Selective and Cooperative Photocycloadditions within Multistranded Aromatic Sheets.

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Photochemistry

Background:

• Oligoamide foldamers are valuable for creating defined molecular architectures.
• Photosensitive units offer dynamic control over molecular structure and function.
• Controlling foldamer conformation and reactivity is crucial for advanced materials.

Purpose of the Study:

• To design and synthesize aromatic oligoamide foldamers incorporating photosensitive diazaanthracene units.
• To investigate the conformational behavior and photoreactivity of these foldamers.
• To demonstrate the ability to orchestrate sequential photoreactions for controlled structural modification.

Main Methods:

• Synthesis of oligoamide foldamers with varying numbers of photosensitive units.
• Nuclear magnetic resonance (NMR) spectroscopy and X-ray crystallography for structural analysis.
• Photochemical [4 + 4] cycloaddition reactions to induce structural changes.

Main Results:

• Foldamers adopted distinct helix-sheet-helix conformations based on the number of turn units (even vs. odd).
• Conformational populations were tunable via solvent, temperature, and helix handedness control.
• Diazaanthracene units exhibited selective photoreactivity, allowing programmed sequential reactions.
• Photoreactions led to structure lengthening and stiffening, with reversible photoproducts.

Conclusions:

• Novel photosensitive foldamers with predictable folding and tunable photoreactivity were successfully developed.
• Sequential photoreactions can be precisely controlled, enabling targeted structural modifications.
• These findings open avenues for designing dynamic and responsive supramolecular systems.