Organic phosphorescence in Pt(II)-complexes linked to organic chromophores for blue-emitting organic light-emitting diodes

Recently, organic persistent room-temperature phosphorescence (OPRTP), entailing triplet-state emission from purely organic units instead of luminescent heavy metal complexes, has emerged as a promising alternative for the development of emitting materials in organic light-emitting diodes (OLEDs). For OPRTP-based devices to achieve acceptable performances, the low emission efficiency caused by weak spin-orbit coupling and high sensitivity to external environmental factors, such as temperature, moisture, and oxygen must be overcome. Herein, four-coordinate N-heterocyclic carbene Pt(II) complexes bearing carbazole (Cz) or naphthalene (Np) groups were assembled and found to exhibit exothermic triplet-triplet energy transfer (TTET) from the high triplet metal-to-ligand charge transfer (3MLCT) state (T1 = 2.97 eV) of the Pt core to the lower triplet states (T1 = 2.58–2.87 eV) of the tethered organic Cz and Np moieties. The presented design strategy enables the persistent organic phosphorescence of organic molecules under ambient conditions and triplet electroluminescence of the organic group via TTET in OLED applications. Organic persistent room-temperature phosphorescence is of interest for the development of emitting materials in organic light-emitting diodes, however, low emission efficiency needs to be overcome. Here, the authors design an N-heterocyclic carbene-based Pt(II) complex that possesses an organic carbazole unit, and demonstrate enhanced persistent 3LC emission under ambient conditions.