Department of Chemistry

Physical and Theoretical Chemistry

Research ImageThe Department of Chemistry at the University of North Carolina at Chapel Hill, offers a wide range of research opportunities in theoretical and experimental physical chemistry. Our program has broadened from its traditional areas of excellence in molecular chemical physics to include research activities in biophysical and surface chemistry, and materials and environmental sciences. Experimental efforts within these areas utilize state-of-the-art instrumentation, such as high-resolution and ultra-fast laser systems, molecular beam techniques, mass spectrometry, ion-scattering, scanning probe microscopy, and magnetic resonance spectrometry.

Research in theoretical chemistry involves developing computational models of chromatin, the structure of complex fluids, and polymer dynamics. Students at UNC have access to high-performance computer workstations, as well as RENCI/UNC Research Computing, which is home to one of the best computing facilities in the world, including a 4160-processor Dell Linux cluster.

 

Recent Research Highlights

Optical Cavity Resonator Modes

Femtosecond pump–probe microscopy is used by researchers in the Papanikolas Group to investigate the charge recombination dynamics at different points within a single needle-shaped ZnO rod. As described in The Journal of Physical Chemistry B, recombination in the tips of the rod occurs through an excitonic or electron–hole plasma state, taking place on a picosecond time scale. Photoexcitation in the larger diameter sections of the interior exhibit dramatically slower recombination that occurs primarily through defects sites, i.e., trap mediated recombination.

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Transient absorption imaging shows that the spatial variation in the dynamics is also influenced by the cavity resonances supported within the hexagonal cross section of the rod. Finite element simulations suggest that these optical resonator modes produce qualitatively different intensity patterns in the two different locations. Near the end of the rod, the intensity pattern has significant standing-wave character, which leads to the creation of photoexcited carriers in the core of the structure. The larger diameter regions, on the other hand, exhibit intensity distributions in which the whispering gallery (WG) mode character dominates. At these locations, the photoexcited carriers are produced in subsurface depletion zone, where the internal fields separate the electrons and holes and lead to a greater degree of trap recombination on longer time scales.

 

Light-Harvesting Peptides

Published in JACS, researchers in the Papanikolas and Waters groups, in collaboration with members of the Meyer group at Carolina Chemistry and the Papoian Group at the University of Maryland, describe how solid-phase peptide synthesis has been applied to the preparation of phosphonate-derivatized oligoproline assemblies containing two different RuII polypyridyl chromophores coupled via "click" chemistry.

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In water or methanol the assembly adopts the polyproline II (PPII) helical structure, which brings the chromophores into close contact. Excitation of the assembly is followed by rapid, efficient intra-assembly energy transfer to the inner RuII. The oligoproline/click chemistry approach holds great promise for the preparation of interfacial assemblies for energy conversion based on a family of assemblies having controlled compositions and distances between key functional groups.

 

Representative Publications

Free Energy Barrier for Melittin Reorientation from a Membrane-Bound State to a Transmembrane State. Sheeba J. Irudayam, Tobias Pobandt, and Max L. Berkowitz. J. Phys. Chem. B, 2013, 117 (43), pp 13457–13463.

Interplay between Vibrational Energy Transfer and Excited State Deactivation in DNA Components. Brantley A. West, Jordan M. Womick, and Andrew M. Moran. J. Phys. Chem. A, 2013, 117 (29), pp 5865–5874.

Uncovering Molecular Relaxation Processes with Nonlinear Spectroscopies in the Deep UV. Brantley A. West, Brian P. Molesky, Paul G. Giokas, Andrew M. Moran. Chemical Physics, Volume 423, 23 September 2013, Pages 92-104.

Gas Phase Acidity Measurement of Local Acidic Groups in Multifunctional Species: Controlling the Binding Sites in Hydroxycinnamic Acids. Andres Guerrero, Tomas Baer, Antonio Chana, Javier González, and Juan Z. Dávalos. J. Am. Chem. Soc., 2013, 135 (26), pp 9681–9690.

Melittin Creates Transient Pores in a Lipid Bilayer: Results from Computer Simulations. Kolattukudy P. Santo , Sheeba J. Irudayam , and Max L. Berkowitz. J. Phys. Chem. B, 2013, 117 (17), pp 5031–5042.

Pump–Probe Microscopy: Spatially Resolved Carrier Dynamics in ZnO Rods and the Influence of Optical Cavity Resonator Modes. Brian P. Mehl, Justin R. Kirschbrown, Michelle M. Gabriel, Ralph L. House, and John M. Papanikolas. J. Phys. Chem. B, 2013, 117 (16), pp 4390–4398.

Interfacial Energy Conversion in RuII Polypyridyl-Derivatized Oligoproline Assemblies on TiO2. Da Ma, Stephanie E. Bettis, Kenneth Hanson, Maria Minakova, Leila Alibabaei, William Fondrie, Derek M. Ryan, Garegin A. Papoian, Thomas J. Meyer, Marcey L. Waters, and John M. Papanikolas. J. Am. Chem. Soc., 2013, 135 (14), pp 5250–5253.

Two-Dimensional Electronic Spectroscopy in the Ultraviolet Wavelength Range. Brantley A. West, and Andrew M. Moran. J. Phys. Chem. Lett., 2012, 3 (18), pp 2575–2581.

Direct Imaging of Free Carrier and Trap Carrier Motion in Silicon Nanowires by Spatially-Separated Femtosecond Pump–Probe Microscopy. Michelle M. Gabriel, Justin R. Kirschbrown, Joseph D. Christesen, Christopher W. Pinion, David F. Zigler, Erik M. Grumstrup, Brian P. Mehl, Emma E. M. Cating, James F. Cahoon, and John M. Papanikolas . Nano Lett., Article ASAP, DOI: 10.1021/nl400265b.

Tunable Energy Transfer Rates via Control of Primary, Secondary, and Tertiary Structure of a Coiled Coil Peptide Scaffold. Dale J. Wilger, Stephanie E. Bettis, Christopher K. Materese, Maria Minakova, Garegin A. Papoian, John M. Papanikolas, and Marcey L. Waters. Inorg. Chem., 2012, 51 (21), pp 11324–11338.