Light harvesting in photosynthetic organisms employ complex arrays of highly ordered chromophores in proteins for the capture and transfer of energy from solar photons. The structural design of the light harvesting proteins leads to extensive delocalization across many molecules of the system. Recent studies demonstrate the involvement of quantum coherence in extraordinarily fast energy transfer pathways in photosynthetic light harvesting proteins. The extent of delocalization may also form vibronic excitons, vibronic excitons, arising from quantum coherent mixing of vibrations with the extensively delocalized electronic states. Vibronic excitons can greatly enhance the excitation energy transfer within light harvesting systems. In this dissertation, the detection and role of quantum coherence in the peridinin-chlorophyll protein (PCP), a mid-visible peripheral light-harvesting protein in marine dinoflagellates that delivers excitation energy to photosystem II, will be discussed. This dissertation will also discuss the role of vibronic coherences, involving organic surface ligands, in the hot carrier cooling process of CdSe semiconductor quantum dots (QDs). Optical broadband two-dimensional electronic spectroscopy (2DES) with ultrashort pulses has been employed on these systems to characterize nonradiative decay and energy transfer pathways in PCP and CdSe QDs. Understanding the advantage gained by the organism through the use of coherent energy transfer mechanisms may enable the development of more efficient light harvesting materials for use in photovoltaic cells or in photocatalysis.
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