Reversible Copper(II)/(I) Electrochemical Potential Switching Driven by Visible Light-Induced Coordinated Ring Rotation

Photoactive Copper Complexes: Properties and Applications

Photocatalyzed and photosensitized chemical processes have seen growing interest recently and have become among the most active areas of chemical research, notably due to their applications in fields such as medicine, chemical synthesis, material science or environmental chemistry. Among all homogeneous catalytic systems reported to date, photoactive copper(I) complexes have been shown to be especially attractive, not only as alternative to noble metal complexes, and have been extensively studied and utilized recently. They are at the core of this review article which is divided into two main sections. The first one focuses on an exhaustive and comprehensive overview of the structural, photophysical and electrochemical properties of mononuclear copper(I) complexes, typical examples highlighting the most critical structural parameters and their impact on the properties being presented to enlighten future design of photoactive copper(I) complexes. The second section is devoted to their main areas of application (photoredox catalysis of organic reactions and polymerization, hydrogen production, photoreduction of carbon dioxide and dye-sensitized solar cells), illustrating their progression from early systems to the current state-of-the-art and showcasing how some limitations of photoactive copper(I) complexes can be overcome with their high versatility.

Chemically Driven Rotatory Molecular Machines

Molecular machines are at the frontier of biology and chemistry. The ability to control molecular motion and emulating the movement of biological systems are major steps towards the development of responsive and adaptive materials. Amazing progress has been seen for the design of molecular machines including light-induced unidirectional rotation of overcrowded alkenes. However, the feasibility of inducing unidirectional rotation about a single bond as a result of chemical conversion has been a challenging task. In this Review, an overview of approaches towards the design, synthesis, and dynamic properties of different classes of atropisomers which can undergo controlled switching or rotation under the influence of a chemical stimulus is presented. They are categorized as molecular switches, rotors, motors, and autonomous motors according to their type of response. Furthermore, we provide a future perspective and challenges focusing on building sophisticated molecular machines.

Wavelength-Dependent Bifunctional Plasmonic Photocatalysis in Au/Chalcopyrite Hybrid Nanostructures

Excited, or "hot" charge carrier generation and transfer driven by the decay of localized surface plasmon resonances (LSPRs) are key steps in plasmonic photocatalysis. Hybrid structures that contain both metal and semiconductor building blocks facilitate the extraction of reactive charge carriers and their utilization for photoelectrocatalysis. Additional functionality arises from hybrid structures that combine noble metal nanostructures with semiconductor components, such as chalcopyrite (CuFeS₂) nanocrystals (NCs), which by themselves support quasistatic resonances. In this work, we use a hybrid membrane to integrate Au nanorods (NRs) with a longitudinal LSPR at 745 nm and CuFeS₂ NCs with a resonance peak at 490 nm into water-stable nanocomposites for robust and bifunctional photocatalysis of oxygen and hydrogen evolution reactions in a wavelength-dependent manner. Excitation of NRs or NCs in the nanocomposite correlates with increased hydrogen or oxygen evolution, respectively, consistent with a light-driven electron transfer between the metal and semiconductor building blocks, the direction of which depends on the wavelength. The bifunctional photoreactivity of the nanocomposite is enhanced by Cu(I)/Cu(II)-assisted catalysis on the surface of the NCs.

Conformationally dynamic copper coordination complexes

The interplay between oxidation state and coordination geometry dictates both kinetic and thermodynamic properties underlying electron transfer events in copper coordination complexes. An ability to stabilize both Cu^I and Cu^II oxidation states in a single conformationally dynamic chelating ligand allows access to controlled redox reactivity. We report an analysis of the conformational dynamics of Cu^I complexes bearing dipicolylaniline (dpa^R) ligands, with ortho-aniline substituents R = H and R = OMe. Variable temperature NMR spectroscopy and electrochemical experiments suggest that in solution at room temperature, an equilibrium exists between two conformers. Two metal-centered redox events are observed which, bolstered by structural information from single crystal X-ray diffraction and solution information from EPR and NMR spectroscopies, are ascribed to the Cu^II/I couple in planar and tetrahedral conformations. Activation and equilibrium parameters for these structural interconversions are presented and provide entry to leveraging redox-triggered conformational dynamics at Cu.

Novel axially-substituted silicon phthalocyanines with pH-modulated fluorescence ON/OFF switching properties

Two novel axially-substituted asymmetric silicon (IV) phthalocyanines, the first one substituted with both polyethylene glycol and indomethacin groups (Pc1) and second one substituted with both polyethylene glycol and mefenamic acid groups (Pc2) have been designed and synthesized for the purpose of pH sensing examinations. Their absorption and fluorescence emission-based spectral properties were investigated in chloroform, tetrahydrofuran and toluene. The pH-sensing properties of Pc1 and Pc2 were examined in detail by using UV-vis absorption and fluorescence spectroscopies in tetrahydrofuran. The effects of the substituents on the spectroscopic properties and pH-sensing behavior of these silicon phthalocyanines were revealed. Pc1 didn’t show a pH response; however, Pc2 exhibited a signal increase from pH 5.40 to 0.37 (turn on) and a drastic quenching when pH went from 0.37 to 5.40 (turn off). The protonation/deprotonation stage of the NH group of Pc2 presented fluorescence-based “on-off” type molecular switch properties.

Heterobimetallic copper(i) complexes bearing both 1,1′-bis(diphenylphosphino)ferrocene and functionalized 3-(2′-pyridyl)-1,2,4-triazole

Copper(i) 1,1′-bis(diphenylphosphino)ferrocene complexes are well regulated by functional 3-(2′-pyridyl)-1,2,4-triazole exhibiting mono-anionic η²(N1,N2) and neutral η²(N1,N2) and η²(N1,N4) chelating modes.

Water-soluble copper(i) complexes bearing 2,2′-bicinchoninic acid dipotassium salt with red-light absorption and repeatable colour change upon freezing operation

The repeatable colour change upon freezing–melting operation of a water solution of a Cu(i) complex is found. Efficient red light absorption is also one of the advantages of this complex.

Molecular rectifiers based on five-coordinate iron(iii)-containing surfactants

The state-of-the-art of metallorganic-based molecular rectification is reviewed with an emphasis on asymmetric five-coordinate Fe^III-containing surfactants in electrode|LB film|electrode assemblies.

Blue and orange oxygen responsive emissions in the solid state based on copper(i) complexes bearing dodecafluorinated diphosphine and 1,10-phenanthroline derivative ligands

The copper(i) complexes bearing dodecafluoronated diphosphine and diimine ligands show reversible oxygen sensing abilities in the solid state.

Supramolecular five-component nano-oscillator

A five-component self-sorted metallo-supramolecular nano-oscillator was designed based on the full orthogonality of three different dynamic complexation motifs.

Luminescent monometallic Cu(i) triphenylphosphine complexes based on methylated 5-trifluoromethyl-3-(2′-pyridyl)-1,2,4-triazole ligands

The photoluminescence properties of Cu(i) complexes can be markedly improved by the N–H deprotonation of the 1,2,4-triazolyl ring.

Synthesis of an optically switchable salicylaldimine substituted naphthopyran for selective and reversible Cu2+ recognition in aqueous solution

A light controlled reversible switch for copper ion was synthesized by substituting photochromic naphthopyran with a salicylaldimine moiety.

Highly emissive copper(i) complexes bearing diimine and bis(diphenylphosphinomethyl)-2,2-dimethyl-1,3-dioxolane

Highly emissive copper(i) complexes bearing 4,5-bis(diphenylphosphinomethyl)-2,2-dimethyl-1,3-dioxolane and 1,10-phenanthroline derivatives were newly synthesized. The quantum yields of the photoluminescence are up to 0.38.

A single-molecular twin rotor: correlated motion of two pyrimidine rings coordinated to copper

A single molecular twin rotor comprising a copper complex exhibits the correlation of the motions of two coordinated pyrimidine rings.

Long-lived and oxygen-responsive photoluminescence in the solid state of copper(i) complexes bearing fluorinated diphosphine and bipyridine ligands

Luminescence properties of a family of newly synthesized copper(i) complexes were investigated. The luminescence in the solid state is highly oxygen responsive.

From self-sorted coordination libraries to networking nanoswitches for catalysis

This feature article sketches our long way from the development of dynamic heteroleptic coordination motifs to the self-sorting of multi-component libraries and finally the design of a new family of triangular nanomechanical switches, which are useful for ON–OFF control of catalysis and in bidirectional communication.

Structural modification on copper(I)-pyridylpyrimidine complexes for modulation of rotational dynamics, redox properties, and phototriggered isomerization

The redox properties of copper pyridylpyrimidine complexes, which undergo linkage isomerism based on pyrimidine ring rotation, were compared under different coordination environments. A newly synthesized compound, [Cu(Mepypm)(L(Mes))]BF4 (1·BF4, Mepypm = 4-methyl-2-(2'-pyridyl)pyrimidine, L(Mes) = 2,9-dimesityl-1,10-phenanthroline) was compared with previously reported complexes of [Cu(MepmMepy)(L(Mes))]BF4 (2·BF4, MepmMepy = 4-methyl-2-(6'-methyl-2'-pyridyl)pyrimidine), Cu(Mepypm)(DPEphos)]BF4 (3·BF4, DPEphos = bis[2-(diphenylphosphino)phenyl]ether), [Cu(Mepypm)(L(Anth))]BF4 (4·BF4, L(Anth) = 2,9-bis(9-anthryl)-1,10-phenanthroline), and [Cu(Mepypm)(L(Macro))]BF4 (5·BF4). Isomer ratios, isomerization dynamics, redox properties, and photoelectron conversion functions varied with the coordination structure. Methyl substituents on the 6-position of the pyridine moiety increased steric repulsion and contributed to quicker rotation, enhanced photoluminescence, and increased photodriven rotational isomerization.

Coordination programming of photofunctional molecules

Our recent achievements relating to photofunctional molecules are addressed. Section 1 discloses a new concept of photoisomerization. Pyridylpyrimidine-copper complexes undergo a ring inversion that can be modulated by the redox state of the copper center. In combination with an intermolecular photoelectron transfer (PET) initiated by the metal-to-ligand charge transfer (MLCT) transition of the Cu(I) state, we realize photonic regulation of the ring inversion. Section 2 reports on the first examples of heteroleptic bis(dipyrrinato)zinc(II) complexes. Conventional homoleptic bis(dipyrrinato)zinc(II) complexes suffered from low fluorescence quantum yields, whereas the heteroleptic ones feature bright fluorescence even in polar solvents. Section 3 describes our new findings on Pechmann dye, which was first synthesized in 1882. New synthetic procedures for Pechmann dye using dimethyl bis(arylethynyl)fumarate as a starting material gives rise to its new structural isomer. We also demonstrate potentiality of a donor-acceptor-donor type of Pechmann dye in organic electronics.