A DFT-based comparative study on the excited states intramolecular proton transfer in 1-hydroxy-2-naphthaldehyde and 2-hydroxy-3-naphthaldehyde

Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of 1-hydroxy-2-naphthaldehyde (1H2NA) and 2-hydroxy-3-naphthaldehyde (2H3NA) were studied using DFT/B3LYP(6-31G) and TD-DFT/B3LYP(6-31G) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer for both the compounds. Excited states PE calculations support the ESIPT process to both 1H2NA and 2H3NA. The wide difference in ESIPT emission process of 1H2NA and 2H3NA have been explained in terms of HOMO and LUMO electron density of the enol and keto tautomer of these two compounds.