Structure control for fine tuning fluorescence emission from side-chain azobenzene polymers.

Area of Science:

• Organic Chemistry
• Polymer Science
• Photophysics

Background:

• Azobenzene dyes are known for their photoresponsive properties.
• Fluorescence in azobenzene systems can be influenced by molecular structure and environment.
• Side-chain polymers offer tunable properties for advanced applications.

Purpose of the Study:

• To synthesize and characterize novel fluorescent azobenzene dyes and their corresponding polymers.
• To investigate the photophysical properties, including fluorescence and photoisomerization, of these new materials.
• To understand the structure-property relationships governing fluorescence and photoresponse in azobenzene-containing polymers.

Main Methods:

• Synthesis of azobenzene dyes with phenol, phenylphenol, and naphthol fluorophores.
• Conversion of dyes into methacrylate monomers with ethyleneoxy spacers.
• Free radical polymerization to form side-chain polymers.
• Spectroscopic characterization including fluorescence quantum yield measurements and UV-Vis irradiation studies.

Main Results:

• Phenylphenol-based azobenzene dye (S2) exhibited high fluorescence (quantum yield 0.2 in DCM).
• The corresponding polymer (P2) retained fluorescence, unlike phenol (P1) and naphthol (P3) based polymers where fluorescence was quenched.
• P2 showed limited trans-to-cis photoisomerization (approx. 17%) and a 2-fold fluorescence enhancement upon UV irradiation, attributed to steric hindrance and inhibited photoinduced electron transfer (PET).
• Concentration-dependent emission and aggregation-induced emission were observed for P2.

Conclusions:

• The phenylphenol moiety's excited-state planarization is crucial for retaining fluorescence in azobenzene polymers.
• Steric repulsion in P2 restricts photoisomerization, enhancing photostability.
• Photoisomerization leads to temporary fluorescence enhancement in P2, likely due to PET inhibition.
• Aggregation can lead to altered emission properties, including aggregation-induced emission.