en.Wedoany.com Reported - Research teams including Zhao Jiang and Ye Meng from Guizhou University in China, together with Xu Bingjia from Wuyi University, have designed an indolo[3,2-b]carbazole molecular framework through a heteroatom-halogen engineering strategy, developing a dual-mode organic long afterglow system that combines persistent thermally activated delayed fluorescence (pTADF) and persistent room-temperature phosphorescence (pRTP).
Afterglow materials can continue to emit light for seconds to minutes after the excitation source is removed, showing promise in applications such as anti-counterfeiting, information security, bioimaging, and optical sensing. Organic long afterglow materials have become a research hotspot in recent years due to their tunable molecular structures, flexible preparation, and good biocompatibility. Organic afterglow is mainly divided into two types: persistent room-temperature phosphorescence (pRTP) originates from the radiative transition of triplet excitons with ultra-long lifetimes; in persistent thermally activated delayed fluorescence (pTADF), triplet excitons generate long-lived singlet excitons through reverse intersystem crossing (rISC), followed by radiative decay. Developing dual-mode afterglow materials that integrate both emission pathways remains challenging because pTADF and pRTP arise from competing decay processes of the same triplet excitons.
The researchers selected indolo[3,2-b]carbazole (ICZ-p1) as the core luminescent framework and employed a synergistic heteroatom-halogen engineering strategy to regulate frontier molecular orbital distribution, excited-state electronic configuration, spin-orbit coupling (SOC), and the singlet-triplet energy gap (ΔE_ST), achieving precise control over intersystem crossing (ISC/rISC) and phosphorescence rates. By doping the molecules into poly(methyl methacrylate) (PMMA) films, triplet excitons were stabilized, enabling organic long afterglow. For F/Cl-ICZ-p1 derivatives, kᵣᶦˢᶜ and kₚ were comparable, producing efficient dual-mode (pTADF + pRTP) emission. At room temperature (298 K), the films exhibited bright green afterglow lasting over 20 seconds, with excited-state lifetimes exceeding 20 seconds. At 320 K, accelerated rISC led to a blue-shifted emission dominated by pTADF, demonstrating temperature-responsive afterglow color tuning.
Br-ICZ-p1 exhibited kₚ dominance, resulting in single-mode pRTP behavior. Its PMMA film showed a brief green afterglow (less than 1 second) at room temperature, with a phosphorescence lifetime of about 20 milliseconds, and no pTADF was detected upon heating. Leveraging photoactivation and long afterglow properties, the researchers explored information storage applications. Using a pre-patterned mask, specific areas of the F-ICZ-p1-PMMA film were selectively irradiated to consume oxygen, thereby writing patterns (the Taiji diagram and its dynamic form). After removing the UV light, the irradiated areas displayed green afterglow images, while unexposed regions remained dark, enabling optical writing and reading. The patterns remained clearly visible for up to 10 minutes but gradually degraded and disappeared after about 50 minutes due to oxygen diffusion (which quenches excited states and limits long-term storage).
To overcome this limitation, a polyvinyl alcohol (PVA) barrier layer was applied to the film. The PVA encapsulation effectively blocked oxygen permeation and prevented afterglow quenching, extending pattern readability to approximately 7 hours, with potential for remote transmission. This significantly improved temporal information storage capability. After this period, the patterns faded, suggesting a time-gated information security strategy consistent with a read-erase mechanism.
This article is compiled by Wedoany. All AI citations must indicate the source as "Wedoany". If there is any infringement or other issues, please notify us promptly, and we will modify or delete it accordingly. Email: news@wedoany.com
