Population and Coherence Dynamics in Light Harvesting Complex II (LH2)

TL;DR

This study uses a theoretical approach to analyze excitation and coherence dynamics in LH2, revealing shorter oscillation times than FMO and the impact of temperature and environment on exciton propagation and coherence.

Contribution

It provides the first detailed theoretical analysis of excitation and coherence dynamics in LH2 at different temperatures using a scaled HEOM approach.

Findings

Oscillation time in LH2 is 300 fs at cryogenic temperature.

Higher temperature and environment accelerate exciton propagation.

Long-lived coherence can exist despite noisy biological conditions.

Abstract

The electronic excitation population and coherence dynamics in the chromophores of the photosynthetic light harvesting complex 2 (LH2) B850 ring from purple bacteria (Rhodopseudomonas acidophila) have been studied theoretically at both physiological and cryogenic temperatures. Similar to the well-studied Fenna-Matthews-Olson (FMO) protein, oscillations of the excitation population and coherence in the site basis are observed in LH2 by using a scaled hierarchical equation of motion (HEOM) approach. However, this oscillation time (300 fs) is much shorter compared to the FMO protein (650 fs) at cryogenic temperature. Both environment and high temperature are found to enhance the propagation speed of the exciton wave packet yet they shorten the coherence time and suppress the oscillation amplitude of coherence and the population. Our calculations show that a long-lived coherence between chromophore electronic excited states can exist in such a noisy biological environment.