Afterglow materials are attracting widespread attention owing to their distinctive and long-lived optical emission properties which create exciting opportunities in various fields. Recent research has led to the discovery of many new afterglow materials featuring high photoluminescence quantum yields (PLQY) and lifetimes of up to several hours under ambient conditions. Afterglow materials are typically categorized according to their luminescence mechanism, such as long-persistent luminescence (LPL), room temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). Through rational design and novel synthetic strategies to modulate spin-orbit coupling (SOC) and populate triplet exciton states (T1), luminophores with long lifetimes and bright afterglow characteristics can be realized. Initial research towards afterglow materials focused mainly on pure inorganic materials, many of which possessed inherent disadvantages such as metal toxicity or low energy emissions. In recent years, organic-inorganic hybrid afterglow materials (OIHAMs) have been developed with high PLQY and long lifetimes. These hybrid materials exploit the tunable structure and easy processing of organic molecules, as well as enhanced SOC and intersystem crossing (ISC) processes involving heavy atom dopants, to achieve excellent afterglow performance. In this review, we begin by briefly discussing the structure and composition of inorganic and organic-inorganic hybrid afterglow materials, including strategies for regulating their lifetime, PLQY and luminescence wavelength. The specific advantages of organic-inorganic hybrid afterglow materials, including low manufacturing costs, diverse molecular/electronic structures, tunable structures and optical properties, and compatibility with a variety of substrates, are emphasized. Subsequently, we discuss in detail the fundamental mechanisms used by afterglow materials, their classification, design principles, and end applications (including sensing, anticounterfeiting, and photoelectric devices, among others). Finally, existing challenges and promising future directions are discussed, laying a platform for the design of afterglow materials for specific applications.

Recent advances in the design of afterglow materials: mechanisms, structural regulation strategies and applications.

Clusteroluminogens (CLgens), nonconjugated structures with visible luminescence at the clustering state, have recently received remarkable attention due to their great theoretical significance and practical values. In carbonyl‐based aliphatic polymers, (n, π*) transition of carbonyl groups and the through‐space interactions have been demonstrated to play an important role in their clusteroluminescence (CL) properties, but it is still a big challenge to manipulate their CL at the molecular level. In this work, six nonconjugated carbonyl‐based polymers with different heteroatoms and steric hindrances were synthesized, and their photophysical properties were systematically studied. These polymers all showed CL but with different emission efficiency and wavelength. Experimental and theoretical studies indicated that the CL properties could be manipulated by changing the electronic structures of carbonyl groups and the rigidity of polymer chains. This work not only gains further insights into the CL mechanism but also provides reliable strategies to design and manipulate non‐conjugated luminescent materials.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/agt2.278

Manipulation of clusteroluminescence in carbonyl‐based aliphatic polymers

Organic light‐emitting diodes (OLEDs) have garnered increasing attention as a promising candidate for application in next‐generation displays and solid‐state lighting devices. The doping technique commonly used to fabricate light‐emitting layers (EMLs) of OLEDs disperses the emitting material in a host matrix to mitigate aggregation‐induced quenching (ACQ). Alternatively, owing to their high efficiency and ease of manufacture, nondoped OLEDs have been developed as a substitute for doped OLEDs. When fabricating nondoped OLEDs, it is essential to suppress the ACQ effect in the EML and efficiently utilize the generated excitons for radiative decay. Since the discovery of aggregation‐induced emission (AIE) by Tang et al., significant work has been done to improve the stability and efficiency of nondoped OLEDs based on fluorescent AIE luminogens (AIEgens). Fluorescent AIEgens, synthesized using various molecular frameworks, such as silole, tetra/triphenylethylene, tetraphenylpyrazine, and tetraphenylbenzene, exhibit high photoluminescence quantum yields in the solid state. Therefore, many studies have reported that fluorescent AIEgen‐based OLEDs have excellent external quantum efficiency and exhibit emission at various wavelengths, including deep‐blue/blue/green emission. With the development of fluorescent AIEgens, delayed fluorescent AIEgens with efficient triplet utilization through reverse intersystem crossing and AIE properties have been adopted as ideal emitters and used in nondoped OLEDs. This review systematically discusses and summarizes recent reports on the development of AIEgens for nondoped OLEDs by grouping them into fluorescent and delayed fluorescent AIEgens. The purpose of this review is to provide deep insights into the design of novel AIEgens for high‐performance nondoped OLEDs.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/agt2.199

Aggregation‐induced emission luminogens for organic light‐emitting diodes with a single‐component emitting layer

The development of intramolecular-lock strategy is an appealing task for designing efficient thermally activated delayed fluorescence (TADF) molecules, but only limited examples have been reported so far. Herein we present a "medium ring"-lock strategy to develop TADF emitters for improving the efficiency of organic light-emitting diodes (OLEDs). The installation of an electron-deficient heptagonal diimide lock onto a highly rotatable biphenyl-based emitter not only enhances electron-withdrawing ability of acceptor that decreases singlet-triplet energy gap (ΔEST), but also endows the skeleton with modest rigidity and flexibility that increases photoluminescence quantum yield (PLQY) in neat film. In particular, the integration of the diimide lock also leads to an increase in horizontal orientation factor (Θ//) from 69% to 83%. Consequently, this modified intramolecular-lock strategy enables an efficient TADF emitter to assemble high-performance non-doped OLEDs with a high external quantum efficiency of 26.2% and a power efficiency of 76.6 lm W-1.

Modified Intramolecular-Lock Strategy Enables Efficient Thermally Activated Delayed Fluorescence Emitters for Non-Doped OLEDs.

Thermally activated delayed fluorescence (TADF) materials with aggregation‐induced emission (AIE) features can overcome aggregation‐caused quenching (ACQ) and emit intensely in aggregate states and thus have attracted enormous attention in the fields of high‐efficiency organic light‐emitting diodes, bioimaging, photodynamic therapy, photocatalysis, etc. However, their corresponding exact working mechanisms at the microscopic level are still far from clear. Herein, by carefully investigating the physical properties of our newly designed TADF material 6‐(10H‐spiro[acridine‐9,9′‐fluoren]‐10‐yl)nicotinonitrile in various states, we concluded that conformational isomerization plays an important role in realizing high photoluminescence quantum yields in its amorphous neat film state, in which the high‐lying quasi‐axial conformations with non‐TADF features and low‐lying quasi‐equal conformations with TADF characteristics serve as the host matrix and dopant, respectively, thus suppressing ACQ in disordered aggregate states. Our work not only offers a new possible microscopic mechanism by using conformational isomerization for the AIE‐TADF phenomenon but also provides a novel method for designing high‐efficiency AIE‐TADF emitters.

Conformational isomerization: A novel mechanism to realize the AIE‐TADF behaviors

Endowing imidazole derivatives with thermally activated delayed fluorescence and aggregation-induced emission properties for highly efficient non-doped organic light-emitting diodes

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Endowing imidazole derivatives with thermally activated delayed fluorescence and aggregation-induced emission properties for highly efficient non-doped organic light-emitting diodes