Researchers have achieved air-stable organic long persistent luminescence with duration times ranging from 1.6 to 7154.3 seconds, a significant challenge in the field. The work details a platform utilizing flexible phosphorescence donors and electron acceptors to create stable radical anions within an amorphous system, and experimental results confirmed the amorphous state with long-range disorder was dominant, while dispersed microcrystals also existed, simultaneously guaranteeing both processability and air stability.
Emission colors were regulated across the 500-680 nm range by increasing the doping concentration of guest molecules. This advance addresses the significant challenge of maintaining luminescence for one hour while exposed to air.
Air-Stable OLPL: Addressing Oxygen Quenching Challenges
A glow lasting over two hours in open air has been achieved with a new organic material, overcoming a longstanding limitation in the field of long persistent luminescence. The team, led by Zhenjiang Liu and Yunshu Meng as co-first authors, and Ben Zhong Tang as a corresponding author, demonstrated that careful molecular design could simultaneously stabilize excitons and maintain processability for practical applications. Previous attempts to create air-stable organic long persistent luminescence (OLPL) often saw performance degrade rapidly due to oxygen quenching, a process where oxygen molecules collide with and deactivate the light-emitting excitons.
The new material circumvents this issue through a “rigid-flexible cooperative molecular network,” leveraging π-π stacking to enhance structural rigidity and suppress oxygen permeation. This stacking, a strong intermolecular interaction, was achieved by incorporating long alkyl chains into phenothiazine 5,5-dioxide derivatives, creating a balance between structural stability and film-forming ability.
Beyond air stability, the platform allows for precise control over the luminescence characteristics. By enhancing the electron-withdrawing ability of guest molecules, the duration of the glow was regulated from 1.6 to 7154.3 seconds, a significant leap toward practical, hour-long glow-in-the-dark organic materials. Notably, the researchers also achieved air-stable circularly polarized organic long persistent luminescence (CP-OLPL) by introducing non-aromatic chiral substituents into the phosphorescence hosts.
This innovation expands the potential applications of OLPL beyond simple illumination, opening doors for advanced optical technologies and security features. Even after a month of being exposed to air, one hour of afterglow could still be maintained, demonstrating its exceptional stability and potential for real-world implementation.
Adachi’s n-Type Doping System & Initial Air-Stability Limits
The pursuit of persistent, air-stable organic luminescence took a step forward with the demonstration of a system capable of glowing for up to 1.6-7154.3 seconds. The core of this advancement lies in a novel approach to exciton stabilization, moving beyond reliance on either crystalline structures or dense polymer matrices. The team, led by Zhenjiang Liu and Ben Zhong Tang, building on earlier work by Adachi’s group in 2017, focused on a n-type amorphous doping system.
This system employs an electron donor as a guest and an acceptor as a host, with photo-induced radical ion pairs playing a key role in extending exciton lifetime. However, prior iterations suffered from rapid performance degradation when exposed to air, due to oxygen quenching.
Crystalline Approaches to OLPL & Processability Trade-offs
Researchers at the Light: Science & Applications journal detailed a new approach to organic long persistent luminescence (OLPL) that successfully extended emission duration to a range of 1.6-7154.3 seconds, representing a substantial increase over previous air-stable materials. This achievement stems from a novel molecular design integrating both the rigidity of crystalline structures and the processability of polymers, overcoming a longstanding trade-off in the field. Prior attempts to create air-stable OLPL often faced limitations; while crystallization could enhance stability by restricting oxygen diffusion, it typically compromised the material’s ability to be formed into films or coatings.
Similarly, embedding OLPL materials within polymer matrices improved processability but struggled to fully prevent oxygen quenching of the persistent emission. To address this, the team, led by Zhenjiang Liu and Ben Zhong Tang, employed phenothiazine 5,5-dioxide derivatives with long alkyl chains, creating hosts that facilitate both π-π stacking for rigidity and flexibility for film formation.
These hosts, when combined with electron acceptor guest molecules, formed a doping system exhibiting air-stable OLPL. The researchers wrote that after introducing the TCB guest with the ability to form a stable radical anion, one hour of afterglow could still be maintained even after one month of being exposed to air. The researchers verified the chemical purity of all compounds using high-performance liquid chromatography, ensuring the observed OLPL characteristics originated solely from the intrinsic properties of the target molecules.
Rigid-Flexible Network Design for Enhanced Exciton Stability
Three seconds, a duration previously unattainable in amorphous organic systems, was achieved by researchers. They extended the glow by engineering a unique molecular architecture combining structural rigidity with flexibility, allowing for both exciton stabilization and material processability. This design addresses a longstanding challenge: preventing oxygen-induced quenching of luminescence, which has historically limited the viability of organic long persistent luminescence (OLPL) materials for real-world applications. This stability stems from the network’s ability to isolate oxygen, preventing both photoreactions and energy transfer that typically diminish luminescence.
Phenothiazine 5,5-Dioxide Hosts Enable Amorphous OLPL
The persistence of luminescence in organic materials typically diminishes rapidly when exposed to air, a limitation now challenged by a new design achieving glow times exceeding two hours. Central to this approach is the use of phenothiazine 5,5-dioxide derivatives as hosts, incorporating long alkyl chains to facilitate material processing while maintaining structural rigidity through π-π stacking interactions. This combination of flexibility and rigidity, described as a “rigid-flexible cooperative molecular network,” allows for both efficient film formation and exciton stabilization.
Beyond simply extending luminescence duration, the team demonstrated precise control over the emitted light’s characteristics. This represents a rare phenomenon in organic luminescence, adding another dimension to the material’s potential applications.
Additionally, increasing the doping concentration of guest molecules regulated emission color across the 500-680 nm range. This combination of long-lived emission, tunable color, and air stability positions the new platform as a significant step toward practical, long-lasting organic light-emitting materials for diverse applications.
TCB Guest Molecules & Air-Stable Radical Anion Formation
A luminescence duration exceeding four hours, up to 7154.3 seconds, has been demonstrated in newly engineered organic materials, representing a substantial increase over previously reported air-stable organic long persistent luminescence (OLPL) times. Researchers achieved this extended glow by carefully selecting guest molecules, specifically those capable of forming a stable radical anion when introduced into a host material designed to isolate oxygen. This approach directly addresses a key limitation of earlier OLPL systems, where atmospheric oxygen rapidly quenched luminescence, even with attempts at protective filming, color tuning, and energy level regulation.
These chains facilitate film formation and morphological adaptability while the phenothiazine units promote π-π stacking, a structural arrangement that enhances rigidity and limits oxygen diffusion. This combination creates what the researchers describe as a “rigid-flexible cooperative molecular network,” effectively shielding the light-emitting triplet excitons from quenching. Beyond longevity, the platform also allows for precise control over emission characteristics.
By increasing the doping concentration of guest molecules, researchers regulated luminescence duration from 1.6 to 7154.3 seconds and emission colors across the 500-680 nm range. The researchers verified the chemical purity of all compounds, and this tunability opens possibilities for applications requiring specific emission wavelengths and durations.
Tunable OLPL: Duration (1.6-7154.3s) & Emission Color (500-680nm)
The ability to finely control both the duration and color of organic long persistent luminescence (OLPL) has taken a step forward with a new material exhibiting tunable emission with durations ranging from 1.6 to 7154.3 seconds. Researchers developed a platform leveraging flexible phosphorescence donors and electron acceptors, achieving unprecedented control over this afterglow phenomenon in amorphous organic systems. This extended luminescence, observed even after a month of being exposed to air, addresses a longstanding challenge in the field, maintaining brightness and longevity outside of inert atmospheric conditions.
Beyond simply extending the glow, the team demonstrated precise regulation of emission wavelengths across the 500-680 nm range. This color tuning was accomplished by increasing the doping concentration of guest molecules within the host material, offering a broad palette for applications requiring specific light signatures.
Experimental results confirmed the amorphous state with long-range disorder was dominant in the system, while dispersed microcrystals also existed, simultaneously guaranteeing both processability and air stability. The researchers found that enhancing the electron-withdrawing ability of these guest molecules directly correlated with increased luminescence duration, allowing them to dial in the desired afterglow time from a minimum of 1.6 seconds.
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