Pyrene as chromophore and electrophore: encapsulation in a rigid polyphenylene shell

Area of Science:

• Organic Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Pyrene derivatives are known for their fluorescence properties.
• Dendrimers offer unique structural control for molecular encapsulation.
• Controlling aggregation is crucial for maintaining optical properties.

Purpose of the Study:

• To synthesize polyphenylene dendrimers encapsulating a tetraethynylpyrene core.
• To investigate the effect of dendrimer shell size on pyrene fluorescence and site isolation.
• To evaluate the potential of these materials for electronic device applications.

Main Methods:

• Divergent and convergent synthesis of polyphenylene dendrimers.
• Spectroscopic analysis including fluorescence quantum yield measurements.
• Fluorescence quenching and temperature-dependent spectroscopy for site isolation studies.
• Alkali-metal reduction to form pyrene radical anions.
• Solubilizing alkyl chain modification for improved processability.

Main Results:

• Polyphenylene dendrimers were synthesized in high yield around a tetraethynylpyrene core.
• High fluorescence quantum yields (>0.92) were maintained, independent of dendrimer size.
• Efficient site isolation of the pyrene core was observed starting from the second dendrimer generation.
• Hampered electron transfer to the core in radical anions confirmed site isolation.
• Improved solubility and film-forming properties were achieved with peripheral alkyl chains.
• Transparent films exhibited blue emission primarily from unaggregated species.

Conclusions:

• Polyphenylene dendrimers effectively isolate tetraethynylpyrene cores, preventing aggregation.
• The synthesized materials exhibit high fluorescence quantum efficiency and good processability.
• These dendrimers are promising candidates for applications in organic electronic devices.