Research Of Novel Multicomponent Organic Room-temperature Phosphorescent Materials And Their Stimuli-responsive Properties Application Exploration

Recently,organic phosphorescence has generated considerable interest in molecular photochemistry.With the deepening and broadening of theory,someone has realized that organic materials which continuously emit luminescence at room temperature are incredibly unique and potentially be employed in some fields such as biological imaging,display,and information encryption.The phosphorescence efficiency and lifetime properties of organic room temperature phosphorescence（RTP）materials are crucial for practical application.In addition to them,the material’s ability to meet different application needs is equally important.In this regard,stimuli-responsive material systems are uniquely advantageous.The luminescent properties of organic RTP materials can be tuned by external stimuli,such as force,heating,illumination,and p H.Stimulus-responsive RTP material could provide the same sensing signal output as a traditional fluorescent emitter and is easier to implement signal encoding and reading in the time dimension.Meanwhile,the mechanism of phosphorescence determines that the RTP sensing signal-response systems are more environmentally sensitive than fluorescence ones and respond more accurately to stimuli.Nevertheless,organic room temperature phosphorescent materials with high-quality luminescence properties（phosphorescence quantum yieldΦ_p≥10%）are still relatively rare,and the research on stimuli-responsive RTP systems is still in its infancy.More energy needs to be devoted to studying RTP mechanisms,thus developing more efficient and general molecular and material design strategies.In response to the above problems,we first explored the dimer RTP behaviour for the dimer in the crystal phase.Further,we investigated the critical influence of the molecular packing state on its RTP.Then,a series of organic room temperature phosphorescent materials was obtained through host-guest doping,and their application potential was investigated in bioimaging,leak test,information display,and encryption.Chapter 1:The"early life"of the organic phosphorescence was briefly reviewed,and the concepts of luminescence,fluorescence,phosphorescence,afterglow,spin,singlet/triplet and the evolution of their scientific connotations are introduced.Then the antecedents and consequences of the relationship between electron spin,multiplicity,and organic phosphorescence are reviewed.Finally,recent research on RTP systems,especially the research status of stimuli-responsive organic RTP materials is discussed.Chapter 2:The role of the molecular dimer,the most straightforward aggregate block in the RTP effect,was explored.It was found that CS-2COOCH₃ crystal can exhibit excimer luminescence,thermally activated delayed fluorescence（TADF）,and long-lived RTP.Since these luminescence properties correspond to different excited state processes,the role of molecular dimer can be revealed clearly.It is confirmed that the dimer-related RTP in CS-2COOCH₃ crystal is single molecule-dominated.Chapter 3:A host-guest doping system with outstanding RTP performance was constructed using a series of phenothiazine derivatives before and after oxidation reported in the previous works of our group.Different from the common doping system that emphasizes the energy process and ignores the structural design of the host/guest molecule itself,in this work,each phenothiazine derivative and the corresponding molecule constitute the doping system.Due to the maximum structural similarity,the doping system preserves the bulk structure of the host material to the greatest extent,and a series of room temperature phosphorescent materials with both high efficiency（>20%）and long lifetime are obtained.Notably,some of these materials are dispersed in the water environment as nanoparticles and have an afterglow duration of up to about25 min could be realized.The host-guest pairs of these doped systems can obtain bright RTP emissions when stimulated by co-crystallization,grinding,or heating.Due to the material’s ultra-long phosphorescence duration,the luminescence signal can be easily captured in subsequent in vivo phosphorescence imaging without real-time photoexcitation,which is the first case of in vivo phosphorescence imaging without real-time photoexcitation during in vivo imaging.Chapter 4:It was found that after phenothiazine derivatives are doped into the polymethyl methacrylate matrix to form a solid solution,the material has photo-induced RTP properties.The phosphorescence efficiency increases with the number of phenothiazine units,and the PM-3 molecule with three phenothiazine units gives a phosphorescence quantum yield of over 22%.Ultraviolet light text/image writing was realized using PM-3 doped materials,and photo-induced RTP materials with cyclic lighting and erasing were obtained,which are highly transparent and flexible.For the first time,materials with photo-induced RTP properties were applied to leak test and crack detection in a transparent matrix,showing excellent performance.It has significant advantages especially compared with traditional luminescent materials for crack identification.Chapter 5:The intrinsic distance dependence and specificity of FRET（F（?）rster Resonance Energy Transfer）made the FRET-based RTP materials exhibit a multiple-stimuli response to mechanical force and heat.Both grinding and heating mixed samples can activate RTP emission.To realize stimulus-responsive RTP effect in a host-guest doping system based on FRET,three main criteria should be satisfied:（1）rigid environment molecules within-host molecules;（2）efficient intersystem crossing（ISC）ability from singlet to triplet state in guest to give potential RTP emission;（3）matched energy levels between host and guest to conduct the FRET process.Furthermore,near-perfect compatibility with existing printing technology is demonstrated for this material,especially for thermal printing.This finding could provide a simple,efficient,commercially viable construction strategy for RTP material.Chapter 6:Based on the strategy proposed in Chapter 5,extending the host-guest doping system from binary to ternary,an organic afterglow material system with tunable colour from blue to yellow was successfully developed.A binary doping system was constructed using DMAP host and Tmb guest,which exhibits high RTP efficiency and long lifetime,with a phosphorescence quantum yield of 13.4%and a lifetime of 2.08 s.The intense interaction between the rigid matrix DMAP and Tmb molecules leads to the efficient energy transfer between the host/guest and a charge transfer between them.These factors together contribute to the excellent RTP performance of the doped system.Further on,by introducing the additional energy acceptor of fluorescein（Fluc）with concentration-dependent emission to construct ternary doping systems,the afterglow colour was extended from blue to yellow.