Ab initio study on the excited state proton transfer mediated photophysics of 3-hydroxy-picolinic acid

► The photophysics of the system is determined by double-ESIPT process. ► The carboxylic group serves as a proton-transmitter unit. ► Proximity of the 1ππ∗ and 1nπ∗ excited states. ► Photophysical pathway of fast radiationless decay of electronic excitation studied. ► Bistability and photochromism of 3HPA allows for designing the molecular switches.