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QUENTRHEL Report Summary

Project ID: 278560
Funded under: FP7-IDEAS-ERC
Country: Italy

Final Report Summary - QUENTRHEL (Quantum-coherent drive of energy transfer along helical structures by polarized light)

A better exploitation of solar energy, one of the major challenges of this century, passes through the development of efficient light-harvesting materials. It was suggested that Nature, our first source of inspiration for light-harvesting, could exploit quantum effects to control and improve the efficiency of such a process. Although the practical relevance of quantum mechanics in biology is still the matter of intense debate in the literature, this does not prevent us from the possibility of applying this idea to artificial materials. Indeed, the central question that steered and stimulated QUENTRHEL research has been ‘can we exploit quantum coherence for functions (even if nature does not)?’
In this context, QUENTRHEL project developed new spectroscopic tools to experimentally characterize the presence, the implications and the factors regulating the relevance of such quantum effects and assess their possible engineering in artificial materials. Multidimensional and chiro-optical coherent spectroscopy setups have been assembled along with innovative data analysis codes to extract a higher amount of information from the spectroscopic signals with an increasing level of reliability.
These new tools have been applied to the study of both biological antenna complexes and biomimetic multi-chromophoric systems, whose structure was designed to reproduce different key features of their natural analogous. The body of information obtained on these complex multi-chromophoric systems has been complement by more basic research on the dynamics of the isolated chromophores, mainly chlorophylls and other tetrapyrrole compounds, the elementary building blocks of any light-harvesting complex. Data obtained studying non-interacting chromophores allowed a deeper knowledge of the fundamental mechanisms regulating the ultrafast relaxation dynamics of molecular materials and provided a solid base of knowledge, crucial for the ensuing interpretation of the responses of more complex interacting systems.
Complex dynamic interactions between the energy transport process and the environment during light-harvesting could be captured. We found several environment properties whose manipulation can lead to a controlled tuning of the ultrafast, also coherent, dynamics of energy transfer in multichromophoric systems. Pivotal in this context is the coupling with suitable vibrational modes of the molecules; the coupling with resonant solvent vibrations; the supramolecular organization and the degree of order of the chromophores; the flexibility of the molecular scaffold to which the chromophores are linked.
In the most favorable configurations, we could demonstrate that partially delocalized states created upon photoexcitation dephase quickly, localizing population on the final acceptor state. In this sense, the presence of coherence appears functional to the energy distribution among chromophores. This is essential information in the current efforts to evaluate possible opportunities to harness coherence to realize control and/or drive energy transduction. Moreover, the comparison between different structures allowed the formulation of reasonable guidelines for the molecular design of optimized ‘quantum’ artificial antenna systems.

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