CO₂ regulates molecular rotor dynamics in porous materials

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Solid-State NMR Spectroscopy

Background:

• Development of porous crystalline materials for molecular motion control.
• Understanding guest-molecule interactions within confined environments.
• Investigating dynamics of molecular rotors in solid-state frameworks.

Purpose of the Study:

• To engineer a hydrogen-bonded framework capable of hosting and modulating ultra-fast molecular rotors.
• To investigate the effect of carbon dioxide (CO2) adsorption on the rotational dynamics of molecular rotors.
• To characterize the CO2-rotor interaction using solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.

Main Methods:

• Synthesis of a crystalline hydrogen-bonded framework with permanent porosity.
• Incorporation of molecular rotors with triple bonds into the framework.
• Variable-temperature 2H NMR spectroscopy to probe rotor dynamics.
• Gas-phase adsorption of CO2 into the porous framework.

Main Results:

• The framework exhibits permanent porosity and houses ultra-fast molecular rotors (10^7 Hz at 216 K).
• CO2 adsorption significantly reduces rotor rotational rates to 10^5 Hz.
• 2H NMR data confirms CO2 interaction with the rotors, influencing their dynamics within the crystal structure.

Conclusions:

• The engineered crystalline framework effectively controls molecular rotor speeds via CO2 adsorption.
• This work presents a method for tuning molecular dynamics in porous materials.
• The findings highlight the potential for responsive materials based on guest-molecule interactions.