Time-Resolved THz Stark Spectroscopy of Molecules in Solution

Stark spectroscopy is an invaluable tool to reveal information about the physicochemical properties of molecules [1]. Sufficiently strong electric fields modify absorption spectra of isotropic ensembles of molecules if ground and excited state energy eigenvalues of the respective optical transition shift in energy due to the interaction with the applied electric field. The measurement gives insight into, for instance, photo-induced electron or charge transfer, nonlinear material properties, biological organization, energy tuning, or solvato-chromism [2], [3]. For decades, it was considered all but impossible to perform Stark spectroscopy on molecules in a liquid solution at room temperature, because their concomitant orientation to the applied electric field results in overwhelming background signals. A way out was to immobilize the solute molecules by freezing the solvent. While mitigating solute orientation, freezing removes the possibility to study molecules in liquid environments at ambient conditions.