Exploiting Structured Environments for Efficient Energy Transfer: The Phonon Antenna Mechanism

Abstract

A non-trivial interplay between quantum coherence and dissipative environment-driven dynamics is becoming increasingly recognised as key for efficient energy transport in photosynthetic pigment-protein complexes, and converting these biologically-inspired insights into a set of design principles that can be implemented in artificial light-harvesting systems has become an active research field. Here we identify a specific design principlethe phonon antenna -that demonstrates how inter-pigment coherence is able to modify and optimize the way that excitations spectrally sample their local environmental fluctuations. We place this principle into a broader context and furthermore we provide evidence that the Fenna-Matthews-Olson complex of green sulphur bacteria has an excitonic structure that is close to such an optimal operating point, and suggest that this general design principle might well be exploited in other biomolecular systems. Introduction.-Experimental techniques such as optical 2D Fourier Transform spectroscopy have recently begun to probe the ultrafast photophysics of energy transport in a range of pigment-protein complexes (PPCs) taken from photosynthetic green sulphur bacteria, marine algae and higher plants [1][2][3][4]. All of the key photosynthetic light reactions (photon capture, energy transport and charge generation) are carried out in PPC structures [5,6], and the often > 90% quantum efficiency with which they carry out these functions has created considerable interest in understanding and exploiting their design features for artifical solar energy applications [5,7]. Surprisingly, recent experiments have found direct evidence for long-lasting quantum coherence amongst the excitons which transport energy in these complexes. In the case of the Fenna-MatthewsOlson (FMO) complex, these coherences can persist on picosecond timescales in cryogenic conditions and are still observable at room temperatures [2,8]. Several phenomenological theories have subsequently shown that there is an optimal mixture of coherent inter-pigment energy transport and stochastic environmental noise that may lead to faster and higher-yield energy delivery in PPC architectures, suggesting that quantum effects may underpin their efficient function [9][10][11][12][13][14][15]. Microscopic investigations have also recently shown the key role of both discrete and continuous environmental fluctuation spectra in stabilising the long-lasting coherences observed in spectroscopy as well as facilitating efficient transport [16][17][18][19][20].

Coherent exciton dynamics in a dissipative environment maintained by an off-resonant vibrational mode

“…In particular, the importance of structured environments in the dynamics and coherence of open quantum systems is now beginning to be recognized. For example, a series of recent theoretical [5][6][7][8][9][10][11][12] and experimental [13][14][15][16] studies has provided strong evidence that strongly coupled discrete molecular vibrations play a significant role in the speed, efficiency, and quantum coherence of energy transfer in photosynthetic and other molecular systems. In a different context, the high degree of control and precision possible in artificial nanosystems has enabled experimental measurement and engineering of noise spectral densities in condensed matter systems.…”

Origin of long-lived oscillations in 2D-spectra of a quantum vibronic model: Electronic versus vibrational coherence

“…However, in the presence of environmental noise, which is inevitable in biological systems, oscillatory features are expected to be shortlived. The observation of persistent oscillations in the non-linear optical spectra of various photosynthetic complexes at both cryogenic and physiological temperatures [1][2][3], together with recent results on individual antenna complexes [4] and synthetic heterodimers [5], has led to a multidisciplinary effort to try and identify the specific mechanisms and conditions that enable biological systems to generate such long-lived oscillatory dynamics [6][7][8][9][10][11] and to elucidate the functional relevance of such coherent dynamics [11][12][13][14][15][16][17][18][19]. These observations are of interest for a variety of reasons.…”

Dissipation enhanced vibrational sensing in an olfactory molecular switch

“…[1][2][3][4][5][6][7][8] In particular, resonant (or near resonant) interactions between environmental degrees of freedom and those inherent to the system are thought to play an important role in numerous physical processes. [9][10][11][12][13][14][15][16][17][18][19][20] However, a comprehensive picture of such dynamics is only beginning to emerge due to the complexity of the systems in question. Here, by focusing on a proposed model for olfaction as a vibrationally-activated molecular switch, we explore the detailed effects of the environment on the dynamics of electron transfer (ET) in an open quantum system, aiming to gain physical insight into vibrationally-assisted transport processes more generally.…”