Toward Mesoscale Order in Multicomponent Organic Thin Films via Hydrogen Bond Directed Supramolecular Topology

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With this award the Macromolecular, Supramolecular and Nanochemistry Program supports Professor Ronald Castellano and his collaborators at the University of Florida to study semiconducting carbon-based (organic) materials. For many downstream applications - displays, lighting, solar cells, transistors, and sensors - the three-dimensional (3-D) arrangement of organic molecules in processed thin (10-1,000 nanometer) films dictates device performance. This study is developing a general self-assembly approach to allow functional organic molecules to form useful superstructures in a self-guided way. In the broadest sense, the work contributes to a general understanding of how to control the 3-D structure of single and multi-component organic matter at the nano-/mesoscale. Broader impacts with respect to education and training come from (1) graduate and undergraduate students being exposed to multidisciplinary science that includes synthetic and physical organic chemistry, spectroscopy, computation, materials processing/characterization, and device fabrication; (2) the student participants, together with the UF Chemistry Club, disseminating standards-aligned experimental modules to K-8 classrooms that embed concepts of the chemical/materials sciences and their own research; and (3) broadening the participation of underrepresented groups in STEM research activities. While it is known how to tailor the electronic and optical properties of individual pi-conjugated molecules as well as to program the arrangements of the molecules in solution, a major bottleneck for their usage is predicting and controlling three-dimensional morphological structure in thin films. This research examines a hierarchical self-assembly approach based on hydrogen bonding to create nanoscale to mesoscale order in thin films of pi-conjugated oligomers irrespective of pi-chromophore structure. The design involves covalently linking typical pi-conjugated components to molecular recognition units capable of directing their supramolecular assembly into predictably shaped aggregates. The resulting topologies are expected to uniquely support the natural segregation of appropriately shaped additives in thin film blends, and allow desirable optoelectronic properties to be achieved. The proposed bottom-up self-assembly approach effectively decouples the morphological structure of organic semiconductor thin films from the intrinsic optoelectronic structure of the constituent pi-conjugated chromophores, allowing these aspects to be independently optimized through rational/theory-guided material design. The specific aims of this collaborative project include modular design and synthesis of pi-conjugated oligomers, evaluation of optoelectronic structure and (supra)molecular ordering in solution and in thin films, and characterization of the optoelectronic properties of and bulk ordering within the thin films using diagnostic devices.