New study on a recently discovered chlorophyll molecule could be key to better solar cells

In a new study published in Nature Communications, a team of researchers led by Prof. Tatsuya Tomo at the Tokyo University of Science, Japan, and including collaborating researchers from Okayama University, Tsukuba University, Kobe University, and RIKEN, revealed new details about the location and functions of Chl f. They wanted to gain insight into the complex process of photosynthesis, as an in-depth understanding of this process could have various future applications, such as the development of solar cells. Talking about the study, Prof. Tomo says, "The initial course of photosynthesis begins when the photosynthetic pigment bound to this photochemical complex absorbs light. We analyzed the structure of a newly discovered photochemical complex, photosystem I with Chl f that has an absorption maximum on the lower energy side of light (far-red light). Moreover, we analyzed the function of Chl f."

What the scientists knew so far was that Chl f is "far-red shifted," which means that this molecule absorbs far-red light from the lower end of the light spectrum. Prof. Tomo and his team wanted to dig deeper, and for this, they studied the alga in which Chl f was first discovered. By using techniques such as cryo-electron microscopy, they analyzed the high-resolution structure of the photosystem in this alga in detail and found that Chl f is located at the periphery of photosystem I (one of the two types of photosystems) but is not present in the electron transfer chain. They also found that far-red light causes structural changes in the photosystem, which are accompanied by the synthesis of Chl f in the algae, leading them to conclude that Chl f causes these structural changes in photosystem I. This was exciting, as this finding is the first to explain how exactly Chl f works. Prof Tomo says, "Our findings revealed that the appearance of Chl f is well correlated with the expression of photosystem I genes induced under far-red light. This indicates that Chl f functions to harvest the far-red light and enhance up-hill energy transfer. We also found that the amino acid sequence of photosystem I was altered so as to accommodate the structure of Chl f."

Understanding the intricacies of photosynthesis has several important applications. For example, mimicking the process of photosynthesis in an artificial system is an elegant method of capturing solar energy and converting it into electricity. Prof Tomo elaborates, "About half of the solar energy that falls on the earth is visible light, and the other half is infrared light. Our research puts forth a mechanism that can use light on the lower energy spectrum, which has never been seen before. Our findings show how to improve the efficiency of energy transfer in photosynthesis and, by extension, also provide important insights into artificial photosynthesis."