Key Takeaways & Executive Findings
- •• • Stimuli-responsive RTP materials enable dynamic afterglow modulation under external triggers (light, pH, heat, mechanical force, solvent), with reported ultralong phosphorescence lifetimes exceeding 1 s and color tunability across the visible spectrum, as exemplified by UV-irradiation-responsive systems achieving dynamic ultralong phosphorescence in polymeric matrices (Nat Commun, 2021, 12: 2297). • • Host-guest doping and polymerization strategies have achieved multistage stimulus-responsive RTP with high contrast and reversibility, enabling temporally programmable luminescence for anti-counterfeiting and encryption; for instance, amorphous molecular 'triplet exciton pump' systems demonstrate dynamic ultra-long RTP with spatial and temporal resolution (Angew Chem Int Ed, 2024, 63: e202317631). • • Single-component molecular crystals and multicomponent copolymers exhibit color-tunable ultralong organic phosphorescence, with emission colors tunable from blue to red and lifetimes up to several seconds, as demonstrated in Nat Photonics (2019, 13: 406) and Nat Commun (2020, 11: 944). • • pH-responsive amorphous RTP polymers based on fluorescein show reversible afterglow switching with response times on the order of minutes, and red-light-excited near-infrared RTP films achieve efficient metal-free phosphorescence, expanding the spectral window for bioimaging and sensing (Chin Chem Lett, 2021, 32: 3039; Natl Sci Rev, 2022, 9: nwab085).
Abstract
Organic room-temperature phosphorescence (RTP) materials have attracted considerable interest due to their unique advantages, such as tunable molecular structures, excellent processability, intrinsic flexibility, and diverse excited-state characteristics. Among these, stimuli-responsive RTP materials, whose luminescence can be modulated by external stimuli (e.g., light, pH, heat, mechanical force or solvent), hold great promise for advanced applications like anti-counterfeiting, information encryption, and sensing. In this review, we systematically summarize recent advances in stimuli-responsive RTP materials, classifying them based on their activation mechanisms. Specifically, we elucidate the fundamental principles governing their stimulus-responsive behaviors and highlight representative examples from various categories. Furthermore, we explore structure-property relationships and design strategies to establish a foundational framework for understanding these materials. This review not only deepens the mechanistic insights into stimuli-responsive RTP systems but also provides strategic guidance for the rational design of next-generation intelligent RTP materials in multidisciplinary fields.
1. Introduction
Conventional inorganic phosphors and organometallic complexes dominate commercial phosphorescence applications, yet they suffer from high cost, toxicity, and limited processability. Metal-free organic RTP materials offer a compelling alternative, but their practical deployment has been hindered by intrinsically weak intersystem crossing (ISC) and rapid non-radiative decay of triplet excitons. Static phosphorescence systems, stabilized via heavy-atom effects, H-aggregation, or crystallization, achieve high efficiency but lack dynamic tunability, restricting their use in adaptive sensing and encryption.
This review addresses the bottleneck by focusing on stimulus-responsive RTP materials, which exploit the environmental susceptibility of triplet states to achieve dynamic, programmable afterglow. By systematically classifying activation mechanisms—photo, pH, thermal, mechanical, and solvent—and analyzing structure-property relationships, we provide a strategic framework for designing next-generation intelligent materials. The reported systems demonstrate reversible on/off switching, color modulation, and ultralong lifetimes, offering a pathway to overcome the static-dynamic dichotomy and enable advanced applications in anti-counterfeiting, information encryption, and biological imaging.
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XU Jiahui, DU Weiguo, ZHONG Xing, WANG Chenrui, SHI Huifang, AN Zhongfu (2026). Stimulus-Responsive Organic Room Temperature Phosphorescence Materials: Mechanisms, Design Strategies, and Emerging Applications. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3932-1
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Frequently Asked Questions
What are the primary mechanisms enabling stimulus-responsive RTP, and how do they achieve reversibility?
Stimulus-responsive RTP relies on the environmental sensitivity of triplet excitons. Reversible modulation is achieved through reversible changes in molecular conformation, aggregation state, or host-guest interactions. For example, UV irradiation can induce photochemical reactions that alter the phosphorescence intensity, while pH changes can protonate/deprotonate functional groups, modulating ISC efficiency. Reversibility is ensured by the reversibility of these stimuli, as demonstrated in systems like pH-responsive amorphous RTP polymers (Chin Chem Lett, 2021) and UV-irradiation-responsive polymeric systems (Nat Commun, 2021).
How do these materials achieve ultralong phosphorescence lifetimes, and what are the reported maximum values?
Ultralong RTP (lifetimes > 100 ms) is achieved by stabilizing triplet excitons through strategies like H-aggregation, crystallization, or rigid host matrices. For instance, single-component molecular crystals exhibit color-tunable ultralong phosphorescence with lifetimes up to several seconds (Nat Photonics, 2019). Multicomponent copolymers also achieve lifetimes exceeding 1 s (Nat Commun, 2020). These long lifetimes enable time-resolved encryption and imaging.
What are the key challenges in scaling up these materials for commercial anti-counterfeiting applications?
Scalability challenges include reproducibility of molecular synthesis, uniform dispersion in polymer matrices, and maintaining high phosphorescence quantum yields in thin films. Additionally, the stimuli-responsive behavior must be robust under ambient conditions (humidity, temperature) and over repeated cycles. For example, UV-irradiation-responsive systems require precise control of irradiation dose and wavelength to avoid degradation. Cost-effective fabrication methods, such as solution processing, are being explored to address these issues.
How do these RTP materials compare to traditional fluorescent security inks in terms of performance and security?
RTP materials offer a higher security level due to their time-domain emission (afterglow) and stimuli-responsive switching, which are difficult to replicate with conventional fluorescent inks. They provide dual anti-counterfeiting features: color and lifetime. For instance, multistage stimulus-responsive RTP systems can be programmed to exhibit different afterglow colors under different stimuli, enhancing security. However, challenges remain in achieving high brightness and stability under UV excitation, which are being addressed through material design.
What are the potential applications of these materials in biological imaging, and what are the limitations?
RTP materials with near-infrared (NIR) emission are promising for biological imaging due to low autofluorescence and deep tissue penetration. Red-light-excited NIR RTP films (Natl Sci Rev, 2022) demonstrate efficient metal-free phosphorescence, enabling in vivo imaging. However, limitations include low quantum yields in aqueous environments and potential toxicity. Surface functionalization and encapsulation strategies are being developed to improve biocompatibility and brightness.
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