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Abstract

The photophysical dynamics of functional materials adopted in photosynthesis and photo- voltaics are important for solar light harvesting. Observations of long-lived quantum coher- ences in photosynthetic complexes have spawned numerous research efforts on the micro- scopic origins, the design principles and the biological significance of these observed beating signals. The remarkable device performance demonstrated by perovskite photovoltaics have also drawn broad scientific interest to the fundamental photophysical properties of these perovskite materials in both bulk single crystals and nanocrystals. In this dissertation, I provide interesting observations and interpretations regarding the ultrafast dynamics of light- harvesting materials. By performing two-dimensional electronic spectroscopy (2DES) on a series of structurally flexible heterodimers with varied electronic transitions both in dilute solution or packed on single-walled carbon nanotubes, we have discovered two prerequisites to the observed vibronic coherences: one is a resonant vibrational mode with the electronic energy gap; the other is limiting the relative orientation between different chromophores. 2DES on a pair of BODIPY dyes attached to a cavitand molecular switch demonstrates the effects of nonradiative transitions on Fo ̀ˆrster resonance energy transfer. Transient absorption spectroscopy on CH3NH3PbBr3 perovskite single-domain single crystals and related theo- retical calculations show that free carriers and localized carriers coexist due to polaron for- mation in bulk perovskite. Transient absorption spectroscopy on CH3NH3PbBr3 perovskite nanocrystals synthesized by a ligand-mediated method demonstrates radiation-fluence in- dependent photoluminescence decay, indicating these nanocrystals are quantum confined. 2DES on perovskite nanocrystals reveals ultrafast dynamics (sub 50-fs exciton relaxation and coherences) and different spectral features that reflect the electronic structure of the NCs. The observations described in this dissertation will be important for understanding the fundamental photophysical properties of these functional light-harvesting materials and guide future material designs used in devices.

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