Photophysical properties of poly(phenylene-co-fluorene) synthesized via solid-state oxidative coupling polymerization

- Solid-state oxidative coupling copolymerization is effective and time-saving.
- Benzene-co-fluorene copolymers have good optical properties.
- The ratios of fluorene in the copolymers can tune the light-emitting properties.
- Blue-shifted λPLmax in solutions is due to the increasing distorted polymer conformations.
- Red-shifted λPLmax in films is due to the formation of polymer aggregates.

A series of benzene-co-fluorene copolymers were synthesized via solid-state oxidative coupling polymerization using FeCl3 as the oxidation catalyst. The structural characterization results confirm that the products are random copolymers composed of 1,4-linked phenylene units and 2,7-linked fluorene units. All the copolymers exhibited good thermal stability. The DSC and XRD results showed that the crystallization of copolymers increased with the increasing fluorene units in the backbones. The relationships among molecular structure, condensed-state structure, and photophysical properties of these polymers were investigated by UV-vis absorption spectroscopy and photoluminescence spectroscopy. The optical properties could be adjusted by using different ratios of fluorene and dibutoxybenzene. Moreover, the polymer concentrations and states affected the emission properties of copolymers. This can be attributed to the change in the effective conjugation length of single polymer and the formation of polymer aggregates and excimers. These unique properties endow the benzene-co-fluorene copolymers with potential applications in optoelectronics.

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