Exciton Structure and Energy Transfer in the Fenna–Matthews–Olson Complex

Abstract

The Fenna-Matthews-Olson (FMO) photosynthetic complex found in green sulfur bacteria has over the last decades been one of the favorite "model" systems for biological energy transfer. However, even after 40 years of studies, quantitative knowledge about its energy-transfer properties is limited. Here, two-dimensional electronic spectroscopy with full polarization control is used to provide an accurate description of the electronic structure and population dynamics in the complex. The sensitivity of the technique has further allowed us to spectroscopically identify the eighth bacterio-chlorophyll molecule recently discovered in the crystal structure. The time evolution of the spectral structure, covering time scales from tens of femtoseconds up to a nanosecond, reflects the energy flow in FMO and enables us to extract an unambiguous energy-transfer scheme.

Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer

“…Our findings qualitatively agree with those in ref. 17, with all our dephasing times being shorter, which is due the difference in temperature between 77 K and the present studies under ambient conditions. Next, we address the question of long-lived coherent oscillations in off-diagonal signals in the 2D spectra.…”

“…Recently, an eighth pigment in the FMO complex was found (54). However, its spatial distance from the other seven pigments is very large, and it is very likely that this pigment is removed in the majority of the complexes during the isolation procedure (17,54). The model parameters (i.e., the site energies m and the electronic couplings Jn,m) were taken from ref.…”

“…These experiments have triggered an enormous interest in a potential new field of "quantum biology" (10)(11)(12)(13)(14), with far-reaching consequences, even for the functionality of the human brain (15) and for technological applications (16). The cornerstone experiments (3-5) remained unconfirmed until recently, when a new effort was made to identify the excitonic energy transfer pathways (17) at 77 K. However, observation of long-lived electronic coherences in the 2D off-diagonal signals was not mentioned in ref. 17.…”

“…The cornerstone experiments (3-5) remained unconfirmed until recently, when a new effort was made to identify the excitonic energy transfer pathways (17) at 77 K. However, observation of long-lived electronic coherences in the 2D off-diagonal signals was not mentioned in ref. 17.…”

Resolving Vibrational from Electronic Coherences in Two-Dimensional Electronic Spectroscopy: The Role of the Laser Spectrum

“…The extra dimension, given by the excitation frequency axis, yields 2D spectra where discrimination of specific features (otherwise overlapped in 1D methods) is now possible [1]. Consequently, 2D-ES has provided new insights into topics as diverse as quantum phenomena in biology [2][3][4], energy transfer [5,6], singlet fission [7], nanomaterials [8,9], reaction dynamics [10][11][12], and many body effects in coupled quantum wells [13][14][15]. However, although 2D-ES greatly facilitates the discrimination of physical phenomena affecting electronic transitions such as line-broadening mechanisms, vibrational and electronic couplings, ambiguities remain in detailed analysis, especially for molecular systems where both vibrational and electronic couplings may play a role.…”