Davydov Splitting of Excitons in Cyclic Bacteriochlorophyll a Nanoaggregates of Bacterial Light‐Harvesting Complexes between 4.5 and 263 K

Abstract

The nature of electronic excitations created by photon absorption in the cyclic B850 aggregates of 18 bacteriochlorophyll molecules of LH2 antenna complexes of photosynthetic bacteria is studied over a broad temperature range using absorption, fluorescence, and fluorescence anisotropy spectra. The latter technique has been proved to be suitable for revealing the hidden structure of excitons in inhomogeneously broadened spectra of cyclic aggregates. A theoretical model that accounts for differences of absorbing excitons in undeformed and emitting exciton polarons in deformed antenna lattices is also developed. Only a slight decrease of the exciton bandwidth and exciton coupling energy with temperature is observed. Survival of excitons in the whole temperature span from cryogenic to nearly ambient temperatures strongly suggests that collective, coherent electronic excitations might play a role in the functional light-harvesting process taking place at physiological temperatures.

Subtle spectral effects accompanying the assembly of bacteriochlorophylls into cyclic light harvesting complexes revealed by high-resolution fluorescence spectroscopy

“…3,5,6 It also explains the much greater sensitivity on temperature of the B850 absorption band position compared with that of the B800 band. 17,25,33 As shown by the single complex measurements, 15 hidden within the inhomogeneously broadened B850 absorption band are the components attributed to several exciton states. The lowest-energy exciton (or rather self-trapped exciton, see below) states with the maximum at ∼885 nm appear distributed over 120 cm −1 , when recorded as full width at half maximum, fwhm.…”

Metal Cations Induced αβ‐BChl a Heterogeneity in LH1 as Revealed by Temperature‐Dependent Fluorescence Splitting

“…[42] In previous studies, V 12 and V 23 were determined to be 300-400 cm À1 forL H2, [11] and 290-500 cm À1 for LH1. The Q y transition energiesf or a-and b-BChl a (e a 0 and e b 0 )a re set to 12 165 cm À1 (822 nm).…”

“…[1][2][3][4][5][6] In LH2 or LH1, bacteriochlorophyll( BChl) a dimers are sandwiched between a-a nd b-polypeptides of 8, 9 [7,8] or 16 [9,10] subunits arranged in ar inglike manner.T he distance between neighboring BChls is % 9 , leadingt oaconsiderable nearest-neighbour coupling strength of 250-400cm À1 . [11,12] So these BChl a aggregates can be theoreticallyd escribed with the Frenkel excitonm odel,w ith static (inhomogeneity in local site energy) and dynamic (interaction with the phononb ath) disorders induced by slow and fast nuclear motions taken into account. [13][14][15][16][17] LH1 of Thermochromatium (Tch.)…”

Principles of light harvesting from single photosynthetic complexes

“…LH2 has an order of magnitude more inhomogeneity in excited state energies than other bacterial LHCs, suggesting that it is particularly sensitive to thermal fluctuations [33]. Specifically, LH2 has an inhomogeneous broadening of 300 cm 21 [34], understand photosynthesis smarter design optimized devices widespread usage Figure 1. Flow chart shows the pathway to artificial photosynthesis.…”