Novel heteroleptic cyclometalated platinum(ii) complexes consisting of 5'-benzoylated 2-phenylpyridinate (ppy) cyclometalated and acetylacetonate ancillary ligands were synthesized, and their photoluminescence (PL) properties were investigated. The 5'-benzoylated complex without any other substituents exhibited phosphorescence-based monomer emission at 479 nm in dichloromethane (10 μM, rt) with a PL quantum yield of 0.28. On the other hand, in poly(methyl methacrylate) (PMMA) film, remarkable excimer emission additionally emerged at ca. 600 nm with a relatively high PL quantum yield of 0.47 as the doping level increased to 0.20 mmmol g, which was comparably intense in comparison with the monomer emission. In the case of the complexes with unsubstituted, 4'-benzoylated, and 5'-fluorinated ppy cyclometalated ligands, excimer emission was modestly generated at the same doping level, and thus the introduction of a benzoyl group to the 5'-position is effective to obtain remarkable excimer emission. The combination of benzoyl and fluoro groups was more effective at inducing excimer emission, and the intensity of excimer emission of the 2-(5-benzoyl-4,6-difluorophenyl)pyridinate-based complex was 3.5 times larger than that of monomer emission at a doping level of 0.20 mmmol g in PMMA. From the analysis of PL lifetimes at varying concentrations, photokinetic profiles were fully analyzed according to the model system for the irreversible excimer formation, and the excimer formation rate constant of the 5'-benzoylated complex was determined in dichloromethane as 2.2 × 10 M s, which is 4.4 times larger than that of the unsubstituted complex. We also fabricated an organic light-emitting diode using the 2-(5-benzoyl-4,6-difluorophenyl)pyridinate-based complex as a single emitter. The device exhibited pseudo-white EL with the Commission internationale de l'éclairage chromaticity coordinates of (0.42, 0.42).
Synthesized solution processable green fluorescent donor–acceptor dyads and their investigated photophysical, electrochemical, and morphological properties for OLED applications.
Doped transport layers are essential for achieving high efficiency in organic light emitting diodes (OLEDs). We have studied the effect of doping the electron transport layer (ETL), tris-(8-hydroxyquinoline) aluminum (Alq3) with different percentages of lithium fluoride (LiF). We have also studied the effect of different electron blocking layers (EBLs) such as Tris (4-carbazoyl-9-ylphenyl)amine (TCTA), N,N'-Bis (naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine(NPB), and Di-[4-(N,N-di-p-tolyl-amino)-phenyl]cyclohexane (TAPC) in an Alq3:2,3,6,7-Tetrahydro-1,1,7,7,-tetramethyl-1H, 5H, 11H −10-(2-benzothiazolyl)quinolizino[9,9a, 1gh] coumarin (C545T) based organic light emitting diode (OLED) with optimized ETL doping. TCTA was found to effectively block the electrons and influence the recombination region in the process. At a brightness of 1000 cd/m2, an improvement of 27.8% was observed in external quantum efficiency (EQE) for the device with TCTA as the EBL and doped Alq3 as the ETL, compared to the one with just NPB as both EBL and HTL.
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