Highly efficient platinum-based emitters for warm white light emitting diodes

Abstract

New cycloplatinated N-heterocyclic carbene (NHC) compounds with chelate diphosphines (P^P) as ancillary ligands, [Pt(R-C^C*)(P^P)]PF₆ (R-C = Naph, P^P = dppm 1A, dppe 2A, dppbz 3A; R = CO₂Et, P^P = dppm 1B, dppe 2B, dppbz 3B), have been prepared. Their photophysical properties have been extensively studied and supported by the time-dependent-density functional theory (TD-DFT). These compounds show a great thermal stability and a very efficient blue (CO₂Et-C^C*) or cyan (Naph^C*) emission in PMMA films (5 wt%), with photoluminescence quantum yield (PLQY) ranging from 53% to 95%. In the solid state, the emission of the Naph^C* derivatives becomes orange (1A, 2A) or white (3A, dual blue and yellow emission) due to the operating π–π intermolecular interactions. We have investigated the potential use of these materials for solid-state lighting (SSL) applications. OLEDs with different architectures containing mixtures of 1B and 3A in different ratios as dopants were fabricated. In addition, two-component white light remote phosphors were obtained by stacking different combinations of 1B or 3B as the blue emitter with [Pt(bzq)(CN)(CNXyl)] (R) (bzq = benzoquinolate, Xyl = 2,6-dimethylphenyl) as the red emitter using a 365 nm LED as pumping source. By changing the blue : red ratio, warm white light with optimal CRI and D_uv values and a great range of nominal CCT (4000–2000 K) was obtained.