Photon upconversion, a process where two low-energy light particles combine into one higher-energy particle, holds promise for applications from photovoltaics to targeted therapies. However, the method typically depends on rare and inefficient molecular collisions with precise alignment. Researchers have been seeking ways to improve both the reliability and efficiency of this process.
Led by photoscientist KOBORI Yasuhiro, the Kobe team devised a molecule that significantly increases the likelihood of successful energy fusion events. By arranging three anthracene molecules around a central boron atom, the team created a structure where an excited state, or triplet exciton, can hop rapidly among the anthracenes. This internal hopping increases the effective interaction space and maintains energy levels, making the energy fusion-known as triplet-triplet annihilation-more probable during molecular encounters.
"Our analysis clarifies how absorbed energy moves and transforms the molecule," said Kobori. "This understanding can guide the design of more effective upconverters."
Reported in Angewandte Chemie International Edition, the new molecular configuration showed a 20% faster rate of triplet fusion compared to previous designs. The hopping speed of the triplet exciton exceeded the typical duration of molecular collisions, improving the orientation match required for upconversion.
In addition, the researchers discovered that luminescence efficiency can be tuned by adjusting the viscosity of the medium. A more viscous environment reduces both molecular encounters and exciton mobility within the molecule. This opens possibilities for using upconversion luminescence to study cellular microenvironments.
By demonstrating how internal energy mobility can be engineered for better efficiency, the Kobe team proposes a broader design strategy that could lead to new classes of high-performance upconverters. Kobori said, "We expect that this development may contribute to solving global energy problems, as well as to expand into a wide range of fields such as cancer therapy and diagnostics, by using harmless low-energy light and in-situ upconversion."
Research Report:Vibronic Trimer Design Enhancing Intramolecular Triplet-Exciton Hopping to Accelerate Triplet-Triplet Annihilation for Photon Upconversion
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