Phosphorescent Mesomorphic Dyads Based on Tetraacetylethane Complexes of Iridium(III)

Inherently dinuclear iridium(III) meso architectures accessed by cyclometalation of calix[4]arene-based bis(aryltriazoles)

Conventional cyclometalation of calix[4]arene bis(aryltriazoles) with iridium(III) chloride hydrate leads to unique meso architectures in which the Ir₂Cl₂ core is cross-bound by two (C^N)₂ ligands, which allows further replacement of the chloride bridges with ancillary ligands while maintaining the dinuclear structures of the complexes having independent or coupled iridium pairs.

Advanced Functional Luminescent Metallomesogens: The Key Role of the Metal Center

The use of liquid crystals for the fabrication of displays incorporated in technological devices (TVs, calculators, screens of eBook's, tablets, watches) demonstrates the relevance that these materials have had in our way of living. However, society evolves, and improved devices are looked for as we create a more efficient and safe technology. In this context, metallomesogens can behave as multifunctional materials because they can combine the fluidic state of the mesophases with properties such as photo and electroluminescence, which offers new exciting possibilities in the field of optoelectronics, energy, environment, and even biomedicine. Herein, it has been established the role of the molecular geometry induced by the metal center in metallomesogens to achieve the self-assembly required in the liquid-crystalline mesophase. Likewise, the effect of the coordination environment in metallomesogens has been further analyzed because of its importance to induce mesomorphism. The structural analysis has been combined with an in-depth discussion of the properties of these materials, including their current and potential future applications. This review will provide a solid background to stimulate the development of novel and attractive metallomesogens that allow designing improved optoelectronic and microelectronic components. Additionally, nanoscience and nanotechnology could be used as a tool to approach the design of nanosystems based on luminescent metallomesogens for use in bioimaging or drug delivery.

Synthesis of Metal–Curcumin Complex Compounds (M = Na⁺, Mg²⁺, Cu²⁺)

Curcumin complex compound, MLn (L = curcumin; M = Na+, Mg2+, Cu2+) has been synthesized from the reaction between curcumin and metal precursors (NaCl, MgSO4.7H2O, CuCl2.2H2O) in ethanol under reflux conditions. Synthesis takes place through the reaction between the metal ions Na+, Mg2+, or Cu2+ as the central atom and curcumin as the ligand. Curcumin has been consumed after the reaction lasts for four hours, shown by thin-layer chromatography in which a new spot appears at higher Rf as the spot of curcumin disappears in the reaction mixture. Compared with the spectrum of  curcumin, the FTIR spectra of the complexes  show changes in the absorption bands and shifts of wave numbers particularly in absorption bands of phenolic –OH and C=O enol groups which strongly indicates the coordination of metal ions with the curcumin ligand which is proposed to be in β–1,3 diketone system. Also, the FTIR spectra of the reaction product showed typical absorption bands for the metal-oxygen group, M–O, at 524 cm–1, 670 cm–1 and 470 cm–1 in Na+–curcumin, Mg2+–curcumin and Cu2+–curcumin, respectively.

Dinuclear metal complexes: multifunctional properties and applications

Dinuclear metal complexes have enabled breakthroughs in OLEDs, photocatalytic water splitting and CO₂reduction, DSPEC, chemosensors, biosensors, PDT and smart materials.

Synthesis, Mesomorphism, and Photophysics of 2,5-Bis(dodecyloxyphenyl)pyridine Complexes of Platinum(IV)

It has been shown for the first time that the Pt^IV complex cis-[Pt(N^C-tolpy)₂ Cl₂ ] (tolpy=2-(4-tolyl)pyridinyl) can be prepared in a one-pot reaction from K₂ [PtCl₄ ], although analogous complexes containing 2,5-bis(4-dodecyloxyphenyl)pyridine (=HL) could be prepared using existing routes. The resulting complexes cis-[Pt(N^C-L)₂ Cl₂ ] are liquid crystals and small-angle X-ray scattering suggests formation of a lamellar mesophase. Surprisingly, heating [Pt(κ² -N^C-L)₂ Cl(κ¹ -N^C-LH)] also leads to a mesomorphic compound, which results from thermally induced oxidation to cis-[Pt(N^C-L)₂ Cl₂ ] and what is presumed to be another geometric isomer of the same formula. The Pt^IV complexes are quite strongly luminescent in deoxygenated solution, with φ≈10 % and show vibrationally structured emission spectra, λ_max (0,0)=532 nm, strongly displaced to the red compared to cis-[Pt(N^C-tolpy)Cl₂ ]. Long luminescence lifetimes of 230 μs are attributed to a lower degree of metal character in the excited state accompanying the extension of conjugation in the ligand. There is no significant difference between the emission properties of the bromo- and chloro-complexes, in contrast with the known complexes cis-[Pt(N^C-ppy)X₂ ], where the quantum yield for X=Br is some 30 times lower than for X=Cl (ppyH=2-phenylpyridine). The lower energy of the excited state in the new complexes probably ensures that deactivating LLCT/LMCT states remain thermally inaccessible, even when X=Br.

Sky-blue emitting bridged diiridium complexes: beneficial effects of intramolecular π-π stacking

The potential of intramolecular π-π interactions to influence the photophysical properties of diiridium complexes is an unexplored topic, and provides the motivation for the present study. A series of diarylhydrazide-bridged diiridium complexes functionalised with phenylpyridine (ppy)-based cyclometalating ligands is reported. It is shown by NMR studies in solution and single crystal X-ray analysis that intramolecular π-π interactions between the bridging and cyclometalating ligands rigidify the complexes leading to high luminescence quantum efficiencies in solution and in doped films. Fluorine substituents on the phenyl rings of the bridge promote the intramolecular π-π interactions. Notably, these non-covalent interactions are harnessed in the rational design and synthesis of the first examples of highly emissive sky-blue diiridium complexes featuring conjugated bridging ligands, for which they play a vital role in the structural and photophysical properties. Experimental results are supported by computational studies.

Highly luminescent 2-phenylpyridine-free diiridium complexes with bulky 1,2-diarylimidazole cyclometalating ligands

While a number of highly emissive dinuclear Ir(iii) complexes have been reported, they have generally been restricted to structures based on 2-phenylpyridine (Hppy) cyclometalates.

Mesomorphism and Photophysics of Some Metallomesogens Based on Hexasubstituted 2,2':6', 2''-Terpyridines

The luminescent and mesomorphic properties of a series of metal complexes based on hexacatenar 2,2':6',2''-terpyridines are investigated using experimental methods and density functional theory (DFT). Two types of ligand are examined, namely 5,5''-di(3,4,5-trialkoxyphenyl)terpyridine with or without a fused cyclopentene ring on each pyridine and their complexes were prepared with the following transition metals: Zn(II) , Co(III) , Rh(III) , Ir(III) , Eu(III) and Dy(III) . The exact geometry of some of these complexes was determined by single X-ray diffraction. All complexes with long alkyl chains were found to be liquid crystalline, which property was induced on complexation. The liquid-crystalline behaviour of the complexes was studied by polarising optical microscopy and small-angle X-ray diffraction. Some of the transition metal complexes (for example, those with Zn(II) and Ir(III) ) are luminescent in solution, the solid state and the mesophase; their photophysical properties were studied both experimentally and using DFT methods (M06-2X and B3LYP).

From Mononuclear to Dinuclear Iridium(III) Complex: Effective Tuning of the Optoelectronic Characteristics for Organic Light-Emitting Diodes

Phosphorescent dinuclear iridium(III) complexes that can show high luminescent efficiencies and good electroluminescent abilities are very rare. In this paper, highly phosphorescent 2-phenylpyrimidine-based dinuclear iridium(III) complexes have been synthesized and fully characterized. Significant differences of the photophysical and electrochemical properties between the mono- and dinuclear complexes are observed. The theoretical calculation results show that the dinuclear complexes adopt a unique molecular orbital spatial distribution pattern, which plays the key role of determining their photophysical and electrochemical properties. More importantly, the solution-processed organic light-emitting diode (OLED) based on the new dinuclear iridium(III) complex achieves a peak external quantum efficiency (η(ext)) of 14.4%, which is the highest η(ext) for OLEDs using dinuclear iridium(III) complexes as emitters. Besides, the efficiencies of the OLED based on the dinuclear iridium(III) complex are much higher that those of the OLED based on the corresponding mononuclear iridium(III) complex.

Ir(iii) complexes designed for light-emitting devices: beyond the luminescence color array

This Perspective highlights the photophysics and recent breakthroughs in the study of emissive Ir(iii) compounds, including a personal account elucidating the role of molecular and electronic structures in controlling the photophysics of heteroleptic [Ir(N^C)₂(L^X)]⁺ complexes.

The potential of the F127-water soft system towards selective solubilisation of iridium(III) octahedral complexes

In order to obtain new functional soft systems for use as templating agents for the construction of functional mesostructured materials, the dynamic ordered soft systems formed by a hydrophilic ionic iridium(III) complex (IrPa) embedded into two different concentration F127-water mixtures have been investigated. To this aim, combined spectral and time-resolved photophysical techniques and rheological methods have been employed. The position of the chromophore inside the micellar, cubic and hexagonal phases of the F127 polymeric neutral surfactant in water was effectively determined. The hydrophilic character of the iridium(III) complex chosen allowed preferential functionalization of the F127 corona in the micellar and cubic phases.

Silver-pyrazole complexes as hybrid multifunctional materials with metallomesogenic and photoluminescent behaviour

New pyridine-functionalised pyrazole compounds [Hpz(R(n)py)] (R(n) = C(6)H(4)OC(n)H(2n+1); n = 12, 14, 16, 18; 1-4) and their corresponding silver complexes [Ag(Hpz(R(n)py))(2)][A] ([A] = NO(3)(-), BF(4)(-); ) have been synthesised and characterised. All of them, with the exception of 1, are liquid crystal materials exhibiting monotropic or enantiotropic SmA mesophases, in contrast to the non-mesomorphic related R(n)-monosubstituted compounds. Because the molecular shape is a factor determinant in the organisation of molecules in the liquid crystal phase, we were interested in solving the crystal structure of representative examples of the mentioned compounds, such as 1 and 6. So, the X-ray crystal structure of [Hpz(R(12)py)] 1 shows the presence of dimeric units through N-H···N hydrogen bonds, which conform to an elongated molecular shape containing a double chain length. On the other hand, the structure of [Ag(Hpz(R(14)py))(2)][NO(3)] 6 also evidenced Ag-Ag bonded dimers from 'U'-shaped cationic entities. These dimers exhibit four chains, two by two alternated, so giving rise to a longer molecular length. Of particular interest was to observe that in both structures, the dimers are layer-like packed, their lamellar structures being related to that of the mesophases found in both kinds of compounds. Furthermore, the analysis of the optical data of the compounds 2 and 4 and the silver compounds 5, 6, 9 and 10 as representative examples pointed out their luminescent behaviour as well as their good ability to act as fluorescent probes for Zn(2+), Cu(2+) and Ag(+). An increase in the fluorescence quantum yields is observed in the final complexes produced in the titrations, this fact being specially notable when 9 was used as the starting compound.

A highly selective and non-reaction based chemosensor for the detection of Hg2+ ions using a luminescent iridium(III) complex

We report herein a novel luminescent iridium(III) complex with two hydrophobic carbon chains as a non-reaction based chemosensor for the detection of Hg(2+) ions in aqueous solution (<0.002% of organic solvent attributed to the probe solution). Upon the addition of Hg(2+) ions, the emission intensity of the complex was significantly enhanced and this change could be monitored by the naked eye under UV irradiation. The iridium(III) complex shows high specificity for Hg(2+) ions over eighteen other cations. The system is capable of detecting micromolar levels of Hg(2+) ions, which is within the range of many chemical systems.