The ordering of small molecules, programmed with functional groups for specific non-covalent interactions, can lead to robust, dynamic, and functional monolayers or thin films. Our group studies these assemblies under well-controlled environments by atomic-resolution scanning tunneling microscopy (structural characterization) and X-ray photoelectron spectroscopy (chemical characterization).

Chemical transformations proceed through a mechanism consisting of elementary chemical steps representing the reactive collisions of individual molecular species.  Fundamentally, such collisions may be described as a quantum mechanical inelastic scattering process involving the rearrangement of kinetic and internal energy. Important parameters, such as reaction cross-sections and kinetic rate constants, can be derived from the solutions of the Schrödinger equation.

Plasmonic nanoantennas provide an opportunity to manipulate light within nanoscale volumes. One approach to creating plasmonic antennas is to organize metal colloids to produce assemblies where coupled localize surface plasmons lead to enhanced optical near fields. Although synthesis of metal colloids is straight forward due to the extensive number of methodologies that have been developed, controlled organization of the particles remains a challenge.

We use ultrafast spectroscopy to study and control the excited-state dynamics of a common photochromic molecular switch. The compound undergoes reversible electrocyclization and cycloreversion reactions that convert the molecule between open- and closed-ring states with very different electronic and optical properties. Our experiments use various excitation schemes to explore different regions of the excited-state potential energy surfaces in order to probe the non-adiabatic dynamics of both the forward and reverse reactions.