Concentrated Salt Solutions and Quantum Dots
The CN stretch is known for its sensitivity for local and global chemical environment changes, and has been used in various form of IR experiment such as KSeCN, KSCN and phenylselenocyanate. In aqueous solutions, ethyl thiocyanate provides a unique perspective from a neutral molecule on the water dynamics.
In concentrated LiCl solution, EtSCN exhibits two peaks in the FTIR spectrum while in water, it only has one. The additional peak probably corresponds to the strong interaction between EtSCN and lithium cation. Currently, we are using pump-probe and 2D IR spectroscopies to investigate the underlying spectral diffusion dynamics.
Colloidal Quantum Dots (QD) are widely used as chromophores, fluorophores, and electronic components due to their high tunability through synthesis. The effect of materials, size, and shape have been under investigation in great detail in the past several decades, and some of the original research has already turned into real products, such as high-resolution Quantum Dots displays. Numerous kinds of modification and functionalization have been applied to QD surfaces to make them more suitable for electron transport, photon gathering, and catalysis. The dynamics happening near the surface must be understood to tune the chemical processes and to rationally improve the design of QDs. Ultrafast IR spectroscopies are great tools for investigating interface dynamics, as has been shown by the monolayer dynamics studies. By choosing a suitable IR probe that is sensitive to solvation and electronic environment, picosecond scale dynamics on QDs are likely to be revealed.
This is a new direction in our group, and an ongoing collaboration with Prof. Emily Weiss’s group in Northwestern University. We are trying to partially replace the oleic acid ligands on QDs with IR probes. Currently, we have obtained the FTIR spectra of our probes on the QDs and are beginning the studies on dynamics.