# Comparison of Chlorophyll and Bacteriochlorophyll Ultrafast Transient Absorption Spectra and Kinetics

## TL;DR

This paper compares the ultrafast light absorption and energy dynamics of two types of photosynthetic pigments to better understand how they convert light into energy.

## Contribution

The study provides a direct comparison of the ultrafast excited-state dynamics of chlorophyll and bacteriochlorophyll pigments using time-resolved absorption spectroscopy.

## Key findings

- Ultrafast spectral and kinetic data reveal similarities and differences in the excited-state dynamics of chlorophyll and bacteriochlorophyll.
- The results clarify how pigment structure influences ultrafast processes in oxygenic and anoxygenic photosynthesis.
- The study spans femtosecond to sub-microsecond timescales to capture transient electronic states.

## Abstract

Oxygenic and anoxygenic photosynthesis are initiated through the absorption of light by chlorophyll and bacteriochlorophyll photosynthetic pigments, respectively, which function as light-harvesting (antenna) and redox pigments on the photosynthetic membrane that trap and convert the absorbed optical energy into chemical energy. While several studies have characterized the ultrafast spectra, kinetics, and structures of the light-harvesting and reaction center complexes that contain the photosynthetic pigments, a detailed understanding of how the ultrafast excited-state dynamics vary across different photosynthetic pigments is lacking. Such information is critical in understanding the molecular mechanisms of both artificial and natural photosynthetic systems. In this study, we conducted ultrafast time-resolved absorption spectroscopy on chlorophyll and bacteriochlorophyll photosynthetic pigments at room temperature to directly compare the spectra and kinetics of their transient, excited electronic states formed following photon absorption. The recorded ultrafast spectral and kinetic data, spanning the femtosecond to sub-microsecond timescales, show interesting similarities and differences between these two distinct types of photosynthetic pigments. These experimental results help clarify the relationship between photosynthetic pigment structure and the resultant ultrafast processes in the oxygenic and anoxygenic photosynthetic reaction mechanisms.