New platinum(II) complexes as triplet emitters for high-efficiency monochromatic pure orange electroluminescent devices

New multi-component orange phosphorescent platinum complexes [Pt(L)(acac)] (Hacac = acetylacetone, HL = (9,9-diethyl-7-pyridin-2-ylfluoren-2-yl)diphenylamine 1, (9,9-diethyl-7-pyridin-2-ylfluoren-2-yl)di(p-tolyl)amine 2) were prepared and characterized by spectroscopic and X-ray crystallographic methods. We report the redox and photophysical properties of 1 and 2 and compare these results with the unsubstituted analogue [Pt(L)(acac)] (HL = 9,9-diethyl-2-pyridin-2-ylfluorene 3). Efficient pure orange-emitting organic light-emitting devices (OLEDs) based on 1 were fabricated. The device performance with 3,5-dicarbazolylbenzene (mCP) as the host can furnish maximium external quantum, current and power efficiencies of 4.65%, 11.75 cd/A and 5.27 lm/W at 7 V, respectively. The device with 4,4′-N,N′-dicarbazolebiphenyl (CBP) as the host can perform better with peak external quantum and current efficiencies of 6.64% and 15.41 cd/A at 7.5 V and a power efficiency of 7.07 lm/W at 6.5 V. Unlike the OLEDs made from other cyclometalated Pt(β-diketonato) complexes in which the electroluminescence spectra generally displayed both the monomeric and excimeric emissions with different relative intensities upon variation of dopant concentration, our devices emit a strong pure orange light with stable CIE color coordinates. From a steric point of view, no evidence of low-energy aggregate emission is observed for a doping level up to 12 wt.%. The present work confers a good platform for the realization of robust triplet emitters in the fabrication of highly efficient monochromatic OLEDs through the design of multifunctional chelating ligands.