Polyamide Cage Molecule——Synthesis And Application In Enhancing The Solid-State Fluorescence Of Dyes

Dye molecules are widely used in the field of organic photoelectric materials.However,dye molecules often self-assemble to form aggregates due to their large conjugated planes.These self-aggregates of dye molecules usually lead to fluorescence quenching.Through interference of the formation of the dye self-aggregation or modulation of the intermolecular distance of dyes,the above issue could be properly addressed.In this thesis,we designed and synthesized a cage molecule containing multiple amide groups,which can interact with cationic dyes and some other dyes with specific functional groups such as carbonyl,carboxyl,and nitryl through hydrogen bonding and thus interfering the self-aggregation of these dye molecules and eventually achieving the enhancement of their solid-state fluorescence.In this thesis,we firstly explored the synthetic routes to the target cage molecule and finally produced the cage in an efficient way.Specifically,1,2,4,5-tetrame-thylbenzene was first brominated with N-bromosuccinimide followed by the substituention with HN（Boc）₂,and then treated with trifluoroacetic acid to afford the key intermediate tetraaminomethylbenzene.After coupling reaction with a mono-acid compound and saponification with sodium hydroxide,the cage precursor was produced.Finally,this precursor was coupled with tetraaminomethylbenzene to give the target cage molecules.Since this cage contains several hydrogen bonding sites,it can be used as an anion detector for the detection of phosphate,bicarbonate and chloride ions in vivo.The effect of the cage on modulating the aggregation and photophysical properties of cationic dyes in solid state was investigated.It was found that the cage was able to recognize various anions with high affinity by NMR studies.Thus,it would be capable to break the self-aggregation of dyes through recognizing the anions of cationic dyes and the cationic chromophore would attach to the surface of the cage molecule with electrostatic andπ-πinteractions.Further analysis by UV-Vis spectroscopy revealed that the cationic dyes with cage showed narrower absorption bands compared to the solid-state sample of dye alone and even exhibited absorption spectra close to those of the dye in solution,indicating that the cage has the ability to disperse the self-aggration of cationic dyes.More importantly,the absolute quantum yield study showed that the samples with cage could gain significantly enhanced fluorescence with the minimum increase from 0.2%to 5.17%and the maximum from 0.5%to 17.85%.These observations evidence the designed cage has the ability to universally enhance the solid-state fluorescence of cationic dyes.At last,the ability of the cage on enhancing the solid-state fluorescence of other dyes were also explored.Similarly,relatively sharp absorption spectra were shown in the solid-state samples with cage.The UV-illuminated images and quantum yield results demonstrated that the cage can,to some extent,enhance the solid-state fluorescence of the tested dyes with the lowest increased from 0.96%to 4.02%and the highest increased from 3.49%to 15.91%.In addition,fluorescence lifetime and fluorescence spectroscopy studies revealed that the sample with cage not only had prolonged fluorescence lifetime,for instance,a bodipy dye prolonged the lifetime from0.94 ns to 2.61 ns,but also showed different emission band,indicating the generation of distinct excitation states in these samples.