Photosynthetic Aggregates are More Than the Sum of Their Parts
Photosynthesis is a remarkably efficient and adaptable process that uses highly organized aggregates of pigments and proteins to capture light and convert it into chemical energy. The organizational structure of these aggregates allows for highly efficient energy transfer and an adaptive photoprotective response. Understanding the hidden interactions underlying the design of the photosynthetic apparatus is critical to the development of biomimetic solar technologies and high-yield biofuels. To uncover the interactions between individual components of photosynthetic aggregates, we use novel combinations of ultrafast spectroscopy and microscopy. By systematically scaling from a single molecule to an aggregate, our work reveals obscured dynamics and interactions, providing new insights into natural light harvesting.
Electronic Couplings Revealed by Disentangling Congested Spectra
Despite their critical importance and decades of study, the electronic structure and dynamics of photosynthetic systems with congested spectra are poorly understood. Even current state-of-the-art nonlinear spectroscopic measurements produce near featureless spectra. One of our projects employs mixed time-frequency domain spectroscopy to resolve the hidden energy transfer dynamics and internal interactions in these congested systems. By accessing electronic overlaps and interactions directly, we can disentangle couplings and electronic structure. This work had important implications for solar technology as the delocalization of excitation pertains to energy transfer and multi-excited states.
Ultrafast Optical Switching in Strained Nanocrystal Heterostructures
Colloidal semiconductor nanocrystal heterostructures have size-tunable optical and material properties that can be designed using synthetic chemical methods. Type II nanocrystal heterostructures are designed for charge separation, isolating the hole in one material and the electron in the other. In these systems, strain can be used as an adjustable parameter, capable of tuning the relative energy levels and changing the charge separation properties of the material. Using polarization controlled ultrafast optical spectroscopy to access the phonon modes, we can periodically strain the nanocrystals, shifting the relative separation of the levels and modifying charge separation. Using strain as an adjustable parameter to control the optical properties of heterostructures will provide new paths towards manufacturing robust, efficient solar cells and novel material systems.
Huxter, V. M., Oliver, T. A. A., Budker, D. and Fleming, G. R., "Vibrational and Electronic Dynamics of Nitrogen-Vacancy Diamond Revealed by Two-Dimensional Ultrafast Spectroscopy." Nature Physics 9, 744-749 (2013)
Dawlaty, J. M., Bennett, D. I. G.*, Huxter, V. M.* and Fleming G. R., "Mapping the Spatial Overlap of Excitons in a Photosynthetic Complex via Coherent Nonlinear Frequency Generation." Journal of Chemical Physics 135, 044201 12 pages (2011). Cover Article and Editor's Choice Selection 2011
Huxter, V. M. and Scholes, G. D., "Acoustic Phonon Strain Induced Mixing of the Fine Structure Levels in Colloidal CdSe Quantum Dots Observed by a Polarization Grating Technique." Journal of Chemical Physics 132, 104506 15 pages (2010)
Huxter, V. M., Kim, J., Lo, S., Lee, A., Nair, P. S. and Scholes, G. D., "Spin Relaxation in Zinc Blende and Wurtzite CdSe Quantum Dots." Chemical Physics Letters 491, 187-192 (2010)
Huxter, V. M. and Scholes, G. D., "Photophysics of Colloidal Semiconductor Nanocrystals." Journal of Nanophotonics 3, 032504 16 pages (2009)
Kim, J., Huxter, V. M., Curutchet, C. and Scholes, G. D., "Measurement of Electron-Electron Interactions and Correlations using Two-Dimensional Electronic Double-Quantum Coherence Spectroscopy." Journal of Physical Chemistry A 113, 12122-12133 (2009)
Huxter, V. M., Lee, A., Lo, S. and Scholes, G. D., "CdSe Nanoparticle Elasticity and Surface Energy." Nano Letters 9, 405-409 (2009)
Huxter, V. M., Mirkovic, T., Nair, P. S. and Scholes, G. D., "Demonstration of Bulk Semiconductor Properties in Processible Nanocrystalline Systems." Advanced Materials 20, 2439-2443 (2008)
Huxter, V. M. and Scholes, G. D., "Nonlinear Optical Approach to Multiexciton Relaxation Dynamics in Quantum Dots." Journal of Chemical Physics 125, 144716 12 pages (2006)
Scholes, G. D., Kim, J., Wong, C. Y., Huxter, V. M., Nair, S. P., Fritz, K. P. and Kumar, S., "Nanocrystal Shape and the Mechanism of Exciton Spin Relaxation." Nano Letters 6, 1765-1771 (2006)
Huxter, V. M., Kovalevskij, V. and Scholes, G. D., "Dynamics within the exciton fine structure of colloidal CdSe quantum dots." Journal of Physical Chemistry B 109, 20060-20063 (2005)
Huxter, V. M., Hamier, J. and Salin, E., "Tandem Calibration Methodology for ICP-MS." Journal of Analytical Atomic Spectroscopy 18, 71-75 (2003)
Huxter, V. M., He, J. and Scholes, G. D., "Nanoscale Excitons and Semiconductor Quantum Dots". In Handbook of Nanophysics: Nanoelectronics and Nanophotonics. Sattler, K. D. Ed; CRC Press - Taylor and Francis (2010)
Huxter, V. M. and Scholes, G. D., "Electronic Energy Transfer and the Role of the Refractive Index". In Continuum Solvation Models in Chemical Physics: Theory and Application. Mennucci, B., Ed; John Wiley, New York (2007)