| In chapter one, the concept of phosphorescence in organic light emitting systems is presented. New platinum (11) porphyrins with strong phosphorescence in the red have been synthesized. When they were doped into aluminum (111) tris (8-hydroxyquinolate) (AIQ3) in the electron transporting and emitting layer of an organic light emitting device, energy transfer occurred between the host AIQ3 and the Pt porphyrin. Bright, saturated red emission with high efficiency at low to moderate current density has been achieved. At high current densities, the electroluminescence efficiency decreased and the perceived emission color blue shifted as a result of mixed emission from the Pt porphyrin and AIQ3. This current dependence was due to the saturation of triplet emissive sites, because of the long-lived phosphorescence state of the Pt porphyrin complex.; In chapter two, the concept of phosphorescent dyes doped in phosphorescent hosts to address the saturation of triplet emissive sites is discussed. Several phosphorescent hosts have been synthesized. When the dye platinum (11) 2, 3, 12, 17-tetraethyl-3, 7, 13, 18-tetramethylporphyrin (PtOX) was doped into the host iridium (111) triphenylpyridine Ir (ppy)3, triplet-triplet energy transfer occurred. The performance and characteristics of the device with this Ire (ply) 3-PtOX system were compared to the previously studied AIQ3-PtOX system. Similar to the AIQ3-PtOX system, the amount of Ire (ppy) 3-host emission increases with increasing current density. Although the host Ire(ppy)3 is much longer lived phosphorescent material than the fluorescent AIQ3, it is still not long lived enough to reduce the saturation of PtOX emissive sites.; In chapter 3, the recent advances of photoinduced electron transfer and its application in artificial photosynthesis are overviewed. In our studies, a number of aromatic dithiols have been synthesized. Their electrochemical properties, monolayer and multiplayer growths have been investigated by a various techniques such as cyclic voltammetry, atomic force microscopy, UV spectroscopy and ellipsometry. Electrodes modified with layers of dithiols as electron donors and layers of viologen as electron acceptors are photoelectrochemically active. Stable photocurrents with moderate quantum efficiencies are resulted under illumination. Their current-voltage characteristics are compared and discussed. |
