Stepwise Excited-state Double Proton Transfer and Fluorescence Decay Analysis

Area of Science:

• Photochemistry
• Physical Chemistry
• Molecular Spectroscopy

Background:

• Excited state intramolecular proton transfer (ESIPT) is a well-known photophysical process.
• Multiple hydroxyl groups in proximity can facilitate sequential ESIPT reactions.
• Stepwise excited state intramolecular double proton transfer (ESIDPT) involves consecutive proton transfers, forming multiple tautomers.

Purpose of the Study:

• To analyze the fluorescence decay kinetics of molecules exhibiting ESIDPT.
• To develop a theoretical framework for understanding fluorescence from normal and multiple tautomeric forms.
• To investigate the ESIDPT process in scutellarein as a model system.

Main Methods:

• Rigorous analysis of fluorescence decay kinetics.
• Development of a three-species model (normal form and two tautomers) for kinetic analysis.
• Quantum-chemical calculations applied to scutellarein.

Main Results:

• The study provides a theoretical framework for analyzing fluorescence decay in ESIDPT.
• The model accounts for emissions from the normal form and two distinct tautomers.
• Quantum-chemical calculations were performed for scutellarein, a relevant model compound.

Conclusions:

• Stepwise ESIDPT can lead to complex fluorescence spectra with multiple emission bands.
• The proposed kinetic model accurately describes systems with two successive proton transfers.
• Scutellarein serves as a suitable model for studying ESIDPT phenomena.