Intermolecular singlet fission in a radical dianion system in solution phase

Area of Science:

• Photochemistry
• Materials Science
• Spectroscopy

Background:

• Singlet fission (SF) is an exciton multiplication process where one singlet exciton generates two triplet excitons.
• Intermolecular SF (xSF) in solution is crucial for developing novel optoelectronic materials.
• Understanding the elementary steps of SF in charged systems is essential for advancing energy conversion technologies.

Purpose of the Study:

• To experimentally investigate solution-phase intermolecular SF (xSF) in a charged radical system.
• To map the detailed mechanistic pathways and identify intermediates in the xSF process.
• To validate the applicability of the established three-step model to charged radical systems.

Main Methods:

• Ultrafast spectroscopy was employed to probe the dynamics of the xSF process.
• A two-step photoinduced electron transfer mechanism was used to generate the PTCDA2- radical dianion.
• Time-resolved measurements were performed to determine the formation and relaxation kinetics of intermediates.

Main Results:

• The study successfully mapped the elementary steps of solution-phase xSF in the PTCDA2- radical dianion system.
• Three key intermediates were identified: excimer 1(S1S0), spin-correlated triplet pair 1(T1T1), and spatially separated triplet pair 1(T1·S0·T1).
• The formation and relaxation time constants for these intermediates were determined, providing a detailed kinetic picture.

Conclusions:

• Solution-phase xSF is achievable in charged radical systems, extending the scope of SF materials.
• The findings validate the three-step model, typically used for crystalline SF, for describing solution-phase xSF in charged systems.
• This research paves the way for designing new charged SF materials for applications in optoelectronics and energy conversion.