Tailoring the efficiency of porphyrin molecular frameworks for the electroactivation of molecular N2.

The combination of compositional versatility and topological diversity for the integration of electroactive species into high-porosity molecular architectures is perhaps one of the main appeals of metal-organic frameworks (MOFs) in the field of electrocatalysis. This premise has attracted much interest in recent years, and the results generated have also revealed one of the main limitations of molecular materials in this context: low stability under electrocatalytic conditions. Using zirconium MOFs as a starting point, in this work, we use this stability as a variable to discriminate between the most suitable electrocatalytic reaction and specific topologies within this family. Our results revealed that the PCN-224 family is particularly suitable for the electroreduction of molecular nitrogen for the formation of ammonia with faradaic efficiencies above 30% in the presence of Ni2+ sites, an activity that improves most of the catalysts described. We also introduce the fluorination of porphyrin at the meso position as a good alternative to improve both the activity and stability of this material under electrocatalytic conditions.

Tetrazine Linkers as Plug-and-Play Tags for General Metal-Organic Framework Functionalization and C60 Conjugation.

The value of covalent post-synthetic modification in expanding the chemistry and pore versatility of reticular solids is well documented. Here we use mesoporous crystals of the metal-organic framework (MOF) UiO-68-TZDC to demonstrate the value of tetrazine connectors for all-purpose inverse electron-demand Diels-Alder ligation chemistry. Our results suggest a positive effect of tetrazine reticulation over its reactivity for quantitative one-step functionalization with a broad scope of alkene or alkyne dienophiles into pyridazine and dihydropyridazine frameworks. This permits generating multiple pore environments with diverse chemical functionalities and the expected accessible porosities, that is also extended to the synthesis of crystalline fulleretic materials by covalent conjugation of fullerene molecules.

Permanent Porosity in Hydroxamate Titanium-Organic Polyhedra.

Following the synthesis of hydroxamate titanium-organic frameworks, we now extend these siderophore-type linkers to the assembly of the first titanium-organic polyhedra displaying permanent porosity. Mixed-linker versions of this molecular cage (cMUV-11) are also used to demonstrate the effect of pore chemistry in accessing high surface areas of near 1200 m2·g-1.

Selective Implantation of Diamines for Cooperative Catalysis in Isoreticular Heterometallic Titanium-Organic Frameworks.

We introduce the first example of isoreticular titanium-organic frameworks, MUV-10 and MUV-12, to show how the different affinity of hard Ti(IV) and soft Ca(II) metal sites can be used to direct selective grafting of amines. This enables the combination of Lewis acid titanium centers and available -NH2 sites in two sizeable pores for cooperative cycloaddition of CO2 to epoxides at room temperature and atmospheric pressure. The selective grafting of molecules to heterometallic clusters adds up to the pool of methodologies available for controlling the positioning and distribution of chemical functions in precise positions of the framework required for definitive control of pore chemistry.

Variation of Interfacial Interactions in PC61BM-like Electron-Transporting Compounds for Perovskite Solar Cells.

The synthesis, characterization, and incorporation of phenyl-C61-butyric acid methyl ester (PC61BM)-like derivatives as electron transporting materials (ETMs) in inverted perovskite solar cells (PSCs) are reported. These compounds have the same structure except for the ester substituent, which was varied from methyl to phenyl to thienyl and to pyridyl. The three latter derivatives performed better than PC61BM in PSCs, mainly attributed to the specific interactions of the fullerenes with the perovskite layer, as evidenced by X-ray photoelectron spectroscopy (XPS) and steady-state and time-resolved photoluminescence (SS- and TRPL) measurements. The experimental results were fully supported by density functional theory (DFT) calculations, which showed that the strongest interactions were exhibited by the compound possessing the pyridyl substituent.

Direct Visualization of Pyrrole Reactivity upon Confinement within a Cyclodextrin Metal-Organic Framework.

Metal-organic frameworks can be used as porous templates to exert control over polymerization reactions. Shown here are the possibilities offered by these crystalline, porous nanoreactors to capture highly-reactive intermediates for a better understanding of the mechanism of polymerization reactions. By using a cyclodextrin framework the polymerization of pyrrole is restricted, capturing the formation of terpyrrole cationic intermediates. Single-crystal X-ray diffraction is used to provide definite information on the supramolecular interactions that induce the formation and stabilization of a conductive array of cationic complexes.

Optimizing CuO p-type dye-sensitized solar cells by using a comprehensive electrochemical impedance spectroscopic study.

We introduce a novel and comprehensive approach for the evaluation and interpretation of electrochemical impedance spectroscopy (EIS) measurements in p-type DSSCs. In detail, we correlate both the device performance and EIS figures-of-merit of a series of devices in which, the calcination temperature, film thickness, and electrolyte concentration have been systematically modified. This new approach enables the separation of the different processes across the dye/semiconductor/electrolyte interface, namely the unfavorable charge recombination and the favorable electron injection/regeneration processes. In addition, studies on non-sensitized CuO and NiO electrodes provide insights into their affinity towards a reaction with the electrolyte - CuO is far less reactive towards the polyiodide species. Overall, this work underlines the superior features of CuO with respect to NiO for p-DSSCs and demonstrates a comprehensive optimization of the CuO-based DSSCs with respect to the device architecture by the aid of EIS analysis.

Combining electron-accepting phthalocyanines and nanorod-like CuO electrodes for p-type dye-sensitized solar cells.

A route is reported for the synthesis of two electron-accepting phthalocyanines featuring linkers with different lengths as sensitizers for p-type dye-sensitized solar cells (DSSCs). Importantly, our devices based on novel nanorod-like CuO photocathodes showed high efficiencies of up to 0.191 %: the highest value reported to date for CuO-based DSSCs.

Influence of peripheral substitution on the magnetic behavior of single-ion magnets based on homo- and heteroleptic Tb(III) bis(phthalocyaninate).

A series of homoleptic ([Tb(III)(Pc)(2) ]) and heteroleptic ([Tb(III)(Pc)(Pc')]) Tb(III) bis(phthalocyaninate) complexes that contain different peripheral substitution patterns (i.e., tert-butyl or tert-butylphenoxy groups) have been synthesized in their neutral radical forms and then reduced into their corresponding anionic forms as stable tetramethylammonium/tetrabutylammonium salts. All of these compounds were spectroscopically characterized and their magnetic susceptibility properties were investigated. As a general trend, the radical forms exhibited larger energy barriers for spin reversal than their corresponding reduced compounds. Remarkably, heteroleptic complexes that contain electron-donor moieties on one of the two Pc ligands show higher effective barriers and blocking temperatures than their homoleptic derivatives. This result is assigned to the elongation of the N-Tb distances in the substituted macrocycle, which brings the terbium(III) ion closer to the unsubstituted Pc, thus enhancing the ligand-field effect. In particular, heteroleptic [Tb(III) (Pc)(Pc')] complex 4, which contains one octa(tert-butylphenoxy)-substituted Pc ring and one bare Pc ring, exhibits the highest effective barrier and blocking temperature for a single-molecule magnet reported to date.

Broadening the absorption of conjugated polymers by "click" functionalization with phthalocyanines.

Conjugated copolymer derivatives of poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and poly(3-hexylthiophene) (P3HT) containing 10% of alkyne functionalities in the side chains have been prepared using the sulfinyl precursor route and the Rieke method, respectively. With the aim of expanding the absorption range of these conjugated polymers for their use in bulk heterojunction (BHJ) polymer:fullerene solar cells, appropriate phthalocyanine (Pc) molecules have been covalently bound through a post-polymerization "click chemistry" reaction between the alkyne functionalities in the side chains of the copolymers and a Pc functionalized with an azide moiety. The resulting poly(p-phenylenevinylene)-Pc (PPV-Pc) material holds a 9 mol% content of Pcs, while the polythiophene-Pc material (PT-Pc) contains a 8 mol% of Pc-functionalization in the side chains. As expected, the presence of the Pc contributes to the extension of the absorption up to 700 nm. BHJ solar cells have been prepared using PPV-Pc and PT-Pc materials in combination with PCBM. Although the Pc absorption contributes to the generation of photocurrent, the overall power conversion efficiencies (PCE) obtained from these cells are lower than those obtained with BHJ P3HT:PCBM (1:1) and MDMO-PPV:PCBM (1:4) solar cells. A plausible explanation could be the moderate solubility of the PPV-Pc and PT-Pc materials that limits the processing into thin films.