Abstract
Multifluorenyl silanes have been studied as potential hosts for organic light emitting diodes. Four molecules, (9,9′-dimethylfluoren-2-yl)nSi(phenyl)4-n (SiFln, n = 1, 2, 3, and 4), with an increasing number of fluorene units have been synthesized and investigated. These compounds possess high triplet energies (2.9 eV), large HOMO−LUMO gaps (∼5.2 eV), and high glass transition temperatures. Their glass transition and sublimation temperatures increase linearly as the fluorene ratio increases, but there are only small changes in their electrochemical or photophysical properties. These studies suggest that the Si center helps maintain the high singlet and triplet energy levels of these molecules. These materials exhibit ambipolar transport characteristics in undoped OLED devices, and the charge conductivity of the devices was enhanced by increasing the fluorene ratios in the host molecules. Compared with phenylsilanes, the fluorenylsilanes show better hole injecting and charge transporting abilities. SiFl4 was investigated as a host material for red, green, and blue phosphorescent devices, giving peak efficiencies of 8, 8, and 3%, respectively.
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