Sterically Hindered Luminescent Pt-II-Phosphite Complexes for Electroluminescent Devices

PtII complexes with one bulky, sterically demanding, tertiary phosphite ancillary ligand and a coordinating chromophore are herein presented. The phosphite ligand, tris(2,4-di-tert-butylphenyl) acts as a bidentate ligand coordinating the platinum ion through the central phosphorus atom and a cyclometalating carbon atom of one of the substituents. The two free phenoxy moieties lie above and below the coordination plane, leading to steric hindrance that avoids aggregation and provides solubility in organic solvents. The other two coordination sites on the central metal ion are occupied by a chromophoric ligand, which is responsible for the energy of the luminescent excited state. This separation of functions, on the two coordinated ligands, allows the use of a wider range of luminophores with good luminescent properties, maintaining the control of the intermolecular interactions with the non-chromophoric ligand. Based on this approach we were able to achieve a bright deep blue emission (λ= 444 nm, Φem=0.38) from a complex with a tailored ligand, which was then used for the fabrication of an electroluminescent device. In addition commercially available luminophores were also employed to synthesize green emitters.