| Monodisperse conjugated oligomers are potentially useful for organic electronics because of chemical purity and structural uniformity, facilitating the elucidation of structure-property relationships and the realization of superior device performance. Nematic liquid crystalline conjugated oligomers with above-ambient glass transition temperatures represent an attractive approach to prepare uniaxially aligned thin films across large areas for linearly polarized light emission and anisotropic charge transport. The temporal stability of blue light-emitting materials is also a major hurdle to practical applications.; This thesis research, therefore, has focused on organic electronic devices incorporating monodisperse conjugated oligomers comprising fluorene and other conjugated units for blue light emission and charge transport. Key results are summarized as follows: (1) The thermotropic and optical properties of monodisperse, conjugated glassy-nematic liquid crystalline oligo(fluorene)s were characterized and related to the molecular structures. The optical dichroism, birefringence, and polarization ratio in fluorescence increased with the molecular aspect ratio. Annealed thin films displayed strongly polarized blue emission with high quantum yield. (2) The same monodisperse materials were incorporated in strongly polarized, efficient, deep blue OLEDs. By employing a conductive alignment layer, an appropriate electron-transport material, and optimizing the light-emitting layer thickness, world-record device performance was achieved. (3) A comparative study of carrier transport in organic field-effect transistors (OFETs) was undertaken to explore the effects of chain length, pendant structure, and backbone composition on field-effect mobility of monodisperse glassy-nematic conjugated oligomers and polymer analogues. The oligomers' extended length was found to dominate the carrier transport properties. In contrast, the charge carrier mobility did not correlate with the persistence length of polymer analogues. (4) Monodisperse model compounds were prepared to study the parameters influencing OLED device stability. Consistent trends across three OLED configurations were observed, which were attributable to the difference in hole mobility. The hole mobilities, measured by transient electroluminescence, affected the recombination zone width and therefore dictated the device performance including lifetime. |
