The structural motif of platinum(II) complexes bearing cyclometalating N‐heterocyclic carbene ligands can be used to design deep‐blue phosphors for application in organic light‐emitting diodes. However, the photophysical properties of the resulting molecules are also highly dependent on the auxiliary ligand. These often allow molecular deformations in the excited state which contribute to non‐radiative decay processes that diminish the attainable quantum yield. The use of bis(pyrazolyl)borate‐based auxiliary ligands enforces a high molecular rigidity due to their unique geometry. The steric crowding in the coordination sphere inhibits deformation processes and results in highly efficient deep‐blue platinum(II) emitters with CIE coordinates below (0.15; 0.15).

We present the synthesis and characterization of six novel bidentate C∧normalC* cyclometalated platinum(ii) complexes derived from saturated N‐heterocyclic carbene precursors, namely 1‐aryl‐3‐methyl‐1H‐4,5‐dihydroimidazolium salts. The title compounds were then synthesized by a multi‐step reaction, which includes an in situ generation of the silver carbene complex, followed by transmetalation to platinum and subsequent introduction of the β‐diketonate ligand. Structural characterization by NMR experiments and solid‐state structures prove the cyclometalation and the saturated backbone of the NHC motif. Photophysical and electrochemical properties of the platinum(ii) complexes were examined and studied in detail by DFT calculations. The title compounds are strongly emissive at room temperature in the sky‐blue region of the visible spectrum and show quantum yields of up to 71 % in a PMMA matrix.

Two novel bidentate C^C* spiro cyclometalated platinum(II) complexes comprising a spiro-conjugated bifluorene ligand and different β-diketonate auxiliary ligands are synthesized and characterized. Their preparation employs a robust and elaborate synthetic protocol commencing with an N-heterocyclic carbene precursor. Structural characterization by means of NMR techniques and solid-state structures validate the proposed and herein presented molecular scaffolds. Photophysical studies, including laser flash photolysis methods, reveal an almost exclusively ligand-centered triplet state, governed by the C^C* spiro −NHC ligand. The high triplet energies and the long triplet lifetimes in the order of 30 μs in solution make the complexes good candidates for light-emitting diode-driven photocatalysis, as initial energy transfer experiments reveal. In-depth time-dependent density functional theory investigations are in excellent accordance with our spectroscopic findings. The title compounds are highly emissive in the bluish-green color region with quantum yields of up to 87% in solid-state measurements.

The combination of strong electron-withdrawing groups in cyclometalated N-heterocyclic carbene ligands (C^C*) with known beneficial auxiliary ligands in phosphorescent platinum(II) complexes leads to efficient light-to-deep-blue emission with quantum yields of up to 92%. All compounds were characterized and investigated regarding their photophysical, electrochemical, and thermal properties, and three complexes could additionally be characterized by solid-state structures. Density functional theory calculations (PBE0/6-311G* with dispersion correction) are reported.

The synthesis of cyclometalated NHC platinum(II) complexes with two types of phosphorus-containing ligands is reported. Different synthetic approaches were utilized for each compound class. Dithiophosphinate and iminophosphonamide ligands form four-membered PtXPX metallacycles with coordination by either sulfur or nitrogen atoms (= X). The complexes are fully characterized, including two solid-state structures. Additionally, the photophysical and electrochemical properties were examined, and the results are rationalized by density functional theory calculations.