The β phase formation limit in two poly(9,9-di-n-octylfluorene) based copolymers

Area of Science:

• Materials Science
• Polymer Chemistry
• Organic Electronics

Background:

• Poly(9,9-di-n-octylfluorene) (PF8) is a widely used polymer in organic electronics.
• The formation of the β phase in PF8 influences its emission properties.
• Copolymerization is a strategy to tune the properties of PF8.

Purpose of the Study:

• To synthesize and characterize PF8 copolymers with varying contents of dibenzothiophene (DBT) and dibenzothiophene-S,S-dioxide (S-unit).
• To investigate the effect of DBT and S-unit incorporation on the formation of the β phase in thin films.
• To determine the limits of β phase formation for device applications.

Main Methods:

• Synthesis of random copolymers of PF8 with DBT (0-20%) and S-unit (2-15%).
• Analysis of absorption and emission spectra of thin films.
• Evaluation of toluene vapor-induced β phase formation.

Main Results:

• The DBT system exhibited a linear decrease in β phase formation with increasing DBT content up to 20%.
• The S-unit copolymers showed β phase presence up to 12% co-monomer content; at 15%, the characteristic absorption peak was absent or masked.
• These findings establish the limits for β phase formation in PF8 copolymer systems.

Conclusions:

• The study demonstrates the practical limits for achieving the β phase in PF8-based copolymers.
• It is feasible to incorporate electron or hole transport units into the polyfluorene backbone while maintaining efficient β phase emission sites.
• This research provides insights for designing advanced PF8 copolymers for optoelectronic devices.