Homogeneous Systems Containing Earth‐Abundant Metal Complexes for Photoactivated CO₂ Reduction: Recent Advances

Photo-driven reduction of CO₂ into advantageous chemicals is a noteworthy pathway to close the carbon cycle and decrease carbon footprint. The use of visible light and ultimately solar radiation is extremely interesting in managing energy issues. Similarly, the employment of cost-effective materials guides to environmentally friendly applications. This Review addresses the homogeneous systems used for photoactivated the CO₂ reduction in the last years, highlighting the earth-abundant metal-based components. Besides those systems composed only of noble metal-free units, hybrid systems, also containing a noble metal-based complex, are also examined, revealing that research needs to increase the attention on more sustainable alternatives

Turning weak emitters into outstanding luminescent materials using rigid host media

The incorporation into rigid silica host structures leads successfully to a significant luminescence enhancement of two zinc(II) dipyrrins, known to be weak emitters in solution. One of these complexes shows a fluorescence efficiency of 55% and prolonged photo-stability once entrapped in silica, demonstrating high potential for applications in energy conversion

Reaching strong absorption up to 700 nm with new benzo[ g ]quinoxaline-based heteroleptic copper( i ) complexes for light-harvesting applications

Heteroleptic copper(I) complexes, with a diimine as a chromophoric unit and a bulky diphosphine as an ancillary ligand, have the advantage of a reduced pseudo Jahn–Teller effect in their excited state over the corresponding homoleptic bis(diimine) complexes. Nevertheless, their lowest absorption lies generally between 350 to 500 nm. Aiming at a strong absorption in the visible by stable heteroleptic Cu(I) complexes, we designed a novel diimine based on 4-(benzo[g]quinoxal-2′-yl)-1,2,3-triazole derivatives. The large π-conjugation of the benzoquinoxaline moiety shifted bathochromically the absorption with regard to other diimine-based Cu(I) complexes. Adding another Cu(I) core broadened the absorption and extended it to considerably longer wavelengths. Moreover, by fine-tuning the structure of the dichelating ligand, we achieved a panchromatic absorption up to 700 nm with a high molar extinction coefficient of 8000 M$^{-1}$ cm$^{-1}$ at maximum (λ = 570 nm), making this compound attractive for light-harvesting antennae

Mononuclear and dinuclear heteroleptic Cu(I) complexes based on pyridyl-triazole and DPEPhos with long-lived excited-state lifetimes

A mononuclear and two dinuclear heteroleptic Cu(I) complexes have been successfully prepared, using the chelating bis [(2-diphenylphosphino)phenyl] ether (DPEPhos) and pyrid-2'-yl-1H-1,2,3-triazole as chelating ligands. They show good luminescence in solution at room temperature with long-lived excited states. Furthermore, bimolecular quenching experiments of these new complexes with the catalyst Ni(cyclam)Cl-2 encourage the use of such compounds as photosensitizers for the photoreduction of carbon dioxide. (C) 2018 Elsevier B.V. All rights reserved.Peer reviewe

Intriguing Heteroleptic ZnII^{II} bis(dipyrrinato) Emitters in the Far-Red Region With Large Pseudo-Stokes Shift for Bioimaging

Novel heteroleptic ZnII bis(dipyrrinato) complexes were prepared as intriguing emitters. With our tailor-made design, we achieved far-red emissive complexes with a photoluminescence quantum yield up to 45% in dimethylsulfoxide and 70% in toluene. This means that heteroleptic Zn$^{II}$ bis(dipyrrinato) complexes retain very intense emission also in polar solvents, in contrast to their homoleptic counterparts, which we prepared for comparing the photophysical properties. It is evident from the absorption and excitation spectra that heteroleptic complexes present the characteristic features of both ligands: the plain dipyrrin (L$_{p}$) and the π-extended dipyrrin (L$_{π}$). On the contrary, the emission comes exclusively from the π-extended dipyrrin L$_{π}$, suggesting an interligand nonradiative transition that causes a large pseudo-Stokes shift (up to 4,600 cm$_{-1}$). The large pseudo-Stokes shifts and the emissive spectral region of these novel heteroleptic Zn$^{II}$ bis(dipyrrinato) complexes are of great interest for bioimaging applications. Thus, their high biocompatibiliy with four different cell lines make them appealing as new fluorophores for cell imaging

Synthesis and biological evaluation of anti-Toxoplasma gondii activity of a novel scaffold of thiazolidinone derivatives

We designed and synthesised novel N-substituted 1,3-thiazolidin-4-one derivatives for the evaluation of their anti-Toxoplasma gondii efficacy. This scaffold was functionalised both at the N1-hydrazine portion with three structurally different moieties and at the lactam nitrogen with substituted benzyl groups selected on the basis of our previous structure-activity relationships studies. Using three different assay methods, the compounds were assessed in vitro to determine both the levels of efficacy against the tachyzoites of T. gondii (IC50 = 5-148 μM), as well as any evidence of cytotoxicity towards human host cells (TD50 = 68 to ≥320 μM). Results revealed that ferrocene-based thiazolidinones can possess potent anti-tachyzoite activity (TI =2-64)

Cyan-Emitting Cu(I) Complexes and Their Luminescent Metallopolymers

Copper complexes have shown great versatility and a wide application range across the natural and life sciences, with a particular promise as organic light-emitting diodes. In this work, four novel heteroleptic Cu(I) complexes were designed in order to allow their integration in advanced materials such as metallopolymers. We herein present the synthesis and the electrochemical and photophysical characterisation of these Cu(I) complexes, in combination with ab initio calculations. The complexes present a bright cyan emission (λem ~ 505 nm) in their solid state, both as powder and as blends in a polymer matrix. The successful synthesis of metallopolymers embedding two of the novel complexes is shown. These copolymers were also found to be luminescent and their photophysical properties were compared to those of their polymer blends. The chemical nature of the polymer backbone contributes significantly to the photoluminescence quantum yield, paving a route for the strategic design of novel luminescent Cu(I)-based polymeric materials

New Photosensitizers Based on Heteroleptic CuI^{I} Complexes and CO2_{2} Photocatalytic Reduction with [NiII^{II}(cyclam)]Cl2_{2}

Earth‐abundant metal complexes have been attracting increasing attention in the field of photo(redox)catalysis. In this work, the synthesis and full characterisation of four new heteroleptic Cu$^{I}$ complexes are reported, which can work as photosensitizers. The complexes bear a bulky diphosphine (DPEPhos=bis[(2‐diphenylphosphino)phenyl] ether) and a diimine chelating ligand based on 1‐benzyl‐4‐(quinol‐2′yl)‐1,2,3‐triazole. Their absorption has a relative maximum in the visible‐light region, up to 450 nm. Thus, their use in photocatalytic systems for the reduction of CO$_{2}$ with blue light in combination with the known catalyst [Ni$^{II}$(cyclam)]Cl$_{2}$ was tested. This system produced CO as the main product through visible light (λ =420 nm) with a TON up to 8 after 4 hours. This value is in line with other photocatalytic systems using the same catalyst. Nevertheless, this system is entirely noble‐metal free

Versatile Heteroleptic Cu(I) Complexes Based on Quino(xa)-line-Triazole Ligands: from Visible-Light Absorption and Cooperativity to Luminescence and Photoredox Catalysis

Four new heteroleptic Cu(I) complexes based on 1, 2, 3-triazolyl-quinoline or quinoxaline and a chelating diphosphine were prepared and fully characterised. The mononuclear derivatives absorb in the visible region, up to 600 nm, while the dinuclear complex has a long-tail absorption up to 800 nm, showing an additional electronic state corroborated by theoretical calculations. Although a methylene group between the triazole and the quino(xa)line moiety increases the bite angle and decreases the luminescence in solution, all complexes emit brightly in the solid-state. Their redox properties in the excited state were determined, proving their ability in serving as photoredox catalysts in atom transfer radical addition successfully