Aggregation-induced emission of 1-methyl-1,2,3,4,5-pentaphenylsilole

Folate receptor-targeted aggregation-enhanced near-IR emitting silica nanoprobe for one-photon in vivo and two-photon ex vivo fluorescence bioimaging

A two-photon absorbing (2PA) and aggregation-enhanced near-infrared (NIR) emitting pyran derivative, encapsulated in and stabilized by silica nanoparticles (SiNPs), is reported as a nanoprobe for two-photon fluorescence microscopy (2PFM) bioimaging that overcomes the fluorescence quenching associated with high chromophore loading. The new SiNP probe exhibited aggregate-enhanced emission producing nearly twice as strong a signal as the unaggregated dye, a 3-fold increase in two-photon absorption relative to the DFP in solution, and approximately 4-fold increase in photostability. The surface of the nanoparticles was functionalized with a folic acid (FA) derivative for folate-mediated delivery of the nanoprobe for 2PFM bioimaging. Surface modification of SiNPs with the FA derivative was supported by zeta potential variation and (1)H NMR spectral characterization of the SiNPs as a function of surface modification. In vitro studies using HeLa cells expressing a folate receptor (FR) indicated specific cellular uptake of the functionalized nanoparticles. The nanoprobe was demonstrated for FR-targeted one-photon in vivo imaging of HeLa tumor xenograft in mice upon intravenous injection of the probe. The FR-targeting nanoprobe not only exhibited highly selective tumor targeting but also readily extravasated from tumor vessels, penetrated into the tumor parenchyma, and was internalized by the tumor cells. Two-photon fluorescence microscopy bioimaging provided three-dimensional (3D) cellular-level resolution imaging up to 350 μm deep in the HeLa tumor.

Ingenious nanoprobes in bioassays

This article has a special focus on the broad range of innovative nanoprobes for signal amplification and new generations of bioassays. Advances in functionalizing gold nanoparticles with oligonucleotides speed up the development of a series of new nucleic acid assays. A biobarcode assay allows signal amplification by utilizing antibody-coated magnetic beads to concentrate the analytes and antibody-coated gold nanoparticle probes to carry a large number of oligonucleotides. Novel signal-amplification technologies, based on either new classes of nanoprobes consisting of releasable fluorophores or with aggregation-induced emission features, can also improve the sensitivity of bioassays. Advances in synthesis and biofunctionalization of quantum dots with unique properties have generated increasingly widespread applications in DNA sorting, multiplexing bioassays and fluorescence resonance energy transfer-based sensing. Ingenious nanoprobes in bioassays can offer PCR-like sensitivity, high selectivity, capacity for massive multiplexing, time efficiency and, most importantly, the ability to be performed at the point- of-care.

Study of aggregation induced emission of cyano-substituted oligo (p-phenylenevinylene) by femtosecond time resolved fluorescence

The aggregation induced emission (AIE) mechanism of the cyano-substituted oligo (p-phenylenevinylene)1,4-bis [1-cyano-2-(4-(diphenylamino) phenyl) vinyl] benzene (TPCNDSB) is investigated by time resolved fluorescence technique. By reconstructing the time resolved emission spectra (TRES), it is found that in solvent of low polarity, the emission is mainly from the local emission (LE) state with high quantum yield, but in high polarity solvent, the emission is mainly from the intramolecular charge transfer (ICT) state, which is a relatively dark state, with low quantum yield. In crystal form, the restriction of transfer from LE state to ICT state results in efficient AIE.

Synthesis, Characterization and Photophysical Properties of Pyridine-Carbazole Acrylonitrile Derivatives

We synthesized three novel highly fluorescent compounds, 2-(2'-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile, 2-(3"-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile, and 2-(4-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile by Knoevenagel condensation. The first two were synthesized without solvent in the presence of piperidine as a catalyst; the third was synthesized without a catalyst and with N,N-dimethylformamide as a solvent. In solution, the molar absorption coefficients showed absorptions at 380, 378, and 396 nm, respectively; in solid state, absorptions were at 398, 390, and 442 nm, respectively. The fluorescence emission was at 540, 540 and 604 nm, respectively, the 2-(4-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile showed a red shift in the emission of 64 nm compared to the other two compounds. The fluorescence quantum yield for the compounds in powder form showed values of 0.05, 0.14, and 0.006, respectively; compared with the value measured for the Alq₃ reference, 2-(3"-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile had a lightly higher value. The third harmonic generation measurement for 2-(2'-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile yielded a χ⁽³⁾ value of 5.5 × 10^-12 esu, similar to that reported for commercial polymers.

Carbazole-based cyano-stilbene highly fluorescent microcrystals

Aggregation-induced enhanced emission (AIEE) is reported for 1-cyano-trans-1,2-bis-(4-carbazolyl)phenylethylene (CN-CPE). The weak luminescence of dilute CN-CPE solutions is enhanced upon aggregate formation into 2-3 μm sized crystals. In contrast to general observations, crystal formation of CN-CPE causes a blue-shift in emission and enhances the intensity. X-ray crystallographic analysis revealed that key factors causing high luminescence efficiency in the crystal are a lack of strong cofacial π-π alignment and the existence of the strong supramolecular interactions due to the intermolecular H-bonding. These factors seem to be responsible for the AIEE phenomenon as molecules of CN-CPE are held in a rigid twisted conformation, thereby increasing the fluorescence intensity in the solid or aggregated states. Accordingly, conformational twisting in the crystal packing process may be responsible for the unusual emission blue-shift in the aggregate.

Aggregation-Induced Emission and Biological Application of Tetraphenylethene Luminogens

Tetraphenylethene derivatives [Ph(PhCH=CHPhR)C=C(PhCH=CHPhR)Ph, R=H, CN, NO2, NPh2] with green, yellow-green, and orange emission colours were designed and synthesized. These molecules are practically non-emissive in their dilute solutions but emit intensely as nanoaggregates in poor solvents, demonstrating a novel phenomenon of aggregation-induced emission. Their blended films with poly(methyl methacrylate) also display bright emissions. Restriction of intramolecular motion in the condensed phase may be responsible for such unusual behaviour. Multilayer electroluminescence devices with a configuration of indium tin oxide/N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine/emitter/tris(8-hydroxyquinolinolato)aluminum (Alq3)/LiF/Al were constructed, which gave green light with a maximum luminance and current efficiency of 12930 cd cm–2 and 3.04 cd A–1 respectively. The tetraphenylethenes can serve as excellent cell staining agents for selectively illuminating the cytoplasm and vesicles of living cells.