Design,synthesis And Performance Of Purely Organic Room Temperature Phosphorescent And White Light Materials With Stimuli-responsive

Stimulus-responsive luminescent materials have been developed on a large scale due to their wide applications in optical data recording,chemical sensors,displays,and biological imaging.etc.So far,most of the research on stimulus responsive materials is based on traditional fluorescent materials,and the research on room temperature phosphorescent materials with stimulus responsiveness is still in its infancy.In addition,compared with multi-component white light emitting materials,there are very few materials that use traditional fluorescence and room temperature phosphorescence dual emission to achieve single-component organic white light emission.This thesis uses the carbazole unit as the electron donor,the pyridine ring,the amide group and the cyano group as the electron acceptor.By synthesizing many isomers,explore the influence of molecular conformation,intramolecular/intermolecular electronic coupling and intermolecular interaction on the luminescence behavior of compounds,and the mechanism of the different response of the material to external stimuli.In the second chapter of the thesis,we designed and synthesized 4 isomers of D-A-A' structure using carbazole as the electron donor,pyridine ring and cyano group as the electron acceptor,and explored the influence of different positions of the substituents on fluorescence and phosphorescent properties.Studies have found that cyano as a pseudo-halogen,can effectively promote the ISC process by promoting the n??*transition,which is conducive to the generation of triplet excitons.At the same time,the strong intermolecular interaction effectively stabilizes the triplet excitons,making all the isomers exhibit ultra-long room temperature phosphorescence properties with the lifetime over 500 ms.In addition,the four isomers can still maintain a strong yellow afterglow after full grinding.By comparing the X-ray diffraction(XRD)of all powders before and after grinding,it is found that the isomers still maintain a very orderly molecular accumulation after grinding,indicating that the isomers have a high degree of crystallinity.More interestingly,due to the difference between the electron withdrawing effect and steric hindrance of cyano groups,the four isomers show different responsiveness to acidic stimuli.Based on the research results in Chapter 2,we use amide groups to replace cyano groups in Chapter 3 to explore the effects of different substituents and their isomerization on the fluorescence and phosphorescence properties of the materials.We designed and synthesized 4 carbazole-nicotinamide isomers.Except for dyad 1,dyad 2,3,and 4 all showed high-efficiency ultra-long room temperature phosphorescence with the highest phosphorescence quantum yield of 21.3%and the longest lifetime of 846 ms.Especially dyad 4 realizes the white light emission of the compound through the color mixing effect of traditional fluorescence and room temperature phosphorescence.The CIE coordinate is(0.26,0.28),and the phosphorescence quantum yield is 11.2%.In addition,dyad 4 has dual-responsive properties of mechanochromism and acidichromism.It is found that the force-induced phase transition from crystalline to amorphous drives the dual-mode mechanochromism(fluorescence shift and phosphorescence on-off),and the protonation of pyridine units results in acidichromism.In summary,the introduction of amide and cyano units helps to enhance the molecular spin-orbit coupling(SOC),promote the intersystem crossing(ISC)process,and facilitate the generation of triplet excitons;at the same time,strong intermolecular interaction or intramolecular/intermolecular electronic coupling can effectively stabilize triplet excitons,making the compo exhibit ultra-long room temperature phosphorescence properties.By introducing a pyridine unit that is easy to protonate,the molecule is responsive to acid stimuli,and the application range of room temperature phosphorescent materials is expanded.