47 research outputs found

    Mechanistic Regimes of Vibronic Transport in a Heterodimer and the Design Principle of Incoherent Vibronic Transport in Phycobiliproteins

    Get PDF
    Following the observation of coherent oscillations in non-linear spectra of photosynthetic pigment protein complexes, particularly phycobilliprotein such as PC645, coherent vibronic transport has been suggested as a design principle for novel light harvesting materials operating at room temperature. Vibronic transport between energetically remote pigments is coherent when the presence of a resonant vibration supports transient delocalization between the pair of electronic excited states. Here, we establish the mechanism of vibronic transport for a model heterodimer across a wide range of molecular parameter values. The resulting mechanistic map demonstrates that the molecular parameters of phycobiliproteins in fact support incoherent vibronic transport. This result points to an important design principle: incoherent vibronic transport is more efficient than a coherent mechanism when energetic disorder exceeds the coupling between the donor and vibrationally excited acceptor states. Finally, our results suggest that the role of coherent vibronic transport in pigment protein complexes should be reevaluated

    Influences of quantum mechanically mixed electronic and vibrational pigment states in 2D electronic spectra of photosynthetic systems: Strong electronic coupling cases

    Full text link
    In 2D electronic spectroscopy studies, long-lived quantum beats have recently been observed in photosynthetic systems, and it has been suggested that the beats are produced by quantum mechanically mixed electronic and vibrational states. Concerning the electronic-vibrational quantum mixtures, the impact of protein-induced fluctuations was examined by calculating the 2D electronic spectra of a weakly coupled dimer with vibrational modes in the resonant condition [J. Chem. Phys. 142, 212403 (2015)]. This analysis demonstrated that quantum mixtures of the vibronic resonance are rather robust under the influence of the fluctuations at cryogenic temperatures, whereas the mixtures are eradicated by the fluctuations at physiological temperatures. However, this conclusion cannot be generalized because the magnitude of the coupling inducing the quantum mixtures is proportional to the inter-pigment coupling. In this study, we explore the impact of the fluctuations on electronic-vibrational quantum mixtures in a strongly coupled dimer. with an off-resonant vibrational mode. Toward this end, we calculate electronic energy transfer (EET) dynamics and 2D electronic spectra of a dimer that corresponds to the most strongly coupled bacteriochlorophyll molecules in the Fenna-Matthews-Olson complex in a numerically accurate manner. The quantum mixtures are found to be robust under the exposure of protein-induced fluctuations at cryogenic temperatures, irrespective of the resonance. At 300 K, however, the quantum mixing is disturbed more strongly by the fluctuations, and therefore, the beats in the 2D spectra become obscure even in a strongly coupled dimer with a resonant vibrational mode. Further, the overall behaviors of the EET dynamics are demonstrated to be dominated by the environment and coupling between the 0-0 vibronic transitions as long as the Huang-Rhys factor of the vibrational mode is small.Comment: 20 pages, 4 figures. arXiv admin note: text overlap with arXiv:1505.0528

    Modelling ultrafast two-dimensional spectroscopy of vibronic systems using non-Markovian hierarchical equations of motion.

    Get PDF
    Two-dimensional spectroscopy utilises a series of ultrafast optical interactions to create excited populations and track the decay of resulting wavepackets. This enables the study of the potential energy surfaces of complex chemical and biological systems, including the rates of relaxation between states and the dephasing of ensembles. But the inherent complexity of the condensed phase, associated with the vast degrees of freedom and disorder, presents significant challenges in modelling such photophysical processes. In particular, the similarity in relaxation timescale of the system and its surrounding environment provides the opportunity for feedback of information, introducing memory effects which have a major impact on the spectral lineshape. The shape and duration of the applied laser pulses also leads to filtering effects, such that spectra of complex systems can easily be misinterpreted. In this research, theoretical models for the simulation of two-dimensional electronic spectroscopy of vibronic systems are developed in both the underdamped and overdamped limits, using the hierarchical equations of motion to account for non-Markovian memory effects. Firstly, an investigation into the origins of spectral broadening from the perspective of quantum information theory finds that underdamped environments involve greater non-Markovian effects, but also that increased inhomogeneous broadening in overdamped environments is correlated with greater measurable non-Markovianity. The role of the laser spectrum is then demonstrated through spectral filtering of the coherence pathways of a vibronic zinc-porphyrin monomer. Changes in the 2D spectra on formation of delocalized exciton states in vibronic dimers are then examined in terms of a series of perylene bisimide homodimers, where the electronic coupling is controlled by increasing the monomer separation distance. Finally, an analysis of vibrational relaxation within a vibronic heterodimer, combined with selective laser excitation, demonstrates the full capability of the model by simulating energy transfer within an excitonic aggregate involving both system and environmental vibrational motion

    Quantum traits in the dynamics of biomolecular systems

    Get PDF
    The majority of biology can be adequately described by classical laws, yet there are suggestions that a variety of organisms may harness non-trivial quantum phenomena to gain a biological advantage. This thesis is concerned with the light induced dynamics in photosynthetic light harvesting antennae. Quantum coherences persisting on picosecond time-scales have been repeatedly observed in a variety of species. This ran contrary to the prevailing theories of energy transfer dynamics in these systems. A consensus has emerged that a delicate competition between electronic and vibrational interactions is responsible for prolonging coherences between electronic states of chromophores. In particular, interactions with specific under-damped vibrational modes are known to play a fundamental role. This thesis demonstrates that room temperature, efficient vibration-assisted energy transfer in a biologically relevant exciton-vibration dimers can manifest and benefit from non-classical fluctuations of collective pigment motions. The inadequacy of a classical description of selected vibrations is further illustrated by identifying features of electronic dynamics that are enhanced by quantum properties. A quan\-tum-thermo\-dynamical form\-alism describing heat and work fluxes between partitions of a closed quan\-tum system is extended to open quan\-tum systems in the non-per\-turb\-ative regime. This reveals non-trivial relations between the electronic interactions among chromophores and the relative contribution of work- and heat-like energy fluxes between electronic and vibrational motions. This in turn highlights relations between structure and energy transformations in photosynthetic complexes. Finally, the thesis investigates energy transfer within and between antennae of purple bacteria acclimated to different illumination conditions. The protein composition is altered depending on the light levels. Consequently, the electronic energy landscape is modified to accelerate intra-complex energy transfer without detriment to inter-complex transfer, thereby promoting or diminishing resonances with specific vibrational motions. This suggests that acclimation may serve to exploit non-trivial quantum phenomena

    Vibration-enhanced quantum transport

    Full text link
    In this paper, we study the role of collective vibrational motion in the phenomenon of electronic energy transfer (EET) along a chain of coupled electronic dipoles with varying excitation frequencies. Previous experimental work on EET in conjugated polymer samples has suggested that the common structural framework of the macromolecule introduces correlations in the energy gap fluctuations which cause coherent EET. Inspired by these results, we present a simple model in which a driven nanomechanical resonator mode modulates the excitation energy of coupled quantum dots and find that this can indeed lead to an enhancement in the transport of excitations across the quantum network. Disorder of the on-site energies is a key requirement for this to occur. We also show that in this solid state system phase information is partially retained in the transfer process, as experimentally demonstrated in conjugated polymer samples. Consequently, this mechanism of vibration enhanced quantum transport might find applications in quantum information transfer of qubit states or entanglement.Comment: 7 pages, 6 figures, new material, included references, final published versio

    Tracking the coherent generation of polaron pairs in conjugated polymers

    Get PDF
    The optical excitation of organic semiconductors not only generates charge-neutral electron-hole pairs (excitons), but also charge-separated polaron pairs with high yield. The microscopic mechanisms underlying this charge separation have been debated for many years. Here we use ultrafast two-dimensional electronic spectroscopy to study the dynamics of polaron pair formation in a prototypical polymer thin film on a sub-20-fs time scale. We observe multi-period peak oscillations persisting for up to about 1 ps as distinct signatures of vibronic quantum coherence at room temperature. The measured two-dimensional spectra show pronounced peak splittings revealing that the elementary optical excitations of this polymer are hybridized exciton-polaron-pairs, strongly coupled to a dominant underdamped vibrational mode. Coherent vibronic coupling induces ultrafast polaron pair formation, accelerates the charge separation dynamics and makes it insensitive to disorder. These findings open up new perspectives for tailoring light-to-current conversion in organic materials

    Electron counting statistics of open quantum systems

    Get PDF
    Electron transport through organic molecules is a process fundamental to life and plays a central role in the emerging field of molecular electronics. This thesis presents an investigation of electron transport through molecular systems from the perspective of full counting statistics. An extension of a Markovian counting statistics framework to a non-perturbative setting is presented which allows for an exact treatment of the phonon bath. This framework is applied to a theoretical photocell device inspired by the photosystem II reaction centre. It is demonstrated that the asymmetric coupling of excitation and charge transfer states to a structured spectral density rather than a smooth low energy background has the effect of reducing the output current along with an associated reduction in the current fluctuations. The insights gained from this are discussed in terms of design principles for pigmentprotein complexes used in nano-electronic devices and their relevance for biological function in vivo. Finally, the asymmetric coupling of excitation and charge transfer states to their vibrational environment is investigated more closely through the dynamics of a dimer model and the effect of the output current statistics of a prototype photocell

    Mechanistic Regimes of Vibronic Transport in a Heterodimer and the Design Principle of Incoherent Vibronic Transport in Phycobiliproteins

    Get PDF
    Following the observation of coherent oscillations in nonlinear spectra of photosynthetic pigment protein complexes, in particular, phycobilliproteins such as PC645, coherent vibronic transport has been suggested as a design principle for novel light-harvesting materials. Vibronic transport between energetically remote pigments is coherent when the presence of a vibration resonant with the electronic energy gap supports transient delocalization between the electronic excited states. We establish the mechanism of vibronic transport for a model heterodimer across a wide range of molecular parameter values. The resulting mechanistic map demonstrates that the molecular parameters of phycobiliproteins in fact support incoherent vibronic transport. This result points to an important design principle: Incoherent vibronic transport is more efficient than a coherent mechanism when energetic disorder exceeds the coupling between the donor and vibrationally excited acceptor states. Finally, our results suggest that the role of coherent vibronic transport in pigment protein complexes should be reevaluated
    corecore