Mapping Charge-Transfer Excitations in Bacteriochlorophyll Dimers from First Principles

TL;DR

This study uses first-principles simulations to analyze charge-transfer excitations in Bacteriochlorophyll dimers, revealing how coupling strength, geometry, and vibrations influence their electronic properties, aiding design of photoactive systems.

Contribution

It provides a detailed first-principles analysis of charge-transfer excitations in Bacteriochlorophyll dimers, including effects of intermolecular distance, orientation, and vibrations, which was not previously systematically studied.

Findings

Identified four regimes of intermolecular coupling affecting excitations.

Constructed an artificial dimer to study geometric effects systematically.

Highlighted the importance of charge-transfer excitations in modeling Bacteriochlorophyll aggregates.

Abstract

Photoinduced charge-transfer excitations are key to understand the primary processes of natural photosynthesis and for designing photovoltaic and photocatalytic devices. In this paper, we use Bacteriochlorophyll dimers extracted from the light harvesting apparatus and reaction center of a photosynthetic purple bacterium as model systems to study such excitations using first-principles numerical simulation methods. We distinguish four different regimes of intermolecular coupling, ranging from very weakly coupled to strongly coupled, and identify the factors that determine the energy and character of charge-transfer excitations in each case. We also construct an artificial dimer to systematically study the effects of intermolecular distance and orientation on charge-transfer excitations, as well as the impact of molecular vibrations on these excitations. Our results provide design rules for tailoring charge-transfer excitations in Bacteriochloropylls and related photoactive molecules, and highlight the importance of including charge-transfer excitations in accurate models of the excited-state structure and dynamics of Bacteriochlorophyll aggregates.