In natural light-harvesting systems, pigment-protein complexes (PPC) convert sunlight to chemical energy with near unity quantum efficiency. PPCs exhibit emergent properties that cannot be simply extrapolated from knowledge of their component parts. In this Perspective, we examine the design principles of PPCs, focussing on the major light-harvesting complex of Photosystem II (LHCII), the most abundant PPC in green plants. Studies using two-dimensional electronic spectroscopy (2DES) provide an incisive tool to probe the electronic, energetic, and spatial landscapes that enable the efficiency observed in photosynthetic light-harvesting. Using the information about energy transfer pathways, quantum effects, and excited state geometry contained within 2D spectra, the excited state properties can be linked back to the molecular structure. This understanding of the structure-function relationships of natural systems constitutes a step towards a blueprint for the construction of artificial light-harvesting devices that can reproduce the efficacy of natural systems.
Applications of ultrafast multidimensional electronic spectroscopy to the study of plant light harvesting systems and colloidal quantum dots