Aggregation-Induced Emission And Applications In Cell Imaging Of Carbazole-Containing Triphenylamine Dendrimers

In this paper, seven aggregation-induced emission(AIE) active dendrimer chromophores, which had different numbers of carbazole-containing triphenylamine moieties as building-blocks and 1,3,4-oxadiazole moiety or benzene as the core were synthesized by Ullmann reaction and Wittig reaction, which were 4-N,N-Bis[4-(3,-6-di-tert-butylcarbazol-9-yl)phenyl]-amino-benzaldehyde(BCPA),2-(4-tert-butylphenyl)-5-{4-[2-[4-N,N-bis-(4-carbazol-9-yl-phenyl)-amino-phenyl]vinyl]phenyl}-1,3,4-oxadizole [Oxa-(CPA)1], 2,5-di-{4-[2-[4-N,N-bis-(4-carbazol-9-yl-phenyl)-amino-phenyl]vinyl]phenyl}-1,3,4-o xadizole[Oxa-(CPA)2],2-(4-tert-butylphenyl)-5-{4-[2-[4-N,N-bis-[4-(3,6-di-tert-butylcarbazol-9-yl)phenyl]-amino-phenyl]vinyl]phenyl}-1,3,4-oxadizole[Oxa-(BCPA)1], 2,5-di-{4-[2-[4-N,N-bis-[4-(3,6-di-tert-butylcarbazol-9-yl)phenyl]-amino-phenyl]vinyl]pheny 1}-1,3,4-oxadizole[Oxa-(BCPA)2], 1,2,4,5-tetra-[2-[4-N,N-bis-(4-carbazol-9-yl-phenyl)-amino-phenyl]-trans-vinyl]-benzene[Ar-(CPA)4], 1,2,4,5-tetra-[2-[4-N,N-bis-[4-(3,6-di-tert-butylcarbazol-9-yl)phenyl]-amino-phenyl]-trans-vinyl]-benzene[Ar-(BCPA)4]. Dye-loaded amino-group-functionalized silica nanoparticles (Si-NPs) and dye-loaded BSA nanoparticles (BSA-NPs) were prepared. The structures of these chromophores were characterized by FT-IR,13C NMR,1H MR or HRMS-MALDI-TOF and the nanoparticles were characterized by TEM. The AIE photophysical properties of these dendrimers were investigated, such as the emission properties of the dendrimers in solid state, different solvents and THF-water systems. The structure-activity relationship of the dendrimers was also studied. Photophysical properties of dye-loaded silica nanoparticles were tested and dye-loaded BSA nanoparticles were successfully applied to cell imaging,1. Seven aggregation-induced emission(AIE) active chromophores, which had different numbers of carbazole-containing triphenylamine moieties as building-blocks and 1,3,4-oxadiazole moiety or benzene as the core were synthesized by Ullmann reaction and Wittig reaction, which were BCPA, Oxa-(CPA)1, Oxa-(CPA)2, Oxa-(BCPA)1, Oxa-(BCPA)2, Ar-(CPA)4, Ar-(BCPA)4. Dye-loaded Si-NPs and dye-loaded BSA-NPs were prepared. The structures of these chromophores were characterized by FT-IR,13C NMR,:H MR or HRMS-MALDI-TOF and the nanoparticles were characterized by TEM. The mechanisms of Ullmann reaction, Wittig reaction and the synthetic route were discussed.2. The emission properties of the dendrimers in solid state were investigated and the structure-activity relationships of the dendrimers were discussed. The results indicated that: ① all the dendrimers are AIE active; ② the emission peaks of the dendrimers in solid state were red-shifted with the increase of the number of the building-blocks. For example, the emission peaks for Oxa-(CPA)1、Oxa-(CPA)2% Ar-(CPA)4 is 494 nm,523 run, 540 nm, respectively.3. The emission properties of the dendrimers in THF were investigated and the results indicated that: ① the emission intensity of the dendrimers increaseed with the increase of the number of the building-blocks. For example, the ratio of the emission intensity for BCPA、Oxa-(BCPA)、Oxa-(BCPA)2 to Ar-(BCPA)4 is 1.0:8.4:9.9:14.5; ② the emission peaks of the 1,3,4-oxadiazoles located in a relatively long wavelength compared to other dendrimers in this paper because the stronger electron-drawing strength of 1,3,4-oxadiazole acceptor.4. Photophysical properties characterized by ICT of the dendrimers were investigated and analyzed. The results indicated that the carbazole-containing triphenylamine dendrimers have the ICT properties due to their D-A structures. For example, the emissions peaks of Oxa-(CPA)1 were red-shifted by 40 nm from the less polar solvent chloroform to polar solvent DMF. The dipole moments of the 1,3,4-oxadiazole dendrimers in ground state and the excited state and HOMO or LUMO were calculated. A larger dipole moment is obtained from double-branched dendimers than that of single-branched ones. The electron distribution condition in the HOMO and LUMO levels indicated an obvious ICT process from the electron-rich region (donor) to the electron-poor region (acceptor).5. AIE properties of the carbazole-containing triphenylamine dendrimers were investigated. A synergic effect of ICT and AIE was observed on the carbazole-containing triphenylamine dendrimers. For example, the emission peak of Oxa-(CPA)1 in THF was at 504 nm with a high emission intensity, and the quantum yield is 0.55. When the water fraction increased to 50%, the emission peaks displayed bathochromic shift from 504 nm to 533 nm and the fluorescence intensity decreased dramatically to a very low value. When the water fraction increased to 80%, a blue-shifted wavelength (from 533 nm to 508 nm) and increased fluorescence intensity with a quantum yield of 0.28 were observed. This phenomenon indicated that with the increase of water fraction, the increase of polarity of the solvent induced an enhancement of ICT effect, then the formation of aggregates caused by the poor dissolving capacity of the solvent restricted the ICT effect. Moreover, RIR effect in aggregates actvated AIE effect.6. Two kinds of dye-loaded nanoparticles were prepared, which were dye-loaded Si-NPs and dye-loaded BSA-NPs. Photophysical properties of dye-loaded Si-NPs were investigated and high quantum yield up to 0.35 for Oxa-(BCPA)1-doped Si-NPs were observed. Through modifying the surface of Si-NPs, excellent biological applications could be realized. Dye-loaded BSA-NPs were successfully applied to cell imaging and showed a better uptake by HeLa cells compared to pure dye NPs, which indicating a promising application for biosensors such as cancer cell detecting.