Photon-Upconverting Ionic Liquids: Effective Triplet Energy Migration in Contiguous Ionic Chromophore Arrays

Area of Science:

• Photochemistry
• Materials Science
• Ionic Liquids

Background:

• Ionic liquids (ILs) possess unique bicontinuous ionic-network structures.
• Photofunctional materials are crucial for advanced optical applications.

Purpose of the Study:

• To develop novel photofunctional ionic liquids.
• To investigate triplet energy migration and photon upconversion in these ILs.
• To optimize the triplet-triplet annihilation (TTA-UC) process.

Main Methods:

• Synthesis of a novel fluorescent ionic liquid with an aromatic 9,10-diphenylanthracene 2-sulfonate anion and an alkylated phosphonium cation.
• Spectral property analysis to reveal chromophore interactions.
• Dissolving a triplet sensitizer to induce TTA-UC.
• Measurement of triplet diffusion constant.

Main Results:

• The developed IL exhibited efficient triplet energy migration among ionic chromophores.
• Pronounced chromophore interactions were observed.
• Photon upconversion via TTA-UC was demonstrated.
• The TTA-UC process was optimized at significantly lower excitation intensities compared to nonionic systems.
• A high triplet diffusion constant (1.63×10⁻⁶ cm²/s) was measured, attributed to ionic chromophore networks.

Conclusions:

• The novel photofunctional ILs facilitate efficient triplet energy migration and TTA-UC.
• The ionic chromophore networks in ILs enhance TTA-UC efficiency and optimize performance at low excitation intensities.
• These findings open new avenues for designing advanced photofunctional materials based on ionic liquids.