|Welcome to the Blank Research Group in the Chemistry Department at the University of Minnesota. Our research group investigates a variety of dynamic events in condensed media. The investigations range from basic chemical reaction dynamics in solution to energy and charge transfer dynamics in new materials targeted at applications in solar energy conversion. Our primary experimental tools are nonlinear time domain spectroscopies, and this includes new methods developed in our laboratory. Computational tools, such as time dependent density functional methods and molecular dynamics simulations, are used to complement the experiments and aid in the interpretation of our data.|
|Work by graduate student Francesc Molins i Domenech|
The behaviour of excess electrons in room temperature ionic liquids (RTILs) is a question of fundamental interest as well as one of great practical importance.On the applied side, the special properties of these liquids (extremely low vapour pressure, especial solvation characteristics and tunability of the properties through design of the constituent ions) make them promising candidates in such diverse applications as coolants in nuclear reactors, solvents for solar cells and advanced electrochemical technology. An understanding of the physical and chemical behavior of electrons injected in these liquids is an important part to the solution of these challenges.
On the fundamental side, the introduction of a Coulomb inteaction between the constituents of the liquid introduces a new wealth of nanoscopic structural features as well as dynamics both in the ultra-fast as in the ns to us regimes. Here our broader goal is two-fold: to investigate the effect that these structural and dynamical features have on the charge separation processes that are better understood in molecular liquids, and to use these processes as a tool to probe ionic liquids and thus challenge the current theoretical understanding.
More specificly, we are interested in such questions as: What is the nature of the excess electron in RTILs and how does it depend on the nature of the ions? Are cavities involved as in the case of some organic solvents such as the cyclic ethers, or are they better described as occupying the LUMOs of the ions? In the case of cavities, are these cavities pre-formed, or do they form as a response to the appearance of the electron? In either case way, what is the response of the liquid to the injected electron? What degrees of freedom are involved at different time scales? Can we control these dynamics?
Optical spectroscopy in these liquids is complicated by unique challenges to their purification. The purification methods that we have developed have shown that the onset of UV absorption is at much lower wavelengths than previously thought and thus we have built an ultra-fast transient absorption experiment with an UV (200 nm) pump and a VIS-NIR (400 nm to 1400 nm) sprectrally resolved probe.
We have so far focused our attention on pyrrolidinium bistriflimide RTILs. We have shown that a single 200 nm photon leads to photoionization and we have followed the dynamics of the ejected electron within the first 800 ps.