| Organic light emitting diodes (OLEDs) represent a highly interdisciplinary subject, where both basic scientific and technological challenges are combined for achieving better device performance and understanding electronic and optical properties of the materials used in these devices. Among current issues in organic LEDs, designing novel emitting and charge transporting materials is a subject of our investigation.; In order to utilize both singlet and triplet excited in the electroluminescence process, phosphorescence can be used. The study of the behavior of previously reported facial tris-cyclometalated iridium complexes in the OLEDs showed the great potential that this chemistry has for organic optoelectronics. We have synthesized two novel groups of phosphorescent iridium ortho -metalated complexes: heteroleptic C-N 2Ir(LX) and homoleptic meridianal mer-Ir(C-N )3 compounds, where C-N is a cyclometalated ligand. In the series of C-N 2Ir(LX) complexes, LX represents an ancillary, bidentate, monoanionic ligand (e.g. acetylacetonate). Absorption and emission spectroscopy study suggests that C-N2Ir(LX) complexes predominantly show either 3MLCT or 3(π-π*)-based lowest excited state depending on the C-N ligand structure. Strong spin-orbit coupling in these complexes allows for efficient emission in the spectral range between 510 and 610 nm. The LX ligand structure influences the emission efficiency dramatically. Emission quenching mechanisms are discussed as well. Both polymer and small-molecule OLEDs prepared with C-N2Ir(LX) phosphors exhibit high efficiency. Among platinum cyclometalated phosphors, we have studied homoleptic cis-Pt(C-N)2 and novel heteroleptic C-NPt(LX) complexes.; We have studied pentaarylcyclopentadienyl radicals (Cp5&phis; •, &phis; = aryl) as potential charge transporting materials in organic LEDs. Formation of Cp5&phis;• upon decomposition of its precursor PbCp5&phis;2 in the vacuum sublimation process has been investigated by energy dispersive, optical, and EPR spectroscopies. Unlike some protonated analogues (Cp5&phis;H), Cp5&phis; • radicals form uniform, amorphous films upon vacuum deposition from the lead precursors, as shown by scanning electron and atomic force microscopies. Preliminary OLED investigations show that the materials may serve as hole conductors. |
