The mesomorphism is reported of a discotic complex of gold(III) that is amphiphilic on account of the presence of both hydrocarbon and fluorocarbon chains. The all-hydrocarbon analogue of the complex shows only a columnar hexagonal phase between the melting and clearing points, whereas this new, amphiphilic example shows a nematic phase between a columnar rectangular phase and a columnar hexagonal phase. The nature and formation of the nematic phase are discussed and it is proposed to be a columnar nematic formed as a result of frustration driven by the amphiphilic nature of the complex.

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The C^N^C ligand 2,6-bis(2,3-dialkoxyphenyl)pyridine forms dimercury and orthopalladated complexes, both of which may be transmetallated to gold(III) complexes; the gold complexes may also be formed directly in a Rh(III)-catalysed process,...

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 1 H ,1 H ,2 H ,2 H -perfluoroalkyl chains. In terms of intermolecular interactions, solution 1 H 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 Col r and a Col h 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.

Realizing both high efficiency and liquid crystallinity in one molecule remains a challenge in thermally activated delayed fluorescence (TADF) emission. Herein, two isomeric compoundsm-DPSAc-LC and p-DPSAc-LC with different connection positions between donor and acceptor moietieswere synthesized and characterized. Diphenylsulfone (DPS) was used as the acceptor, acridine (Ac) was used as the donor, and biphenyl derivatives (LC) were employed as the mesogenic group. Both compounds showed a smectic mesophase evidenced by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and temperature-dependent small-angle X-ray scattering (SAXS). The compound p-DPSAc-LC clearly exhibited thermally activated delayed fluorescence due to the much more distorted geometry, whereas m-DPSAc-LC showed simple fluorescence. Compared to the parent TADF molecules without appended mesogenic groups (DPS-Ac), these liquid-crystalline emitters possessed higher hole mobilities and improved device performance. The OLEDs fabricated via solution processing using the liquid-crystalline compound p-DPSAc showed a maximum external quantum efficiency of ∼15% and as such is the first example of a liquid-crystalline TADF material in an OLED device.