Interpreting the charge transfer to solvent state in the photoionization of potassium ferrocyanide in an aqueous solution

The photoionization reaction of potassium ferrocyanide has been known for a long time, yet there are few reports on the electronic structure analysis of the charge transfer to solvent (CTTS) state in this reaction. Herein, femtosecond transient absorption spectra of potassium ferrocyanide in the UV-Vis region were studied, and its photoionization under low energy excitation was observed. Using time-dependent density functional theory methods, the absorption spectra of potassium ferrocyanide were calculated in both implicit and explicit solvent models, and the electronic structure of the molecule was discussed in detail. Evidence suggests that a portion of the electron density in the CTTS state of potassium ferrocyanide is located on the empty orbital of the solvent water molecule. The vertical excitation energies calculated by the explicit solvent model are in agreement with the experimental results of the CTTS state. By elucidating the photoionization of potassium ferrocyanide from the molecular electronic structure, our results offer a method for further comprehension of the CTTS state of metal complexes and photochemical reactions. Evidence suggests that a portion of the electron density in the CTTS state of potassium ferrocyanide is located on the empty orbital of the solvent water molecule.