# The light-harvesting complex 2 of allochromatium vinosum: B800 absorption band splitting and exciton relaxation

## TL;DR

This paper develops a model Hamiltonian combining Frenkel exciton theory and quantum master equations to explain the absorption features and exciton relaxation dynamics in the light-harvesting complex 2 of Allochromatium vinosum.

## Contribution

It introduces a detailed system-bath model that accurately reproduces absorption spectra and exciton relaxation times for Alc. vinosum LH2, advancing understanding of its excitonic interactions.

## Key findings

- Identification of two excitonic bands from different pigment pools.
- Reproduction of absorption band splitting around 800 nm.
- Explanation of exciton relaxation dynamics in LH2.

## Abstract

Allochromatium (Alc.) vinosum has a double-peak structure of its absorption band around 800~nm. Previously, the excitonic origin of this feature has been demonstrated experimentally, but a detailed understanding still lacks a model Hamiltonian being able to reproduce absorption as well as exciton relaxation time scales. Here, we propose a system-bath model which accommodates these observables. It combines Frenkel exciton theory for a dimerized and energetically heterogeneous B800 pigment pool with a quantum master equation approach describing phase and energy relaxation according to an experimental spectral density. The analysis of this model shows that the LH2 of Alc. vinosum features an interesting interplay of two excitonic bands, which are originating from the different pigment pools.