Evidence for Photoinduced Polaron Generation in a High Persistence Length Low Bandgap Conjugated Polymer in Solution

Area of Science:

• Materials Science
• Photophysics
• Polymer Chemistry

Background:

• Conjugated polymers are crucial for organic electronics.
• Understanding photogeneration mechanisms is key to improving device performance.
• Indacenodithiophene-benzothiadiazole copolymers (C8-IDTBT) are promising materials.

Purpose of the Study:

• Investigate the excited-state structural dynamics of C8-IDTBT.
• Elucidate the photogenerated charge carrier species and their evolution.
• Determine the efficiency of polaron formation in conjugated polymers.

Main Methods:

• Ultrafast time-resolved infrared (TRIR) spectroscopy.
• Pulse radiolysis measurements and charge-modulation spectroscopy.
• Quantum-chemical calculations.

Main Results:

• Vibrational features assigned to polaron pairs developed within 10 ps and decayed over 4 ns.
• A three-state kinetic model showed dynamic equilibrium between polarons and excitons on picosecond timescales.
• Exciton dissociation occurred in 3-5 ps, polaron reformation in 20-100 ps.
• Polaron generation efficiency exceeded 50%.

Conclusions:

• Efficient intramolecular charge photogeneration occurs in C8-IDTBT.
• Bound polaron formation is demonstrated in isolated polymer chains.
• Findings offer fundamental insights into photophysics of conjugated polymers.