Ultra-broadband 2D electronic spectroscopy of carotenoid-bacteriochlorophyll interactions in the LH1 complex of a purple bacterium

Abstract

Articles you may be interested inUltra-broadband 2D electronic spectroscopy of carotenoid-bacteriochlorophyll interactions in the LH1 complex of a purple bacterium We investigate the excitation energy transfer (EET) pathways in the photosynthetic light harvesting 1 (LH1) complex of purple bacterium Rhodospirillum rubrum with ultra-broadband two-dimensional electronic spectroscopy (2DES). We employ a 2DES apparatus in the partially collinear geometry, using a passive birefringent interferometer to generate the phase-locked pump pulse pair. This scheme easily lends itself to two-color operation, by coupling a sub-10 fs visible pulse with a sub-15-fs near-infrared pulse. This unique pulse combination allows us to simultaneously track with extremely high temporal resolution both the dynamics of the photoexcited carotenoid spirilloxanthin (Spx) in the visible range and the EET between the Spx and the B890 bacterio-chlorophyll (BChl), whose Q x and Q y transitions peak at 585 and 881 nm, respectively, in the near-infrared. Global analysis of the one-color and two-color 2DES maps unravels different relaxation mechanisms in the LH1 complex: (i) the initial events of the internal conversion process within the Spx, (ii) the parallel EET from the first bright state S 2 of the Spx towards the Q x state of the B890, and (iii) the internal conversion from Q x to Q y within the B890. C 2015 AIP Publishing LLC.[http://dx

A new energy transfer channel from carotenoids to chlorophylls in purple bacteria

“…Taking into account the additional 0.1 eV downshift of the S y state to its own potential minimum as discussed above, the emission energy of the S y state is lower than that of the S 2 state for N  ≥ 9 and the gap between them remains at ∼ 0.1 eV. This agrees well with the transient absorption studies that the dark state lies below the S 2 state for Cars with N  ≥ 9 11 , and also 2DES measurements that the potential minimum of the dark state is 0.1 eV below that of the S 2 state for N  = 10, 11, and 13 6, 10, 21 .…”

“…More importantly, variation of the S y emission energy with respect to the conjugation length is parallel to the S 2 state, and their energy gap is kept at a small value (~ 0.1 eV) for Cars with N  > 9. This is consistent with the experimental findings, such as those in 2DES, that the emission energy gap between the dark state and the S 2 state is about 300 cm −1 and independent of the conjugation length 4, 6, 10, 21 . This small energy gap ensures the extremely fast (~10 fs) internal conversion from the S 2 state to the dark state as observed experimentally 4, 5, 11 .…”

“…Especially, the conjugation-length dependence of the 1B u − state is not in accord with that of the dark state as observed in the emission spectra and transient absorption spectra 16–20 . Recent two-dimensional electronic spectroscopy (2DES) and high-time resolution broadband pump-probe spectroscopy measurements on Cars spheroidene ( N  = 10), rhodopin glucoside (RG) ( N  = 11) and spirilloxanthin ( N  = 13) demonstrate clearly the decay of the S 2 state to the dark state and the energy transfer channel from the dark state to the Q x state of Chls 6, 10, 21, 22 . From these experiments, emission energy of the dark state seems to lie a little bit (~0.1 eV) below that of the S 2 state, irrespective of the conjugation length of Cars.…”

Two-dimensional action spectroscopy of excitonic systems: Explicit simulation using a phase-modulation technique

“…The spectra are grouped as rephasing (first row) and nonrephasing (second row). Usually, the rephasing and the nonrephasing spectra are summed in order to obtain the absorptive signal, which is also known as the total correlation [44][45][46].…”

“…The total correlation spectra can also be easily measured in a pump-probe geometry [44][45][46], where the coherent response from the sample is heterodyned with the probe field. The total correlation spectra are important in quantifying the homogeneous and the inhomogeneous broadening.…”