A large part of our research focuses on photosynthetic solar energy conversion in light harvesting systems. Natural light-harvesting antenna systems are a prominent component in the photosynthetic machinery. Numerous highly absorptive molecules, bound onto a protein scaffold, capture sunlight and funnel that energy to power reaction centers—specialized biological solar cells. While reaction center architecture is basically conserved across a multiplicity of photosynthetic species, light-harvesting antennae exhibit remarkable diversity as well as the ability to adapt to local light conditions and to regulate the operation of reaction centers. Researchers are learning that arrangements of the light-absorbing molecules are not random, but are carefully positioned to optimize flow of energy from the point where sunlight is absorbed to a reaction center. Typically, that energy funnel comprises ~200 molecules and energy is transferred, via a sequence of quantum mechanical energy transfer processes, distances of ~20–100 nm with near unit quantum efficiency.
Why study light harvesting?
Through bio-inspiration we can learn how to design clever materials for energy capture, we discover new examples of photophysical processes, we more deeply understand light-initiated chemical dynamics. If researchers could learn how to move energy with such precision and efficiency over comparable distance, then enormous leaps in the development of cheap organic solar cell technology would ensue.
Coherent Energy Transfer
For almost a decade now, discoveries from our group as well as others ( UC Berkely…) suggest that light-harvesting in some photosynthetic proteins involves quantum-coherence. This has captured the attention of researches for several reasons. First, it means that quantum mechanical probability laws can prevail over the classical laws of kinetics, allowing the possibility that light-initiated processes can by controlled using the interference principles first described by Schrödinger, Dirac, Feynman, and others. Second, it raises the fascinating question: have these organisms developed quantum-mechanical strategies for light-harvesting to gain an evolutionary advantage?
SD McClure, DB Turner, PC Arpin, T Mirkovic, GD Scholes “Coherent oscillations in the PC577 cryptophyte antenna occur in the excited electronic state” The Journal of Physical Chemistry B 118 (5), 1296-1308 (2014)
C Smyth, DG Oblinsky, GD Scholes ”B800–B850 coherence correlates with energy transfer rates in the LH2 complex of photosynthetic purple bacteria” Physical Chemistry Chemical Physics (2015)
Elisabetta Collini, Cathy Y. Wong, Krystyna E. Wilk, Paul M. G. Curmi, Paul Brumer, and Gregory D. Scholes, “Coherently wired light-harvesting in photosynthetic marine algae at ambient temperature” Nature 463, 644–648 (2010).
A Chenu, GD Scholes ”Coherence in Energy Transfer and Photosynthesis” Annual review of physical chemistry (2014)
Gregory D. Scholes, Graham R. Fleming, Alexandra Olaya-Castro and Rienk van Grondelle, “Lessons from nature about solar light harvesting” Nature Chem. 3, 763–774 (2011).
G. D. Scholes & G. Rumbles, Excitons in nanoscale systems, Nature Materials 5, 683–696 (2006).
E. Collini & G. D. Scholes, Quantum coherent energy migration in a conjugated polymer at room temperature, Science 323, 369-373 (2009).
G. D. Scholes, Long range resonance energy transfer in molecular systems, Annu. Rev. Phys. Chem. 54, 57–87 (2003).