Magic-Angle Exciton Coupling in a Molecular Solid: Optical Consequence of Null-Coulombic Coupling

Area of Science:

• Photochemistry and Photophysics
• Materials Science
• Solid-State Chemistry

Background:

• Excitonic coupling is crucial for understanding excited-state dynamics in molecular aggregates.
• Magic angle configurations typically result in weak dipolar Coulombic coupling between chromophores.
• Documented instances of magic angle excitonic coupling and its optical consequences are rare.

Purpose of the Study:

• To investigate the optical properties of CF3DPT solids, particularly focusing on excitonic coupling in a magic angle configuration.
• To demonstrate a rare experimental observation of magic angle excitonic coupling and its impact on fluorescence.
• To elucidate the interplay between Coulombic and charge transfer (CT) coupling in aggregated molecular systems.

Main Methods:

• Synthesis and characterization of CF3DPT solids.
• Experimental measurement of fluorescence quantum efficiency in the aggregated solid state.
• Computational calculations to validate experimental findings on electronic coupling.

Main Results:

• CF3DPT solids exhibited a high fluorescence quantum efficiency of 62 ± 3% in the aggregated state.
• Experimental and computational results confirmed null-Coulombic coupling, characteristic of a magic angle configuration.
• Significant charge transfer (CT) coupling was identified as a key factor influencing the observed optical properties.

Conclusions:

• The study presents a rare example of magic angle excitonic coupling in CF3DPT solids.
• The observed high fluorescence quantum efficiency is attributed to the specific electronic coupling environment, including null-Coulombic and significant CT coupling.
• Findings provide fundamental insights into excited-state electronic processes and optical behavior in molecular aggregates with magic angle configurations.