Bengaluru: A research team from the Department of Inorganic and Physical Chemistry (IPC) at the Indian Institute of Science (IISc) has designed an organic molecule that breaks two stubborn barriers at once: it phosphoresces (a material that glows for a prolonged period after ceasing excitation) at room temperature and does so without any heavy or toxic metals. Even more remarkably, the compound emits circularly polarised luminescence (CPL)—a special polarisation of light where the wave spirals as it moves forward, similar to a corkscrew—prized for use in safer, eco-friendly, next-generation 3D displays, encrypted QR codes, medical imaging, and anti-counterfeiting labels. CPL is one of the intriguing aspects of this molecule.
Why it matters
- Metal-free: Most afterglow materials rely on rare or hazardous metals. The IISc molecule avoids them entirely, lowering cost and toxicity.
- Room-temperature afterglow: Organic phosphors usually need liquid-nitrogen cooling (77 K) for prolonged emission. Here, the glow persists at ambient temperature, opening the door to practical applications including security inks, wearable sensors, low-power OLED pixels, and bio-imaging probes.
- Built-in chirality: The molecule’s rigid, chiral framework not only unlocks its long-lived emission but also produces CPL, potentially enabling data to be encrypted at multiple levels.
How the molecule works
The boron-nitrogen (B–N) containing organic molecule is made from readily available, cost-effective chemicals, and such compounds are generally called aminoboranes. In this system, researchers connected two naphthalene-based aminoborane units and locked them around a central axis. This rigid structure suppresses non-radiative decay, curbing energy loss as heat and enabling long-lived phosphorescence. Interestingly, the locked chiral structure also results in polarised light emission, which is valuable for applications like 3D displays and advanced optical technologies.
In a study published in Communications Chemistry, the team showcased the potential of this new molecule. The researchers formulated inks using phosphorescent molecules and demonstrated how hidden information can be selectively revealed.
A 'time-gated' security writing demo
Under UV light, an ink containing the new phosphor was used to write “1180”. This was intentionally designed as a decoy, while a hidden message—“IISC”—was encoded within the same text strategically. This delayed-reveal capability can offer an elegant route to security tags, encrypted labels and tamper-proof authentication technologies.
Talking to ETV Bharat, Jusaina Eyyathiyil, the lead author of the study, discussed the motivation behind the research work. She said that the inspiration stemmed from one of the long-standing quests in organic photophysics: how to achieve multiple advanced light-emitting properties such as persistent glow in the dark (room-temperature phosphorescence) and circularly polarised light emission from a single, small organic molecule. Having both these features in one material can be extremely useful for real-world applications, especially in anti-counterfeiting inks, security tags, and bio-imaging, where reliable and distinctive optical signatures are crucial.
She explained that a molecule absorbs energy and becomes excited when hit with a beam of light with the right energy. Normally, it quickly returns to its original state by releasing the energy as light, called fluorescence, which typically lasts only a few nanoseconds. But sometimes, the energy takes a longer route through a rare process known as intersystem crossing, and the molecule emits light more slowly and for a longer duration, called phosphorescence.
Jusaina further explained that achieving phosphorescence at room temperature is generally challenging. At room temperature, molecules undergo various vibrational and rotational motions that often cause the excited energy to dissipate as heat, quenching the light emission. Under cryogenic conditions (such as 77 K using liquid nitrogen), these motions are suppressed, and phosphorescence is more likely to be observed. However, in our system, we have succeeded in generating a measurable afterglow even at room temperature.
"Replacing carbon–carbon bonds with boron–nitrogen bonds creates excited states with different symmetries, which facilitates efficient phosphorescence,” explained Professor P Thilagar, the corresponding author of the study. "This substitution enhances spin flipping—a key intersystem crossing process that effectively populates the molecule’s triplet state. Since such electron spin transitions are quantum mechanically forbidden, they occur more slowly, which in turn allows the molecule to emit phosphorescence over a longer duration.”
![In picture: P Thilagar [Professor, IPC, IISc]](https://etvbharatimages.akamaized.net/etvbharat/prod-images/09-06-2025/prof-pthilagar_0906newsroom_1749440696_811.jpg?)
Jusaina explained that chemically, a boron–nitrogen (B–N) bond is similar to a carbon–carbon (C–C) bond in terms of electron count, but differs significantly in its electronic properties. Previous studies from researchers around the world have shown that purely carbon-based frameworks are not very effective at producing afterglow, while frameworks incorporating heteroatoms tend to perform better and are a well-established strategy in this field.
She said, "Guided by these insights, we introduced B–N bonds into a full carbon molecular framework to extend the duration of afterglow. To improve performance further, we introduced molecular chirality into the design. Chiral molecules, which have non-superimposable mirror image structures, are widely found in nature. Incorporating chirality increased the rigidity of the molecule, helping to suppress energy loss through vibrations and thereby prolonging the afterglow. Chirality also enabled circularly polarised light emission—a rare and valuable feature for advanced optical applications.”
Challenges & Collaborations
Talking about the challenges during the project, the authors noted that determining the molecule's structure was one of the early hurdles. Single-crystal X-ray diffraction, a gold standard for molecular structure determination, was difficult to achieve with the in-house facility due to poor-quality crystals. To overcome this, the team collaborated with Professor Neal Hickey’s group at the University of Trieste, Italy, for sophisticated, high-quality radiation-based crystallographic characterisation. Additionally, circularly polarised luminescence measurements were carried out in collaboration with Professor Jatish Kumar’s group at IISER Tirupati. These collaborative efforts played a key role in strengthening the findings.
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Jusaina Eyyathiyil also mentioned that optimising the security writing application was a challenge. “We mixed the phosphorescent compound with a well-known polymer, PMMA, to formulate the ink. The right ratio of these components was critical to get sharp, readable text images,” she said. “Several iterative experiments with support from co-author Subhajit Ghosh were especially helpful in getting the application to work. Thilagar’s guidance was also crucial during this phase.”
The team believes that their material holds strong application potential, particularly in energy-efficient electroluminescent displays (such as OLEDs), where long-lived emitters could help reduce power consumption. Although the compound performed impressively in security-writing demonstrations, the researchers acknowledge that the emission intensity still needs enhancement for broader use in display and bio-imaging technologies. Further work is underway to fine-tune the molecular structure and improve brightness.
With its rare combination of room-temperature afterglow, chirality, and metal-free design, this small organic molecule represents a promising step toward safer, smarter, and more sustainable light-emitting materials.
