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International audience; Immobilization of well-defined homogenous (electro)catalysts onto conductive supports offers an attractive strategy for designing advanced functional materials for energy conversion. In this context, this study reports (i) the introduction of a pyrene anchoring group on a PNP-pincer Ir-I complex previously described as a selective catalyst for the electrodriven CO2 reduction (CO2RR) into CO in DMF/water mixtures, (ii) the comparison of its CO2RR activity in DMF/water mixtures with the ones of two pyrene-free reference complexes, and (iii) its activity in pure water after immobilization onto carbon nanotubes (CNTs). Surprisingly, in homogeneous conditions we find HCOO-, instead of CO, as the main CO2 reduction product for the three catalysts. After immobilization on CNTs, even if non-negligible competitive proton reduction reaction is observed in fully aqueous media, the complex is still able to drive CO2RR and produce HCOO- with a significantly lower overpotential with respect to solution studies.

Covalent triazine frameworks (CTFs) are a class of porous organic polymers that continuously attract growing interest because of their outstanding chemical and physical properties. However, the control of extended porous organic framework structures at the molecular scale for a precise adjustment of their properties has hardly been achieved so far. Here, we present a series of bipyridine-based CTFs synthesized through polycondensation, in which the sequence of specific building blocks is well controlled. The reported synthetic strategy allows us to tailor the physicochemical features of the CTF materials, including the nitrogen content, the apparent specific surface area, and optoelectronic properties. Based on a comprehensive analytical investigation, we demonstrate a direct correlation of the CTF bipyridine content with the material features such as the specific surface area, band gap, charge separation, and surface wettability with water. The entirety of these parameters dictates the catalytic activity as demonstrated for the photocatalytic hydrogen evolution reaction (HER). The material with the optimal balance between optoelectronic properties and highest hydrophilicity enables HER production rates of up to 7.2 mmol/(h·g) under visible light irradiation and in the presence of a platinum cocatalyst.

Heterogenization of molecular catalysts via their immobilization within extended structures often results in a lowering of their catalytic properties due to a change in their coordination sphere. Metal–organic polyhedra (MOP) are an emerging class of well-defined hybrid compounds with a high number of accessible metal sites organized around an inner cavity, making them appealing candidates for catalytic applications. Here, we demonstrate a design strategy that enhances the catalytic properties of dirhodium paddlewheels heterogenized within MOP (Rh-MOP) and their three-dimensional assembled supramolecular structures, which proved to be very efficient catalysts for the selective photochemical reduction of carbon dioxide to formic acid. Surprisingly, the catalytic activity per Rh atom is higher in the supramolecular structures than in its molecular sub-unit Rh-MOP or in the Rh-metal–organic framework (Rh-MOF) and yields turnover frequencies of up to 60 h–1 and production rates of approx. 76 mmole formic acid per gram of the catalyst per hour, unprecedented in heterogeneous photocatalysis. The enhanced catalytic activity is investigated by X-ray photoelectron spectroscopy and electrochemical characterization, showing that self-assembly into supramolecular polymers increases the electron density on the active site, making the overall reaction thermodynamically more favorable. The catalyst can be recycled without loss of activity and with no change of its molecular structure as shown by pair distribution function analysis. These results demonstrate the high potential of MOP as catalysts for the photoreduction of CO2 and open a new perspective for the electronic design of discrete molecular architectures with accessible metal sites for the production of solar fuels.

Heterogenization of molecular catalysts via their immobilization within extended structures often results in a lowering of their catalytic properties due to a change in their coordination sphere. Metal-organic polyhedra (MOP) are an emerging class of well-defined hybrid compounds with a high number of accessible metal sites organized around an inner cavity, making them appealing candidates for catalytic applications. Here, we demonstrate a design strategy that enhances the catalytic properties of dirhodium paddlewheels heterogenized within MOP (Rh-MOP) and their three-dimensional assembled supramolecular structures, which proved to be very efficient catalysts for the selective photochemical reduction of carbon dioxide to formic acid. Surprisingly, the catalytic activity per Rh atom is higher in the supramolecular structures than in its molecular sub-unit Rh-MOP or in the Rh-metal-organic framework (Rh-MOF) and yields turnover frequencies of up to 60 h

Covalent Triazine Frameworks (CTFs) are a class of Porous Organic Polymers which attracts continuously growing interest because of their outstanding chemical and physical properties. However, the control of extended porous organic frameworks’ structures at the molecular scale for a precise adjustment of their properties has hardly been achieved so far. Here, we present a series of bipyridine-based CTFs synthesized through polycondensation, in which the sequence of specific building blocks is well controlled. The reported synthetic strategy allows to tailor the physicochemical features of the CTF materials, including nitrogen content, apparent specific surface area and opto-electronic properties. Based on a comprehensive analytic investigation, we demonstrate a direct correlation of the CTF bipyridine content with the material features such as specific surface area, bandgap, charge separation and surface wettability with water. The entirety of those parameters dictates the catalytic activity as demonstrated for the photocatalytic hydrogen evolution reaction (HER). The material with the necessary balance between opto-electronic properties and highest hydrophilicity enables HER production rates of up to 7.2 mmol·h-1·g-1 under visible light irradiation and in the presence of a platinum co-catalyst.

The molecular-level structuration of two full photosystems into conjugated porous organic polymers is reported. The strategy of heterogenization gives rise to photosystems which are still fully active after 4 days of continuous illumination. Those materials catalyze the carbon dioxide photoreduction driven by visible light to produce up to three grams of formate per gram of catalyst. The covalent tethering of the two active sites into a single framework is shown to play a key role in the visible light activation of the catalyst. The unprecedented long-term efficiency arises from an optimal photoinduced electron transfer from the light harvesting moiety to the catalytic site as anticipated by quantum mechanical calculations and evidenced by in situ ultrafast time-resolved spectroscopy.

Two new molybdenum complexes (Bu