Excited State Dynamics Of Molecular Switches

Currently working on this project: Cassie Ward, Amanda Houk, and Tim Quincy

Techniques: Pump-Probe, Pump-Repump-Probe, 2PA

The first project looks at excited state dynamics of color-changing photoswitches. These molecules reversibly convert between two isomers with very different absorption spectra and are prime candidates for use in high-density data storage devices, such as 3-dimensional, many-layer DVDs. Our experiments follow the transformation from one isomer to another after the system absorbs a photon. Those ring-opening and ring-closing reactions involve up to three electronic states.

A key question that physical chemists want to answer is exactly how a system transfers from one electronic state to another, a process called non-adiabatic transition. Non-adiabatic transitions generally occur through conical intersections, where the potential energy surfaces cross. Conical intersections are a hot topic these days because they are ubiquitous in excited state reactions. We use new excitation schemes, such as simultaneous and sequential two-photon excitation, to explore the reaction mechanisms of photo-switching and then apply what we learn to steer the reaction and thus improve conversion yields for ring-opening and closing.

Working with collaborators in the Femtoscopy Lab at the University of Rome, we can probe changes in the vibrational structure on the excited-state surface using Femtosecond Stimulated Raman Spectroscopy (FSRS). This new technique allows us to learn about the vibrational structure of the photoswitch as it undergoes the cyclization reaction.