Synthesis and Characterization of Iridium based Metal Complexes and their applications in OLED

Abstract

Organic light-emitting devices (OLEDs) are emerging from the stage of research curiosity to the levels of important commercial applications. They are gaining acceptance as a promising flat panel display technology in this new millennium. However, OLEDs require further research and development, in particularly high performance emitting materials and electrodes, and novel device architectures since LCDs have a higher efficiency and longer operational lifetimes at the moment. The most important part of OLED devices is the electroluminescence layer, for which polymer and small molecular weight metal chelates can be used. The small molecule based metal chelates are the appropriate candidates as they are processed by conventional vacuum deposition techniques. Small molecule based Ir metal complexes can be used in OLED devices as electron and hole transport layer. It can also be used an emissive layer because of their wide spectral response in the visible region. Two Iridium metal complexes [Ir(PBD)2(Thenoyltrifluoroacetylacetone)] and [Ir(PBD)2(2,2,6,6- tetramethyl 3,5-heptadione)] have been synthesized and characterized by different characterization technique (FT-IR, NMR, UV-visible and photoluminescence spectroscopy). Excitation and emission properties of both the materials are extensively studied. The excitation spectra of [Ir(PBD)2(Thenoyltrifluoroacetylacetone)] shows absorption peak at 370 nm due to -* transition from primary ligand and relatively weaker absorption peak at 433 nm due to metal to secondary ligand charge (1MLCT) transition. The excitation spectra of [Ir(PBD)2(2,2,6,6-tetramethyl 3,5-heptadione)] shows absorption peak at 362 nm due to -* transition from primary ligand and relatively weaker absorption peak at 441 nm due to metal to secondary ligand charge (1MLCT) transition. The range of 441-500 nm associated with both 3MLCT and 3-* transition. Both the complexes [Ir(PBD)2(Thenoyltrifluoroacetylacetone)] and [Ir(PBD)2(2,2,6,6-tetramethyl 3,5-heptadione)] shows emission peaks at 559 nm and 549 nm respectively. To investigate the electroluminescent properties of the complexes organic light emitting diode have been fabricated with the structure ITO/α-NPD/(30nm)/ Ir(PBD)2(Thenoyltrifluoroacetylacetone)(35nm)/BCP(6nm)/Alq3(28nm)/LiF(1nm).Electroluminescence spectra of the fabricated device show a broad electroluminescence peak at 565 nm. The current-voltage characteristic of the device shows turn on voltage about 9V. Therefore the present study provides a convenient way for colour tuning of the metal complexes by changing the secondary ligand