3-Azafluorenone Derivatives with Small HOMO-LUMO Gaps, Allowing Visible-Light Absorption

Area of Science:

• Organic Synthesis
• Photochemistry
• Materials Science

Background:

• 3-Azafluorenone derivatives are valuable scaffolds in materials science.
• Limited synthetic routes have historically restricted access to diverse analogs.

Purpose of the Study:

• Develop a versatile synthetic strategy for 3-azafluorenone derivatives.
• Explore structure-property relationships, focusing on optical and redox characteristics.

Main Methods:

• Synthetic organic chemistry techniques, including tert-butyl protection of ketocarboxylic acids.
• Spectroscopic characterization (UV-Vis absorption, fluorescence).
• Electrochemical analysis (cyclic voltammetry).
• Time-dependent density functional theory (TD-DFT) calculations.

Main Results:

• Efficient synthesis of previously inaccessible 3-azafluorenone analogs.
• Incorporation of diverse substituents (electron-donating, -withdrawing, π-extended) enabled.
• Substituents significantly modulated photophysical properties (bathochromic/hypsochromic shifts) and redox potentials.
• Most derivatives exhibited high excited-state reduction potentials (> +1.6 V vs SCE).
• TD-DFT calculations validated experimental observations.

Conclusions:

• Established detailed structure-property relationships for 3-azafluorenones.
• Provided design principles for tuning optical and redox properties.
• Demonstrated potential of these derivatives for photoredox catalysis.