Solvent Polarity Independent Symmetry-Breaking Charge Separation in a Slip-Stacked Covalent Terrylene Monoimide Dimer

Area of Science:

• Organic electronics
• Photovoltaics
• Materials science

Background:

• Efficient photoinduced charge separation is crucial for organic photovoltaics (OPVs).
• Conventional methods often require polar solvents to stabilize charge-separated states, limiting applications.
• Designing materials for low-polarity environments remains a significant challenge.

Purpose of the Study:

• To investigate a slip-stacked terrylene monoimide dimer (TMI2) with intrinsic electronic asymmetry.
• To demonstrate efficient symmetry-breaking charge separation (SB-CS) independent of solvent polarity.
• To establish a molecular design principle for OPVs in low-dielectric media.

Main Methods:

• Ultrafast spectroscopic techniques.
• Investigation of a slip-stacked terrylene monoimide dimer (TMI2).
• Analysis of vibronic coherences and vibrational fingerprints.

Main Results:

• TMI2 exhibits highly efficient SB-CS across various solvent polarities.
• The process is enabled by the permanent dipole moment of TMI and intramolecular charge-transfer (ICT) character.
• A specific intermolecular mode (193 cm-1) drives initial state mixing, and the radical ion pair product has a distinct vibrational signature.

Conclusions:

• Intrinsic electronic asymmetry in TMI2 circumvents the need for polar solvents for charge separation.
• This molecular design principle allows efficient charge separation in low-dielectric environments.
• The findings have significant implications for developing next-generation organic optoelectronic materials.