Towards a 2-in-1 Photocatalyst Based on a Ruthenium-Coordinated Nanographene

The Sun illuminates our planet’s surface with more energy in one hour than the energy we consume globally in one year. Plants have evolved to absorb this abundant solar energy to produce fuels (carbohydrates) and oxygen (as a side product). Chemists now seek to mimic nature by creating efficient photocatalysts (PCs) that can absorb light in the solar spectrum to photochemically reduce CO2 and oxidize H2O, producing fuels and other value-added chemicals. To design such PCs, a deep understanding of their molecular photophysics is necessary. With optical transient absorption spectroscopy, one can observe the evolution of a system’s photophysical dynamics in real time. Using such time-resolved spectroscopic techniques, we can observe the excited states of our systems from hundreds of femtoseconds out to several microseconds. We couple our experiments with DFT-based calculations which are used to predict these photophysical dynamics outside the lab. Employing these tools, the agreement between experimental and theoretical results is evaluated. Understanding excited state dynamics is key to designing better PCs for improved energy absorption and conversion, leading to improved catalytic efficiency. This thesis provides, in chronological order, our roadmap for developing a novel 2-in-1 PC based on a photocatalytic ruthenium polypyridyl unit coordinated to a nanographene photosensitizer. First, the body of recently published literature covering the photophysics of PAHs, graphene quantum dots (GQDs), and graphene nanoribbons (GNRs) is reviewed. Second, experimental and computational work investigating GQD and GNR photophysics is discussed. Third, the photophysics of a model Ruthenium bipyrimidine complex is explored. Lastly, preliminary results on two 2-in-1 PCs are presented: Ru-tpy-flake and Ru-dqp-flake. The work presented in this thesis indicates the promising avenue of achieving efficient CO2 reduction photocatalysis using 2-in-1 PCs with light-harvesting nanographene ligands.