Anion Recognition by a Pincer-Type Host Constructed from Two Polyamide Macrocyclic Frameworks Jointed by a...

Area of Science:

• Supramolecular Chemistry
• Photochemistry
• Host-Guest Chemistry

Background:

• Development of light-responsive molecular systems is crucial for advanced materials.
• Macrocyclic hosts offer unique binding properties due to their preorganized structures.
• Azobenzene derivatives are widely used photo-switchable chromophores.

Purpose of the Study:

• To synthesize a sterically crowded, light-responsive host molecule.
• To investigate the photoisomerization behavior of the host within a rigid macrocyclic framework.
• To explore the anion binding properties of the host in its different isomeric states.

Main Methods:

• Synthesis of host 1 via post-functionalization using double amidation.
• X-ray crystallography to determine the solid-state structure and intermolecular interactions.
• UV-Vis spectroscopy and NMR titration to study photoisomerization and anion binding.
• Kinetic studies to analyze thermal back-isomerization rates.

Main Results:

• Host 1 was synthesized in 93% yield, featuring a sterically hindered azobenzene core within a 26-membered macrocycle.
• X-ray structures revealed unique π-π stacking interactions of the azobenzene unit.
• Reversible cis-trans photoisomerization was achieved with UVA and blue light, with significantly slowed thermal back-isomerization compared to non-macrocyclic analogs.
• Trans-1 selectively bound dihydrogenphosphate anions, while cis-1 showed reduced affinity.

Conclusions:

• The rigid macrocyclic framework effectively modulates the azobenzene photoisomerization dynamics.
• The synthesized host exhibits light-controlled anion recognition, particularly for dihydrogenphosphate.
• This work presents a promising platform for developing photo-switchable anion sensors and materials.