Fig. 2: Impact of the membrane environment on energetics and relaxation dynamics of carotenoids.
a Absorptive 2D spectrum of LHCII in detergent (left) and in the membrane (right) in the Car S2/S1 region at T = 533 fs. Contour lines are drawn at 15% intervals. White dashed lines indicate the shift in Car S1 → SN transition energy (\(\Delta {E}_{{{\rm{S}}}_{1}-{{\rm{S}}}_{{\rm{N}}}}\)). Colored sticks indicate the energy levels of the Car S2 states. b Intensity of the Car S1 ESA relative to the initial Car S2 population at T = 533 fs in detergent (gray) and in membrane discs (green). The relative S1 intensity was obtained by normalizing the S1 ESA intensity to the initial S2 GSB intensity immediately after photoexcitation (T = 30 fs). c Comparison of Car S1 ESA decay constants in detergent (gray) and in membrane discs (green). Due to the limited temporal window of our 2DES measurement (T = 0−8 ps), we are unable to determine the accurate S1 lifetimes and therefore confine our discussion to relative changes in these timescales. d Absorptive 2D spectrum of the Car–Chl cross peak region at T = 300 fs (in detergent). Colored sticks indicate the energy levels of the Car S2 and Chl Q states. e Ratio of Car–Chl cross peak intensity obtained by dividing the sum of all cross peak intensities in the membrane by that in detergent. Error bars in b, c, and e are s.d. from three independent measurements. f Projection of the 2D spectra shown in a onto the ωt-axis for a 600 cm−1 ωτ interval centered at ωτ = 20,000 cm−1 (gray: detergent, green: membrane). g A closer view of the boxed region in f, where both traces are normalized to the same scale to emphasize the energy shift.
