Game of Crowns: Na⁺ Is Coming! Red NIR-Emissive Hybrid Liquid Crystals Containing Discotic Crown Ethers and Na₂Mo₆X₈ ⁱCl₆ (Xⁱ = Cl or Br)

Molecular or supramolecular materials that can self-organizeintocolumns such as discotic liquid crystals are of interest for severalapplications in the field of optoelectronics. We show in this workthat red near-infrared (NIR)-emissive metal cluster compounds of generalformula Na2Mo6X8 Cl-i(6) (X-i = Cl or Br) can be readily complexed withdiscotic liquid crystals containing a crown ether. Three cavity sizeshave been tested with crown ethers bearing 4, 5, or 6 oxygen atoms.In all cases, 1:1 complexes were formed, thanks to the well-knownsupramolecular interactions existing between the Na+ cationsof the metal cluster salt and the crown ether derivatives. All obtainedhybrids are homogeneous, emit in the red NIR region, and show liquidcrystalline properties on a wider temperature range than their precursors.Charge transport properties have been investigated by using a spacecharge limited current device. Obtained results demonstrate that metalcluster compounds can enhance the charge carrier mobility by 5 ordersof magnitude compared to the native discotic organic ligands. Consideringthat the presented organic crown ether derivatives are not the bestcandidates to design optoelectronic devices because of their inherentlylow conductivity, but that similar compounds were developed to designproton conductive porous framework, our results open promising perspectivesfor the use of metal cluster compounds in devices dedicated to sucha field.