(a)

1. Organic semiconductors: Exciton and charge carrier dynamics on macroscopic and microscopic levelsOksana Ostroverkhova, Oregon State University, DMR 0748671 • Our work explores optoelectronic properties of small-molecular weight organic semiconductors from macroscopic (thin films) to microscopic (single-molecule) levels. • This year’s highlights include: • In functionalized anthradithiophene (ADT)-based donor-acceptor (D/A) composites (macroscopic level), we: • Established exciton and charge photogeneration and recombination dynamics, depending on the relative HOMO and LUMO energies of D and A molecules and on the D/A spatial separation • On the single-molecule (microscopic) level, we: • Imaged novel functionalized fluorinated pentacene (Pn) molecules in various environments on a single-molecule level • Determined single-molecule-level photophysics and molecular alignment of Pn molecules functionalized with various side groups R, depending on the side group size and host matrix (a) (c) (b) (d) Transition dipole moment of Pn-F8-R Figure: Pentacene derivatives Pn-F8-R (top left) used as acceptors in D/A composites (macroscopic level, (a) and (b)) and as single-molecule reporters (microscopic level, (c) and (d)). (a) and (b): Depending on the D/A spatial separation (which is controlled by side groups R), different mechanisms of charge photogeneration contribute to transient photocurrent. (c) and (d): Molecular orientation (polar angle) of single Pn-F8-R molecules, depending on the side group R and on the host matrix (polymer PMMA or crystalline BTBTB). A.D. Platt et al., Phys. Rev. B 84, 235209 (2011); M. J. Kendrick et al., J. Phys. Chem. C116, ASAP article (2012), DOI: 10.1021/jp305913s; B. Purushothaman et al., Chem. Comm. 48, 8261 (2012)

2. Involvement of undergraduate students in research and development of research instrumentation and software and in outreach activitiesOksana Ostroverkhova, Oregon State University, DMR 0748671 Undergraduate students, including under-represented women students, are actively involved in both research and educational activities carried out by our group. Two undergraduate students (one female) were involved in the project this year. Currently, Alex Robertson (senior, nuclear engineering major) carries out experiments and data analysis in single-molecule fluorescence spectroscopy under the supervision of graduate student Whitney Shepherd, and Afina Neunzert (senior, physics major) explores optoelectronic properties of organic semiconductors under the supervision of graduate student Mark Kendrick. Afina is a second author in our recent publication (Kendrick et al., J. Phys. Chem. C 2012), is a recipient of Janet Richens Wiesner University Honors College Scholarship for Undergraduate Women in Science, and is a participant of a REU Summer 2012 program at Caltech. Our group regularly participates in outreach events demonstrating optical effects to freshmen and as a part of various courses offered on campus, as well as develops educational materials. One recent example of the latter is web-based tutorials on intermolecular interactions contributed by graduate student Whitney Shepherd (see http://www.physics.orst.edu/ ~ostroveo/research/index.html, under “Resources”). Undergraduate student Afina Neunzert is involved in measurements and modeling of organic optoelectronic devices Undergraduate student Alex Robertson is aligning single molecule spectroscopy setup