Filling the Green Gap of a Megadalton Photosystem I Complex by Conjugation of Organic Dyes

Abstract

Photosynthesis is Nature's major process for converting solar into chemical energy. One of the key players in this process is the multiprotein complex photosystem I (PSI) that through absorption of incident photons enables electron transfer, which makes this protein attractive for applications in bioinspired photoactive hybrid materials. However, the efficiency of PSI is still limited by its poor absorption in the green part of the solar spectrum. Inspired by the existence of natural phycobilisome light-harvesting antennae, we have widened the absorption spectrum of PSI by covalent attachment of synthetic dyes to the protein backbone. Steady-state and time-resolved photoluminescence reveal that energy transfer occurs from these dyes to PSI. It is shown by oxygen-consumption measurements that subsequent charge generation is substantially enhanced under broad and narrow band excitation. Ultimately, surface photovoltage (SPV) experiments prove the enhanced activity of dye-modified PSI even in the solid state.

Aqueous-soluble bipyridine cobalt(ii/iii) complexes act as direct redox mediators in photosystem I-based biophotovoltaic devices

“…However, current designs still function well below the internal quantum efficiency shown for PSI and photosynthetic charge separation in general, 9,14 suggesting room for device improvement. There are many different approaches being studied for the improvement of PSI-based biohybrid devices, including improving the unidirectionality of deposited PSI on electrodes, 15,16 improvement of the optical cross-section of PSI to increase light harvesting capabilities, 17,18 and interest in creation of solid-state devices [19][20][21] A key area of improvement is in PSI reduction rates to help increase dye regeneration rates. Reduction of T. elongatus PSI by its native biological redox mediator, the one-electron shuttle protein cytochrome c 6 , has (1) PSI absorbs a photon, (2) which then promotes the special chlorophyll pair PSI-P700 to an excited state.…”

Enhancement of Light Absorption Ability of Synthetic Chlorophyll Derivatives by Conjugation with a Difluoroboron Diketonate Group

“…However, both Chls‐ a / b can partially utilize the intense green light at λ ≈500–600 nm from the sun's illumination, which is termed the “green gap”. The low absorbance between their characteristic Soret and Qy bands with maxima in the purple and red regions, respectively, is disadvantageous for the simple production of efficient solar energy conversion systems by using their pigments . Some oxygenic phototrophs partially cover this gap with the help of other pigments in proteins, including bilins in phycobilisomes…”

Green Catalysts: Applied and Synthetic Photosynthesis

“…This 676 nm light is near the optimal excitation wavelength for PSI. However, the efficiency of PSI electron generation through the absorption of incident photons is limited by its poor absorption in the "green gap" of its absorption spectrum [7]. One approach to increase the optical cross-section of reaction centers is the incorporation of synthetic dyes that absorb in different regions of the UV-Vis spectrum, enabling a transfer of energy from the dyes to the reaction center [7].…”

“…However, the efficiency of PSI electron generation through the absorption of incident photons is limited by its poor absorption in the "green gap" of its absorption spectrum [7]. One approach to increase the optical cross-section of reaction centers is the incorporation of synthetic dyes that absorb in different regions of the UV-Vis spectrum, enabling a transfer of energy from the dyes to the reaction center [7]. Dye-modified PSI activity has been shown to be enhanced even in solid state devices as evident via surface photovoltage (SPV) experiments [7].…”

“…The coupling of approximately 30 ATTO 590 dye molecules to PSI increased the oxygen consumption activity of PSI by over 4-fold, and the addition of Lumogen Red allowed for greater energy transfer to PSI via Förster resonance energy transfer. Expanding the light harvesting capabilities of PSI through conjugation of dyes [7,12] is likely to be an area of further focus for improving outputs of future reaction center-based biohybrid devices.…”