# Unraveling Charge-Transfer States and Their Ultrafast Dynamics in Artificial Light-Harvesting Complexes

## TL;DR

Scientists designed artificial proteins to mimic photosynthesis, capturing light efficiently and enabling ultrafast energy conversion with potential applications in solar cells and medicine.

## Contribution

De novo designed proteins are shown to emulate natural photosynthetic processes by enabling efficient charge transfer and energy conversion.

## Key findings

- Dimerization increases the charge-transfer character of the excited state compared to monomeric ZnP.
- Dimers exhibit additional nonradiative relaxation pathways and transient species not seen in monomers.
- Artificial proteins can replicate key features of natural photosynthesis, offering tunable scaffolds for light-harvesting optimization.

## Abstract

Photosynthesis relies
on highly organized pigment–protein
complexes in order to store sunlight energy as biochemical energy.
These complexes capture light with remarkable efficiency and are responsible
for ultrafast charge separation within a finely tuned energy landscape
provided by the protein environments, producing one of nature’s
most sophisticated energy conversion systems. Inspired by nature, de novo designed proteins have been proven to be versatile
platforms to emulate the function of natural light-harvesting complexes
and reaction centers. With Stark and ultrafast transient absorption
spectroscopies, we explored the exciton and charge-transfer (CT) mixing,
as well as the excited-state dynamics, of a chlorophyll a analogue (Zn-pheophorbide a) in dimers formed within
4-α-helix bundles whose design was previously guided by molecular
dynamics simulations. Due to dimerization, we observe an increase
in the CT character of the excitonically coupled dimers’ excited
state in comparison to monomeric ZnP. Furthermore, additional nonradiative
relaxation pathways, together with the formation of transient species
absent in monomeric systems, were observed for the dimers. We demonstrate
that de novo designed proteins can replicate key
features of photosynthetic energy conversion, serving as tunable scaffolds
for optimizing light-harvesting processes. Ultimately, these systems
have promising applications including photovoltaic cells and biomedical
treatments based on sustainable materials.