Quantum coherence in photosynthesis for efficient solar-energy conversion

Abstract

The crucial step in the conversion of solar to chemical energy in Photosynthesis takes place in the reaction center where the absorbed excitation energy is converted into a stable charge separated state by ultrafast electron transfer events. However, the fundamental mechanism responsible for the near unity quantum efficiency of this process is unknown. Here we elucidate the role of coherence in determining the efficiency of charge separation in the plant photosystem II reaction centre (PSII RC) by comprehensively combining experiment (two-dimensional electronic spectroscopy) and theory (Redfield theory). We reveal the presence of electronic coherence between excitons as well as between exciton and charge transfer states which we argue to be maintained by vibrational modes. Furthermore, we present evidence for the strong correlation between the degree of electronic coherence and efficient and ultrafast charge separation. We propose that this coherent mechanism will inspire the development of new energy technologies.

Design principles of natural light-harvesting as revealed by single molecule spectroscopy

“…The design principles of charge separation, which takes place in the so-called reaction centre, are now beginning to be understood. The speed and efficiency of charge separation are based on a finely designed structure that minimises free energy losses, enables selected vibrations to drive quantum coherent processes, and allows control over the multiple pathways that can be followed by an excitation in the reaction centre [5]. The process of photosynthetic light harvesting has proven to be even more complex.…”

Quantum modeling of ultrafast photoinduced charge separation

“…In fact, the mean squared displacement of the initial excitation in a one-dimensional system is proportional to the number of steps N in the case of a classical diffusive motion and to N 2 in the quantum case [117]. If and how we might exploit this property to design better photovoltaic or solar fuel production devices is a very debated and lively topic of discussions in the scientific community [118,119]. While we were preparing this Topical Review, several reviews appeared specifically on this subject [120,121,122].…”

Stability and Polaronic Motion of Self-Trapped Holes in Silver Halides: Insight through DFT+UCalculations

“…While the full treatment of polarons in AgCl requires necessarily the inclusion of the Jahn-Teller effect this hampers realizing a simple, analytical model providing an overview of the properties of 6 these systems. Thus, we will start providing such a model to improve it, in a second step, including more advanced features like the Jahn-Teller effect.…”

“…Nevertheless , this task is not simple as it requires the use of large supercells as well as an accurate treatment of electron correlation to account for the delicate balance of energies (particularly electron self-interaction) leading to localization of the charge carrier 7 . In systems of current technological interest, where intensive research is being carried out, this is further aggravated due to factors like structural disorder appearing in organic polymers 6 or magnetic disorder associated to the metal-insulator transition of the manganites 3 .…”

“…This idea of a localized charge carrier composed by an electron (or hole) and its surrounding lattice distortion, called polaron, has had a strong influence in later research and it is nowadays often invoked to explain many atractive phenomena like high-temperature superconductivity in the cuprates [2][3] or colossal magnetoresistance in manganites 2, 4-5 . Furthermore, polarons play a key role in explaining transport in organic materials (both natural, like light-harvesting molecules in plants 6 or proteins key to the vision process in animals 7 , and artificial 8 , like organic light emitting diodes and transistors), or the performance of Li-air batteries where materials like Li2O2 and Li2CO3 are involved 9 .…”