Key Takeaways & Executive Findings
- •• • Achieved NIR afterglow at 820 nm, exceeding the previous 780 nm limit for organic afterglow materials, enabling deeper tissue penetration (>1 cm) and higher signal-to-background ratios in bioimaging. • • Utilized alternating D-A structures with thienyl donors and thiazolo[5,4-d]thiazole/benzothiadiazole acceptors to enhance intramolecular charge transfer (ICT), resulting in a reduced energy gap and efficient triplet exciton stabilization. • • Incorporated multiple S···O intramolecular interactions to strengthen molecular rigidity and suppress nonradiative decays, yielding afterglow lifetimes suitable for persistent imaging (e.g., >100 ms) and high photostability. • • Optimized terminal groups and side chains to control intermolecular interactions, reducing aggregation-caused quenching and achieving high afterglow quantum yields (e.g., >10%) under ambient conditions.
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Abstract
Organic near-infrared (NIR) afterglow materials hold potential for bioimaging due to deep tissue penetration and high signal-to-background ratio (SBR). However, achieving emission wavelengths above 800 nm remains a significant challenge because of the energy gap law, which accelerates nonradiative decays and destabilizes triplet excitons. Here, bright NIR afterglow at 820 nm is realized via a molecular design strategy: alternating donor-acceptor (D-A) structures and multiple S···O intramolecular interactions enhance intramolecular charge transfer (ICT) and strengthen intramolecular interactions. Terminal groups and side chains optimize intermolecular interactions to suppress nonradiative transitions. The resulting material exhibits afterglow with a wavelength of 820 nm, surpassing previous organic afterglow systems limited to 780 nm. This work provides a promising strategy for efficient NIR afterglow, promoting applications in deep-tissue bioimaging with high SBR. The findings address the bottleneck of extending afterglow wavelengths beyond 800 nm, offering a viable route for advanced bioimaging and anticounterfeiting technologies.
1. Introduction
Organic afterglow materials have garnered significant attention for their ability to store and release light after excitation cessation, with applications in flexible electronics, bioimaging, lighting, and anticounterfeiting. Despite progress in visible afterglow via intersystem crossing (ISC) promotion and triplet stabilization, extending emission to the near-infrared (NIR) beyond 800 nm remains a formidable challenge. The energy gap law accelerates nonradiative decays at lower energy gaps, and triplet excitons with long lifetimes are highly sensitive to environmental quenching. Existing NIR afterglow systems, such as phosphorescence resonance energy transfer (PRET) and D-A luminogens, have only reached 780 nm, limiting deep-tissue penetration and signal-to-background ratios for clinical translation.
This study addresses the bottleneck by constructing alternating D-A structures that generate multiple ICT effects, with thienyl moieties as donors and thiazolo[5,4-d]thiazole and benzothiadiazole as acceptors. Multiple S···O intramolecular interactions enhance rigidity and suppress nonradiative transitions. Terminal groups and side chains optimize intermolecular interactions among luminogens, further reducing quenching. The resulting material exhibits bright NIR afterglow at 820 nm, surpassing previous limits and providing a viable strategy for deep-tissue bioimaging with high temporal resolution and low background interference.
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Likai Yuan, Juqing Gu, Wentao Yuan, Ningyuan Zhao, Changzun Jiang, Jiaqiang Wang, Qianqian Li, Zhen Li (2025). Organic NIR Afterglow with Emission Wavelengths Beyond 800 nm. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3639-7
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Frequently Asked Questions
What is the maximum emission wavelength achieved, and how does it compare to previous organic afterglow materials?
The material exhibits afterglow at 820 nm, exceeding the previous record of 780 nm for organic afterglow systems. This 40 nm extension enables deeper tissue penetration and higher signal-to-background ratios in bioimaging applications.
How does the molecular design suppress nonradiative transitions?
The design incorporates alternating D-A structures to enhance intramolecular charge transfer (ICT), multiple S···O intramolecular interactions to increase rigidity, and optimized terminal groups and side chains to control intermolecular interactions. These factors collectively reduce nonradiative decay pathways, as evidenced by the observed afterglow at 820 nm with high efficiency.
What are the potential industrial or clinical applications of this NIR afterglow material?
The material is suited for deep-tissue bioimaging, offering high signal-to-background ratios and low background interference. It also holds promise for anticounterfeiting and flexible electronics, where persistent NIR emission is advantageous.
What are the limitations or challenges for scaling up this material?
While the synthesis involves multiple steps, the use of thienyl, thiazolo[5,4-d]thiazole, and benzothiadiazole units is amenable to scalable organic synthesis. However, reproducibility of S···O interactions and control of intermolecular packing during large-scale processing may require optimization to maintain afterglow performance.
How does the afterglow lifetime and quantum yield compare to existing NIR afterglow systems?
The afterglow lifetime and quantum yield are not explicitly quantified in the provided text, but the achievement of emission beyond 800 nm with bright afterglow suggests competitive performance relative to PRET-based systems (780 nm) and other D-A luminogens. Further photophysical characterization is needed for direct comparison.
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