Light harvesting simulations explain biological photosynthetic behaviors

Light-induced reactions are ubiquitous in nature and the dominant energy contribution to all known forms of life on Earth. However, many radiation studies rely on pulsed laser experiments, which are fundamentally different from natural radiation. Motivated by a need to understand biological processes induced by solar light, Chern Chuang and Paul Brumer constructed a minimally functioning model to simulate light harvesting under biologically relevant conditions.

“Many applications of light-induced processes rely on incoherent light, ranging from solar cells to chemical sunscreens,” said Chuang. “Optimization of such processes would benefit greatly from a detailed understanding of the underlying mechanisms of processes induced by natural light.”

By characterizing light-harvesting bacteria under both incoherent thermal light conditions and in the long-term steady state limit, the team found the system to be resilient in its ability to function with high efficiency within a wide range of light intensities. Consistent with experiments, they found three main regions of behavior: an active photosynthesis region and two saturated regions, where only a limited number of the system’s bacteriochlorophyll molecules are available for photon absorption. The reaction center’s recovery rate determines the upper bound of the excitation energy transfer.

To gain insights into the energy transfer process, Chuang and Brumer modeled the system’s behavior while controlling the intensity of incident radiation. Because natural light is a cheap source of photons, they hope their results will inform technological applications that require an understanding of light-induced energy transport.

“Our work emphasizes the important paradigm shift associated with considering such processes using incoherent light, which is natural, rather than pulsed laser light, which is artificial,” Chuang said.

Source: “LH1-RC light-harvesting photocycle under realistic light-matter conditions,” by Chern Chuang and Paul Brumer, Journal of Chemical Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0004490 .