest limit of detection (1 ng/L) and the highest sensitivity (216,105 µA/mg·L-1) in comparison with reported literature data were obtained. Cu/GRQD/CNT showed good results using multiple pulse amperometry technique (MPA) and a favorable shifting of the potential detection to mitigate potential interferences. Both GRQD-based paste electrodes have a great potential for practical utility in DOX determination in water at trace concentration levels, using GRQD/CNT with DPV and in pharmaceuticals formulations using Cu/GRQD/CNT with MPA.

Vibrational and Nuclear Magnetic Resonance Properties of 2,2'-Biquinolines: Experimental and Computational Spectroscopy Study.

Experimental (IR, Raman and NMR) techniques and quantum chemical (DFT) methods have been applied to investigate the vibrational and NMR properties of a new ligand based on 2,2'-biquinoline (bq) functionalized with polar hydrophilic tetraethylene glycol monomethylether (TEG) chains (bq_TEG). Vibrational and NMR spectra of the ligand have been explained based on DFT computational data obtained at B3LYP/6-311+G(d,p) level of theory. For the spectroscopic analysis we started from the parent molecule 2,2'-biquinoline and explained the changes in the spectra of bq_TEG in close relation to the corresponding spectra of bq. Our data point to a trans conformation of bq_TEG in solid state, as wells as in liquid phase. The excellent agreement between the experimental and computed data allowed for a reliable assignment of the vibrational and NMR spectra, both for bq and bq_TEG.

Playing with PtII and ZnII Coordination to Obtain Luminescent Metallomesogens.

Blue-green luminescent terpyridine-containing PtII and ZnII complexes are reported. Equipped with lipophilic gallate units, which act as monodentate ancillary coordinating ligands and/or as anions, they display low-temperature mesomorphic properties (lamello-columnar and hexagonal mesophases for PtII and ZnII complexes, respectively). The mesomorphic properties were investigated by polarised optical microscopy, differential scanning calorimetry, thermogravimetric analysis and X-ray scattering of bulk materials and oriented thin films. The model of self-assembly into the lamello-columnar phase of the PtII complex has been described in detail. The optical properties of the complexes were investigated in the liquid and condensed liquid crystalline states, highlighting the delicate balance between the role of the metal in determining the type of excited state responsible for the emission, and the role of the ancillary ligand in driving intermolecular interactions for proper mesophase formation.

Cu(I) Coordination Complex Precursor for Randomized CuOx Microarray Loaded on Carbon Nanofiber with Excellent Electrocatalytic Performance for Electrochemical Glucose Detection.

A homoleptic ionic Cu(I) coordination complex that was based on 2,2'-biquinoline ligand functionalized with long alkyl chains (Cu(I)-C18) was used as a precursor to modify a carbon nanofiber paste electrode (Cu-C18/CNF). Randomized copper oxide microelectrode arrays dispersed within carbon nanofiber paste (CuOx/CNF) were obtained by electrochemical treatment of Cu-C18/CNF while using cyclic voltammetry (CV). The CuOx/CNF exhibited high electrocatalytic activity towards glucose oxidation at +0.6 V and +1.2 V vs. Ag/AgCl. Infrared Spectroscopy (FTIR) and scanning electron microscopy (SEM) characterized the electrodes composition. Cyclic voltammetry (CV), square wave-voltammetry (SWV), and multiple-pulsed amperometry (MPA) techniques provided optimized conditions for glucose oxidation and detection. A preconcentration step that involved 10 minutes accumulation at open circuit potential before SWV running led to the lowest limit of detection and the highest sensitivity for glucose detection (5419.77 µA·mM-1·cm-2 at + 1.1 V vs. Ag/AgCl) vs. Cu-based electrodes reported to date in literature.

Plasmon-mediated cancer phototherapy: the combined effect of thermal and photodynamic processes.

A nanoplatform for simultaneous cellular imaging, and photodynamic and photothermal therapies has been designed and realized by embedding a purposely synthesized highly luminescent water soluble iridium(iii) compound into gold core-silica shell nanoparticles. These multifunctionalities arise mainly from the photophysical properties of the cyclometalated complex: (i) the heavy atom promotes, through excited triplet state formation, energy transfer processes towards molecular oxygen, with the generation of 1O2 (photodynamic effect); (ii) the overlap of the iridium(iii) complex emission band with the plasmonic resonance of gold nanostructures allows excitation energy transfer towards the metallic core (photothermal effect); (iii) the remarkable iridium(iii) complex luminescence feature, which is preserved despite energy transfer processes, makes the whole system an efficient luminescent bio-probe (imaging). Photophysical and photothermal investigations have been carried out, whereas in vitro photo-cytotoxicity tests have been performed on human glioblastoma cells (U87MG), highlighting significant cancer cell death at a very low photosensitizer concentration (<0.5 µM), by means of a synergistic photodynamic and photothermal effect.

Multifunctional material based on ionic transition metal complexes and gold-silica nanoparticles: synthesis and photophysical characterization for application in imaging and therapy.

A new combination of luminescent ionic transition-metal complexes (M = Ru(II) or Ir(III)) with gold silica-based nanoparticles (GSNPs) gives a promising nanomaterial for application in biomedical fields. Herein we report the synthesis and the photophysical properties of Ru(II) and Ir(III) complexes doped gold core-polysiloxane shell particles prepared by microemulsion method and characterized by Transmission Electron Microscopy, Dynamic Light Scattering and UV-Vis spectroscopy. The cytotoxicity and photodynamic activity of the obtained 50 nm-diameter nanoparticles were evaluated in vitro, providing noteworthy results. Furthermore, their intrinsic phosphorescence allows the localization of the photosensitizing nanoparticles into the cytosol of tumor cells by fluorescence confocal microscope. These valuable features designate them as multifunctional nanoplatforms for theranostic purposes.

Luminescence mechanochromism in cyclometallated Ir(III) complexes containing picolylamine.

The synthesis, crystal structure and luminescence properties of three cyclometalated Ir(III) complexes of general formula [(ppy)(2)Ir(pam)]X, where X = Cl(-) (1), PF(6)(-) (2), ClO(4)(-)(3), and pam = 2-picolylamine, are described. While 2 and 3 crystallize in a unique form, two pseudo-polymorphs, a solvated (1a) and a non-solvated (1b) species, have been observed for compound 1. 1a crystallizes in the monoclinic centrosymmetric space group P2(1)/c. On the contrary, 1b, 2 and 3 crystallize in the non-centrosymmetric space group P2(1)2(1)2(1) (1b) and Pca2(1) (2 and 3), respectively. All the crystalline supramolecular materials have been fully photophysically characterized. While 1 shows a bright blue-green emission in both solution and solvated crystalline state 1a, crystals of 1b, 2 and 3 show a significantly red shifted emission with respect to solution. Unexpectedly, and differently from 1a, mechanical stimuli-responsive colour and luminescence changes have been observed for 1b, 2 and 3. Upon mechanical grinding the colour of the crystalline solids changes from orange to yellow while the emission energy is partially (2 and 3) or completely (1b) converted from orange to green. The grinding-triggered colour and luminescence changes have been attributed to a crystal-to-amorphous phase conversion for all crystalline solids.

2,2'-Biquinolines as test pilots for tuning the colour emission of luminescent mesomorphic silver(I) complexes.

The synthesis and characterization of a series of 2,2'-biquinolines differently substituted in the 4,4'-position and their corresponding silver(I) derivatives obtained through reaction with silver triflate in a 1 : 1 stoichiometric ratio are reported. In order to perform a systematic investigation on the role played by the substituents on the coordination to the silver(I) centre, structural studies through single crystal X-ray diffraction have been performed on two Ag(I) model complexes. Unlike their analogous 2,2'-bipyridine ligands, the biquinolines have been found to behave only as chelated ligands towards the silver(I) ion, irrespective of the substituents. The coordination sphere of the Ag(I) is filled by a solvent molecule and, depending on the presence and nature of the substituents on the organic ligand, by an oxygen atom coming from a coordinated triflate or from a carboxylic group of a symmetrically related molecule, giving rise to neutral or ionic species. For the highest Ag(I) triflate homologues the presence of long and flexible peripheral tails makes it possible to achieve liquid crystalline properties with columnar organization whose high order is due to the large and rigid core. Moreover, the metal coordination induces in all the Ag(I) species interesting emission properties both in solution and condensed states, giving rise to blue or green emitters, depending on the nature of the substituents on the biquinoline units.

Anion dependent mesomorphism in coordination networks based on 2,2'-bipyridine silver(I) complexes.

The reaction of the promesogenic dihexadecyl-2,2'-bipyridine-4,4'-dicarboxylate (L16) with a number of AgX salts produces a series of silver(I) complexes [(L16)Ag(sac)], 1, [(L16)Ag(NO3)], 2, [(L16)Ag(OTf)], 3, and [(L16)3Ag2](ClO4)2, 4, whose stoichiometries, molecular architectures, supramolecular networks and mesomorphic behaviour are "anion dependent". In spite of the large differences in the single molecular structure, the one-dimensional coordination networks involving the triflate and perchlorate in complexes 3 and 4, are the key element for inducing significant argentophilic intermolecular interactions responsible for the induction of lamello-columnar mesomorphism in both Ag(I) derivatives. Moreover, a series of Ag(I) triflate model complexes have been synthesized and in order to get more insights about their solid state architectures, systematic structural studies have been performed.