Ultraviolet (UV) and infrared (IR) spectra of protonated dopamine (DAH + ) and its hydrated clusters DAH + (H2O)1-3 are measured by cryogenic ion spectroscopy. DAH + monomer and hydrated clusters with up to two water molecules show a broad UV spectrum while it turns to a sharp, wellresolved one for DAH + -(H2O)3. Excited state calculations of DAH + (H2O)3 reproduce these spectral features. The conformer-selected IR spectrum of DAH + (H2O)3 is measured by IR dip spectroscopy and its structure is assigned with the help of quantum chemical calculations. The excited state lifetime of DAH + is much shorter than 20 ps, the cross correlation of the ps lasers, revealing a fast relaxation dynamics. The minimal energy path along the NH →  proton transfer coordinate exhibits a low energy barrier in the monomer while this path is blocked by the high energy barrier in DAH + (H2O)3. It is concluded that the excited state proton transfer in DAH + is inhibited by water-

Electronic and vibrational spectroscopy in a cryogenic ion trap have been applied to protonated dopamine water clusters and assigned with the help of quantum chemistry calculations performed in the ground...