Stimulus-responsive room temperature phosphorescence in purely organic luminogens

Luminogens that exhibit stimulus-responsive room temperature phosphorescence(RTP)have attracted significant attention for their applications in a wide range of fields such as data storage,sensors,and bio-imaging.However,very few such materials are known,partly because of the unclear internal mechanism.In this review,we summarize recent advances in the field of stimulusresponsive RTP in purely organic luminogens,focusing on their unique emission behaviors and internal mechanisms governing the phenomena.We also attempt to identify the relationship between the mechanism,luminogens,and possible applications.

The initial attempt to reveal the emission processes of both mechanoluminescence and room temperature phosphorescence with the aid of circular dichroism in solid state

A phenothiazine derivative PtzChol containing non-conjugated chiral cholesterol group was designed and synthesized. By analyzing the single crystal structure of PtzChol carefully, coupled with the circular dichroism(CD) signals before and after grinding, it was found that the introduction of cholesterol produced a positive effect on the production of chiral space group, on mechanoluminescence(ML) and room temperature phosphorescence(RTP), and throughout the entire light-emitting process, the CD signal could well reflect the changes of molecular arrangement.

Host–guest materials with room temperature phosphorescence:Tunable emission color and thermal printing patterns

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.

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.

Direct demonstration of triplet excimer in purely organic room temperature phosphorescence through rational molecular design

Organic luminogens with room temperature phosphorescence(RTP)have been paid great attention and developed rapidly for their wide application values.Until now,the internal mechanism and source of phosphorescence are still obscure,especially for the relationship between molecular dimer and RTP emission.Hence,we designed and synthesized eight phenothiazine 5,5-dioxide derivatives to directly reveal how the monomer and dimer in packing affect the RTP behavior.Dimers with strongπ-πstacking(θ<20.66°;d<3.86A)lead to pure triplet excimer emission,while those with weakπ-πstacking(27.02°<θ<40.64°;3.84A<d<4.41A)contribute to dual RTP emissions of both monomer and triplet excimer.The valuable information of this work would promote the further development of this research field,as well as others in aggregate.

Organic luminescent materials:The concentration on aggregates from aggregation-induced emission

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.