Molecular structure important for charge transfer in artificial photosynthesis

The fundamental process of charge transfer underlies many renewable energy technologies. Going back to the basics, Philip et al. studied the speed of charge transfer in two highly similar molecules commonly used in artificial photosynthesis. The two molecules differ only in the attachment positions of the electron donors and acceptors, demonstrating how small changes in molecular structure can have big effects.

“If you look at these molecules, you wouldn’t expect at first glance that they would have such different properties,” said author Ferdinand Grozema. “It was actually kind of surprising. We can see that the differences have very distinct effects on the charge transfer properties of those molecules.”

Using ultra short laser pulses, the researchers directly measured how fast the charge transfer occurred after the two types of molecules were excited. The molecules, which are used as light-harvesting antennae for artificial photosynthesis, were nearly identical but had two groups of atoms interchanged, making them structural isomers. Since the change in the structure altered the electron distribution, there was a modification in the properties, including a noticeable time lag with one of the molecules.

In setting up the experiments, the researchers also developed tricks to produce the isomer molecules. These synthetic techniques allowed them precise control in creating the desired molecular configuration – something that is typically very hard to achieve.

The new results provide fundamental information about charge transfer speeds that is useful in a variety of areas. It could also open doors to future applications.

“Now that we understand these differences, it can be used to design molecules for these kinds of applications much more efficiently,” Grozema said.

Source: “Directing charge transfer in perylene based light-harvesting antenna molecules,” by Abbey M. Philip, Chao Chun Hsu, Zimu Wei, Magnus B. Fridriksson, Ferdinand C. Grozema, and Wolter F. Jager, Journal of Chemical Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0021454 .