AsianScientist (May. 20, 2026)–Fluorescent dyes are like molecular highlighters, allowing researchers to follow chemical changes and cellular structures otherwise invisible to the naked eye. The light-emitting molecules are widely used in bioimaging and photodynamic therapy to help visualise or damage diseased cells. However, much like ink fading in water, traditional fluorescent dyes often fade or degrade in harsh acidic environments.
The fragility limits their use in settings where strong acids are unavoidable, including hydrogen fuel cells and industrial filtration systems, where scientists often need fluorescent probes to track chemical activity. Among the widely used fluorescent dyes are BODIPYs (boron-dipyrromethenes), highly valued for their intense and tunable fluorescence. Their weakness is a reaction called deboronation, where strong acids strip away the central boron atom responsible for their glow, instantly extinguishing it.
Researchers at Hokkaido University have now developed a new class of fluorescent dye capable of surviving even superacids stronger than concentrated sulfuric acid. The study was published in Nature Communications by a team led by Yasuhide Inokuma, a professor at the Institute for Chemical Reaction Design and Discovery (WPI-ICReDD).
Previous attempts to improve BODIPY’s acid resistance focused mainly on modifying the chemical groups attached to boron, yielding dyes that survived only down to about pH 1—mildly acidic by chemical standards—before degrading in strongly acidic, water-free environments.
The Hokkaido team took a different approach by redesigning the molecular framework surrounding the boron centre itself. The researchers drew inspiration from calix[3]pyrrole, a ring-shaped molecular structure known for binding boron atoms unusually tightly. They built a rigid macrocycle, a large ring-like molecular structure, around the fluorescent core, where three nitrogen atoms coordinate strongly to the boron centre, making it far more resistant to acid-induced boron loss.
The redesign dramatically improved the dye’s resilience. When immersed in fluorosulfonic acid, a superacid roughly 1,000 times stronger than sulfuric acid, the new dye maintained a fluorescence efficiency of 90 percent after 12 hours, with no boron loss detected at the 24-hour mark.
Conventional BODIPYs lost all fluorescence within one hour in a far milder acid, and the previously reported acid-resistant BODIPY analogues degraded within 15 minutes in methanesulfonic acid.
The macrocyclic dye also survived 48 hours at 180°C without spectral change and resisted photodegradation under continuous LED irradiation, outperforming both comparators, which showed significant bleaching.
The structural redesign introduced a built-in on/off fluorescence switch that exploits acid rather than succumbing to it. Under neutral conditions, the dye is dark because a third pyrrole unit—a nitrogen-containing ring added to complete the macrocycle—diverts energy away from light emissions through a photoinduced electron transfer process, preventing the dye from glowing. When exposed to strong acid, the pyrrole ring binds to a hydrogen ion, cutting off the energy diversion and restoring fluorescence. The acid, in effect, acts as a molecular on-switch rather than destroying the dye.
That acid-activated switching proved useful for imaging materials that have long resisted fluorescence-based analysis. Nafion beads, commonly used in fuel-cell membranes whose strong internal acidity rapidly degrades conventional BODIPYs, emitted bright fluorescence after treatment with the new dye, while a standard BODIPY produced little detectable signal under similar conditions.
Reversible switching was also proven in sulfonated gels and ion-exchange resins, where adding a base quenched the fluorescence and acid revived it across multiple cycles, with no dye leaching from the materials, a finding that points to practical durability in real-world applications.
“We hope this work will inspire the development of fluorescent molecules capable of illuminating extreme chemical environments, demonstrating how molecular weaknesses can become powerful design principles,” said Inokuma in a Springer Nature Blog.
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Source: Springer Nature Research Communities ; Image: Magnific
This article can be found at: Superacid-resistant macrocyclic BODIPYs
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