Phototriggered fluorescence color changes in azobenzene-functionalized conjugated polymers

Area of Science:

• Polymer Science
• Photochemistry
• Materials Science

Background:

• Poly(p-phenylenevinylene) (PPV) derivatives are known for their unique optical and electronic properties.
• Azobenzene functionalization introduces photoresponsive behavior, allowing for light-induced structural changes.
• Polymer conformation significantly influences spectral properties like fluorescence.

Purpose of the Study:

• To investigate the phototriggered spectral changes in azobenzene-functionalized PPV derivatives (MPA-10-PPV and HPA-10-PPV).
• To understand the relationship between azobenzene photoisomerization, polymer conformation, and fluorescence properties.
• To explore the reversibility and potential applications of these light-induced changes.

Main Methods:

• Fluorescence spectroscopy was used to study MPA-10-PPV and HPA-10-PPV.
• Photoisomerization of azobenzene groups was induced using UV and visible light.
• Solvent mixtures (dichloromethane-methanol) were used to control polymer coil dimensions.

Main Results:

• Trans --> cis azobenzene photoisomerization caused small blue shifts in MPA-10-PPV's fluorescence spectrum in toluene.
• These spectral shifts were reversible upon visible light irradiation.
• Significant, visible color changes (yellow-orange to green) were observed in HPA-10-PPV solutions (65:35 dichloromethane-methanol) due to reversible UV-phototriggered polymer coil expansion.

Conclusions:

• Azobenzene photoisomerization reversibly alters the conformation and spectral properties of functionalized PPV polymers.
• The observed spectral shifts and color changes are attributed to light-induced expansion and contraction of polymer coils.
• These findings demonstrate the potential for developing photoresponsive materials with tunable optical characteristics.