Study On The Room Temperature Phosphorescence Properties Of N-Arylcarbazole Derivatives Doped In Polymers

Organic room temperature phosphorescence(RTP)materials are materials that emit light continuously at room temperature through inter-system crossing from the triplet state.Compared to traditional phosphorescent materials containing rare metal salts,organic RTP materials were widely used in chemical sensing,biological imaging,luminescent displays,information encryption and anti-counterfeiting due to the low cost,ease of design and low toxicity.The key to achieving long RTP emission is to generate and stabilize triplet excitons.Organic RTP materials can be divided into molecule RTP crystals and RTP polymers.By doping organic phosphores into polymers,not only the rigid environment for stable triplet state emission can be provided,but also the good processing performance and economy that crystals do not possess was obtained.Therefore,organic doped RTP(ODRTP)polymers have become an important direction for RTP material research.However,ODRTP materials are mostly based on polyvinyl alcohol(PVA)and polyacrylamide(PMMA).The types of ODRTP matrices need to be expanded as well as their RTP properties should be improved,especially rare research was reported on RTP elastomers,excitation-dependent RTP polymers and their RTP mechanisms.Based on reviewing and analysing the current research of organic RTP materials,several N-aromatic carbazole derivatives doped with PVA,PMMA,and thermoplastic elastomer styrene-isoprene-styrene(SIS)were designed and synthesized by this thesis.Naromatic carbazole derivatives were previously thought to easily dissipate triplet state energy through molecular rotation,and the rigid,polar polymer PVA and PMMA could not stabilize their emission of ultra-long RTP.However,these molecules can not only exhibit ultra-long RTP in PVA and PMMA,but also be stabled by non-polar SIS.The specific research results are as follows.In this thesis,N-(2-cyano-5-bromophenyl)-carbazole(2Q5X)was doped into SIS as phosphore.The dispersion of dopant was promoted through solution mixing and thermoplastic processing,and then RTP polymers were obtained.The experiment found that thermoplastic processing does not damage the RTP properties,which lays the foundation for large-scale economic production of RTP products.Only 1‰ doping amount can obtain 1.1 s RTP lifetime,which is the RTP elastomers exhibiting the longest lifetime so far.The contrast experiment was carried out and shows that non-polar rigid polystyrene can also stabilize 2Q5 X emission of RTP,but it was far less effective than 2Q5X/SIS,while diene rubber such as PI is not efficient RTP matrix.Given the significantly different light activation time and RTP afterglow,this study for the first time proposes that stress concentration at the rubber-plastic interface can better stabilize ultra-long RTP.This new view is further confirmed by using HIPS as the matrix to obtain RTP properties superior to those obtained with PS as the matrix,and the same regular experimental results were obtained with the isomer of 2Q5 X,2Q4X.Therefore,this work not only develops new RTP materials,but also challenges existing RTP concepts and reveals new mechanisms and strategies for stabilizing organic RTP.By doping PVA and PMMA with 1% by weight of 2Q5 X and its hydrolysis product2J5 X,their RTP afterglow were both green after 365 nm light excitation while 2J5X/PVA emitted blue RTP after 254 nm light excitation.By reducing the doping amount,materials with blue RTP after both 254 nm and 365 nm excitations can be obtained,and the excitation-,concentration-dependent RTP were achieved.Then 2Q5 X was doped with PMMA,which intended to improve the compatibility of the dopant with the matrix.The spectrum showed a distinct blue RTP peak at 1% doping and emitted blue RTP with reduced doping concentration.Based on these experimental results,combined with the dopant hardly emitting RTP in both crystalline and amorphous states,this work proposes that blue and green RTP originate from the molecular dispersion and cluster states of the dopant.The cluster molecular state is limited by the matrix,but the mutual distance is within the F(?)rster radius,resulting in spatial electromagnetic interaction and a decrease in the molecular triplet state,leading to the emission of green RTP.This provides a new strategy for regulating the stimulus-responsive RTP polymer by controlling the dispersion state of the dopant.In summary,this paper enriches the mechanism of organic room-temperature phosphorescence by studying RTP stabilized by rubber-plastic phase interface in polymer and RTP regulated by dispersion state,and provides new strategies for the development of ODRTP materials.