Sulfur-Bridged Terthiophene Dimers: How Sulfur Oxidation State Controls Interchromophore Electronic Coupling

Area of Science:

• Photophysics
• Organic electronics
• Supramolecular chemistry

Background:

• Symmetric dimers are key for optimizing energy transfer and charge separation in optoelectronic devices.
• Sulfur-bridged terthiophene dimers offer tunable electronic coupling via sulfur oxidation states.

Purpose of the Study:

• To analyze the photophysics of sulfur-bridged terthiophene dimers.
• To investigate how sulfur oxidation state affects electronic coupling and photophysical properties.

Main Methods:

• Steady-state and time-resolved optical spectroscopy.
• Electronic structure theory calculations.
• Analysis of terthiophene dimers with varying sulfur oxidation states (sulfide, sulfoxide, sulfone).

Main Results:

• Photoexcitation forms a delocalized charge resonance state (S1) that rapidly (<10 ps) relaxes to a charge-transfer state (S1*).
• Increased sulfur oxidation state and solvent polarity enhance charge-transfer character in S1*.
• S1* exhibits a decreased intersystem crossing rate, leading to higher photoluminescence quantum yield.

Conclusions:

• Electrostatic screening by sulfur electrons controls charge-transfer character.
• Tuning sulfur bridge oxidation state modifies interchromophore interactions without changing molecular geometry or solvent polarity.
• This offers a novel strategy for designing functional supermolecules for organic electronics.