Decay- and evolution-associated spectra of time-resolved fluorescence of LHCII aggregates

Abstract

Non-photochemical quenching (NPQ) is responsible for the protection of the photosynthetic apparatus of plants from photodamage at high-light conditions. It is commonly agreed that NPQ takes place in the major light-harvesting complexes (LHCII), however, its exact mechanisms are still under debate. Valuable information about its molecular nature can be provided by measuring time-resolved fluorescence (TRF) spectra of LHCII complexes and their aggregates. Previously [Chmeliov et al., Nat. Plants 2, 16045 (2016)], we analysed the corresponding TRF spectra using the multivariate curve resolution method and proposed a three-state model to describe the spectroscopic data. Usually, such data is described in terms of global analysis resulting in decay or evolution-associated spectra. In this work, we apply such analysis to the TRF data of LHCII aggregates and show that, although mathematically feasible, it cannot be directly related to the physical kinetic model. Nevertheless, a careful examination supplemented with additional spectroscopic information still results in the same three-state model proposed before.

Light-harvesting complexes access analogue emissive states in different environments

“…As a result of the aggregate size, energy transfer is expected to follow a diffusive regime where a kinetic analysis in terms of DAS and exponential decays was shown not to be appropriate. 6 , 45 , 46 The current CP29 data reveal fluorescence kinetics that are qualitatively similar to those previously obtained for the oligomers of LHCII. 6 , 23 , 33 Such kinetics were interpreted in term of a heterogeneous picture where the LHC units in the aggregate can be found in different emissive states, characterized by different spectra and/or lifetimes, similar to what previously observed in single-molecule 4 , 17 , 18 and bulk 5 , 6 , 20 – 22 experiments on isolated LHCs.…”

Charge-Transfer States at Metal–Organic Interface Limit Singlet Fission Yields: A Photonically Enhanced Pump–Probe Study

“…We first examined SF in the bare TIPS-PEN layer (reference sample). From global analysis, , we obtain three time constants corresponding to the evolution of excitonic species (Supporting Information, Sections S11 and S12): τ 1 ∼ 1 ps, τ 2 ∼ 16 ps, and τ 3 ∼ 361 ps). An offset (fourth component) was also obtained and indicates a triplet-exciton lifetime much longer than the range of accessible pump–probe delays.…”

“…To capture interdependent relationships between excitons during evolution, we perform target analysis , (Figure ) yielding the spectrally resolved amplitudes referred to as species-associated difference spectra (SADS). Motivated by the simplified description of SF as a series of sequential processes (eq ), we apply a sequential kinetic model to analyze the transient response of the reference sample (Figure a).…”

“…Although the four detected time constants are similar across all samples (see Table 2), we demonstrate below that the few-hundreds-picoseconds dynamics (τ 3 ) is fundamentally different between the reference and metal-contacted samples. To capture interdependent relationships between excitons during evolution, we perform target analysis 41,45 (Figure 2) yielding the spectrally resolved amplitudes referred to as species-associated difference spectra (SADS). Motivated by the simplified description of SF as a series of sequential processes (eq 1), we apply a sequential kinetic model to analyze the transient response of the reference sample (Figure 2a).…”

Decay-Associated Fluorescence for Boron Determination in Uranium-Based Nuclear Fuels

“…DAS is the derived spectra of the individual fluorescent species, which contribute to the total fluorescence. − Construction of the DAS with global analysis (global analysis is the simultaneous analysis of all measurements) is done according to eqs and : F ( λ , t ) = ∑ i a i ( λ ) a − t / τ i DAS ( λ , t ) = a i ( λ ) τ i F SS ( λ ) ∑ i a i ( λ ) τ i where i = 1 denotes component 1 (τ 1 = 1.92 ns) is the free ligand (free chromotropic acid), i = 2 denotes component 2 (τ 2 = 7.13 ns) is attributed to the boron–chromotropic acid complex, and FSS (λ) is the measured steady-state fluorescence spectrum. In global analysis, the decay times of the species are fixed while the pre-exponential factors are varied in iterations until convergence is reached.…”