Bairong He

Aggregation‐Induced Emission and Efficient Solid‐State Fluorescence from Tetraphenylethene‐Based N,C‐Chelate Four‐Coordinate Organoborons

In it together: Thermally stable N,C-chelate four-coordinate organoborons were attained by grafting intramolecular B⋅ ⋅ ⋅N coordination into tetraphenylethene-pyridine and -quinoline adducts. They exhibit aggregation-induced emission characteristics (see figure), and high fluorescence quantum yields approaching unity in solid films.

Biocompatible Green and Red Fluorescent Organic Dots with Remarkably Large Two-Photon Action Cross Sections for Targeted Cellular Imaging and Real-Time Intravital Blood Vascular Visualization.

Fluorescent organic dots are emerging as promising bioimaging reagents because of their high brightness, good photostability, excellent biocompatibility, and facile surface functionalization. Organic dots with large two-photon absorption (TPA) cross sections are highly desired for two-photon fluorescence microscopy. In this work, we report two biocompatible and photostable organic dots fabricated by encapsulating tetraphenylethene derivatives within DSPE-PEG matrix. The two organic dots show absorption maxima at 425 and 483 nm and emit green and red fluorescence at 560 and 645 nm, with high fluorescence quantum yields of 64% and 22%, respectively. Both organic dots exhibit excellent TPA property in the range of 800-960 nm, affording upon excitation at 820 nm remarkably large TPA cross sections of 1.2×10(6) and 2.5×10(6) GM on the basis of dot concentration. The bare fluorophores and their organic dots are biocompatible and have been used to stain living cells for one- and two-photon fluorescence bioimagings. The cRGD-modified organic dots can selectively target integrin αvβ3 overexpressing breast cancer cells for targeted imaging. The organic dots are also applied for real-time two-photon fluorescence in vivo visualization of the blood vasculature of mouse ear, providing the spatiotemporal information about the whole blood vascular network. These results demonstrate that the present fluorescent organic dots are promising candidates for living cell and tissue imaging.

Multichannel Conductance of Folded Single‐Molecule Wires Aided by Through‐Space Conjugation

Deciphering charge transport through multichannel pathways in single-molecule junctions is of high importance to construct nanoscale electronic devices and deepen insight into biological redox processes. Herein, we report two tailor-made folded single-molecule wires featuring intramolecular π-π stacking interactions. The scanning tunneling microscope (STM) based break-junction technique and theoretical calculations show that through-bond and through-space conjugations are integrated into one single-molecule wire, allowing for two simultaneous conducting channels in a single-molecule junction. These folded molecules with stable π-π stacking interaction offer conceptual advances in single-molecule multichannel conductance, and are perfect models for conductance studies in biological systems, organic thin films, and π-stacked columnar aggregates.

Integration of aggregation-induced emission and delayed fluorescence into electronic donor–acceptor conjugates

A series of luminogens comprised electron donors and acceptors are found to possess two types of interesting photophysical processes of aggregation-induced emission (AIE) and delayed fluorescence. According to theory calculation, restriction of intramolecular motions accounts for their AIE characteristics. Moreover, a separated distribution of the HOMOs and the LUMOs of these luminogens leads to small ΔEST values and therefore delayed fluorescence.

Silole‐Based Red Fluorescent Organic Dots for Bright Two‐Photon Fluorescence In vitro Cell and In vivo Blood Vessel Imaging

Robust luminescent dyes with efficient two-photon fluorescence are highly desirable for biological imaging applications, but those suitable for organic dots fabrication are still rare because of aggregation-caused quenching. In this work, a red fluorescent silole, 2,5-bis[5-(dimesitylboranyl)thiophen-2-yl]-1-methyl-1,3,4-triphenylsilole ((MesB)2 DTTPS), is synthesized and characterized. (MesB)2 DTTPS exhibits enhanced fluorescence efficiency in nanoaggregates, indicative of aggregation-enhanced emission (AEE). The organic dots fabricated by encapsulating (MesB)2 DTTPS within lipid-PEG show red fluorescence peaking at 598 nm and a high fluorescence quantum yield of 32%. Upon excitation at 820 nm, the dots show a large two-photon absorption cross section of 3.43 × 10(5) GM, which yields a two-photon action cross section of 1.09 × 10(5) GM. These (MesB)2 DTTPS dots show good biocompatibility and are successfully applied to one-photon and two-photon fluorescence imaging of MCF-7 cells and two-photon in vivo visualization of the blood vascular of mouse muscle in a high-contrast and noninvasive manner. Moreover, the 3D blood vasculature located at the mouse ear skin with a depth of over 100 μm can also be visualized clearly, providing the spatiotemporal information about the whole blood vascular network.

High Fluorescence Efficiencies and Large Stokes Shifts of Folded Fluorophores Consisting of a Pair of Alkenyl-Tethered, π-Stacked Oligo-p-phenylenes

A series of pure hydrocarbon fluorophores containing a pair of π-stacked oligo-p-phenylenes have been synthesized and analyzed by NMR and X-ray crystallography. They show good fluorescence in solutions and enhanced fluorescence in the aggregated state. Large Stokes shifts (up to 214 nm) have been achieved in these folded fluorophores in virtue of intramolecular energy transfer, and balanced structural rigidity and flexibility. These folded fluorophores provide perfect models for understanding the energy and charge transfer process in π-stacked systems.

Naphthalene-substituted 2,3,4,5-tetraphenylsiloles: synthesis, structure, aggregation-induced emission and efficient electroluminescence†

Two thermally stable naphthalene-substituted 2,3,4,5-tetraphenylsiloles, 1,1-dimethyl-2,5-bis[4-(naphthalen-1-yl)phenyl]-3,4-diphenylsilole (D-1-NpTPS) and 1,1-dimethyl-2,5-bis[4-(naphthalen-2-yl)phenyl]-3,4-diphenylsilole (D-2-NpTPS), have been synthesized and fully characterized. D-2-NpTPS shows redder absorption and emission than D-1-NpTPS due to the better conjugation between naphthalen-2-yl groups and phenyl rings at the 2,5-positions of the silole core. While they are weakly fluorescent in solutions, strong luminescence is induced when aggregated in poor solvents or fabricated into solid films, with high fluorescence quantum yields up to 99%, demonstrating their aggregation-induced emission (AIE) feature. Efficient non-doped organic light-emitting diodes utilizing D-1-NpTPS and D-2-NpTPS as light-emitting layers are fabricated. Remarkably high electroluminescence efficiencies of 10.5 cd A−1, 7.3 lm W−1, and 3.2% are acheived by the D-2-NpTPS device.

Synthesis, Structure, Photoluminescence, and Electroluminescence of Siloles that Contain Planar Fluorescent Chromophores

Herein, a new series of siloles that were 2,5-substituted with planar fluorescent chromophores (PFCs), including fluorene, fluoranthene, naphthalene, pyrene, and anthracene, were synthesized and characterized. These compounds showed weak emission in the solution state, owing to active intramolecular rotation (IMR), but the synergistic effect from electronic coupling between the PFC and the silole ring compensated for the emission quenching by the IMR process to some extent, thereby affording higher emission efficiencies than those of 2,3,4,5-tetraphenylsiloles in solution. These new siloles showed enhanced emission efficiencies in the aggregated state. The electroluminescence (EL) color and efficiency of new siloles were sensitive towards the PFC. Siloles containing naphthalene moieties showed green EL emission, whilst those containing anthracene moieties showed orange EL emission. The siloles containing pyrene moieties exhibited yellow EL emission at 546 nm, with a peak luminance of 49000 cd cm(-2) and a high current efficiency of 9.1 cd A(-1).

Efficient electroluminescence from excimers of 1,3,6,8-tetrakis(3,5-dimethylphenyl)pyrene.

Excimers are generally considered as detrimental to OLEDs. For pyrene-based chromophores, however, this is not always true. In this contribution, two new methylated tetraphenylpyrenes, 1,3,6,8-tetra-o-tolylpyrene (TTPy) and 1,3,6,8-tetrakis(3,5-dimethylphenyl)pyrene (TDMPPy), were synthesized through Suzuki coupling reactions. TDMPPy absorbs and emits light at longer wavelengths than TTPy due to its more planar conformation and thus better conjugation. TDMPPy is prone to excimer formation, thus leading to a strong bathochromic shift (84 nm) in the photoluminescence spectrum of its film. TDMPPy exhibits efficient electroluminescence originating from pyrene excimers, affording a maximum luminance of 26,670 cd m(-2) and a current efficiency as high as 10.8 cd A(-1) in a non-doped OLED (ITO/PEDOT:PSS (50 nm)/NPB (30 nm)/TDMPPy (30 nm)/TPBI (40 nm)/Ca:Ag).

Di(naphthalen-2-yl)-1,2-diphenylethene-based conjugated polymers: aggregation-enhanced emission and explosive detection

Fluorescent conjugated polymers based on a new AIE building block, di(naphthalen-2-yl)-1,2-diphenylethene, are synthesized and characterized. These polymers show interesting aggregation-enhanced emission and function well in explosive detection in aqueous media.