We measure several fundamental electronic properties of molecules such as charge transfer and electronic delocalization using a technique known as Stark spectroscopy. Stark spectroscopy involves applying large electric fields to molecules in films or matrices and analyzing the effects of the field perturbation on the absorption or emission spectrum. We have recently focused on the properties of MEH-PPV and other molecules used to make to organic light emitting diodes (OLED's). Stark spectroscopy reveals the mechanism by which a large applied electric field, such as those present in OLEDs, produces undesirable emission quenching and suggests strategies for minimizing this loss of device efficiency through modifications of the polymer structure.
Emission properties of Single Molecules and Aggregates
Recent years has seen a huge growth in the use of organic conjugated oligomers and polymers in the design of light emitting diodes (OLEDs) and photovoltaic cells. When these molecules are placed in thin films to fabricate devices, they typically form aggregates. These confer several desirable properties for device function such as protection from oxidative damage and enhanced charge transport. However, they also typically shift the wavelength of emission to lower energies and often significantly reduce its intensity. Our group is using microscopy and spectroscopy to investigate the relationships between molecular structure and the brightness and photo-stability of molecules in the solid state, both in isolation (i.e. as single molecules) and as aggregates. We are also developing methods to image aggregation in films at high resolution and to follow the nucleation of aggregates in the solution phase.
- "Effects of Solvent Properties on the Spectroscopy and Dynamics of Alkoxy-Substituted PPV Oligomer Aggregates," Woong Young So, Jiyun Hong, Janice J. Kim, Gizelle A. Sherwood, Kelly Chacon-Madrid, James H. Werner, Andrew P. Shreve, and Linda A. Peteanu, J. Phys. Chem. B 116 10504 (2012)
- "Wavelength Dependence of the Fluorescence Quenching Efficiency of Nearby Dyes by Gold Nanoclusters and Nanoparticles: The Roles of Spectral Overlap and Particle Size," Chowdhury, Sanchari; Wu, Zhikun; Jaquins-Gerstl, Andrea; Liu, Shengpeng; Dembska, Anna; Armitage, Bruce A.; Jin, Rongchao; Peteanu, Linda A., J. Phys. Chem. C 115, 20105 (2011)
- "Visualizing Core-Shell Structure in Substituted PPV Oligomer Aggregates Using Fluorescence Lifetime Imaging Microscopy (FLIM)," Peteanu, Linda A.; Sherwood, Gizelle A.; Werner, James H.; Shreve, Andrew P.; Smith, Timothy M.; Wildeman, Jurjen, J. Phys. Chem. C 115 15607 (2011)
- "Fluorescent DNA Nanotags Featuring Covalently Attached Intercalating Dyes: Synthesis, Antibody Conjugation, and Intracellular Imaging," Stadler, Andrea L.; Delos Santos, Junriz O.; Stensrud, Elizabeth S.; Dembska, Anna; Silva, Gloria L.; Liu, Shengpeng; Shank, Nathaniel I.; Kunttas-Tatli, E.; Sobers, Courtney J.; Gramlich, Philipp M. E.; Carell, Thomas; Peteanu, Linda A.; McCartney, Brooke M.; Armitage, Bruce A., Bioconjugate Chem. 22, 1491 (2011)
- "pH-Responsive Fluorescent Molecular Bottlebrushes Prepared by Atom Transfer Radical Polymerization," Nese, Alper; Lebedeva, Natalia V.; Peteanu, Linda; Sheiko, Sergei, S.; Matyjaszewski, Krzysztof, Macromolecules 44 5905 (2011)