Abstract
Zn chlorin (Znchl) is easy to synthesize and has similar optical properties to those of bacteriochlorophyll c in the nature, which is expected to be used as a light-harvesting antenna system in artificial photosynthesis. In order to further explore the optical characteristics of Znchl, various sizes of a parallel layered Znchl-aggregate model and the THF-Znchl explicit solvent monomer model were constructed in this study, and their excited state properties were simulated by using time-dependent density functional theory (TDDFT) and exciton theory. For the Znchl monomer, with a combination of the explicit solvent model and the implicit solvation model based on density (SMD), the calculated excitation energy agreed very well with the experimental one. The Znchl aggregates may be simplified to a Zn36 model to reproduce the experimental absorption spectrum by the Förster coupling theory. The proposed Znchl aggregate model provides a good foundation for the future exploration of other properties of Znchl and simulations of artificial light-harvesting antennas. The results also indicate that J-aggregrates along z-direction, due to intermolecular coordination bonds, are the dominant factor in extending the band of Znchl into the near infrared region.
Highlights
The chlorosomes in green photosynthetic bacteria are the largest light-harvesting antennae in the nature, which are composed of more than 200,000 bacteriochlorophyll (Bchl) c, d, and e molecules [1]. They can collect solar energy in low-light conditions, and the acquired energy may be transferred to the photosynthetic reaction center very quickly, so green photosynthetic bacteria can be found in conditions of low light [2]
The Qy excitation energies of the Zn chlorin (Znchl) monomer model and Znchl supramolecular aggregates were simulated by time-dependent density functional theory (TDDFT) and exciton theory respectively
Functional combined with the solvation model based on density (SMD) solvent model, the Qy excitation energy by TDDFT was in good agreement with the experimental excitation energy, which confirms that the THF
Summary
The chlorosomes in green photosynthetic bacteria are the largest light-harvesting antennae in the nature, which are composed of more than 200,000 bacteriochlorophyll (Bchl) c, d, and e molecules [1]. They can collect solar energy in low-light conditions, and the acquired energy may be transferred to the photosynthetic reaction center very quickly, so green photosynthetic bacteria can be found in conditions of low light [2]. Several teams simulated and characterized the structures of chlorosomes in natural green sulfur bacteria by means of cryo-electron microscopy, and proposed three possible structures, i.e., layered [8], tubular [9], and spiral [10] ones, respectively, which provide some clues for the construction of artificial light capture antenna models
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