A DFT/TD-DFT Study on the ESIPT-Type Flavonoid Derivatives with High Emission Intensity

Area of Science:

• Photochemistry
• Computational Chemistry
• Organic Chemistry

Background:

• 4′-N, N-dimethylamino-3-hydroxyflavone (DMA3HF) derivatives are investigated for their photophysical properties.
• Substituent effects on excited-state intramolecular proton transfer (ESIPT) are crucial for understanding molecular behavior.

Purpose of the Study:

• To investigate how electron-withdrawing (-CN) and electron-donating (-NH2) groups influence the ESIPT process and photophysical characteristics of DMA3HF.
• To elucidate the electronic mechanisms governing these changes.

Main Methods:

• Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations were employed.
• Electronic structure was analyzed using Natural Bond Orbital (NBO), fuzzy bond order, and frontier molecular orbital (FMO) analyses.

Main Results:

• The hydrogen bond intensity in the excited state follows the order: DMA3HF-NH2 > DMA3HF > DMA3HF-CN.
• Electron-donating -NH2 group promotes the ESIPT reaction without altering photophysical properties.
• Electron-withdrawing -CN group enhances UV absorption but inhibits the ESIPT reaction.
• Fluorescence intensity in the keto form was observed to be relatively strong for all studied molecules.

Conclusions:

• Substituent choice critically impacts the ESIPT dynamics and photophysical properties of DMA3HF derivatives.
• -NH2 substitution facilitates ESIPT, while -CN substitution enhances UV absorption at the expense of ESIPT.
• Computational methods provide valuable insights into structure-property relationships for flavone derivatives.