2-(1'-Pyridin-2'-one)benzimidazole was synthesized in order to determine its structure in the solid state, its NMR properties, and its behavior in absorption -emission electronic spectroscopy. To rationalize these properties, ab initio calculations have been carried out on its ground and excited states. A three-center N-H...O=C hydrogen bond connects the molecules in the crystal forming chains parallel to the c axis. The intramolecular hydrogen bond promotes coplanarity of both ring systems. In the ground state, only the N-H tautomer exists as a local minimum of the potential energy surface, while in the excited-state, both tautomers are found to be stable. The main consequence is that the photochemical behavior of this compound is governed by the existence of a proton transfer in its excited state.