Measuring the current form nature’s “solar panels” using ultrafast lasers

IBEC and ICFO researchers have developed and validated a novel photoelectrochemical electron spectroscopy technique to probe charge separation dynamics, a crucial step for photosynthesis, in photosynthetic complexes. Photosynthesis is the process by which some organisms (for instance, plants, algae and some bacteria) transform light energy into chemical energy. This process begins with the absorption of light (photons) by certain pigments (mainly chlorophyll) and ends with a flow of electrons that sustain the biochemical reactions that make life on Earth possible. One intermediate step that had never been directly probed, mainly because it occurs at ultrafast timescales, is the so-called charge separation. Once the pigment absorbs a photon, an electron is excited to a higher energy level. This extra energy is then transferred to specific locations, called reaction centers, causing an electron of the chlorophyll in those centers to be again excited and transferred to another complex (the acceptor molecule). Consequently, the chlorophyll becomes positively charged, which means that charge separation has occurred. This charge difference is crucial because it sets up a flow of high-energy electrons that will drive the rest of the photosynthetic process. To decipher photosynthetic complexes and engineer novel photosynthetic strategies, it is thus key to probe the pathways leading to charge separation. This phenomenon has recently been tackled in a joint work between IBEC and ICFO researchers, also in collaboration with the University of Padua and Vrije Universiteit Amsterdam. The team has developed and validated a novel Photoelectrochemical Two-Dimensional Electronic Spectroscopy (PEC2DES) technique, which allows to directly probe charge separation dynamics in photosynthetic complexes. The discovery could be used in biohybrid devices and sensors that rely on the precise control and understanding of electron transfer processes within complex protein assemblies.