Theoretical Study on the Competition Mechanism between ESIPT and TICT in N-H Indanone Derivatives

Area of Science:

• Photophysics and Photochemistry
• Supramolecular Chemistry
• Organic Electronics

Background:

• Hydroxyl (OH)-type hydrogen bond (H-bond) systems are well-studied for their photophysical properties.
• Amino (NH)-type H-bond compounds, like indanone derivatives, exhibit unique photophysical behavior.
• Low emission quantum yields (Φ < 9%) are commonly observed in NH-type H-bond systems but often lack a clear mechanistic explanation.

Purpose of the Study:

• To investigate the photophysical behavior of NH-type H-bond compounds based on indanone derivatives.
• To elucidate the mechanism behind the remarkably low emission quantum yields observed in these systems.
• To understand the interplay between excited state intramolecular proton transfer (ESIPT) and twisted intramolecular charge transfer (TICT) dynamics.

Main Methods:

• Comprehensive analysis of H-bond dynamics.
• Detailed investigation of electronic structures.
• Study of excited state dynamics and kinetics, including computational modeling.

Main Results:

• Demonstrated a barrier-dependent dynamic competition between ESIPT and twisted intramolecular charge transfer (TICT).
• Conclusively associated the nonradiative decay pathway along the TICT coordinate with intersystem crossing (ISC).
• Found that smaller substituents (R) are unfavorable for lowering the torsional barrier, impacting photophysical properties.

Conclusions:

• The study provides a mechanistic explanation for low emission quantum yields in NH-type ESIPT systems, linking it to TICT-induced intersystem crossing.
• The findings highlight the critical role of H-bond dynamics and electronic structure in controlling photophysical pathways.
• Preliminary results suggest that substituent size plays a crucial role in modulating the torsional barrier and overall fluorescence efficiency.