Synthesis, Mesomorphism, Photophysics, and Device Properties of Liquid-Crystalline Pincer Complexes of Gold(III) Containing Semiperfluorinated Chains.

Gold(III) complexes of C∧N∧C-coordinating 2,6-diphenylpyridine pincer ligands with arylacetylide co-ligands are known triplet emitters at room temperature. We have reported previously that by functionalizing both the pincer ligand and the phenylacetylene with alkoxy chains, liquid crystallinity may be induced, with the complexes showing columnar mesophases. We now report new derivatives in which the phenylacetylene incorporates one, two, or three 1H,1H,2H,2H-perfluoroalkyl chains. In terms of intermolecular interactions, solution 1H NMR experiments suggest that the semiperfluoroalkyl chains promote a parallel, head-to-head arrangement of neighboring molecules relative to one another, rather than the anti-parallel, head-to-tail orientation found for the all-hydrocarbon materials. In terms of the liquid crystal properties, the complexes show columnar phases, with the addition of the more rigid fluorocarbon chains leading to a stabilization of both the crystal and liquid crystal mesophases. Mesophase temperature ranges were also wider. Interestingly, the amphiphilic nature of these complexes is evident through the observation of a frustrated columnar nematic phase between a Colr and a Colh phase, an observation recently reported in detail for one compound (Liq. Cryst., 2022, doi: 10.1080/02678292.2021.1991017). While calculation shows that, despite the "electronic insulation" provided by the dimethylene spacer group in the semiperfluoroalkyl chains, a small hypsochromic shift in one component of the absorption band is anticipated, experimentally this effect is not observed in the overall absorption envelope. Complexes with substituents in the 3,3',4,4'-positions of the phenyl rings of the pincer ligand once more show higher-luminescence quantum yields than the analogues with substituents in the 4,4'-positions only, associated with the lower-energy-emissive state in the former. However, in contrast to the observations with all-hydrocarbon analogues, the luminescence quantum yield of the complexes with 3,3',4,4'-substitution on the pincer increases as the number of semiperfluoroalkyl chains on the phenylacetylide increases, from 20% (one chain) to 34% (three chains). External quantum efficiencies in fabricated OLED devices are, however, low, attributed to the poor dispersion in the host materials on account of the fluorinated chains.

Unprecedented reductive cyclisation of salophen ligands to tetrahydroquinoxalines during metal complex formation.

The synthesis of novel tetrahydroquinoxalines by a metal induced one-electron reductive cyclisation of salophen ligands was found to occur when a salophen ligand was treated with chromium(ii) chloride or decamethylcobaltocene.

Probing the Hydrogenation of Vinyl Sulfoxides Using para-Hydrogen.

Vinyl sulfoxides are an important functional group used in a wide range of organic transformations. Here, we use [IrCl(COD)(IMes)] where IMes = 1,3-bis(2,4,6-trimethyl-phenyl)imidazole-2-ylidene and COD = cis,cis-1,5-cyclooctadiene to rapidly hydrogenate phenylvinylsulfoxide. We use para-hydrogen-induced hyperpolarization (PHIP) to follow this reaction with [IrCl(H)2(IMes)(S(O)(Ph)(Et))2] dominating in the later stages. Decomposition to form the reduced C-S bond cleavage product [Ir2(H)3(κ2-H)(κ2-SPh)2(IMes)2(S(Et)(Ph)O)] limits turnover. The related product [Ir2(H)4(κ2-S)(IMes)2(S(O)(CH2Ph)2)2] is formed from dibenzylsulfoxide, demonstrating the wider utility of this transformation.

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

It has been shown for the first time that the PtIV 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 PtIV complexes are quite strongly luminescent in deoxygenated solution, with φ≈10 % and show vibrationally structured emission spectra, λmax (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.

1,2,4-Triazolium ions as flexible scaffolds for the construction of polyphilic ionic liquid crystals.

A novel scaffold for the construction of self-organised ionic liquids and ionic liquid crystals bearing both perfluorocarbon and hydrocarbon moieties has been developed. The phase behaviour and physical properties of these materials can be tuned as a function of chain length and fluorine content and significant structural elaboration is possible, giving a highly flexible system.