Ionic to neutral conversion induced by resonant excitation of molecular vibrations coupled to intermolecular charge transfer

In organic molecular compounds, intramolecular vibration is sometimes coupled with intermolecular charge transfer (CT). In such materials, vibrational excitation by a midinfrared (MIR) pulse causes collective intermolecular CTs that can be a route to an electronic-state conversion. Here, we report that an ionic-to-neutral (IN) conversion in tetrathiafulvalene-p-chloranil (TTF-CA) can be driven by a strong vibrational excitation induced by an MIR pulse. Using MIR-pump subcycle-reflectivity-probe and second-harmonic-generation-probe measurements, we discuss the coherent electron and lattice dynamics during and after the IN conversion, which are distinct from the dynamics of the photoinduced transition by electronic excitation alone.