Varying the Interpentacene Electronic Coupling to Tune Singlet Fission

Area of Science:

• Organic Photovoltaics
• Photochemistry
• Materials Science

Background:

• Singlet fission (SF) is a process where one high-energy exciton splits into two lower-energy excitons.
• Controlling intramolecular forces is crucial for efficient SF in organic materials.
• Pentacene derivatives are promising candidates for SF applications.

Purpose of the Study:

• To investigate the impact of molecular spacers on pentacene-pentacene interactions.
• To understand how these interactions modulate the key steps in singlet fission.
• To optimize the efficiency of both singlet fission and subsequent triplet-triplet annihilation.

Main Methods:

• Design and synthesis of four pentacene dimers with varying spacers (A-D).
• Utilized transient absorption spectroscopy to study excited-state dynamics.
• Employed electron paramagnetic resonance (EPR) to probe triplet states.

Main Results:

• Spacers A and B facilitated rapid SF via superexchange and hopping mechanisms, yielding up to 162% ¹(T₁T₁) quantum yields.
• Spacers C and D showed reduced electronic coupling, favoring a superexchange mechanism.
• Spacers C and D exhibited higher ⁵(T₁T₁) quantum yields (up to 85%) for triplet-triplet annihilation compared to A and B.

Conclusions:

• Molecular spacer design significantly influences the mechanism and efficiency of singlet fission in pentacene dimers.
• Optimizing spacer electronic coupling is key to controlling the balance between SF and triplet-triplet annihilation.
• This study provides insights for designing advanced materials for efficient solar energy conversion via singlet fission.