Excited state intramolecular proton transfer in 1,4-dihydroxyanthraquinone

Excited state intramolecular proton transfer process is of great importance in solar light conversion and white light emitting systems. The excited state intramolecular proton transfer process of 1,4-dihydroxyanthraquinone in acetonitrile was investigated by steady-state spectroscopy, transient absorption spectroscopy and density functional theory (DFT) calculations. It was demonstrated that 1,4-dihydroxyanthraquinone has three different structures in acetonitrile, namely, the original structure, the single proton transfer structure and the double proton transfer structure. The presence of multiple structures in the ground state is responsible for the observation of the wide and vibrational absorption spectrum of this molecule. The results of theoretical calculations as well as experimental results of ultraviolet (UV)-visible absorption and emission spectroscopy indicate that the intramolecular excited state proton transfer process exists in the single proton transfer structure. The relaxation pathways of this tautomer were revealed by transient absorption spectroscopy, global and target analysis.