Electrochemical Characterization and CO2 Reduction Reaction of a Family of Pyridazine-Bridged Dinuclear Mn(I) Carbonyl Complexes.

Three recently synthesized neutral dinuclear carbonyl manganese complexes with the pyridazine bridging ligand, of general formula [Mn2(µ-ER)2(CO)6(µ-pydz)] (pydz = pyridazine; E = O or S; R = methyl or phenyl), have been investigated by cyclic voltammetry in dimethylformamide and acetonitrile both under an inert argon atmosphere and in the presence of carbon dioxide. This family of Mn(I) compounds behaves interestingly at negative potentials in the presence of CO2. Based on this behavior, which is herein discussed, a rather efficient catalytic mechanism for the CO2 reduction reaction toward the generation of CO has been hypothesized.

Triarylamine-based hydrido-carboxylate rhenium(i) complexes as photosensitizers for dye-sensitized solar cells.

Two new dyes based on a dinuclear rhenium complex and (E)-3-(5-(4-(bis(2',4'-dibutoxy-[1,1'-biphenyl]-4-yl)amino)phenyl)thiophen-2-yl)-2-cyanoacrylic acid (namely D35) have been investigated as sensitizers for dye sensitized solar cells (DSSCs). Two different pyridazine ligands have been used, namely 4-pyridazine-carboxylic acid for dye 2 ([Re2(µ-H)(-D35)(CO)6(µ-pyridazine-4-COOH)]) and 4-pyridazinyl-butanoic acid for dye 3 ([Re2(µ-H)(-D35)(CO)6(µ-pyridazine-4-C3H6-COOH)]). The performances of these new dyes have been compared with those of the dye containing the bare 4-diphenylaminobenzoic acid, namely TPA, as the ancillary ligand (dye 1). Compared to dye 1, dyes 2 and 3 show an impressive tenfold increase in the absorption intensity in the range of 487-493 nm on TiO2 films, with great improvement of the light harvesting. Cyclic voltammetry experiments, performed on derivatives containing the methyl ester of the pyridazine ligands, show narrow electrochemical band gaps in the range of 1.36-1.84 eV. Solar cells with each dye have been prepared, using both iodide/triiodide and cobalt redox couples as the electrolytes, platinum or carbon as the counter electrodes, and TiO2 or SnO2 as the metal oxide photoelectrodes, respectively. The best DSSC results have been obtained using dye 3, with an overall solar-to-electric conversion efficiency of 3.5%, which greatly overcomes the previous result of 1.0% obtained for dye 1 in a not-optimized setup of the device. The performances of dye 3 are due to the presence of D35 ligand, which further suppresses the recombination of the injected electron with the electrolyte and with the oxidized state of the dye.

Luminescent conjugates between dinuclear rhenium complexes and 17α-ethynylestradiol: synthesis, photophysical characterization, and cell imaging.

Three new luminescent conjugates between dinuclear rhenium complexes and an estradiol, namely E2-Re, are described. The derivatives have the general formula [Re2(µ-Cl)2(CO)6(µ-R-pydz-17α-ethynylestradiol)] (R-pydz = functionalized 1,2-pyridazine), where the estradiol moiety is covalently bound to the ß position of the pyridazine ligand. Different synthetic pathways are investigated, including the inverse-type [4 + 2] Diels Alder cycloaddition reaction between the electron poor 1,2,4,5-tetrazine and 17α-ethynylestradiol for the synthesis of E2-Re1. The three E2-Re conjugates are purified on silica gel and isolated in a spectroscopically pure form in moderate to good yields (28-50%). All the E2-Re conjugates are comprehensively characterized from the spectroscopic and photophysical points of view. Cellular internalization experiments on human MCF-7 and 231 cells are also reported, displaying interesting staining differences depending on the nature of the spacer linking the estradiol unit to the organometallic fragment. Furthermore, the suitability of these conjugates to also stain simple multicellular organisms, i.e. Ciona intestinalis embryos and larvae at different stages of development, is reported here for the first time.

Searching for Models Exhibiting High Circularly Polarized Luminescence: Electroactive Inherently Chiral Oligothiophenes.

Two new inherently chiral oligothiophenes characterized by the atropisomeric 3,3'-bithianaphtene scaffold functionalized with fused ring bithiophene derivatives, namely 4H-cyclopenta[2,1-b3:4b']dithiophene (CPDT) and dithieno[3,3-b:2',3'-d]pyrrole (DTP), were synthesized. The racemates were fully characterized and resolved into antipodes by enantioselective HPLC. The enantiomers were analyzed through different chiroptical techniques: electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) were employed to attribute the absolute configuration (AC). Comparison of experimental and calculated VCD spectra confirmed the DFT calculated conformational characteristics. The compound functionalized with two CPDT units was oxidized with FeCl3 , and ECD and CPL of the resulting material were measured. Circularly polarized luminescence (CPL) was measured to verify if inherently chiral oligothiophenes could be promising systems for chiral photonics applications.

Inherently Chiral Spider-Like Oligothiophenes.

The racemate of an inherently chiral "spider-like" octathiophene monomer T83 , in which chirality is generated by torsion in its backbone, was synthesized. The racemate was resolved into configurationally stable antipodes by HPLC on a chiral stationary phase. Electrooxidation of the enantiomers resulted in materials displaying high enantiorecognition ability towards the antipodes of some chiral probes. Moreover, the T83 racemate demonstrated great aptitude to stimulate formation of 3D rigid architectures if used as a cross-linking monomer for molecular imprinting. This feature was exploited to devise a molecularly imprinted polymer-based chemosensor selective for a thymine-adenine oligonucleotide.

Inherently chiral macrocyclic oligothiophenes: easily accessible electrosensitive cavities with outstanding enantioselection performances.

Linear conjugated oligothiophenes of variable length and different substitution pattern are ubiquitous in technologically advanced optoelectronic devices, though limitations in application derive from insolubility, scarce processability and chain-end effects. This study describes an easy access to chiral cyclic oligothiophenes constituted by 12 and 18 fully conjugated thiophene units. Chemical oxidation of an "inherently chiral" sexithiophene monomer, synthesized in two steps from commercially available materials, induces the formation of an elliptical dimer and a triangular trimer endowed with electrosensitive cavities of different tunable sizes. Combination of chirality with electroactivity makes these molecules unique in the current oligothiophenes literature. These macrocycles, which are stable and soluble in most organic solvents, show outstanding chiroptical properties, high circularly polarized luminescence effects and an exceptional enantiorecognition ability.

A soft copper(II) porous coordination polymer with unprecedented aqua bridge and selective adsorption properties.

Herein, the synthesis, crystal structure, and full characterization of a new soft porous coordination polymer (PCP) of ([Cu(2)(dmcapz)(2)(OH(2))]DMF(1.5))(n) (1) formulation, which is easily obtained in the reaction of CuX(2) (X = Cl, NO(3)) salts with 3,5-dimethyl-4-carboxypyrazole (H(2)dmcapz) is present. Compound 1 shows a copper(II) dinuclear secondary building unit (SBU), which is supported by two pyrazolate bridges and an unprecedented H(2)O bridge. The dinuclear SBUs are further bridged by the carboxylate ligands to build a diamondoid porous network. The structural transformations taking place in 1 framework upon guest removal/uptake has been studied in detail. Indeed, the removal of the bridging water molecules gives rise to a metastable evacuated phase (1 b) that transforms into an extremely stable porous material (1 c) after freezing at liquid-nitrogen temperature. The soaking of 1 c into water allows the complete and instantaneous recover of the water-exchanged material (1 a'). Remarkably, 1 b and 1 c materials possess structural bistability, which results in the switchable adsorptive functions. Therefore, the gas-adsorption properties of both materials have been studied by means of single-component gas adsorption isotherms as well as by variable-temperature pulse-gas chromatography. Both materials present permanent porosity and selective gas-adsorption properties towards a variety of gases and vapors of environmental and industrial interest. Moreover, the flexible nature of the coordination network and the presence of highly active convergent open metal sites confer on these materials intriguing gas-adsorption properties with guest-triggered framework-breathing phenomena being observed. The plasticity of Cu(II) metal center and its ability to form stable complexes with different coordination numbers is at the origin of the structural transformations and the selective-adsorption properties of the studied materials.

Highly emitting concomitant polymorphic crystals of a dinuclear rhenium complex.

The dinuclear complex [Re(2)(µ-Cl)(2)(CO)(6)(µ-4,5-(Me(3)Si)(2)pyridazine)] gives in the solid state two polymorphs (yellow, 1Y, and orange, 1O), which can be either concomitantly or separately obtained on varying the crystallization rate. Both crystal phases exhibit intense photoluminescence from the lowest lying triplet metal-to-ligand charge transfer state, much stronger than in solution (quantum yields 0.56 and 0.52, for 1O and 1Y respectively, vs 0.06 in toluene), likely due to the restricted rotation of the Me(3)Si groups in the solid state. A clean, irreversible 1O → 1Y single-crystal-to-single-crystal phase transition occurs at 443 K, as revealed by variable temperature X-ray diffraction analysis. In spite of the absence of any strong intermolecular interactions in both forms, 1O and 1Y show very different absorption and emission maxima (λ(abs) 370 and 393 nm, λ(em) 534 and 570 nm, for 1Y and 1O, respectively). This behavior highlights the importance of the local organization of molecular dipoles in perturbing the photophysical properties of the molecule in the crystal.