Chirality Remote Control in Nanoporous Materials by Circularly Polarized Light.

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Photochemistry

Background:

• Controlling molecular chirality dynamically is a significant challenge, especially during processes like photoisomerization which typically yield racemic mixtures.
• Isolation of specific enantiomers is crucial for harnessing enantiospecific properties, but achieving this selectively remains difficult.
• Chirality in molecules is often lost or suppressed in solution or upon isomerization, necessitating new methods for its control and induction.

Purpose of the Study:

• To develop a nanoporous solid capable of dynamically controlling and inducing chirality using circularly polarized light (CPL).
• To investigate the enantioselective enrichment of chiral isomers within a metal-organic framework (MOF) scaffold.
• To explore the potential of CPL for chiral resolution and information storage in solid-state materials.

Main Methods:

• Synthesis of a metal-organic framework (MOF) functionalized with photoswitchable fluorinated azobenzene linkers.
• Photoisomerization studies using unpolarized and circularly polarized light (CPL) with varying wavelengths (green and violet).
• Characterization of molecular conformations and enantiomeric enrichment using experimental techniques and first-principle DFT calculations.

Main Results:

• Circularly polarized light (CPL) was shown to induce chiral photoresolution in the azobenzene-based MOF, leading to optically active materials.
• Right-CPL selectively enriched specific enantiomers (e.g., S-enantiomers from R-isomers), demonstrating reversible and light-handedness-dependent control.
• DFT calculations and experimental verification confirmed that the MOF scaffold stabilizes nonplanar, chiral conformations for both trans and cis azobenzene isomers, unlike the planar achiral trans isomer in solution.

Conclusions:

• The reticulation of linkers within the MOF is essential for enabling chiral photoresolution, a phenomenon not observed in solution.
• This study successfully demonstrates the induction of chirality and optical activity in solid materials using CPL.
• The findings open new avenues for chiral resolution techniques and potential applications in optical information storage.