Aryl Alcohol Photocatalysts

The development and understanding of simple, organic molecular photocatalysts holds appeal due to possibility for increased sustainability and access to new reactivities. We have shown that upon excitation of a simple substituted naphthol opens up excited-state redox events that can lead to the naphthol being a high energy hydrogen atom donor. Initial results recently published in JACS show that upon excitation of the naphthol photocatalyst and a molecular photosensitizer in the presence of a sacrificial electron donor and a proton source leads to the catalytic production of H2. Data support a multiphoton mechanism which is analagous to the Natural photosynthesis Z-scheme. Our molecular Z-scheme can drive reactions that are uphill by 500+ kJ/mol while circumventing the high-energy constraints associated with the reduction ofthe naphthol catalyst in the ground state. This approach offers a new paradigm for the generation of high energy hydrogen atom donor catalyst and the production of solar fuels.

Hybrid Catalysts Using Atomic Layer Deposition

Homogeneous molecular catalysts are valued for their reaction specificity but face challenges due to complexities in final product separation, catalyst recovery, and catalyst instability. Heterogenizing molecular catalysts, by attachment to a solid support to generate a hybrid molecular/heterogeneous catalyst, could increase catalyst stability by preventing bimolecular catalyst inteactions that lead to decomposition while also simplifying catalyst separation and recovery. Extended catalyst stability can be achieved by "encasing" the molecular calayst with a metal oxide layer via atomic layer deposition (ALD). We demonstrate the advantages of this ALD-hybrid catalyst approach by achieving catalytic cross-coupling using a non-noble metal hybrid catalyst in high aqueous content solvents. The molecular nickel catalyst chosen exhibited limited catalytic turnovers under homogeneous conditions due to extremely short catalyst lifetimes, but when heterogenized and immobilized with an optimal ALD layer thicknesses product yields of > 90% can be obtained with this hybrid catalyst approach.