Triplet-state and singlet oxygen formation in fluorene-based alternating copolymers

Area of Science:

• Materials Science
• Photochemistry
• Polymer Chemistry

Background:

• Fluorene-based alternating copolymers are crucial in organic electronics.
• Understanding their photophysical properties, particularly triplet states, is key for device optimization.
• Intersystem crossing and triplet energy levels influence charge transport and emission.

Purpose of the Study:

• To characterize the triplet states of fluorene-based A-alt-B alternating copolymers.
• To investigate the influence of thiophene and other units on triplet state formation and energy.
• To correlate triplet properties with copolymer structure and conjugation.

Main Methods:

• Pulse radiolysis-energy transfer experiments for spectral analysis.
• Flash photolysis with laser excitation to determine triplet quantum yields (PhiT).
• Time-resolved phosphorescence to measure singlet oxygen sensitization and photoacoustic calorimetry.

Main Results:

• Spectra of eight copolymers containing phenylene, thiophene, benzothiadiazole, and oligothienylenevinylene groups were obtained.
• Thiophene units generally increased intersystem-crossing quantum yields due to the heavy sulfur atom.
• Specific copolymers (PFP, PFTSO2, F8BT) exhibited low triplet formation yields, while fluorene-thiophene copolymers showed localized triplet states.

Conclusions:

• Thiophene incorporation significantly impacts triplet state dynamics in fluorene-based copolymers.
• The heavy sulfur atom in thiophene enhances intersystem crossing.
• Copolymer structure dictates triplet energy localization, with fluorene-thiophene copolymers exhibiting more localized states than homopolymers.