The study of purely organic room‐temperature phosphorescence (RTP) has drawn increasing attention because of its considerable theoretical research and practical application value. Currently, organic RTP materials with both high efficiency (ΦP > 20%) and a long lifetime (τP > 10 s) in air are still scarce due to the lack of related design guidance. Here, a new strategy to increase the phosphorescence performance of organic materials by integrating the RTP host and RTP guest in one doping system to form a triplet exciplex, is reported. With these materials, the high‐contrast labeling of tumors in living mice and encrypted patterns in thermal printing are both successfully realized by taking advantage of both the long afterglow time (up to 25 min in aqueous media) and high phosphorescence efficiency (43%).

The research of organic luminescent materials in aggregate has drawn more and more attention for their wide applications. To adjust the luminescent properties for aggregates, a deep understanding of the corresponding internal mechanism is needed. In this short review, a brief introduction of aggregation‐induced emission (AIE) and some other solid state luminescence behaviors derived from or parallel to AIE is presented. Particularly, the relationship between emission property and intermolecular/intramolecular interactions is summarized, with the aim to guide the further development of organic optoelectronic materials in aggregate.

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Many luminescent stimuli responsive materials are based on fluorescence emission, while stimuli-responsive room temperature phosphorescent materials are less explored. Here, we show a kind of stimulus-responsive room temperature phosphorescence materials by the covalent linkage of phosphorescent chromophore of arylboronic acid and polymer matrix of poly(vinylalcohol). Attributed to the rigid environment offered from hydrogen bond and B-O covalent bond between arylboronic acid and poly(vinylalcohol), the yielded polymer film exhibits ultralong room temperature phosphorescence with lifetime of 2.43 s and phosphorescence quantum yield of 7.51%. Interestingly, the RTP property of this film is sensitive to the water and heat stimuli, because water could destroy the hydrogen bonds between adjacent poly(vinylalcohol) polymers, then changing the rigidity of this system. Furthermore, by introducing another two fluorescent dyes to this system, the color of afterglow with stimulus response effect could be adjusted from blue to green to orange through triplet-to-singlet Förster-resonance energy-transfer. Finally, due to the water/heat-sensitive, multicolor and completely aqueous processable feature for these three afterglow hybrids, they are successfully applied in multifunctional ink for anti-counterfeit, screen printing and fingerprint record.

Two stable, purely organic luminogens exhibit both mechano- (ML) and photoluminescence (PL) with dual fluorescence-phosphorescence emissions at room temperature. Careful analysis of the crystal structures, coupled with theoretical calculations, demonstrate that room-temperature phosphorescence and ML properties are strongly related to molecular packing. In particular, the formation and fracture of molecular dimers with intermolecular charge-transfer properties has a significant effect on intersystem crossing, as well as excited triplet state emissions, in both PL and ML processes.

The research of purely organic materials with long afterglow has drawn more and more attention, especially for those with stimulus-response characteristic. So far, this kind of material is really very scarce and their performance is not good enough. In this study, we successfully developed an efficient heatingresponsive room-temperature phosphorescence material with phosphorescence efficiency and lifetime up to 13.4% and 2.08 s through the simple host-guest doping strategy. Further on, by introducing the additional energy acceptor of fluorescein with concentration-dependent emission to construct ternary doping systems, the afterglow color was extended from blue to yellow. Accordingly, the multicolor thermal printings have been easily realized, showing the great practical application prospects.

Conspectus Room temperature phosphorescence (RTP) materials, which could respond to external stimuli, such as force, heat, light, electric filed, etc., have drawn increasing attention for their broad application prospects, especially in the fields of anticounterfeiting, sensors, data storage, and so on. In comparison with the traditional fluorescence ones, RTP materials show much longer emission lifetimes, which can be even caught by the naked eye. Thus, the change in emission lifetime under an external stimulus for RTP materials can be also a potential monitoring parameter, in addition to emission color and intensity. In other words, the number of visual monitoring parameters could increase from two to three in RTP materials, which would greatly facilitate their practical applications. Until now, RTP materials have been typically limited to metal-containing inorganic materials, particularly rare-earth phosphors. Their emissions are governed by the slow liberation of trapped charge carriers from isolated traps of impurities, defects, or ions through thermal stimulation with low luminescence efficiency. However, these materials suffer from some intrinsic disadvantages, including high cost, potential toxicity, and instability in aqueous environments. In order to solve these problems, the purely organic RTP materials should be a good choice. However, these kinds of materials are really scarce now, especially for the ones with stimulus response characteristic. To develop purely organic RTP materials with a stimulus response effect, we and other scientists have tried a lot. Luckily, some progresses have been made. In this Account, we present our recent progress on the stimulus-responsive room temperature phosphorescence of organic materials, mainly focusing on the internal mechanism and potential applications. First, the fundamental knowledge is described to illustrate the importance and main principles of the stimulus-responsive RTP effect. Then, some typical stimulus-responsive RTP materials based on different internal mechanisms are discussed. Mainly, two kinds of stimulus-responsive RTP materials were introduced, namely, single-component and multicomponent ones. Correspondingly, their dynamic change of the RTP property under external stimulus occurred based on the distinct internal mechanisms. For single-component materials, the changes in molecular structure, packing, or conformation, have played a significant role in their corresponding stimulus-responsive RTP effect. As for multicomponent materials, the changed oxygen concentration in matrix and intermolecular distance between different components were found more during the stimulus-responsive RTP process. Accordingly, different potential applications were explored based on the different stimulus-responsive RTP processes. With the classification of stimulus-responsive RTP materials based on different internal mechanisms, the corresponding design strategy could be well proposed, thus guiding the further development of this research field.

Achieving stimulus-responsive ultralong room temperature phosphorescence (RTP) in organic materials especially with full-color tunable emissions is attractive and important but rarely reported. Here, a strategy was reported to realize stimulus-responsive RTP effect with color-tunable emissions by using water as solvent in the preparation process without any organic solvent through covalent linkage of arylboronic acids with different π conjugations and polymer matrix of polyvinyl alcohol. The yielded polymer films exhibit outstanding RTP performance (2.43 s). Furthermore, an excitation-dependent RTP film was obtained, and the afterglow color changes from blue to green, then to red as the excitation wavelength increases. The RTP property of all the above materials is sensitive to water and heat stimuli, because the rigidity of the system could be broken by water. Last, they were successfully applied in a multilevel information encryption and multicolor paper and ink.