Studies on the synthesis and the transport properties of organic materials
AuthorHreha, Richard Douglas
AdvisorMarder, Seth R.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractA series of photo-crosslinkable arylamine-based hole-transport copolymers has been synthesized. The synthetic methodology employed allows for the redox potential of the polymer to be tuned by the incorporation of electron-donating or withdrawing moieties. Upon exposure to ultraviolet radiation, the copolymers become insoluble, as evidenced by ultraviolet-visible absorption spectroscopy. The ability to switch the solubility of the polymers enable one to photo-pattern the materials, a feature that is useful for the fabrication of multilayer organic light-emitting diodes (OLEDs) by solution processing techniques. OLEDs using the methacrylate based hole-transport polymers have been fabricated and the performance of the devices has been evaluated. 2,7-Bis(p-methoxyphenyl- m'-tolylamino)-9,9-dimethylfluorene, 2,7-bis(phenyl- m'-tolylamino)-9,9-dimethylfluorene, and 2,7-bis( p-fluorophenyl-m'-tolylamino)-9,9-dimethylfluorene have been synthesized using palladium-catalyzed reaction of the appropriate diarylamines with 2,7-dibromo-9,9-dimethylfluorene. These molecules have glass-transition temperatures 15-20°C higher than those for their biphenyl-bridged analogues, and are 0.11-0.14 V more easily oxidized. The hole mobilities of the three fluorene derivatives (blended with polystyrene) have been measured by the time-of-flight technique and are lower than the corresponding biphenyl-bridged analogues. Analysis of transport data according to the disorder formalism yields parameters similar to those for the biphenyl species, but with lower zero-field mobility values. Density functional theory based calculations suggest that the enforced planarization of the fluorene bridge leads to a larger reorganization energy, due to increased vibration contributions in the bridge for the neutral/cation electron-exchange reaction relative to the analogous biphenyl-bridged system. OLEDs have been fabricated using blends of the fluorene-bridged compounds with polystyrene as the hole-transport layer and Alq₃ as electron-transport layer and lumophore. Device performance shows a correlation with the ionization potential of the amine materials paralleling that seen in biphenyl-based systems. Monomers based on the fluorene bridged arylamine-based hole transport materials were also synthesized. Monomers having methacrylate, styrene, and norbornene moieties have been synthesized and their hole mobilities measured. Adding a methacrylate or norbornene moiety had no effect on the hole mobility. The mobility of the norbornene polymer was significantly higher than the methacrylate polymer.
Degree ProgramGraduate College