Aggregation Induced Emission-based Nanocomposites For Fluorescence Analysis

To take advantage of the photophysical processes of aggregation-induced emission (AIE) phenomenon, the luminophors with AIE characteristic could serve as building units, to produce a series of AIE-active materials with the function of assembly. They are singly charged, doubly charged, and multiply charged, to realize the behaviors of self-assembly, intercalation assembly, and layer-by-layer assembly,resulting in the formation of highly efficient luminescent systems.Moreover, different assembly modes and units can lead to different functions for imaging analysis and sensing applications.For singly-charged AIE-active materials, tetraphenylethene-cored sodium dodecyl sulfonate (TPE-SDS) was designed and synthesized.Through the study of its variations in surface activity, conductivity, and optical properties with different concentrations, TPE-SDS was proved to be an AIE-active anionic surfactant. Moreover, spherical micelles derived from the self-assembly of TPE-SDS molecules in water could be directly observed by confocal fluorescent microscopy due to the high emission efficiency of TPE-SDS molecules in an orderly aggregation. As the salinity increases, the transitions of spherical micelles to rodlike micelles to wormlike micelles, could also be visualized. On the other hand, with the help of co-surfactant, TPE-SDS molecules could self-assemble in nonpolar solvent to form spherical reverse micelles (water-in-oil microemulsion). Interestingly, the size of microemulsion droplets was inversely proportional to their luminescence intensity. Based on the analysis of microemulsion droplet geometry, it can be concluded that the intermolecular distance between adjacent TPE-SDS molecules at the oil-water interface gets longer with increasing the microemulsion droplet size, resulting in a weakened restriction of intramolecular rotation. This find coincides with the present AIE mechanism.In addition, TPE-cored dodecyl trimethyl ammonium bromide(TPE-DTAB) was synthesized to be served as an AIE-active cationic surfactant. Then, TPE-DTA+ cations were intercalated into the interlayers of montmorillonite (MMT) via ion exchange method, to produce TPE-DTAB intercalated organic MMT (TPE-DTAB-MMT). Structural characterizations of TPE-DTAB-MMT through powder X-ray diffraction,Fourier transform infrared spectra, and surface potential measurements suggest that the TPE-DTA+ ions inside MMT interlayers have a variety of orderly arrangements, resulting in an increased hydrophobicity of MMT.Moreover, intramolecular motions of TPE-DTA+ ions can be significantly restricted by the two-dimentional confined interlayers, leading to a slowed nonradiative decay rate and therefore an enhanced fluorescence quantum yield. Owing to its hydrophobicity and high-efficient luminescence, TPE-DTAB-MMT can not only disperse well in organic polymer matrix for producing organic-inorganic composites, but also be directly observed for the evaluation of its three-dimentional macrodispersion in composites by confocal fluorescent microscopy. The same is true for TPE-SDS modified LDHs. The proposed fluorescence imaging based on high-efficient emitting assemblies provides several important advantages over electron microscope imaging, and opens a new avenue in the development of direct three-dimensional observation of inorganic filler macrodispersion in organic-inorganic composites.For doubly-charged AIE-active materials, the opposite ends of 9,10-di((E)-styry1)anthracene (DSA) were attached with two sulfonate groups (BSDSA). Then, the host-guest hybridized BSDSA/LDH luminescent films were fabricated by layer-by-layer assembly between BSDSA and inorganic LDH nanosheets on the solid substrates. Moreover,the molecular conformation of BSDSA among the LDH nanosheets can be more distorted by co-assembly with polymer, resulting in a tunable emission from yellow to green. The rigid LDH layers can efficiently restrict the intramolecular motions of BSDSA molecules, leading to a high quantum yield of the fabricated luminescent films. Upon heating the BSDSA/LDH luminescent film from 25? to 85 ?, its luminescence color could be changed from yellow to yellow-green with a decreased intensity. The highly efficient luminescent films (layer-by-layer assemblies) could stimulate a large family of AIE-LDH luminescent films and guide the future development of the novel generation of tunable and switchable solid-state luminescence materials.In comparison to doubly-charged BSDSA, multiply-charged gold nanoclusters (Y-AuNCs) with AIE characteristic are much easier for electrostatic layer-by-layer assembly. Quartz glass slides were dipped into a Y-AuNCs solution and poly(allyl amine) (PAH) solution by turns, to fabricate the yellow-emitting Y-AuNCs/PAH films. On the other hand, the conventional luminescent AuNCs (R-AuNCs) were also assembled with PAH to produce the red-emitting R-AuNCs/PAH films. Their optical properties were characterized by absorption and emission spectroscopy,and steady-state fluorescence spectroscopy. As expected, the quantum yield of Y-AuNCs in Y-AuNCs/PAH film is more than twice that in solution. Moreover, the fluorescence intensity of Y-AuNCs/PAH film with 5 layers is similar to that of R-AuNCs/PAH film with 25 layers.Based on these phenomena, a multi-color fluorescence sensing system was constructed by using R-AuNCs/PAH film as the control unit and Y-AuNCs/PAH film as the detection unit, and used for ratiometric fluorescence detection of explosive with detection limit of 10-10 M.