New insights on the ESIPT process based on solid-state data and state-of-the-art computational methods

Area of Science:

• Photochemistry
• Computational Chemistry
• Materials Science

Background:

• Excited-state intramolecular proton transfer (ESIPT) is a crucial photophysical process.
• Benzothiazole derivatives serve as excellent model systems for studying ESIPT.
• Understanding ESIPT mechanisms is vital for developing advanced functional materials.

Purpose of the Study:

• To investigate the excited-state intramolecular proton transfer (ESIPT) in benzothiazole derivatives.
• To compare experimental findings with state-of-the-art computational methods.
• To elucidate the role of molecular structure and interactions in facilitating ESIPT.

Main Methods:

• Utilized a workflow approach combining experimental and theoretical calculations.
• Employed advanced computational techniques like DLPNO-CCSD(T) for reference energies.
• Performed molecular dynamics simulations and charge density difference testing for ESIPT analysis.

Main Results:

• Theoretical vibrational analysis revealed enhanced intramolecular hydrogen bond strength, promoting ESIPT.
• π-stacking was identified as a key factor in benzothiazole stabilization and strong hydrogen bonding.
• Molecular dynamics showed ESIPT occurring rapidly (enol to keto in ~8.7 fs, regeneration in ~24 fs).
• Excellent agreement was observed between experimental and theoretical emission spectra for ESIPT-active benzothiazoles.

Conclusions:

• Benzothiazole derivatives demonstrate efficient and rapid ESIPT, driven by strong intramolecular hydrogen bonds and π-stacking.
• The study validates advanced computational methods for analyzing ESIPT mechanisms.
• Discrepancies in non-ESIPT systems highlight the importance of considering intermolecular interactions.