Fluorescence enhancement via structural rigidification inside a self-assembled Pd₄ molecular vessel

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Photochemistry

Background:

• Aggregation-induced emission (AIE) active molecules exhibit weak luminescence in dilute solutions due to intramolecular motion.
• High emission is typically observed in aggregates or the solid-state, limiting their application in solution-based systems.
• Restricted Intramolecular Motion (RIM) is a key mechanism for achieving high emission in AIE molecules.

Purpose of the Study:

• To develop a strategy for enhancing the emission of AIE-active molecules in dilute solutions.
• To investigate the effect of molecular confinement on the photophysical properties of AIE molecules.
• To design and construct a supramolecular host system for AIE guest molecules.

Main Methods:

• Synthesis of a tetradentate ligand (L) and a palladium(II) precursor ([cis-(en)Pd(NO3)2], M).
• Assembly of a Pd4 molecular vessel (MP1) through coordination of M and L in a 2:1 molar ratio.
• Encapsulation of an AIE-active molecule (SG) within the cavity of MP1 and characterization of its photophysical properties.

Main Results:

• The Pd4 molecular vessel (MP1) successfully encapsulated the AIE-active molecule SG.
• Encapsulation within MP1 significantly restricted the intramolecular motion of SG.
• SG exhibited a notable enhancement in emission intensity in dilute solution upon complexation with MP1.

Conclusions:

• Confinement-driven restriction of intramolecular motion within a supramolecular host is an effective strategy to achieve high emission of AIE molecules in dilute solution.
• This approach overcomes the limitation of weak luminescence in solution for AIE compounds.
• The developed strategy holds potential for designing advanced materials with high emission capabilities in both aggregated and dilute solution states.