Ir(III) Cyclometalated Complexes Containing Phenylphenanthridine Ligands with Different Substitutions: Effects on the Electrochemiluminescence Properties.

A family of neutral bis-cyclometalated Ir(III) complexes based on phenanthridine (phent) derivates as cyclometalating ligands and picolinate as an ancillary ligand are described. The influence of extended conjugation, rigidity, and hydrophobicity as well as the electronic nature of the substituents were investigated in relation to the photoluminescence, PL, and electrochemiluminescence, ECL, properties. A significant increase of ECL in aqueous media is observed upon extension of the aromatic system or by substituting the phenyl with a dibenzofurane moiety, in compounds 2 and 3, respectively. Under real immunoassay conditions, these complexes achieve up to 4-fold higher ECL efficiency than the commercial ruthenium standard. These values, among the highest reported in the literature under these conditions, confirm the potential of iridium complexes as alternative labels in commercial instruments.

Luminescent dinuclear Cu(I) complexes containing rigid tetraphosphine ligands.

The synthesis and the photophysics of three dinuclear copper(I) complexes containing bis(bidentate)phosphine ligands are described. The steric constraint imposed by tetrakis(di(2-methoxyphenyl)phosphanyl)cyclobutane) (o-MeO-dppcb) in combination with 2,9-dimethyl-1,10-phenanthroline in one of the complexes leads to interesting photophysical properties. The compound shows an intense emission at room temperature in deoxygenated acetonitrile solution (Φ = 49%) and a long excited-state lifetime (13.8 µs). Interestingly, at low temperature, 77 K, the emission maximum shifts to lower energy, and the excited-state lifetime increases. This observation leads to the conclusion that a mixing between the excited triplet and singlet states is possible and that the degree of mixing and population of state strongly depends on temperature, as the energy difference is quite small. The electroluminescent properties of this compound were therefore tested in light-emitting electrochemical cells (LEECs), proving that the bright emission can also be obtained by electrically driven population of the singlet state.

Redox control of molecular motions in bipyridinium appended calixarenes.

A series of redox-responsive architectures featuring two bipyridinium units introduced onto the lower rim of a calixarene skeleton has been synthesized. The redox-triggered intramolecular dimerization of the reduced bipyridiniums has been investigated by electrochemistry, spectroelectrochemistry and by theoretical chemistry. The spectroscopic signature of the intramolecular dimers was found to evolve significantly with the size of the alkyl linker introduced between the calixarene skeleton and the bipyridinium units. On account of experimental data supported by theoretical calculations, these differences have been attributed to the extent of the orbital overlap in the π-dimerized species, involving either four or only two of the pyridine rings of the bipyridinium radical cations stacked in eclipsed or staggered conformations, respectively.

Redox control of rotary motions in ferrocene-based elemental ball bearings.

Rotational motions of ferrocene-based carousels have been achieved by electron transfer centered on π-dimerizable 4,4'-bipyridinium substituents introduced on both cyclopentadienyl rings through covalent linkers of different size, geometry, and flexibility. Detailed spectroscopic, electrochemical, and theoretical analyses demonstrate that rigid and fully conjugated linkers allow the quantitative formation of intramolecular π-dimers resulting from optimized orbital overlaps within the HOMO of the electrochemically generated bis-radical species. The tetra-cationic "charge-repelled" conformers, the self-assembled π-dimers, and their electron triggered interconversions have been investigated by UV-vis, NMR, and ESR spectroscopy, electrochemistry, X-ray diffraction analysis, and theoretical calculations. These studies support the conclusion that the rotation of both cyclopentadienyl rings in ferrocene can be controlled electrochemically using noncovalent reversible interactions arising from π-radical coupling processes.

Redox-responsive porphyrin-based molecular tweezers.

Pinching pacman! Switching between the "open" and "closed" arrangements of pacman-like bisporphyrin architectures can be achieved by redox control of noncovalent interactions (see figure). The open/close molecular motion, triggered by reduction of π-dimerizable bipyridinium units, has been shown to allow the complexation of a bidentate ligand pinched between both metalloporphyrins.

Electrochemical synthesis of a thiophene-containing cyclo[9]pyrrole.

A new member of the cyclo[n]pyrrole class of expanded porphyrins could be prepared from the corresponding thiophene-containing terpyrrole precursor through use of a mild electrochemical oxidative procedure. The isolated macrocycle, featuring nine heterocyclic subunits directly connected through their α,α'-positions, is the largest cyclo[n]pyrrole derivative reported to date (see figure).

Electrochemical syntheses of cyclo[n]pyrrole.

Cyclo[8]pyrrole was obtained efficiently when 3,3',4,4'-tetraethylbipyrrole was subjected to bulk electrolysis, with yields spanning a range from close to 0 % with tetra-n-butylammonium fluoride as the electrolyte, to almost 70 % when tetra-n-butylammonium hydrogensulfate was used for this purpose. These observations are consistent with the conclusion that the reaction is controlled by anion-related factors such as a specific templating effect. Note that cyclo[8]pyrrole was the only detectable macrocyclic product obtained from 3,3',4,4'-tetraethylbipyrrole under the conditions of the electrochemical oxidation. When similar electrolyses were performed by using 3,4-diethylpyrrole as the starting material, two products could be isolated, which were identified as being the cyclo[7]pyrrole and cyclo[8]pyrrole, respectively. Detailed analyses of the oxidized forms of cyclo[7]pyrrole and cyclo[8]pyrrole revealed that under the conditions of the electrolysis these latter species are not stable.

Electrochemically driven intramolecular ring closure of a linear hexapyrrole.

[24]hexaphyrin(1.0.1.0.0.0) was electrochemically synthesized in good yield starting from a linear hexapyrrolic precursor. This straightforward approach provides an efficient "green" alternative to the reported chemical synthesis, which requires the use of trifluoroacetic acid as the solvent and toxic chromium(VI) salts as the oxidant.

Perylene-Based All-Organic Redox Battery with Excellent Cycling Stability.

Organic materials derived from biomass can constitute a viable option as replacements for inorganic materials in lithium-ion battery electrodes owing to their low production costs, recyclability, and structural diversity. Among them, conjugated carbonyls have become the most promising type of organic electrode material as they present high theoretical capacity, fast reaction kinetics, and quasi-infinite structural diversity. In this letter, we report a new perylene-based all-organic redox battery comprising two aromatic conjugated carbonyl electrode materials, the prelithiated tetra-lithium perylene-3,4,9,10-tetracarboxylate (PTCLi6) as negative electrode material and the poly(N-n-hexyl-3,4,9,10-perylene tetracarboxylic)imide (PTCI) as positive electrode material. The resulting battery shows promising long-term cycling stability up to 200 cycles. In view of the enhanced cycling performances, the two organic materials studied herein are proposed as suitable candidates for the development of new all-organic lithium-ion batteries.

Bidentate NHC

A bidentate C^N donor set derived from an N-heterocyclic carbene (NHC) precursor linked to a trifluoromethyl (CF3) functionalized pyrazole ring is described for the first time. The ligands have been employed to prepare four new phosphorescent complexes by the coordination of platinum(II) centres bearing cyclometalated phenyl-pyridine/triazole-pyridine chelates. The electronic and steric environments of these complexes were tuned through the incorporation of suitable substituents in the phenyl-pyridine/triazole-pyridine ligands, wherein the position of the phenyl-ring substituent (a CF3 group) also directs the selective adoption of either a trans or a cis configuration between the C(NHC) and the C(phenyl) donor atoms. Molecular structures obtained by X-ray diffraction for three of the complexes confirm a distorted square-planar configuration around the platinum centre, and DFT calculations show that the substituents have a significant influence on the energies of the frontier orbitals. Moreover, a platinum(II) complex featuring the new bidentate NHC^pyrazolate ligand and a bulky adamantyl functionalized pyridine-triazole luminophore was observed to be highly emissive and exhibiting a sky-blue luminescence (λ(Em) = 470 nm) with photoluminescence quantum yields as high as 50% in doped PMMA matrices. A complete photophysical investigation of all of the complexes in solution as well as in the solid state is herein reported.