Controlling Solid State Structures of Conjugated Polymers: Optoelectronic and Transport Effects

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Conjugated molecules are promising components of thin film transistors (TFTs) and organic light-emitting diodes (OLEDs). Their performance characteristics in these devices are critically dependent on their solid state structure and morphology which, in turn, depends on their molecular structure. In this project, conjugated oligomers and molecular packing in a predicted manner will be synthesized. Molecular properties, e.g. ionization potential, electron affinity, polarizability, etc., will be fine tuned by synthesizing co-polymers or "co-oligomers" using component structures that impart the desired characteristics. A combination of X-ray crystallography and spectroscopy will be used to determine the molecular packing and its effect on the optoelectronic properties of the new materials. For TFTs, the optimum packing motif has the molecules arranged in closely spaced (3.5A) -stacks with the axis of the stacking direction collinear with the direction of current flow. Langmuir-Blodgett techniques will be used to align the functionalized molecules on substrate (electrode) surfaces, and effects of molecular structure and solid state packing on the transport properties will be determined. These new materials will have well defined solid state structures that may give better performance in flat panel displays, "smart cards", environmental sensors, and related applications involving conjugated polymers and organic solids.