Triplet Photophysics in Donor-Acceptor and pi-Conjugated Systems

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With this award, the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry is supporting Professor Kirk Schanze at the University of Florida to study the interaction of light with organic and metal-containing semiconducting molecules and polymers with the objective of understanding the fundamental processes that occur when they absorb light energy. A key goal is to understand the role played by electron spin on the properties of the materials. Electron spin state is important as it relates to the interaction of molecules with light because it determines the efficiency in applications such as light-emitting diodes (LEDs) and in solar cells. The effect of metals such as platinum, selenium, and tellurium on the electron spin is also being investigated. The project is being carried out by a team including undergraduate and graduate students with emphasis on participation by underrepresented groups. An international collaboration is included with a group at the King Abdulla University of Science and Technology (KAUST) in Saudi Arabia. The project is expected to have broad impact because the organic semiconductors that are the focus of these studies are being used to develop plastic electronic materials used in flexible light emitting devices and displays, solar cells, sensors and radio frequency ID tags. Thus, the basic science being developed under this grant may have long term implications in technology development for the national health, defense and security sectors.The project will initially involve the chemical synthesis of new semiconducting organic, organometallic and polymeric materials. Second, the properties of the new materials will be characterized by various techniques, including measurement of their light absorption and light emission characteristics. Specifically, pulsed laser techniques will used to understand the time evolution of the intermediate excited states that are formed upon light absorption by these new semiconducting materials. These experiments will be carried out on timescales ranging from picoseconds to microseconds. The results will be interpreted within new or existing physical chemical models, enabling the assignment of the electronic spin state characteristics of these intermediates. This should permit the development of quantitative structure-property relationships which relate the molecular and polymer structure to how the systems interact with light energy. Computational chemistry will be used in specific cases to model the electronic structure of the materials, and this information will aid in the interpretation of the experimental results. Select materials are to be used in prototype device applications, including organic solar cells and field-effect transistor configurations, with the objective of relating the physical chemical information to material device performance. The results of the study are expected to enhance understanding of the optoelectronic properties of donor-acceptor conjugated systems, with a particular focus on the role played by triplet molecular excited states in such systems.