Advances in ligand-to-metal charge transfer catalyze a new field
Advances in ligand-to-metal charge transfer catalyze a new field lead image
Photosensitizers operate by absorbing light and transferring energy or charge to another nearby molecule. In photocatalysis, that increase in energy triggers a chemical reaction under milder conditions than a traditional heat-driven process.
Metal-to-ligand charge transfers (MLCT) and ligand-to-metal charge transfers (LMCT) present two important metal-centered charge transfer photoexcitations. In the former, light excites electrons in the metal and that charge migrates to the attached (usually organic) supporting scaffold. In the latter, the molecule absorbs light and promotes electrons from the supporting scaffold to move to the metal center.
MLCT is frequently used in catalysis, but LMCT is much less common and its fundamentals are not well-studied. Li et al. reviewed recent developments in LMCT, discussed its potential applications, and examined what analysis and physical measurements need to be conducted to use this less common photocatalysis technique.
“Because of the solvents and reaction conditions used, MLCT tends to result in more stable excited states, whereas LMCT would traditionally lead to degradation of the catalyst,” said author Han Sen Soo. “We and others have found ways to avoid or exploit this degradation.”
LMCT processes can generate even more reactive radicals, leading to a chain of subsequent reactions. This can be a benefit for applications like degrading and upcycling plastics, which the group is currently exploring.
The authors hope their review will encourage others to probe and understand LMCT reactions instead of simply using them or their more illustrious counterpart.
“We hope we will inspire more scientists to actually perform physical chemistry measurements and theoretical calculations on these LMCT systems,” said Soo.
Source: “Emergence of ligand-to-metal charge transfer in homogeneous photocatalysis and photosensitization,” by Chenfei Li, Xin Ying Kong, Zheng Hao Tan, Crystal Ting Yang, and Han Sen Soo, Chemical Physics Reviews (2022). The article can be accessed at https://doi.org/10.1063/5.0086718 .
