In a lab in Taipei, scientists have figured out how to make a material glow with near-infrared light at around 1,000 nanometers — and they did it by tweaking the middle of a molecule shaped like the letter C.
That wavelength matters because near-infrared light can travel through the human body and help doctors see inside it, and it could also power future security cameras that "see" in the dark. But for years, pushing organic (carbon-based) light out to these long wavelengths came at a steep cost: efficiency collapsed. The closer the colors got to those deep wavelengths, the more the molecules wasted their energy as heat instead of light. It was like turning up the volume on a radio and getting nothing but static.
A team from National Taiwan University, National Yang Ming Chiao Tung University, National Taiwan Ocean University and Academia Sinica took a different approach. Instead of trying to fix one part of the problem, they redesigned the molecule's core. They swapped out a benzene-centered framework for new cores built from sulfur and selenium — elements that are rich in electrons. That electron-rich character nudged the light's color further toward 1,000 nanometers, while the rigid C-shaped structure kept the molecule from collapsing and wasting energy.
The results were promising. One new dye, called CT-F, reached a solid-state photoluminescence quantum yield — a measure of how efficiently a material turns light into glow — of 14.3% at 970 nm. The selenium versions, CT-Se and CT-2Se, pushed the colors even deeper into the near-infrared.
Then came the clever part. Even though CT-F was the intrinsically brighter material, it was CT-Se that showed the most balanced flow of electrons and "holes" — the positive counterparts that pair with electrons to make light. This balance let charges recombine more effectively inside an actual device, a hyperfluorescent OLED that pairs the C-shaped dye with a highly emissive deuterated platinum complex acting as an energy sensitizer. The CT-Se device hit 3.07% external quantum efficiency with its emission peaking at exactly 1,000 nm.
To clean up a bit of leftover light from the sensitizer, the team added a small amount of a conjugated polymer called PM6 as an energy-transfer relay. The optimized device reached 3.56% external quantum efficiency at 995 nm — a figure the authors call a record among metal-free organic emitters peaking around 1,000 nm.
"By combining electron-rich molecular cores with careful control of energy transfer and charge balance, we can move organic OLED emission toward 1,000 nanometers while limiting the efficiency losses that usually occur at these wavelengths," said co-corresponding author Pi-Tai Chou, a chemistry professor at National Taiwan University.
The work, published in Advanced Materials, shows that making deep-near-infrared light efficient isn't about optimizing any one property — it's about coordinating molecular design, charge transport and energy transfer all at once. For biomedical imaging and night vision, that coordination could one day mean clearer, brighter pictures without the usual efficiency trade-off.