Investigating carotenoid photophysics in photosynthesis with 2D electronic spectroscopy

Carotenoids are accessory pigments in photosynthesis that serve a range of functions such as light harvesting, photoprotection, and structural stabilization. Such versatility is enabled by their unique electronic structure, which includes one or more dark excited states and is readily modulated by changes in their physical and chemical structures. In this review, we describe the ultrafast photophysical mechanisms of carotenoid-mediated energy transfer and energy dissipation, which underlie the light-harvesting and photoprotective functions of carotenoids in photosynthesis, and how recent developments in 2D electronic spectroscopy enable the investigation of these mechanisms. We focus on three light-harvesting complexes (LHCs) found in purple bacteria, green plants, and marine algae, which utilize distinct carotenoid molecules to optimize the photophysics for their survival and fitness.