Methacrylate-based copolymers as tunable hosts for triplet-triplet annihilation upconversion.

Area of Science:

• Materials Science
• Photochemistry
• Polymer Chemistry

Background:

• Triplet-triplet annihilation upconversion (TTA-UC) offers promising applications in solar energy harvesting, bioimaging, and anti-counterfeiting.
• Integrating TTA-UC chromophores into solid hosts presents a challenge, balancing high efficiency in liquids with the durability of solids.

Purpose of the Study:

• To develop tunable methacrylate copolymers as hosts for TTA-UC.
• To investigate the relationship between polymer glass transition temperature and TTA-UC efficiency.
• To understand the impact of polymer host properties on TTA-UC mechanisms.

Main Methods:

• Synthesized methacrylate copolymers by varying co-monomer ratios of n-hexyl methacrylate (HMA) and 2,2,2-trifluoroethyl methacrylate (TFEMA).
• Utilized a model sensitizer/emitter pair: palladium(ii) octaethylporphyrin (PdOEP) and diphenylanthracene (DPA).
• Analyzed upconversion quantum yield, phosphorescence decays, and threshold intensity as a function of polymer glass transition temperature (Tg).

Main Results:

• Upconversion quantum yield increased with decreasing glass transition temperature, reaching a maximum of 1.6 ± 0.2% in air.
• Increased PdOEP aggregation in glassy polymers led to non-radiative relaxation pathways, quenching the triplet state.
• Threshold intensity for TTA-UC was highly sensitive to Tg, indicating a switch in mechanism from diffusion-based to exciton migration.

Conclusions:

• Methacrylate copolymers offer tunable hosts for efficient TTA-UC, with efficiency inversely related to Tg.
• Polymer aggregation and associated non-radiative pathways significantly impact upconversion performance.
• The study provides insights into optimizing TTA-UC materials for practical applications by controlling host properties.