The Undergraduate Biological Research Program (UBRP) at the University of Arizona has supported research on charge transfer processes involving dye molecules. Jason Tyler, an undergraduate chemistry major in the Monti Group, has been doing several experiments regarding these charge transfer processes. Jason is working with a system comprised of a dye molecule known as PTCDI, an insulating layer made of self-assembling molecules, and a charge acceptor known as titanium dioxide.

The overall aim of the research is to study the charge transfer kinetics of charge donors interacting with charge acceptors in complex environments and at the single molecule level. These sorts of charge transfer processes are important to many biological processes (e.g. photosystem II) as well as the development of organic solar cells. A confocal microscope, made for operation in vacuum, was designed and built in part by Jason with the support of UBRP. Studying fast kinetics at the single molecule level is difficult and overcoming some of the difficulties has necessitated the unwavering attention of postdoc Brandon Tackett. While Brandon is busy bringing the microscope into operation, Jason has been conducting several experiments that help the Monti group better understand the charge transfer system.
The insulating layer of self-assembling molecules can be made to varying degrees of thickness. Changing the thickness of the insulating layer changes the kinetics of the charge transfer process, in general, the further away the dye molecule is from the charge acceptor, the less charge transfer occurs. The system has been carefully selected such that only two dominant processes occur when the charge donor absorbs a photon: the molecule either transfers charge or fluoresces. Jason has been busy trying to see whether this effect can be seen in bulk. In other words, he adsorbs the dye onto the powdered titanium dioxide, places the resulting adsorption product into a suspension, and studies it using fluorescence spectroscopy. In addition, he uses differential scanning calorimetry to try to determine the enthalpy of the dye adsorption and to determine whether there are multiple, distinct dye adsorption sites. He also uses imaging techniques including scanning tunneling microscopy and atomic force microscopy to look at this system when it is made on single crystalline TiO2. These experiments intend to work towards and provide supporting information to the single molecule experiments. As it stands now, charge transfer in heterogeneous systems is poorly understood. This system is one step in understanding the complexities of charge transfer in heterogeneous systems.

Tyler's work is supported in part by a grant to UA from the Howard Hughes Medical Institute (#52005889).

Jason Tyler, UBRPer in Dr. Oliver Monti's Lab, Chemistry