Prof. Steve Buratto, University of California, Santa Barbara

Photophysics of Organic Semiconductors Probed by Single Molecule Fluorescence and High Spatial Resolution Chemical Imaging

AACP Seminar Series

One of the most active and important areas in nanoscience and technology is the development of optoelectronic devices from flexible and inexpensive organic components. A critical consideration for designing and optimizing the organic materials used in optoelectronics is the electronic communication between individual chromophoric subunits. It is well known that the relative orientation and distance between individual molecules in the solid affects electronic delocalization and therefore the bulk luminescence properties. In our research we take a “bottom-up” approach to understanding chromophore-chromophore coupling by studying the luminescence from individual molecules, clusters of molecules and ultimately thin films. I will discuss our results of probing the fluorescence from single molecules of a new class of tetrahedral oligo(phenylenevinylene) (OPV) molecules, where four OPV “arm” molecules are linked via a single sp3 carbon center. Our results show that these tetrahedral molecules contain multiple chromophores with limited inter-arm coupling, but significant molecular motion about the central carbon. This motion leads to fluctuations in the both the polarizability axis of the molecule and the fluorescence intensity on the timescale of 100 ms to 10 s.
We also show direct comparisons of the conformation and shape of the OPV “arm” molecules and their luminescence properties on a single molecule level and in thin films. This data originates from a new chemical imaging method that combines two diagnostic tools in physical chemistry: gas-phase ion mobility mass spectrometry and single molecule fluorescence spectroscopy. These results show that the structures observed in the gas phase are strongly correlated to the categories of molecules observed in the single molecule polarization anisotropy measurements with nearly identical distributions for the two OPV molecules studied. These categories are determined by the number of cis vinylene linkages in the OPV structure and are shown to directly influence the fluorescence intensity, the structure of the tetrahedral molecules formed from these OPV arms and the morphology of films made from these molecules.

For more information contact Prof. Christine Payne (404-385-3125).