DFT based computational study on the excited state intramolecular proton transfer processes in o-hydroxybenzaldehyde

Area of Science:

• Computational Chemistry
• Photochemistry
• Molecular Spectroscopy

Background:

• o-hydroxybenzaldehyde (OHBA) exhibits dual emission, suggesting complex photophysical processes.
• Intramolecular proton transfer is a key phenomenon in understanding excited-state dynamics.

Purpose of the Study:

• To investigate the potential energy (PE) curves for intramolecular proton transfer in OHBA.
• To elucidate the mechanisms behind dual emission in OHBA using theoretical calculations.

Main Methods:

• Density Functional Theory (DFT) with B3LYP/6-31G(d) for ground state calculations.
• Time-Dependent DFT (TD-DFT) with B3LYP/6-31G(d) for excited state calculations.
• Analysis of potential energy surfaces and oscillator strength variations.

Main Results:

• Ground state intramolecular proton transfer (GSIPT) is computationally found to be non-viable in OHBA.
• Excited state intramolecular proton transfer (ESIPT) is supported, consistent with experimental observations.
• Potential energy diagrams and oscillator strength variations confirm dual emission originating from S(1) and S(2) states.

Conclusions:

• The study confirms the ESIPT mechanism in OHBA, explaining its characteristic dual emission.
• Theoretical calculations align with experimental findings regarding emission pathways.
• HOMO/LUMO analysis further supports the ESIPT process in enol and keto tautomers.