Guest-Dependent Fluorescence Response by a Highly Emissive s-Tetrazine Pd₂L₄ Cage

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Chemical Sensing

Background:

• Fluorescent cage molecules are valuable for selective chemosensing.
• s-Tetrazines possess desirable fluorescent and redox properties.
• Integrating fluorescent tetrazines into coordination cages is an underexplored area.

Purpose of the Study:

• To synthesize and characterize a novel fluorescent coordination cage incorporating an s-tetrazine ligand.
• To investigate the anion binding and sensing capabilities of the developed coordination cage.
• To explore the host-guest chemistry within the electron-deficient cage cavity.

Main Methods:

• Self-assembly of a Pd2L4 coordination cage using 3,6-bis(pyridin-3-yloxy)-1,2,4,5-tetrazine.
• Characterization via NMR spectroscopy, ESI-MS, and X-ray crystallography.
• Electrochemical analysis using cyclic voltammetry and fluorescence spectroscopy.

Main Results:

• A rigid helical coordination cage structure was successfully synthesized.
• The cage encapsulates anions within its electron-deficient cavity.
• The cage retains the fluorescence of the tetrazine ligand and exhibits selective binding for nitrate anions (K = 2300 M-1).
• Distinct fluorescence quenching responses were observed for bound nitrate versus non-encapsulated hexafluorophosphate anions.

Conclusions:

• The study reports the first fluorescent s-tetrazine-based coordination cage.
• The developed cage demonstrates potential for selective anion sensing through host-guest interactions.
• The distinct fluorescence responses highlight the utility of this system in differentiating anions.