MIT chemists developed a stable class of fluorescent molecules that emit in the red to near-infrared (NIR) region. The research, published in Nature Chemistry, centers on borenium ions, positively charged boron-based molecules, long seen as promising emitters for biomedical imaging due to their ability to fluoresce in the deep-red to NIR spectrum.
Until recently, these ions were too unstable to use outside tightly controlled lab environments.
Led by Professor Robert Gilliard, the team stabilized borenium ions by binding them to carbodicarbene (CDC) ligands. This structural approach created air- and moisture-stable compounds in the form of powders, films, crystals, and colloidal suspensions, all emitting light between red and NIR wavelengths.
These wavelengths are critical for biomedical imaging because they penetrate tissue more effectively than blue or green light, reducing background interference and allowing for clearer imaging of structures deep within the body.
The researchers focused on red to near-IR because such dyes penetrate tissue better and face fewer challenges with autofluorescence.
Optical Efficiency Through Ion-Pair Design
In addition to improving environmental stability, the CDC ligands enabled fine control of the compounds’ optical properties. By manipulating the interactions between the borenium cations and their accompanying anions, the team achieved exciton coupling, an effect that shifted both emission and absorption further into the infrared range.
The resulting materials demonstrated solid-state luminescence with emission peaks up to 730 nm and high quantum yields, reaching into the 30 % range, remarkably efficient for this region of the electromagnetic spectrum.
Computational, crystallographic, and photophysical studies confirmed that the CDC ligands stabilized the boron center electronically, and also directed charge localization and controlled ion-pair assembly. Combining π-extension and charge management, this design strategy offers a blueprint for developing other efficient main-group red/NIR emitters.
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Versatile Applications in Imaging and Electronics
The materials’ chemical stability and tunable emission make them well-suited to multiple technologies. According to the researchers, one of the most immediate areas they're targeting is biomedical imaging. Collaborations are underway with teams at MIT and the Broad Institute to test the compounds in cellular imaging environments.
Encapsulated in polymers, the dyes could serve as injectable agents for imaging tumors or internal structures. Their temperature sensitivity also opens the door to applications as molecular thermometers, particularly for monitoring temperature-sensitive items like vaccines during storage and transport.
In thin-film form, the dyes may be integrated into organic light-emitting diodes (OLEDs), especially in flexible or wearable electronic displays. The high emission efficiency and environmental stability also make them attractive for sensors, smart materials, and anticounterfeiting technologies.
Next Steps in Development
Future efforts will explore extending the emission further into the NIR by incorporating additional boron atoms into the molecular framework. However, doing so could reduce stability, so new carbodicarbene ligands are being designed to offset those effects.
According to the researchers, the new platform's stability and performance give it such potential. Applying this combination to multiple scientific fields could be a big change for sensor tech.
Journal Reference
Deng, C., Tra, B. Y., Zhang, X., Zhang, C., & Gilliard, R. J. (2025). Unlocking red-to-near-infrared luminescence via ion-pair assembly in carbodicarbene borenium ions. Nature Chemistry, 1-11. DOI:10.1038/s41557-025-01941-6, https://www.nature.com/articles/s41557-025-01941-6
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