Transient Terahertz Stark Effect: A Dynamic Probe of Electric Interactions in Polar Liquids

Electric forces acting on molecules in liquids at ambienttemperaturefluctuate at terahertz (THz) frequencies with a direct impact on theirelectronic and optical properties. We introduce the transient THzStark effect to modify the electronic absorption spectra of dye moleculesand, thus, elucidate and determine the underlying molecular interactionsand dynamics. Picosecond electric fields of megavolts/cm induce anonequilibrium response of the prototypical Betaine-30 in polar solutionthat is probed via transient absorption changes. The field-inducedbroadening of the absorption band follows the THz intensity in time,with a minor impact of solvent dynamics. The ground and excited statedipole energies in the THz field govern this response, allowing fora quantification of electric forces in a structurally frozen molecularenvironment.

Automated summary

We introduce the transient THz Stark effect to modify the electronic absorption spectra of dye molecules and determine molecular interactions and dynamics. The non-equilibrium response of Betaine-30 in a polar solution is probed via transient absorption changes induced by picosecond electric fields. The response is governed by the dipole energies in the THz field, allowing for quantification of electric forces in a structurally frozen molecular environment.