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Gregory Scholes

Gregory Scholes

Academic Title: Adjunct D.J. LeRoy Distinguished Professor

Phone: 416-946-7532

Office: LM 241

Email:

Research Homepage: http://www.chem.utoronto.ca/staff/SCHOLES/scholes_home.html

Research

Around 3.5 billion years ago the first photosynthetic organisms worked out how to capture energy from sunlight and use it to drive life-sustaining biochemical processes. In the process, they transformed a primitive Earth's inhospitable CO2-rich atmosphere to the life supporting mix of gases we know today. Photosynthetic organisms have mastered a means of sustaining their vast energy needs by using abundant solar power. The scale of this process is extraordinary; they convert CO2 into 105 billion tons of biomass annually. Recognizing the limitations of our present energy resources and implications for the environment, progressive nations are striving to solve challenges impeding the wider use of renewable energy resources, particularly solar energy. In parallel, energy efficient technologies, like lights made from thin sheets of plastic, are being developed.

What is particularly inspiring in biological systems is their efficient use of energy. Examples include the chemistry mediated by enzymes and the unidirectional electron transfer in photosynthetic reaction centers. Developing the ability to control chemistry at such a level of detail is a grand challenge for this century. Achieving that goal will require “clarification of deep physical and chemical issues.” Accordingly, the forefront of physical chemistry is changing. We now need to think how the innovative experiments under development today will provide unforeseen insights into difficult, important problems. The vision of my research program is to resolve such questions in the area of light-initiated processes in complex chemical, materials, and biological systems through the deeper insights provided by incisive experimental approaches. The projects that teams of students and postdocs in the Scholes Group are presently working on include:

(a) Quantum effects in biology. More than 10 million billion photons of light strike a leaf each second. Incredibly, almost every red-coloured photon is captured by chlorophyll pigments and initiates steps to plant growth. Recently we reported that marine algae use quantum mechanics in order to optimize photosynthesis, a process essential to its survival. These and other insights from the natural world promise to revolutionize our ability to harness the power of the sun. In a review published in Nature Chemistry (2011) we described the principles learned from studies of various natural antenna complexes and suggested how to utilize that knowledge to shape future technologies. We forecast the need to develop ways to direct and regulate excitation energy flow using molecular organizations that facilitate feedback and control—not easy given that the energy is only stored for a billionth of a second. Our research explores energy transfer dynamics in optimal synthetic light-harvesting systems and is introducing the idea of molecular ‘light harvesting circuits’. The novelty of these circuits is that the way they work can only be predicted using the laws of quantum mechanics.

(b) Ultrafast energy and charge transfer in conjugated polymers and organic photovoltaics. Conjugated polymers are fascinating macromolecular semiconductors, used predominantly in organic displays and organic solar cells. In ongoing research we are investigating ultrafast processes initiated by photoexcitation, including energy transfer dynamics and the nature of charge separation at heterojunctions (interfaces between conjugated polymer domains and electron acceptors).

(c) The theory of electronic energy transfer. Despite a century of study, researchers are still learning about basic physical chemistry by studying how the energy of absorbed light hops from one molecule to another. Our studies range from examining how proteins influence energy transfer at an atomic level of detail to the development of fundamental physical models that help us address questions basic to quantum mechanics and chemical dynamics.

Selected Publications

[1] 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).

[2] 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).

[3] G. D. Scholes & G. Rumbles, Excitons in nanoscale systems, Nature Materials 5, 683–696 (2006).

[4] E. Collini & G. D. Scholes, Quantum coherent energy migration in a conjugated polymer at room temperature, Science 323, 369-373 (2009).

[5] G. D. Scholes, Long range resonance energy transfer in molecular systems, Annu. Rev. Phys. Chem. 54, 57–87 (2003).

[6] David Beljonne, Carles Curutchet, Gregory D. Scholes and Robert Silbey, “Beyond Förster resonance energy transfer in biological and nanoscale systems” J. Phys. Chem. B Feature Article 113, 6583–6599 (2009).

[7] Marcus Jones, Shun S. Lo, & Gregory D. Scholes, “Quantitative modeling of the role of surface traps in CdSe/CdS/ZnS nanocrystal photoluminescence decay dynamics” Proc. Natl. Acad. Sci. USA 106, 3011–3016 (2009).

[8] Cathy Y. Wong, Jeongho Kim, P. Sreekumari Nair, Michelle C. Nagy & Gregory D. Scholes, “Relaxation in the exciton fine structure of semiconductor nanocrystals” J. Phys. Chem. C Feature Article 113, 795–811 (2009).

[9] Daniel B. Turner, Yasser Hassan, and Gregory D. Scholes “Exciton superposition states in CdSe nanocrystals measured using broadband two-dimensional electronic spectroscopy“ Nano Lett. (in press 2012).