Spectroscopic characterization of the exciton coherence lengths and dynamics in organic molecular crystalline materials

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Christopher Bardeen of the University of California-Riverside is supported by the Experimental Physical Chemistry Program to carry out research that aims to understand whether it is possible to take advantage of quantum delocalization (singlet excitons) or long lifetimes (triplet excitons and excimers) to significantly improve the energy transport properties of organic materials. The research plan is designed to accomplish three objectives. First, the electronic structure and dynamics of singlet excitons in molecular crystal materials as a function of monomer structure and morphology will be determined, utilizing temperature-dependent time- and wavelength-resolved fluorescence. Second, the dynamics of other types of longer-lived excited states, specifically triplets and excimers, will be investigated in molecular crystal materials. Third, a two-photon standing wave approach will be developed to measure directly the effective exciton diffusion length in crystalline materials in standard solar cell geometries. The photophysical understanding obtained in the first two objectives is expected to form the basis of the interpretation of how photocurrent generation depends on excitation position within organic thin films. This research project is designed to improve our understanding of energy transport processes in conjugated organic materials. This understanding in turn could aid in the design of improved materials for solar cells, and thus address an important societal problem: the need for clean, inexpensive, and renewable energy. Graduate students and postdoctoral associates will be trained in technologically vital areas. As well, a hands-on light/solar energy demonstration will be developed and implemented with students at a local middle school in Riverside.