Toward Piezoresistive Devices That Exploit Bullvalene's Structural Versatility.

Area of Science:

• Molecular Chemistry
• Nanotechnology
• Surface Science

Background:

• Bullvalene molecules are known for dynamic shape-shifting via Cope rearrangements.
• Previous studies in scanning tunneling microscopy break junctions showed restricted bullvalene isomerization and piezoresistivity.
• Understanding isomer behavior in confined environments is crucial for molecular device applications.

Purpose of the Study:

• To investigate electron-transfer rates and structural possibilities of bullvalene in self-assembled monolayers (SAMs).
• To explore how confinement density influences bullvalene isomerism and conductivity.
• To establish a foundation for utilizing bullvalene's isomerism in nano-electromechanical systems (NEMS).

Main Methods:

• Synthesis of bis-4-phenyl acetylene bullvalene and formation of SAMs on Au(111).
• Attachment of ferrocene tail groups using copper-catalyzed azide-alkyne cycloaddition (CuAAC).
• Electrochemical measurements for SAM coverage and electron-transfer rates, supported by Density Functional Theory (DFT) simulations.

Main Results:

• Bullvalene molecules on the surface exist as a single isomer at any given time.
• The specific isomer present is dependent on the monolayer coverage density.
• DFT simulations confirm steric and packing effects dictate coverage-dependent isomeric selectivity.

Conclusions:

• Confinement in SAMs restricts bullvalene to specific isomers, controllable by surface coverage.
• This isomer selectivity offers a pathway to tune electronic properties for NEMS applications.
• Identified SAM structures provide viable options for future molecular device development.