Supramolecular Assembly-Improved Triplet-Triplet Annihilation Upconversion in Aqueous Solution

Area of Science:

• Supramolecular Chemistry
• Photochemistry
• Materials Science

Background:

• Triplet-triplet annihilation (TTA) upconversion is a process that converts lower-energy photons to higher-energy photons.
• Achieving efficient TTA upconversion in aqueous solutions is challenging due to low emitter concentrations and aggregation-caused quenching.
• Novel molecular designs are needed to enhance TTA upconversion in water.

Purpose of the Study:

• To synthesize and characterize novel water-soluble cyclodextrin derivatives for supramolecular TTA upconversion.
• To investigate the self-assembly behavior and photophysical properties of these derivatives in aqueous solution.
• To evaluate the TTA upconversion efficiency of the assembled supramolecular system.

Main Methods:

• Synthesis of 9,10-diphenylanthracene-modified γ-cyclodextrin derivatives (A1 and A2).
• Characterization of nanoscale assemblies using dynamic light scattering (DLS), SEM, NMR, fluorescence, and circular dichroism.
• Measurement of fluorescence quantum yields and TTA upconversion quantum yields using a ruthenium sensitizer.

Main Results:

• A1 and A2 self-assembled into nanoscale structures in water via host-guest complexation and π-π stacking.
• High fluorescence quantum yields (82% and 90%) were maintained in the aggregated state, indicating no fluorescence quenching.
• A significant TTA upconversion quantum yield of up to 6.9% was achieved in the supramolecular system, far exceeding non-assembled emitters.

Conclusions:

• Water-soluble cyclodextrin derivatives can form self-assembled supramolecular structures that promote efficient TTA upconversion in aqueous solution.
• The enhanced TTA upconversion is attributed to efficient triplet energy migration and energy transfer within the stacked emitters facilitated by host-guest complexation.
• This supramolecular approach offers a promising strategy for developing efficient light-harvesting and upconversion systems in aqueous media.