energy transfer
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2022 ◽  
Vol 243 ◽  
pp. 118666
Viktor Anselm ◽  
Tim Pier ◽  
Thomas Jüstel

Ruixiang Wu ◽  
Xiaoshuai Wang ◽  
Jingjing Luo ◽  
Xin Liu ◽  
Bin Li ◽  

2022 ◽  
Vol 12 ◽  
Callum Gray ◽  
Tiejun Wei ◽  
Tomáš Polívka ◽  
Vangelis Daskalakis ◽  
Christopher D. P. Duffy

Higher plants defend themselves from bursts of intense light via the mechanism of Non-Photochemical Quenching (NPQ). It involves the Photosystem II (PSII) antenna protein (LHCII) adopting a conformation that favors excitation quenching. In recent years several structural models have suggested that quenching proceeds via energy transfer to the optically forbidden and short-lived S1 states of a carotenoid. It was proposed that this pathway was controlled by subtle changes in the relative orientation of a small number of pigments. However, quantum chemical calculations of S1 properties are not trivial and therefore its energy, oscillator strength and lifetime are treated as rather loose parameters. Moreover, the models were based either on a single LHCII crystal structure or Molecular Dynamics (MD) trajectories about a single minimum. Here we try and address these limitations by parameterizing the vibronic structure and relaxation dynamics of lutein in terms of observable quantities, namely its linear absorption (LA), transient absorption (TA) and two-photon excitation (TPE) spectra. We also analyze a number of minima taken from an exhaustive meta-dynamical search of the LHCII free energy surface. We show that trivial, Coulomb-mediated energy transfer to S1 is an unlikely quenching mechanism, with pigment movements insufficiently pronounced to switch the system between quenched and unquenched states. Modulation of S1 energy level as a quenching switch is similarly unlikely. Moreover, the quenching predicted by previous models is possibly an artifact of quantum chemical over-estimation of S1 oscillator strength and the real mechanism likely involves short-range interaction and/or non-trivial inter-molecular states.

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