New Way of Photon-Upconversion

Billions of molecular lightbulbs, powered by invisible infrared photons, generate visible light. (Source: M. A. Ashley)

Columbia University scientists, in colla­boration with researchers from Harvard, have succeeded in deve­loping a chemical process to convert infrared energy into visible light, allowing inno­cuous radiation to pene­trate living tissue and other materials without the damage caused by high-inten­sity light exposure. “The findings are exciting because we were able to perform a series of complex chemical trans­formations that usually require high-energy, visible light using a non­invasive, infrared light source,” said Tomislav Rovis, pro­fessor of chemistry at Columbia.

“One can imagine many potential appli­cations where barriers are in the way to control­ling matter. For example, the research holds promise for enhancing the reach and effectiveness of photo­dynamic therapy, whose full potential for managing cancer has yet to be realized”, Rovis said. The team, which includes Luis M. Campos, asso­ciate professor of chemistry at Columbia, and Daniel M. Congreve of the Rowland Insti­tute at Harvard, carried out a series of experi­ments using small quantities of a novel compound that, when stimu­lated by light, can mediate the transfer of electrons between molecules that other­wise would react more slowly or not at all.

Their approach, a triplet fusion upcon­version, involves a chain of processes that essen­tially fuses two infrared photons into a single visible light photon. Most techno­logies only capture visible light, meaning the rest of the solar spectrum goes to waste. Triplet fusion upcon­version can harvest low-energy infrared light and convert it to light that is then absorbed by the solar panels. Visible light is also easily reflected by many surfaces, whereas infrared light has longer wave­lengths that can pene­trate dense materials.

“With this tech­nology, we were able to fine-tune infrared light to the necessary, longer wave­lengths that allowed us to noninva­sively pass through a wide range of barriers, such as paper, plastic molds, blood and tissue,” Campos said. The researchers even pulsed light through two strips of bacon wrapped around a flask

Scientists have long tried to solve the problem of how to get visible light to penetrate skin and blood without damaging internal organs or healthy tissue. Photo­dynamic therapy (PDT), used to treat some cancers, employs a photo­sensitizer, that is trig­gered by light to produce a highly reactive form of oxygen that is able to kill or inhi­bit the growth of cancer cells. Current photo­dynamic therapy is limited to the treatment of localized or surface cancers. “This new tech­nology could bring PDT into areas of the body that were pre­viously inacces­sible,” Rovis said.

“Rather than poisoning the entire body with a drug that causes the death of malignant cells and healthy cells, a nontoxic drug combined with infrared light could selec­tively target the tumor site and irradiate cancer cells”, Rovis added. The tech­nology could have far-reaching impact. Infrared light therapy may be instru­mental in treating a number of diseases and condi­tions, including trau­matic brain injury, damaged nerves and spinal cords, hearing loss, as well as cancer.

Other potential appli­cations include remote manage­ment of chemical storage solar power produc­tion and data storage, drug development, sensors, food safety methods, moldable bone-mimic compo­sites and processing micro­electronic com­ponents. The researchers are currently testing photon-upcon­version techno­logies in addi­tional biological systems. “This opens up unpre­cedented oppor­tunities to change the way light interacts with living organisms,” Campos said. “In fact, right now we are employing upcon­version techniques for tissue engi­neering and drug delivery.” (Source: U Columbia)

Reference: B. D. Ravetz et al.: Photoredox catalysis using infrared light via triplet fusion upconversion, Nature 565, 343 (2019); DOI: 10.1038/s41586-018-0835-2

Link: Luis Campos Research Group, Dept. of Chemistry, Columbia University, New York, USA

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