Squaraine dyes as efficient coupling bridges between triarylamine redox centres

Area of Science:

• Organic Chemistry
• Materials Science
• Photochemistry

Background:

• Indolenine squarylium dyes are investigated for their electronic and optical properties.
• Organic mixed-valence systems are crucial for understanding electron transfer and delocalization.
• Electron-donating amine redox centers can significantly influence dye properties.

Purpose of the Study:

• Synthesize novel indolenine squarylium dyes with amine redox centers.
• Characterize the electronic structure and redox chemistry of these dyes.
• Investigate the impact of structural modifications on electronic delocalization and optical properties.

Main Methods:

• Synthesis of indolenine squarylium dyes with amine redox centers.
• Cyclic voltammetry and spectro-electrochemistry for redox and electronic structure analysis.
• Density Functional Theory (DFT) calculations to complement experimental data.

Main Results:

• Synthesized mono-, di-, and trications of indolenine squarylium dyes.
• Monocations exhibit cyanine-like delocalization (Robin-Day class III) due to the squaraine bridge.
• Achieved TA3, the longest reported completely delocalized bis(triarylamine) radical cation.
• Demonstrated that altering dye symmetry impacts optical properties.
• Identified an anti-ferromagnetically coupled open-shell singlet state for dianisylamine-substituted squaraine dications.

Conclusions:

• Indolenine squarylium dyes with amine redox centers act as electron-rich bridges, enabling strong electronic coupling.
• The squaraine bridge facilitates extensive electron delocalization in these systems.
• Structural modifications, such as symmetry changes, tune the optical properties of the dyes.
• The electronic state of dications depends on substituents and coupling mechanisms.