Stimulus-Responsive Room Temperature Phosphorescence Materials: Internal Mechanism, Design Strategy, and Potential Application

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.

Automated summary

Researchers have started to develop purely organic RTP materials to address issues like high metal content, cost, potential toxicity, and instability. Progress has been made in this direction, and the classification of stimulus-responsive RTP materials based on different internal mechanisms is presented to guide further development in this research field.