Solar light harvesting by energy transfer: from ecology to coherence

Abstract

Over billions of years, evolutionary pressure has facilitated the development of sophisticated and diverse light-harvesting systems in photosynthetic organisms, enabling them to adapt to a variety of habitats and light conditions. Today, driven by the need for cheap and efficient solar power, we turn to photosynthetic organisms and their light-active supramolecular assemblies for bio-inspiration. By studying natural systems, we can learn more about the basic principles behind the fine-tuned functionalities of light capture and energy transfer on the molecular level. In this review, we use ideas from evolutionary ecology and quantum mechanics to elucidate the parameters that underpin the efficient and robust light-harvesting machinery of natural light-harvesting systems. The family of antenna proteins of cryptophyte algae serves as an example to illustrate the evolutionary diversification process on a structural and consequently a photophysical level. Two-dimensional electronic spectroscopy experiments reveal the existence of coherence among vibronic levels in the initial response of light-harvesting proteins to femtosecond optical excitation. We discuss what implications quantum transport processes might have for light harvesting.

Quantum diffusion and thermalization at resonant tunneling

“…We showed that one may steer the system into equilibrium or keep it relatively coherent (in the sense of quantum reversibility) depending on the specific choice of quench parameters. This paves the way for future experiments on many-body thermalization [9] and new theoretical explorations on optimally controlling the quantum evolution of complex many-body systems [1,21].…”

“…On small scales, quantum mechanics describes interactions and dynamics. One typical example of a complex quantum system are photosynthetic molecules (complexes) in which transport properties seem to be governed by quantum mechanical interference [1]. Strong correlations between the constituents make even "small" systems very complicated.…”

Exciton Dynamics in Phthalocyanine Molecular Crystals

“…16,18 A few examples in related self-assembled systems (porphyrins) have shown that exciton diffusion can efficiently occur by means of a coherent mechanism. 19 Recently, an octa(butyl)-substituted metal-free phthalocyanine, H2-OBPc (1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine, see Figure 1a) has been synthesized and exhibited good crystallinity properties (1D π-stacked arrangements, see Figure 1b) in thin films. 20,21 The high degree of crystallinity of the solution-processed thin films allowed Rawat et al to investigate the correlation between long-range order and the nature of the lowest exciton states of the aggregate.…”

“…[1][2][3][4] Two limiting transport regimes (coherent and incoherent) are commonly invoked to describe the exciton diffusion in molecular materials or aggregates. 5 In the coherent regime, the exciton wavefunction is delocalized over several molecular units or, in some cases, over the whole molecular aggregate, whereas in the opposite (incoherent) regime, the exciton wavefunction is completely localized on a molecular unit.…”

Inelastic Multiple Scattering of Interacting Bosons in Weak Random Potentials

“…Its implications reach from astronomical questions, e. g. how photons propagate through interstellar clouds [1], over condensed matter systems, where e. g. the movement of charges is of everyday relevance [2,3], to biology, where e. g. quantum properties of excitonic transport in light harvesting complexes in photosynthesis are currently debated, see e. g. [4]. Besides the interdisciplinary character of transport, transport also poses a problem of scales [5].…”