Coherent Speedup of Excitation Energy Transfer in PC645

Abstract

The fundamental principle governing the robust excitation energy transfer (EET) in the light-harvesting complexes remained elusive. Recent spectroscopic observations of the EET attract attention toward the role of the quantum effects in the biological systems. In this study, along with the time evolution, the distance between the quantum states of the pigments is also considered for a detailed illustration of the effect of the quantum coherence on the speed of the excitation transfer. The comparative analysis of the coherently delocalized EET with the incoherent discrete hopping reveals that the coherent superposition speedup the excitation transfer process, for instance, with the initially localized excitation, coherence provides a ∼4-fold enhancement to the excitation transfer rate.

Dynamics of Excitons in Conjugated Molecules and Organic Semiconductor Systems

“…In this case, a resonant condition for energy transfer takes place and EET occurs by the coherent mechanism, which can significantly speed up the EET rate, for example, by a 4-fold enhancement in the PC645 complex. 377 However, if energetic disorder exceeds the coupling between the donor and vibrationally excited acceptor states then the incoherent vibronic transport is more efficient than a coherent mechanism. 378 Direct evidence of the coherent energy transfer is quantum oscillations or quantum beats in the excitonic population of an acceptor (Figure 39b).…”

“…On the other hand, vibrations intertwined with electronic excitations through coherent superposition can create specific vibronically hot excitonic energy transfer pathways where the superposition energy matches the donor–acceptor energy gap. In this case, a resonant condition for energy transfer takes place and EET occurs by the coherent mechanism, which can significantly speed up the EET rate, for example, by a 4-fold enhancement in the PC645 complex . However, if energetic disorder exceeds the coupling between the donor and vibrationally excited acceptor states then the incoherent vibronic transport is more efficient than a coherent mechanism …”

Determining interchromophore effects for energy transport in molecular networks using machine-learning algorithms

“…Furthermore, HEOM includes more dynamical processes than FRET and yields more detailed, more exact results. 53,57 The total Hamiltonian H ˆtot is composed of the system H ˆs, environmental bath H ˆe, and system-environmental coupling H ˆse contributions (eqn ( 5)-( 8)). 58 In these equations, E n is the state energy, l n is the reorganization energy, and V nm is the coupling for Sites n and m. Furthermore, m nj is the mass, o nj is the angular frequency, p ˆnj is the momentum operator, c nj is the coupling, and x ˆnj is the position operator of Site n and environmental bath oscillator j.…”

Multiple Quantum-Coherent Energy Transfer Pathways in Photosynthesis: Electronic-Vibrational Mixing within Photosystem II CP43/CP47 Antenna

“…With this contribution, our objective is to determine whether ET in CP43/CP47 proceeds via a quantumcoherent mechanism. In this manner we aim to shed light on the long-lasting debate 20,21 about the presence and role of coherence in light-harvesting with confronting views both in favour [22][23][24][25][26][27] and against 28,29 the fact that non-trivial quantum coherent effects play a fundamental role in determining the speed and e ciency of ET. Furthermore, we revisit the ET process within CP43/CP47 to improve our understanding about the possible ET pathways in these biologically relevant light-harvesting complexes.…”

“…The electronic coherence between two states creates correlations between the wavefunctions of the states enabling the excitation energy to move rapidly and to coherently sample multiple pathways in space 1,3,[33][34][35] . Consequently, electronic coherence provides directionality 36 , speed, robustness (low sensitivity to the intrinsic energetic disorder found in biological systems), and e ciency to energy transfer [22][23][24] and electron transfer 34,[37][38][39][40] processes. The mixed electronic-vibrational coherence (so-called vibronic; that is, vibrationassisted electronic coherence) corresponds to electronic coherence promoted by an intra-molecular vibration of the system.…”