Tunable Interlayer Interactions in Exfoliated 2D van der Waals Framework Fe(SCN)₂(Pyrazine)₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Chemical Synthesis

Background:

• Two-dimensional (2D) materials, isolated via weak van der Waals forces, offer unique topological physics.
• Tuning the properties of isolated 2D materials while maintaining their monolayer structure presents significant chemical challenges.
• Interlayer excitons in 2D materials are of great interest due to their long-lived emission, but are synthetically difficult to tune.

Purpose of the Study:

• Investigate 2D electroactive sheets that exfoliate into colloidal nanosheets.
• Explore the tunable optical properties arising from aggregation upon oxidation.
• Provide a molecular synthetic chemistry basis for manipulating opto-electronic behavior in van der Waals materials.

Main Methods:

• Exfoliation of 2D electroactive sheets in solution.
• Inducing aggregation upon oxidation to study optical properties.
• Modulating interlayer excitons through solvent, electrolyte, oxidation state, and framework composition.

Main Results:

• Demonstrated tunable interlayer charge transfer absorption and photoluminescence in aggregated nanosheets.
• Observed optical behavior analogous to tunable interlayer excitons.
• Achieved modulation of interlayer excitons via controlled chemical and environmental parameters.
• Identified framework sheets with the largest known interlayer binding strengths and long interlayer exciton lifetimes.

Conclusions:

• The framework sheets exhibit tunable opto-electronic behavior through control of molecular synthetic chemistry.
• Specific orbital interactions contribute to strong interlayer binding and long exciton lifetimes.
• This work provides a microscopic understanding for manipulating long-range opto-electronic properties in van der Waals materials.