|
Ultrafast photoinduced isomerization is a fundamental process governing molecular dynamics both in biologically relevant chromophores and in functional materials, e.g. those based on molecular switches and motors. It is widely accepted that the efficiency of isomerization is governed by the dynamics through conical intersections, the regions of the potential energy landscape, where two potential energy surfaces cross. Recent developments in computational chemistry can help identifying conical intersections in isolated chromophores molecules and describe the relaxation dynamics. However, the complex environments hosting the chromophores have a profound influence on the dynamics through conical intersection making direct application of these methods to “real life” problems a very challenging task and underscoring the importance of experimental investigations.
Most all-optical time-resolved spectroscopic techniques cannot directly capture the dynamics at conical intersections both because it is very fast and because the gap between the two electronic states vanishes at the intersection. However, the XUV-based spectroscopic techniques and, in particular, XUV time-resolved photoelectron spectroscopy (TRPES) give promise in delivering detectable signals from the regions of conical intersections. TRPES of molecular chromophores requires application of photoemission methods to the liquid phase samples (molecular solutions). Our group has recently become the first to demonstrate liquid phase TRPES of organic molecules by combining an ultrafast tunable XUV source with a microliquid jet sample delivery method and time-of-flight photoelectron detection.
In this contribution we will report on the recent results applying this method to the prototypical molecules, Methyl Orange and Metanil Yellow. The experimental results are complemented by high-level time-dependent density functional theory (TDDFT) surface hopping calculations to reveal electronic state involved in ultrafast relaxation of the molecules. We will further show preliminary results for several bio-mimetic chromophores and will discuss the experimental challenges of the techniques, when working with samples of low concentration and using different solvents.
|
