Oxahelicene-Based Pd₂L₄ Cages: Synthesis, Optical Properties, and Guest Encapsulation

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Organic Synthesis

Background:

• Helicene-based ligands offer unique three-dimensional structures for molecular assembly.
• Oxahelicenes introduce heteroatoms, modifying electronic and structural properties.
• Palladium(II) ions are widely used in self-assembly due to their predictable coordination geometry.

Purpose of the Study:

• To synthesize novel 7-oxa[5]- and 9-oxa[7]helicene ligands (L1 and L2) with pyridyl coordination sites.
• To investigate the self-assembly of these ligands with Pd(II) ions into supramolecular cages.
• To characterize the photophysical properties and guest-encapsulating abilities of the resulting palladium cages.

Main Methods:

• Synthesis of oxahelicene-based ligands L1 and L2.
• Self-assembly reactions with Pd(II) ions.
• Spectroscopic characterization (NMR, MS).
• Photophysical measurements (fluorescence quantum yield, CD, CPL).
• Density Functional Theory (DFT) calculations.

Main Results:

• Successful synthesis of ligands L1 and L2.
• Formation of Pd2L4 supramolecular cages through self-assembly.
• Pd2L14 cages exhibited high fluorescence quantum yields (ΦF = 0.50).
• Pd2L24 cages displayed significant circular dichroism (CD) and circularly polarized luminescence (CPL) activity.
• The oxahelicene framework enabled guest encapsulation.

Conclusions:

• Oxahelicene ligands are effective building blocks for constructing Pd(II)-based supramolecular cages.
• The synthesized cages possess tunable photophysical properties, including fluorescence and CPL.
• These cages demonstrate potential for applications in molecular recognition and sensing due to their guest-encapsulating capabilities.