Fig. 4: Time- and frequency-resolved fluorescence spectroscopy of photosynthetic membranes at the single-photon level.

a Energy level scheme of the BChls in the LH2 and LH1 complexes, indicating the cascade of EET processes leading to light capture in the RC and charge separation; b time and frequency-resolved fluorescence spectrum of LH2 of the purple photosynthetic bacterium R. acidophilus, following single-photon excitation of B800 BChls and EET to B850 taken with 200 interferometer scan points, 1 min each (total acquisition time, 3.3 h). The inset shows the same measurement, retaken with 100 scan points, 2 s dwell time, 3.3 min total acquisition time; c fluorescence decay at 860 nm taken from (b) after integrating along the wavelength axis) and fit (dashed line), blue continuous line single photon excitation, black dotted line femtosecond pulse excitation (the inset shows the decay taken from the inset to (b)); d wavelength-integrated time-resolved fluorescence decay of the photosynthetic membrane of Rhodobacter sphaeroides, following single-photon excitation at 800 nm with open (blue trace) and closed (red trace) RCs; e time-integrated fluorescence spectra of the photosynthetic membrane with open (blue) and closed (orange dashed) RCs.