Abstract

It is unclear whether there is an intermediate dark state between the S2 and S1 states of carotenoids. Previous two-dimensional electronic spectroscopy measurements support its existence and its involvement in the energy transfer from carotenoids to chlorophylls, but there is still considerable debate on the origin of this dark state and how it regulates the energy transfer process. Here we use ab initio calculations on excited-state dynamics and simulated two-dimensional electronic spectrum of carotenoids from purple bacteria to provide evidence supporting that the dark state may be assigned to a new Ag+ state. Our calculations also indicate that groups on the conjugation backbone of carotenoids may substantially affect the excited-state levels and the energy transfer process. These results contribute to a better understanding of carotenoid excited states.

Highlights

  • It is unclear whether there is an intermediate dark state between the S2 and S1 states of carotenoids

  • With many-body Green’s function theory, we study the excited-state dynamics of rhodopin glucoside (RG) (N = 11) in Rps. acidophila (Fig. 2) and spirilloxanthin (N = 13) in Rhodospirillum rubrum

  • We prove that putting some protein fragments near Cars has limited effects on the excitation energies of Cars (Supplementary Fig. 2)

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Summary

Introduction

It is unclear whether there is an intermediate dark state between the S2 and S1 states of carotenoids. The origin and nature of a dark state, which lies bfoertbwiedednenthSe1s(t2roAngg−l)ysotantee-,phhaostotrnigaglelorewdedinSte2n(s1eBrue+s)eastracthe and and the has been under debate This dark state would have a critical role in mediating the Car-to-Chl energy transfer process and the depopulation of the S2 state[4,5,6,7,8,9,10,11]. The 1Bu− state is the popular choice for the attribution of the dark state (Fig. 1b), and it seems to be the only choice based on the present theory on the excited-state structure of polyenes, which are closely related to the Cars This assignment is controversial due to the contradiction between the properties of the dark state measured experimentally and the behavior of the.

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