Triphenylamine Derivatives With Aggregation-Induced Emission: Synthesis, Fabricaton Of Fluorescent Nanoparticles And Living Cell Imaging

In this paper, four fluorescent molecules with aggregation induced emission (AIE) characteristic were synthesized by Wittig, Heck coupling and Schiff Base condensation reactions, where the pyridyltriphenylamine moiety acted as building block while 1,3,4-oxadiazole unit and rhodamine B unit served as terminal groups. They were 2-(4-tert-butylphenyl)-5-{4-[2-[4-N,N-bis-(4-iodine phenyl)-amino-phenyl]vinyl]phenyl}-1,3,4-oxadiazole (PT1), 2-(4-tert-butylphenyl)-5-{4-[2-[4-N,N-bis-(2-pyridyl vinyl)-amino-phenyl]vinyl]phenyl}-1,3,4-oxadiazole (OPTO), 2-(4-tert-butylphenyl)-5-{4-[2-[4-N,N-bis-(4-pyridyl vinyl)-amino-phenyl]vinyl]phenyl}-1,3,4-oxadiazole (PPTO) and (E)-4-N,N-[(4-pyridyl vinyl)phenyl]amino-methyl vinyl-amino-3',6'-bis-(diethyl amino)-spiro[isodihydrogen indole-1,9'-xanthene]-3-one (PTRh), respectively. And the structures of these compounds were characterized by melting points analysis,1HNMR and HRMS-MALDI-TOF. Then, the AIE features of these dye were tested when they were in different states, including solid powder, the mixtures of organic solvents and water. Based on the AIE characteristic of these chromophores, the silica nanoparticles (SiNPs) doped with dye (PTI, OPTO and PPTO) were fabricated. And next, the fluorescent properties of these dye-loaded SiNPs were investigated and the sizes of nanoparticles were confirmed by TEM. Besides, the fluorescent SiNPs finally were applied into living cell imaging. And due to the special properties of end-capped group pyridine, the behaviors of OPTO and PPTO responding to H+were studied. Additionally, the research on behavior of PPTO combining with BSA was conducted. On the other hand, the selective recognition for heavy metal ion, Hg2+, of fluorescent probe PTRh based on rhodamine-pyridyltriphenylamine was investigated. And the proposed mechanism of recognition for Hg2+ was discussed briefly in this contribution. Moreover, PTRh was utilized to recognize Hg2+ of living cells.1. According to Wittig, Heck coupling and Schiff Base condensation reactions, fluorescent molecules, PTI?OPTO?PPTO and PTRh, were prepared, where pyridyltriphenylamine moiety was building block and 1,3,4-oxadiazole unit and rhodamine B unit were terminal groups. And then, structures of these compounds were characterized by melting points analysis,1HNMR and HRMS-MALDI-TOF. Finally, the mechanisms and condition optimization of Wittig, Heck coupling and Schiff Base condensation reactions were talked about in details.2. The fluorescence properties of the four chromophores in their solid and solution states and their aggregation induced emission characteristics were investigated. And the results indicated:(1) all these dye in their aggregated states showed bright fluorescence, and the emission peak of PTI, OPTO and PPTO were 484 nm,537 nm and 535 nm. However, the difference was that PTRh appeared doublet (508 nm and 580 nm), which may be ascribed to the linkage between rhodamine and pyridyltriphenylamine. (2) PTI, OPTO and PPTO in the THF solution emitted strong luminescence and their quantum yields were 19.0%,18.4% and 26.0%, respectively. Besides, PTRh also presented good fluorescent properties in Ethanol solution. (3) the four dye performed similar luminescent phenomena in THF/H2O mixtures. With the contents of water increasing, the fluorescence intensities gradually decreased overall. But they still presented strong emission.3. The silica nanoparticles encapsulating with dye (PTI, OPTO and PPTO) were prepared based on microemulsion method. It was found that these dye-doped SiNPs were well disperse in water, emitting bright blue-green fluorescence and TEM also showed SiNPs were monodisperse and spherical. And the values of quantum yield were calculated to be 11.7%, 10.7% and 9.5%. Their emission peaks were about 472 nm,488 nm and 488 nm which were shorter than these of the pure THF solutions. The reason could be that types of solvents or intra-particle environment were different in different states. Finally, these nanoparticles were successfully applied in cell imaging.4. The pH effects of OPTO and PPTO were studied. The results of experiments showed the combination constants (pKa) between proton and dye OPTO and PPTO were calculated to be 5.01 and 5.09 based on titration curves, indicating that PPTO can interact with H+ more easily than OPTO. Besides, frontier orbital theory further demonstrated the above conclusion. What's more, the behavior of PPTO responding to BSA were also investigated. It was observed that, after PPTO interacted with BSA, the fluorescence of BSA was gradually quenched. In view of some references and theoretical calculations, the quenching belonged to static quenching. And the quenching constant (Ksv) was 1.15×105.5. The recognition behavior of fluorescent probe PTRh for Hg2+ were investigated. It was interesting to find that PTRh performed highly selective recognition for Hg2+ in Ethanol/H2O. Before adding Hg2+, the solution emitted green luminescence and the emission peak was 515 nm, which was characteristic emission of pyridyltriphenylamine moiety, indicating the Rhodamine spirocycle of PTRh was in "off" state. However, when PTRh was treated with Hg2+, new peak centred at 585 nm appeared. In other words, Rhodamine spirocycle was opened. Then, according to fluorescence titration curves, the proposed mechanism of PTRh recognizing Hg2+ was based on fluorescence resonance energy transfer (FRET). And the energy transfer efficiency and limit of detection were calculated to be 83.7% and 32 nM, respectively. Last but most importantly, the probe PTRh could be successfully used for recognition of intracellular Hg2+.