Charge-transfer complexes, also known as electron donor-acceptor (EDA) complexes, involve the association of an electron-rich substrate (donor) and an electron-poor substrate (acceptor) in the ground state. While the individual substrates may not absorb in the visible region, the charge-transfer complex often does, creating a new alternative to initiate redox reactions with visible light irradiation. While these methodologies have proven useful, they often require specifically tailored substrates, limiting the overall scope of these transformations. In order to increase the generality of this approach, the Pitre lab is focusing on developing catalytic systems for charge-transfer photochemistry, which include the use of photocatalysts that activate alkyl halides towards visible-light irradiation through halogen-bonding interactions.
Charge-transfer complexes can also occur between a substrate and the surfaces of heterogeneous materials, like inorganic semiconductors. In previous work, Pitre, Yoon, and Scaiano demonstrated that visible light photocatalysis with titanium dioxide can be initiated through ligand-to-metal charge-transfer (LMCT) interactions between organic molecules, such as indole, and the semiconductor surface. In the Pitre lab, we are interested in exploring the extent of which these LMCT interactions can be utilized to drive visible light photocatalysis with titanium dioxide in order to expand its utility as a photocatalyst in organic synthesis.
Pitre, S. P.; Yoon, T. P.; Scaiano, J. C. Titanium Dioxide Visible Light Photocatalysis: Surface Association Enables Photocatalysis with Visible Light Irradiation. Chemical Communications 2017, 53, 4335–4338.