IR/UV spectroscopy on jet cooled 3-hydroxyflavone (H2O)n (n = 1,2) clusters along proton transfer coordinates in the electronic ground and excited states.

The structure and reactivity of isolated 3-hydroxyflavone (3-HF) aggregates with one and two water molecules has been investigated by applying combined infrared/ultraviolet (IR/UV) spectroscopy in a supersonic jet both for the electronic ground and excited states. In combination with density functional theory (DFT) calculations, the IR spectra of the S(0) states recorded from the upper fingerprint region to the OH stretching vibrations are assigned to the most stable isomers of the clusters. For the first electronically excited (pi pi(*)) state of the 3-HF(H(2)O)(2) cluster structural information are obtained from the IR spectra in combination with time-dependent-DFT (TD-DFT) calculations. No proton transfer structure is observed in the case of a low excess energy within the electronically excited state. By raising the excitation energy, additional bands appear that can be assigned to a tautomeric form indicating the induction of a proton transfer reaction.