A Exploration of Higher Acenes

The acenes are a fascinating class of aromatic hydrocarbons that have found use in a wide variety of semiconductor applications. These materials have also long been of interest to theoretical chemists, due to the unique aromatic character of the Iinearlyfused aromatic backbone, and their intermediate structure between polyacetylene and graphene. Progress in the understanding the structure and properties of acenes is remarkable considering that the largest oligomer in the series to receive extensive study is only the pentamer (pentacene). This project aims to dramatically increase the number of hexacene, heptacene and higher acene derivatives available for study, by devising a functionalization strategy to improve the stability of these reactive chromophores. Our recent preparation of a stable hexacene derivative and a relatively stable heptacene derivative serve as proof-of-principle for this project. The focus of this proposal will be to expand this work, using knowledge we have gained working with substituted pentacenes to develop appropriate strategies for the synthesis of stabilized higher acenes. Intellectual merits of this proposal include the development of a rational functionalization strategy to stabilize a previously inaccessible class of aromatic materials (hexacenes, heptacenes, and larger acenes). In the case of hexacenes, investigations will focus on optimizing these materials for applications in thin-film electronic devices such as transistors. Since transistor performance appears to increase along with increasing acene length, it is expected that hexacene-based devices could outperform pentacene, the current benchmark material. Investigations of the influence of side-chains on thin film formation will further the applicability of small-molecule semiconductors to problems in organic electronics. In contrast, the work on heptacene and larger acenes will focus on stabilization. A wide array of steric and electronic factors will be investigated to determine an optimum functionalization strategy for the isolation of stable heptacene-based materials. The most successful approach will then be applied to larger acenes such as octacene and nonacene - compounds that may have unusual electronic structures. Broader impacts of this work include the development of general methods for the solubilization, stabilization and crystallization of acenes and heteroacenes. These methods are sufficiently general to be applied to other long-aspect-ratio aromatic systems. The availability of larger acenes for physical and device studies will significantly expand the base of knowledge regarding this important class of fused aromatic compounds. The stable materials synthesized as part of this project will be made Widely available to scientists in academia, industry and at national laboratories. The project will train graduate and undergraduate students in the synthesis of high-purity organic materials, and their characterization by a variety of solution-state, single-crystal and thin-film methods. Students will also travel to collaborators in engineering departments, to become educated in aspects of device fabrication techniques and device analysis. Undergraduates from Appalachian and other rural regions of Kentucky will be particularly encouraged to participate in these out of state visits, to help encourage them to broaden their horizons and pursue graduate degrees at universities outside their home state. These students will emerge from their studies ready to participate fully in interdisciplinary organic electronics research environments. The current outreach work with a local high school will also be continued with this project, particularly involving local students with the deposition and characterization of organic thin films