Engineering Ultrafast Molecular Rotors via Chalcogen bonds.

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Crystallography

Background:

• Chalcogen bonds are σ-hole interactions with significant potential for creating novel materials.
• Amphidynamic materials, particularly molecular rotors, are crucial for developing advanced molecular machines.
• Existing molecular rotor designs often lack robustness or crystalline order.

Purpose of the Study:

• To report the first crystalline molecular rotors stabilized by chalcogen bonds.
• To investigate the ultrafast rotational dynamics within these novel chalcogen-bonded structures.
• To demonstrate the utility of chalcogen bonds in designing robust crystalline molecular machines.

Main Methods:

• Synthesis of phenylselenocyanate-based stators and 1,4-diazabicyclo[2.2.2]octane rotators.
• X-ray crystallography to analyze the Se···N contacts and crystal packing.
• Solid-state ¹H NMR T₁ spin-lattice relaxation measurements to probe rotational dynamics.
• Computational analysis to support experimental findings on rotational barriers and packing.

Main Results:

• Successful assembly of crystalline molecular rotors utilizing exceptionally short and directional Se···N chalcogen bonds (Nc = 0.76-0.81; ∠NC-Se···N = 174-175 °).
• Observation of ultrafast rotational dynamics in the hundreds of MHz range.
• Determination of low activation energy barriers (Ea = 1.22-2.78 kcal mol^-1) for rotation, consistent with packing and computational data.

Conclusions:

• Chalcogen bonds are effective in constructing robust, crystalline molecular rotors.
• The reported molecular rotors exhibit high-speed rotation, showcasing their potential for dynamic applications.
• This work establishes chalcogen bonds as a powerful strategy for designing sophisticated crystalline molecular machines.