Abstract: We investigated dynamic process of hydrogen bonding of the 1-hydroxy-2-naphthaldehyde (HN12) molecule and molecular isomer in the ground and excited states by means of the density functional theory and timedependent density functional theory. The results show that the hydrogen bond length becomes shorter and the redshift phenomenon of infrared spectrum of the hydroxyl group in the hydrogen bond appears when the HN12 molecule in the ground state is excited to the first electron excited state. The excited state intramolecular proton transfer reactions can take place. The reverse proton transfer reaction is difficult to take place in the excited state, but the reverse proton process is easy to appear in the ground state. There is a cyclic mechanism between the ground state and excited state in the HN12 molecule and the molecular isomer.

Key words: intramolecular proton transfer, ground state, hydrogen bond, excited state