Linearly acenaphthylene-fused pentacene exhibiting efficient singlet fission

Area of Science:

• Materials Science
• Photochemistry
• Organic Electronics

Background:

• Acenes are promising for singlet fission (SF) to boost solar cell efficiency beyond the Shockley-Queisser limit.
• Acene stability is a major challenge, and current stabilization methods alter their electronic properties, hindering SF.
• Cyclopentannulation at peri-positions modifies electronic structure, preventing efficient singlet fission.

Purpose of the Study:

• To develop a novel strategy for stabilizing acenes while preserving their photophysical properties for singlet fission.
• To investigate the impact of linearly fusing acenaphthylene units on acene stability and SF performance.
• To explore new molecular designs for efficient and stable singlet fission materials.

Main Methods:

• Synthesis of linearly fused acenaphthylene pentacenes.
• Spectroscopic characterization (UV-Vis absorption, fluorescence, TREPR spectroscopy).
• X-ray crystallography for structural analysis.
• Photophysical measurements including fluorescence lifetime and triplet quantum yield determination.

Main Results:

• Acenaphthylene-fused pentacenes exhibit red-shifted absorption/emission and longer fluorescence lifetimes, retaining pentacene spectral features.
• These new acenes show stability comparable to pentacene despite narrower HOMO-LUMO gaps.
• X-ray crystallography reveals a slip-stack columnar packing, differing from pentacene's herringbone motif.
• Efficient, ultrafast singlet fission occurs in thin films, yielding a high triplet quantum yield (~158%).
• TREPR spectroscopy confirms the SF mechanism and identifies the quintet (5TT) state.

Conclusions:

• Linear fusion of acenaphthylene provides a viable strategy to stabilize acenes for singlet fission applications.
• The new materials maintain desirable photophysical properties for efficient SF, overcoming previous design limitations.
• The slip-stack columnar packing and strong vibronic coupling contribute to the observed efficient SF.
• This work opens new avenues for designing stable, high-performance organic materials for next-generation solar energy conversion.