The bicyclic ditopic linker 2,2′-biselenophene-5,5′-dicarboxylic acid (H 2 SpSp), specifically designed for metal–organic framework (MOF) construction, has been synthesized in good yield and fully ...characterized. The corresponding zirconium MOF (Zr-MOF) Zr6O4(OH)4(SpSp)3.8Cl4.4 (1; where missing linkers are replaced by chloride anions as shown by X-ray fluorescence and elemental analysis) is isostructural with its bithiophene and bithiazole analogues. Starting from 1, an extension of the biselenophene-based Zr-MOF family has been successfully achieved, exploiting the structural analogy of the five-membered heterocycles selenophene, thiophene, and thiazole. Thus, three mixed-linker MOFs containing variable amounts of different bis(heterocyclic) dicarboxylic acids have been prepared and fully characterized: the two double-mixed Zr6O4(OH)4(SpSp)2.6(TpTp)1.3Cl4.2 (2; H2TpTp = 2,2′-bithiophene-5,5′-dicarboxylic acid) and Zr6O4(OH)4(SpSp)2(TzTz)1.8Cl4.4 (3; H2TzTz = 2,2′-bithiazole-5,5′-dicarboxylic acid) materials, as well as the triple-mixed Zr6O4(OH)4(SpSp)1.6(TpTp)1.2(TzTz)1.4Cl3.6 (4) compound. The four MOFs are luminescent under UV irradiation, exhibiting emission wavelengths falling in the blue-green visible region, as observed for their constitutive linkers. These materials open new horizons in the preparation of porous luminescent sensors or multicolor emitters for light-emitting diodes.
Overall water splitting represents one of the most promising approaches toward solar energy conversion and storage, which is, however, severely challenged by the four-electron/four-proton nature of ...the oxygen evolution reaction (OER). One option to overcome this issue is to replace OER with a more useful reaction, for simultaneous production of both hydrogen and chemicals of interest. For the purpose, in this paper a cheap, hydrothermally prepared Ti-doped nanostructured hematite photoanode was employed for the first time as highly stable, heterogeneous catalyst for the low bias, efficient and highly selective photoinduced oxidation of benzylamine to N-benzylidenebenzylamine, and for the simultaneous production of hydrogen in a double solvent/environment cell. A preliminary estimate indicates the possibility to obtain a ∼150 μmol h−1 H2 production, with the contemporary production of stoichiometric benzylidene N-benzylamine in a 5 × 5 cm2 area electrode. This study contributes to overcome the 40-year lasting issues limiting the use of hematite in industrial photoelectrochemical sunlight conversion and storage, due to poor performance of hematite and lack of economic value of oxygen production, providing solid evidence for the use of hematite in alternative oxidation reactions of industrial importance.
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•Photoinduced oxidation of benzylamine and simultaneous hydrogen evolution in a double solvent/environment cell.•Ti-doped nanostructured hematite photoanodes prepared by hydrothermal synthesis.•External bias as low as +0.6 V needed for complete photoelectrochemical process.•∼150 μmol h−1 H2 production rate and contemporary production of stoichiometric N-benzylidenebenzylamine in a 5 × 5 cm2 electrode.•The role of Ti doping thoroughly investigated by electrochemical impedance spectroscopy.
Because of its ability to form stable complexes with a wide variety of metal ions, cyclam (1,4,8,11-tetraazacyclotetradecane) is one of the most studied ligands in coordination chemistry. ...Functionalizing the cyclam unit with photoactive dendrons open a door to construct giant homo- and heteroleptic metal complexes that display interesting spectroscopic properties, particularly as far as luminescence is concerned. Light is a tool both to study metal coordination processes, and to act as input or output in order to achieve the desired function.
This paper reviews some results obtained with metal complexes of cyclam-based dendrimers capable of acting as: (i) sensor, (ii) logic gates, and (iii) molecular antennae.
Tetraphenylmethane appended with four pyridylpyridinium units works as a scaffold to self‐assemble four ruthenium porphyrins in a tetrahedral shape‐persistent giant architecture. The resulting ...supramolecular structure has been characterised in the solid state by X‐ray single crystal analysis and in solution by various techniques. Multinuclear NMR spectroscopy confirms the 1 : 4 stoichiometry with the formation of a highly symmetric structure. The self‐assembly process can be monitored by changes of the redox potentials, as well as by modifications in the visible absorption spectrum of the ruthenium porphyrin and by a complete quenching of both the bright fluorescence of the tetracationic scaffold and the weak phosphorescence of the ruthenium porphyrin. An ultrafast photoinduced electron transfer is responsible for this quenching process. The lifetime of the resulting charge separated state (800 ps) is about four times longer in the giant supramolecular structure compared to the model 1 : 1 complex formed by the ruthenium porphyrin and a single pyridylpyridinium unit. Electron delocalization over the tetrameric pyridinium structure is likely to be responsible for this effect.
Giant multichromophore: A tetrahedral shape‐persistent supramolecular structure has been fully characterised in the solid state (by X‐ray diffraction) and in solution (by NMR, electrochemical and photophysical analysis). Excitation of either the scaffold (blue in the image) or the peripheral ruthenium porphyrins results in an ultrafast photoinduced electron transfer from the ruthenium porphyrins to the scaffold.
A series of functionalized persulfurated benzene molecules were synthesized. Their photophysical properties and crystal structures were analyzed. All compounds are non-emitting in solution at room ...temperature, but in a sharp contrast, quantum yields can be very high (up to 100%) in the solid state at 298 K or in a rigid matrix at low temperatures. This is a consequence of a decrease of intramolecular rotations and motions, but conformational and rotamer issues along with substituent effects might also play a role. These compounds are among the rare examples of highly phosphorescent organic materials, due to a Crystallization Induced Phosphorescence or to an Aggregation Induced Phosphorescence. Compound 1 is among the most phosphorescent solid known to date. They thus represent an alternative to heavy metal ion-based triplet emitters in solid state.
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•A family of persulfurated molecular asterisks was synthesized and fully characterized.•They display very intense phosphorescence in the solid state and in a rigid matrix.•X-ray crystal structures were analyzed and compared to the emission properties.•Phosphorescent nanoparticles were obtained by a reprecipitation method.
The photosensitivity of metal complexes has been known for a long time. Early studies on ligand photosubstitution and photoredox decomposition reactions of metal complexes of simple inorganic ligands ...(e.g. NH
3, CN
−) have been followed by accurate investigations on the photophysical behavior (luminescence quantum yields and lifetimes) and on the use of metal complexes in bimolecular processes (energy and electron transfer). A large number of complexes, stable towards photodecomposition, but capable of undergoing excited state redox processes, have been used for interconverting light and chemical energy. More recently, combination of supramolecular chemistry and photochemistry has led to the design and construction of multicomponent systems capable of performing light induced functions. In this field, luminescent and/or photoredox reactive metal complexes are presently used as essential components for a bottom-up approach to the construction of molecular devices and machines. Examples of molecular devices for processing light signals and of molecular machines powered by light energy, based on coordination compounds, are illustrated.
The Front Cover shows a Dream Wedding! Bismuth and photoredox catalysis get married in this photoredox allylation reaction of aldehydes in aqueous solvent. The green reaction conditions (organic ...photoredox catalyst, available and not toxic metal, aqueous solvent) employed and the broad scope open new perspectives in the field of photoredox radical to polar cross over reactions. The profile of a well know Italian town on water is in the skyline. Where celebrate a better wedding? More information can be found in the Communication by G. Cozzi et al.
Pyrene‐based materials have gained considerable attention as stimuli‐responsive chemical sensors. We designed a polysulfurated arene system based on a tetra(phenylthio)pyrene core decorated with four ...carboxylic acid units. Three different regioisomers, ortho, meta and para were studied in organic and aqueous solution. These systems are soluble in water at pH≥8 due to the deprotonation of carboxylic acids. The addition of metal ions cannot only quench the fluorescence of the central pyrene core, but also control the formation of three‐dimensional nanoscopic objects in a dual mode function. Several divalent metal ions were tested and compared. Addition of ethylenediaminetetraacetic acid (EDTA) disassembles the non‐emissive supramolecular system and restores the initial fluorescence of the pyrene core.
Complexation power: Three novel regioisomers of a tetrasulfurated pyrene with four carboxylic acids (ortho, meta, para) were designed to complex divalent metal ions and to generate supramolecular polymers in aqueous solution. Depending on the presence of metal ions, the initial fluorescence of the pristine molecule is quenched, while generating supramolecular structures, leading to a dual mode sensor based on changes in aggregation and emission.
A new class of neutral cyclometalated iridium(III) complexes with enantiomerically pure C1‐symmetric phenol‐oxazolines (3 a,b) have been synthetized in high yields and fully characterized. Resolution ...of the corresponding ΔR and ΛR or ΔS and ΛS isomers was easily achieved by conventional flash chromatography. The corresponding Δ and Λ helicities have been confirmed by CD spectroscopy and X‐ray crystallography. Regarding the absorption and luminescence properties with unpolarized light, no significant difference between Δ and Λ isomers has been observed. A strong blue luminescence is observed for deaerated solutions of complexes 5 a and 5 b in CH3CN.
Phox and hounds: Δ and Λ isomers of IrIII complexes based on 2‐phenyl‐pyridyl (ppy) cyclometalating ligands and chiral phenol‐oxazoline ancillary ligands (see figure) are readily available through simple separation on an achiral stationary phase. Blue luminescence, combined with an excellent emission quantum yield (Φem=0.80), is recorded for complexes with F2ppy ligands.
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