Efficient near-infrared emitting tetradentate bis-cyclometalated platinum (IV) complexes for solution-processed polymer light-emitting diodes

Two novel tetradentate bis-cyclometalated platinum (IV) complexes of TPA-2q-PtCl2 and 3TPA-2q-PtCl2 with CˆN*NˆC cyclometalated ligands and two coordinated chlorine atoms were synthesized and characterized. The crystal structure of TPA-2q-PtCl2 shows a trans-form irregular octahedral geometry by measurement of single-crystal X-ray diffraction, where two CˆN coordination moieties are twisted and two chlorine atoms are located on both sides of platinum atom. A medium absorption band in a range of 450-474 nm is observed, which is assigned to the metal-to-ligand charge-transfer (MLCT) and intramolecular charge transfer (ILCT). And two obvious emission peaks at about 635 and 750 nm are displayed for both platinum (IV) complexes in 2-methyltetrahydrofuran solutions, which originate from the ILCT and MLCT characters to the lowest excited state. Using one of platinum (IV) complexes as a single dopant and a blend of poly(vinylcarbazole) as a host matrix, their single-emissive-layer polymer light-emitting diodes (PLEDs) exhibit an outstanding near-infrared emission with an electroluminescent (EL) peak of 750 nm. The better electroluminescent properties are obtained in the 3TPA-2q-PtCl2 doped devices with an external quantum efficiency of 0.85% and a radiance of 164 μW/cm−2. This is the first reported sample about tetradentate biscyclometalated platinum (IV) complexes used as organic NIR electroluminescent materials for promising application in PLEDs.

Graphical abstractTwo novel tetradentate bis-cyclometalated platinum (IV) complexes TPA-2q-PtCl2 and 3TPA-2q-PtCl2 were synthesized and characterized. Using one of both platinum (IV) complexes as a single dopant, the single-emissive-layer PLEDs exhibited outstanding near-infrared emission. Furthermore, better EL properties were obtained in the 3TPA-2q-PtCl2 doped devices with an EQE of 0.85% and a radiance of 164 μW/cm−2 with an emission peak at 750 nm.Download high-res image (215KB)Download full-size image