Quantum-CORMs: quantum dot sensitized CO releasing molecules

The synthesis and photodecomposition behaviour of a family of CO releasing molecules (CORMs) based on [Mn(CO)₃bpy] derivatives connected to a semiconductor Quantum Dot (QD) sensitizer is described here. Compared to the non-sensitized complexes, such systems show a 2 to 6-fold increase of the photodecomposition rate upon irradiation with visible light

Red-light activated photoCORMs of Mn(I) species bearing electron deficient 2,2′-azopyridines

The realization of CO releasing molecules triggered by light (photoCORMs) within the phototherapeutic window (λ > 600 nm) constitutes an important goal for potential therapeutic applications of the molecules. The activation of photoCORMs with red/NIR light would enable exploiting the higher depth of penetration of this radiation with respect to higher energy photons. In this article we report a family of carbonyl Mn(I) complexes capable of releasing CO when triggered with red light (≥625 nm). Such complexes are based on 2,2′-azopyridine ligands modified by the introduction of electron-donating or electron-withdrawing substituents. Our results indicate that electron deficient ligands induce a gradual decrease of the HOMO−1/LUMO gap of the species (i.e. of the orbitals involved in the lowest energy transition), thus enabling a fine tuning of their visible absorption maxima between 630 and 693 nm. The synthesis of the complexes and their photodecomposition behaviour towards CO release are described. We suggest that this approach could be generalized for further development of low-energy activated photoCORMs

Heptacoordinate Co(II) catalyst for light-driven hydrogen production in fully aqueous medium

Photocatalytic hydrogen production is an appealing way to store solar energy as chemical fuel. The most studied molecular catalysts for H2 production are based on earth-abundant metals such as Ni, Co and Fe. Efforts have been recently focused on the design of Co complexes with distorted octahedral geometries induced by tetra- or pentapyridyl ligands. We synthesized a new Co(II) complex based on a hexapyridyl ligand that leads to the formation of an unusual heptacoordinate structure. In this paper, we review the characterization of the new catalyst and the optimization of the conditions for hydrogen evolution. The high activity reached after two hours of irradiation under visible light (475 nm) suggests that heptacoordinate cobalt complexes, not used so far in the field of light-driven hydrogen evolution, represent a promising alternative platform for the development of highly active and stable photocatalysts

Functional metathesis catalyst through ring closing enyne metathesis: one pot protocol for living heterotelechelic polymers

Enyne ring closing metathesis has been used to synthesize functional group carrying metathesis catalysts from a commercial (Ru-benzylidene) Grubbs’ catalysts. The new Grubbs-type ruthenium carbene was used to synthesize living heterotelechelic ROMP polymers without any intermediate purification. Olefin metathesis with a mono substituted alkyne followed by ring closing metathesis with an allylic ether provided efficient access to new functional group carrying metathesis catalysts. Different functional benzylidene and alkylidene derivatives have been investigated in the synthesis of heterotelechelic polymers in one pot

Heterotelechelic polymers by ring‐opening metathesis and regioselective chain transfer

Heterotelechelic polymers were synthesized by a kinetic telechelic ring-opening metathesis polymerization method relying on the regioselective cross-metathesis of the propagating Grubbs’ first-generation catalyst with cinnamyl alcohol derivatives. This procedure allowed the synthesis of hetero-bis-end-functional polymers in a one- pot setup. The molecular weight of the polymers could be controlled by varying the ratio between cinnamyl alcohol derivatives and monomer. The end functional groups can be changed using different aromatically substituted cinnamyl alcohol derivatives. Different monomers were investigated and the presence of the functional groups was shown by NMR spectroscopy and MALDI-ToF mass spectrometry. Labeling experiments with dyes were conducted to demonstrate the orthogonal addressability of both chain ends of the heterotelechelic polymers obtained

Synthesis of hydrophilic and hydrophobic carbon quantum dots from waste of wine fermentation

Wine lees are one of the main residues formed in vast quantities during the fermentation of wine. While toxic when applied to plants and wetlands, it is a biodegradable material, and several alternatives have been proposed for its valorization as: dietary supplement in animal feed, source for various yeast extracts and bioconversion feedstock. The implementation of stricter environment protection regulations resulted in increasing costs for wineries as their treatment process constitutes an unavoidable and expensive step in wine production. We propose here an alternative method to reduce waste and add value to wine production by exploiting this rich carbon source and use it as a raw material for producing carbon quantum dots (CQDs). A complete synthetic pathway is discussed, comprising the carbonization of the starting material, the screening of the most suitable solvent for the extraction of CQDs from the carbonized mass and their hydrophobic or hydrophilic functionalization. CQDs synthesized with the reported procedure show a bright blue emission (λmax = 433 ± 13 nm) when irradiated at 366 nm, which is strongly shifted when the wavelength is increased (e.g. emission at around 515 nm when excited at 460 nm). Yields and luminescent properties of CQDs, obtained with two different methods, namely microwave and ultrasound-based extraction, are discussed and compared. This study shows how easy a residue can be converted into an added- value material, thus not only reducing waste and saving costs for the wine- manufacturing industry but also providing a reliable, affordable and sustainable source for valuable materials

Synthesis, characterization and cellular location of cytotoxic constitutional organometallic isomers of rhenium delivered on a cyanocobalmin scaffold

Constitutional isomers of cyanocobalamin adducts based on a fluorescent rhenium tris-carbonyl diimine complex were prepared, characterized and tested against PC-3 cancer cells. The adducts differ only in the relative binding position of the organometallic species which is either bound at the cyano or the 5′-hydroxo group of vitamin B₁₂. When tested for their cytotoxic potency, the species showed IC₅₀ values in the low μM rage. Upon conjugation to the vitamin an energy transfer process causes an extremely low quantum yield of fluorescence emission, making the conjugates unsuitable for fluorescence imaging. However, by exploiting the vibrational signature of the fac-[Re(CO)₃]⁺ core, their cellular distribution was evaluated via FTIR spectromicroscopy

Correlation of MLCTs of Group 7 fac-[M(CO)3]+ complexes (M = Mn, Re) with bipyridine, pyridinylpyrazine, azopyridine, and pyridin-2-ylmethanimine type ligands for rational photoCORM design

A mathematical correlation of the MLCT absorption maxima of structurally related fac‐ [M(CO)3L2Br] complexes (M = Mn, Re; L2 = bidentate ligand) is obtained by the comparison of a total of 50 species bearing bipyridine, pyridinylpyrazine, azopyridine and pyridin‐2‐ylmethanimine L2 type ligands. The empirical relationship is first derived by the initial comparison of the MLCT absorption maxima of 26 previously published complexes and subsequently used to predict the same absorption value of 24 other species. In order to check the validity of the prediction, several new complexes were prepared. These were spectroscopically characterized and, where possible, their X‐ ray solid‐state structure elucidated. The initial mathematical correlation allowed to predict MLCT absorption maxima of the unknown species with an average discrepancy of 12 nm. The relationship was subsequently refined to an average error of 6 nm with following derived formula CalcMnmLCT = (ObsReMLCT/0.88) – 15.1 (where CalcMnmLCT = predicted values of Mn complexes MLCT and ObsReMLCT = experimentally observed MLCT transitions of Re complexes). The correlation and the formula, the significance of which are discussed, may prove useful in the long run for the rational design of Mn‐based photoCORMs starting from known data of widely investigated fac‐[Re(CO)3L2Br] complexes

Heptacoordinate Coii complex: a new architecture for photochemical hydrogen production

The first heptacoordinate cobalt catalyst for light-driven hydrogen production in water has been synthesized and characterized. Photochemical experiments using [Ru(bpy)₃]²⁺ as photosensitizer gave a turnover number (TON) of 16300 mol H₂ (mol  cat.)⁻¹ achieved in 2 hours of irradiation with visible (475 nm) light. This promising result provides a path forward in the development of new structures to improve the efficiency of the catalysis