The role of mixed vibronic Qy-Qx states in green light absorption of light-harvesting complex II

Eric A Arsenault,Masakazu Iwai,Yusuke Yoneda,Krishna K Niyogi,Graham R Fleming

doi:10.1038/s41467-020-19800-y

Abstract

The importance of green light for driving natural photosynthesis has long been underappreciated, however, under the presence of strong illumination, green light actually drives photosynthesis more efficiently than red light. This green light is absorbed by mixed vibronic Qy-Qx states, arising from chlorophyll (Chl)-Chl interactions, although almost nothing is known about these states. Here, we employ polarization-dependent two-dimensional electronic-vibrational spectroscopy to study the origin and dynamics of the mixed vibronic Qy-Qx states of light-harvesting complex II. We show the states in this region dominantly arise from Chl b and demonstrate how it is possible to distinguish between the degree of vibronic Qy versus Qx character. We find that the dynamics for states of predominately Chl b Qy versus Chl b Qx character are markedly different, as excitation persists for significantly longer in the Qx states and there is an oscillatory component to the Qx dynamics, which is discussed. Our findings demonstrate the central role of electronic-nuclear mixing in efficient light-harvesting and the different functionalities of Chl a and Chl b.

Highlights

The importance of green light for driving natural photosynthesis has long been underappreciated, under the presence of strong illumination, green light drives photosynthesis more efficiently than red light
This effort has increasingly led to a deeper understanding of Chl–Chl interactions, which predominately manifest energetically in the red edge of the light-harvesting complex II (LHCII) absorption spectrum[14]
We present direct evidence that this spectral region is dominated by Chl b character, which together with previous in vivo studies indicates that Chl b enhances the ability of green plants and algae to harvest green light[1,24,25,26]

Summary

Introduction

The importance of green light for driving natural photosynthesis has long been underappreciated, under the presence of strong illumination, green light drives photosynthesis more efficiently than red light. An assignment for the feature at 1670 cm−1 was not totally conclusive, the spectral regions around 1650 cm−1 and 1670 cm−1 evolved on similar timescales and it is clearly a dominant ESA in the band of mainly Chl b origin, suggesting that the 1670 cm−1 band has significant character from more localized Chl b states.

Results

Conclusion