Role of hydrogen bonding in excited state intramolecular proton transfer of Indole-7-Carboxaldehyde: A theoretical and experimental study

Excited state intramolecular proton transfer (ESIPT) has been studied in Indole-7-Carboxaldehyde (I7C). DFT, TDDFT, CIS theories with B3LYP/6-311++G (d, p), etc. basis sets have been used to obtain structural parameters and energies of I7C in ground, excited states for cis (Nc), trans (Nt) and zwitterionic (Z∗) conformers. Photo-physical pathway involving ESIPT from cis (Nc) to zwitterion (Z∗) agrees well with the dual fluorescence at 451 and 862 nm obtained from computed results and experimental observations. Potential energy surface scan confirms the existence of ESIPT by asymmetric double minima in the excited state pathway along the Reaction Coordinate –N15–H12 donor.