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Rongrong Hu,
C F Azael Gómez-Durán,
Jacky W Y Lam,
José L Belmonte-Vázquez,
Chunmei Deng,
Sijie Chen,
Ruquan Ye,
Eduardo Peña-Cabrera,
Yongchun Zhong, Kam Sing Wong,
Ben Zhong Tang
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ABSTRACT: A series of tetraphenylethene-containing BODIPYs with emissions from visible to near-IR and large Stokes shifts up to 142 nm have been designed and synthesized. They show solvatochromic fluorescence and can be utilized as fluorescent visualizers for intracellular imaging.
Chemical Communications 09/2012; 48(81):10099-101. · 6.17 Impact Factor
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Na Zhao,
Zhiyong Yang,
Jacky W Y Lam,
Herman H Y Sung,
Ni Xie,
Sijie Chen,
Huimin Su,
Meng Gao,
Ian D Williams, Kam Sing Wong,
Ben Zhong Tang
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ABSTRACT: Melding a benzothiazolium unit with tetraphenylethene generates a new hemicyanine luminogen with aggregation-induced emission characteristics; the luminogen exhibits crystochromism and its solid-state emission can be repeatedly tuned from yellow or orange to red by grinding-fuming or grinding-heating processes due to the transformation from the crystalline to the amorphous state and vice versa.
Chemical Communications 07/2012; 48(69):8637-9. · 6.17 Impact Factor
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Zujin Zhao,
Jacky W Y Lam,
Carrie Y K Chan,
Shuming Chen,
Jianzhao Liu,
Ping Lu,
Mario Rodriguez,
José-Luis Maldonado,
Gabriel Ramos-Ortiz,
Herman H Y Sung,
Ian D Williams,
Huimin Su, Kam Sing Wong,
Yuguang Ma,
Hoi Sing Kwok,
Huayu Qiu,
Ben Zhong Tang
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ABSTRACT: Stereoregular tetraphenylethene derivatives (Z)-o-BCaPTPE and (Z)-o-BTPATPE featured with chiasmatic conformations and aggregation-enhanced emission characteristics are synthesized using a McMurry reaction. Both luminogens exhibit high hole and electron mobilities. Organic light-emitting diodes (OLEDs) using (Z)-o-BCaPTPE and (Z)-o-BTPATPE as both the light-emitting and electron-transporting layers show high efficiencies.
Advanced Materials 12/2011; 23(45):5430-5. · 13.88 Impact Factor
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ABSTRACT: A theoretical and experimental study of phase-controlled beam combining based on noncollinear frequency doubling is described. Optimized second-harmonic power and improved output intensity distribution are simultaneously achieved by a closed-loop phase control system via an adaptive algorithm. It is shown that the profile of the combined beam at the second-harmonic with 12 noncollinear frequency inputs can be shaped to a near-fundamental Gaussian mode, with a power enhancement of more than two orders of magnitude, compared to the second-harmonic signal generated with a single beam.
IEEE Journal of Quantum Electronics 04/2011; · 1.88 Impact Factor
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Jianzhao Liu,
Jacky W. Y. Lam,
Cathy K. W. Jim,
Jason C. Y. Ng,
Jianbing Shi,
Huimin Su,
Kwok Fai Yeung,
Yuning Hong,
Mahtab Faisal,
Yong Yu, Kam Sing Wong,
Ben Zhong Tang
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ABSTRACT: The atom-economical alkyne polyhydrothiolations of aromatic diynes (1) and dithiol (2) catalyzed by rhodium complexes proceed smoothly under mild conditions at room temperature in a regioselective manner, producing sole anti-Markovnikov products of poly(vinylene sulfide)s (3) with high molecular weights (Mw up to 31500) and stereoregularities (E content up to 100%) in high yields (up to 95.2%). The stereostructures of the polymers are readily tuned by engineering control on the sequential addition of monomers during the polymerization process and postmanipulation by light irradiation. All the poly(vinylene sulfide)s are soluble in common organic solvents and exhibit good film-forming ability and high optical transparency. The functional pendants in 1 have endowed 3 with novel properties such as aggregation-enhanced emission characteristics, optical limiting to harsh laser pulses, and ceramization capability to semiconducting nanoparticles. The polymers are thermal and UV curable, enabling the fabrication of fluorescent photopatterns. Their thin films show high refractive indices (nD = 1.75−1.70) and low optical dispersions (down to 0.006) at telecom important wavelengths. Their refractive indices vary with their stereostructures and can be modulated by UV irradiation.
12/2010;
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ABSTRACT: Hierarchical tree-, mushroom- and cockscomb-like ZnO arrays with increasing branching order and complexities have been grown in situ on cheap zinc plates by a simple hydrothermal oxidation approach. Their morphology, crystal structure and orientation relationship are characterized by powder X-ray diffraction, scanning electron microscopy (SEM) and cross-sectional high-resolution transmission electron microscopy (HRTEM). The wurtzite ZnO arrays, growing mainly in the [0001] direction, show a special orientation relationship between the stem and the branch as well as a novel stem-branch boundary which might be attributed to the least mismatch between [symbol: see text] and (0002) lattice planes. The co-solvent ethylenediamine (en) was used to control the morphology and complexing of these complex ZnO nanostructures. Correspondingly, the physical properties of ZnO nanostructure assembly arrays were tuned and a stronger UV emission was observed with negligible emissions in the visible range, indicating the highly crystalline features of the complex ZnO micro-/nanostructured materials.
Nanoscale 09/2010; 2(9):1674-83. · 5.91 Impact Factor
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Jianzhao Liu,
Yongchun Zhong,
Jacky W. Y. Lam,
Ping Lu,
Yuning Hong,
Yong Yu,
Yanan Yue,
Mahtab Faisal,
Herman H. Y. Sung,
Ian D. Williams, Kam Sing Wong,
Ben Zhong Tang
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ABSTRACT: Hyperbranched poly(2,5-silole)s [hb-P1(m), m = 1, 6] are synthesized for the first time in this work. 1,1-Dialkyl-2,5-bis(4-ethynylphenyl)-3,4-diphenylsiloles [1(m)] were polymerized by TaBr5, affording hb-P1(m) with high molecular weights (Mw up to 2.5 × 105) in high yields (up to 98%). The structures of hb-P1(m) were characterized by spectroscopic methods and the degree of branching of hb-P1(6) was determined to be 0.55. The hyperbranched polymers are soluble and stable, with no changes in solubility observed after they have been stored under ambient conditions for more than two years. Absorption and emission spectra of hb-P1(m) are red-shifted from those of 1(m), indicating that the polymers are more conjugated than the monomers. Both 1(m) and hb-P1(m) are nonemissive or weekly fluorescent when dissolved in their good solvents but become highly emissive when aggregated in their poor solvents or fabricated into thin solid films, showing unusual phenomena of aggregation-induced (AIE) and -enhanced emissions (AEE). Restriction of intramolecular rotations in the aggregate state is rationalized to be the main cause for the AIE and AEE effects. Photoluminescence (PL) of 1(m) and hb-P1(m) is tunable by varying their concentrations and morphologies. The polymers are readily cured when heated to high temperatures or upon photoirradiation, furnishing cross-linked networks with novel excitation wavelength-dependent emissions in the red spectral region. Photolithography of hb-P1(m) generates fluorescent photopatterns, with the exposed and unexposed areas emitting lights with different colors. The polymers function as sensitive fluorescent chemosensors for the detection of explosives, with a superamplification effect observed in the emission quenching of the polymer nanoaggregates by picric acid.
05/2010;
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ABSTRACT: We demonstrate a novel approach for the easy fabrication of photonic crystals (PCs) with arbitrary optical lattice using two-photon holographic lithography (HL). The quadratic dependence of the two-photon absorption process dramatically increases the contrast of the pattern and the low absorption coefficient of the photoresist at 720 nm lead to a high aspect ratio and low fluctuation of the pattern. By applying such a technique, defect-free and highly uniform one-dimensional gratings, two-dimensional quasicrystals, and three-dimensional (3D) face center cube-type PCs of high aspect ratio and small filling factor are obtained. This two-photon based HL technique is particularly suitable for making 3D PCs and quasicrystals with complex and fine structural details.
Journal of Applied Physics 05/2010; · 2.17 Impact Factor
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Ping Lu,
Jacky W. Y. Lam,
Jianzhao Liu,
Cathy K. W. Jim,
Wangzhang Yuan,
Ni Xie,
Yongchun Zhong,
Qin Hu, Kam Sing Wong,
Kevin K. L. Cheuk,
Ben Zhong Tang
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ABSTRACT: A silicon-containing hyperbranched polymer (hb-P1/2) with σ*-π* conjugation was prepared in a good yield and high molecular weight by rhodium-catalyzed alkyne polyhydrosilylation of 1,2-bis(4-ethynylphenyl)-1,2-diphenylethene (1) with tris(4-dimethylsilylphenyl)amine (2). The polymer was thermally stable, losing merely 5% of its weight when heated to ≈445 °C. Whereas hb-P1/2 was weakly luminescent when molecularly dissolved, it became highly emissive when supramolecularly aggregated, showing an aggregation-induced emission (AIE) phenomenon. A superamplification effect was observed when the AIE nanoaggregates were used as fluorescent chemosensor for explosive detection: the quenching efficiency was greatly increased in a nonlinear fashion with increasing quencher concentration.
Macromolecular Rapid Communications 04/2010; 31(9‐10):834 - 839. · 4.60 Impact Factor
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ABSTRACT: Turning "stone" into "gold": pyrene, a faint fluorophore in the solid state, is transformed into a bright emitter by decorating it with tetraphenylethene units; the new luminogen is thermally and morphologically stable and its light-emitting diode shows excellent performance, with external quantum efficiency and current efficiency up to 4.95% and 12.3 cd A(-1), respectively.
Chemical Communications 04/2010; 46(13):2221-3. · 6.17 Impact Factor
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ABSTRACT: A phase controlled beam combining via nonlinear optical conversion is proposed and demonstrated. This process involves the combining of the fields at the second harmonic frequency generated by non-collinear input fields. The arrangement of the excitation configuration allows the generated second-harmonic light waves to propagate collinearly, with phases coherently correlated. The manipulation of the conversion efficiency is then possible with the phase control of the input fields. The combined second-harmonic fields are shown to be conveniently and robustly variable from zero to a maximum value that greatly exceeds the second-harmonic field generated by a single laser beam. By using a self-adaptive control algorithm, it is possible to optimize the output without prior knowledge on each beamlet property. Either the second-harmonic output beam profile or the total second-harmonic output power can be optimized with the control algorithm.
Optics Express 02/2010; 18(3):2995-9. · 3.59 Impact Factor
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ABSTRACT: We report a facile method for the fabrication of 2-dimensional networks of Au nanoparticle−nanocavity dual structures supported on dielectric nanosieves. The optical extinctions of the as-fabricated network films were found to be dominated by optical transmission, a signature characteristic to nanocavities. The surfaces of the as-fabricated Au films were found to be hydrophobic toward water with a measured contact angle of 125.4° but quite wettable with ethanol with a contact angle of 9.5° at room temperature and are readily convertible to totally hydrophobic or hydrophilic when chemically modified with self-assembled monolayer of molecules with desired functional groups. High quality surface-enhanced Raman spectra (SERS) from a monolayer of self-assembled 4-mercaptobenzoic acid (4-MBA), an electrostatic double layer of 4-mercaptobenzoic acid and rhodamine-6G (4-MBA-R6G), and nonspecifically adsorbed R6G were obtained, respectively, demonstrating that the dual structured network films are active, stable, and uniform as substrates in SERS. Employing the SERS spectra from a monolayer of self-assembled 4-MBA, the enhancement factors of 106 and 105 were achieved with excitations at 632.8 and 785 nm, respectively. Discrete dipole approximation (DDA) calculations were conducted to examine the electric field intensity distributions on linearly and circularly aggregated nanoparticles, two typical local aggregation patterns of nanoparticles in the as-fabricated network films. The DDA calculations reveal an important relationship between three factors: the generation of the hottest E-field spot on a linear chain aggregate, the position of the extinction peak of the aggregate, and the excitation wavelength used. It was found that the hottest spot on a linear aggregate is generated only when the excitation wavelength is in resonance with the extinction peak of the aggregate. An “effective aggregation number” scale is proposed to measure the effectiveness of the aggregation of nanoparticles in 1- and 2-dimensions at a given excitation. A “hot-spot” delocalization picture is proposed for the nanocavities formed by circular aggregation of nanoparticles to account for the observed isotropic SERS on the as-fabricated films.
Journal of Physical Chemistry C. 01/2010; 114:10463-10477.
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ABSTRACT: We have devised dye-sensitized solar cells (DSSCs) with >6% efficiency by employing composite photoanodes of SnO(2) nanoparticles/ZnO nanotetrapods. Benefiting from material advantages of both constituents, the composite photoanodes exhibit extremely large roughness factors, good charge collection, and tunable light scattering properties. Among the three composite photoanodes with widely differing compositions tested, the best performance (efficiency = 6.31%) was obtained with a weight ratio of SnO(2)/ZnO 2:1 mainly due to the highest saturated J(sc) achieved at a thinnest film thickness. Charge collection losses in composite films with more ZnO nanotetrapods content and thus necessarily larger film thicknesses appear to be a main limiting factor on IPCE and therefore J(sc), which undermines the gain from their favorable light scattering ability. An ultrathin layer of ZnO spontaneously shelled on SnO(2) nanoparticles is found to enhance V(oc) primarily by lifting the band edges rather than by suppressing recombination. Finally, by intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS), we have identified that recombination in SnO(2)/ZnO composite films is mainly determined by the ZnO shell condition on SnO(2), whereas electron transport is greatly influenced by the morphologies and sizes of the ZnO crystalline additives. In particular, ZnO nanotetrapods have proved to be superior in electron transport and therefore charge collection over ZnO particles additives in the SnO(2)/ZnO composite-based DSSCs.
The Journal of Physical Chemistry A 12/2009; 114(9):3127-38. · 2.95 Impact Factor
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Yuning Hong,
Hao Xiong,
Jacky Wing Yip Lam,
Matthias Häussler,
Jianzhao Liu,
Yong Yu,
Yongchun Zhong,
Herman H Y Sung,
Ian D Williams, Kam Sing Wong,
Ben Zhong Tang
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ABSTRACT: Whereas most conventional DNA probes are flat disklike aromatic molecules, we explored the possibility of developing quadruplex sensors with nonplanar conformations, in particular, the propeller-shaped tetraphenylethene (TPE) salts with aggregation-induced emission (AIE) characteristics. 1,1,2,2-Tetrakis[4-(2-triethylammonioethoxy)phenyl]ethene tetrabromide (TPE-1) was found to show a specific affinity to a particular quadruplex structure formed by a human telomeric DNA strand in the presence of K(+) ions, as indicated by the enhanced and bathochromically shifted emission of the AIE fluorogen. Steady-state and time-resolved spectral analyses revealed that the specific binding stems from a structural matching between the AIE fluorogen and the DNA strand in the folding process. Computational modeling suggests that the AIE molecule docks on the grooves of the quadruplex surface with the aid of electrostatic attraction. The binding preference of TPE-1 enables it to serve as a bioprobe for direct monitoring of cation-driven conformational transitions between the quadruplexes of various conformations, a job unachievable by the traditional G-quadruplex biosensors. Methyl thiazolyl tetrazolium (MTT) assays reveal that TPE-1 is cytocompatible, posing no toxicity to living cells.
Chemistry 12/2009; 16(4):1232-45. · 5.93 Impact Factor
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ABSTRACT: We report a study of the optical and electric properties of Au nanoparticle networks grown on the porous alumina membrane by dry atom sputtering deposition approach. An effective cluster model was developed to evaluate the dielectric function and the electrical conductivities of the nanoparticle networks by taking into account the effects of the Au particle size, the Au volume fraction, and the particle-particle interaction. The calculated transmission spectra from the model were in good agreement with the experimental data. The percolation threshold of the as-fabricated structure was predicted to occur at Au volume fraction of 0.18, consistent with the dc electric resistance measurement.
Optics Express 11/2009; 17(24):22223-34. · 3.59 Impact Factor
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Rongrong Hu,
Erik Lager,
Angélica Aguilar-Aguilar,
Jianzhao Liu,
Jacky W. Y. Lam,
Herman H. Y. Sung,
Ian D. Williams,
Yongchun Zhong, Kam Sing Wong,
Eduardo Peña-Cabrera,
Ben Zhong Tang
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ABSTRACT: Boron dipyrromethene (BODIPY) derivatives 1 and 2 consisting of donor and acceptor units with dual photoresponses to solvent polarity and luminogen aggregation are developed through taking advantage of twisted intramolecular charge transfer (TICT) and aggregation-induced emission (AIE) processes. In nonpolar solvents, the locally excited (LE) states of the BODIPY luminogens emit intense green lights. Increasing solvent polarity brings the luminogens from the LE state to the TICT state, causing a large bathochromic shift in the emission color but a dramatic decrease in the emission efficiency. The red emission is greatly boosted by aggregate formation or AIE effect: addition of large amounts of water into the solutions of 1 and 2 in the polar solvents causes the luminogens to aggregate supramolecularly and to emit efficiently. The emission can be enhanced by increasing solvent viscosity and decreasing solution temperature, indicating that the AIE effect is caused by the restriction of the intramolecular rotations in the aggregates of the luminogens.
09/2009;
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ABSTRACT: Absolute quantum efficiencies of surface-plasmon-enhanced photoluminescence from Au capped Alq3 films were measured using an integrating sphere. The metal “mirror” and directional enhancement effects due to surface roughness which usually occur in forward/backward collection measurements were eliminated using this integrating sphere technique. Up to 40% of the enhanced photoluminescence observed using the forward/backward collection method was shown to have come from mirror and/or enhanced directional scattering effects. Purcell factors obtained from the integrating sphere data and from time-resolved photoluminescence measurements were consistent, confirming surface-plasmon coupling. Incorporating a thin spacer layer enhanced the quantum efficiency and also eliminated nonradiative recombination due to the metal layer. The results clearly show the importance of using an integrating sphere when measuring overall surface-plasmon quantum efficiencies to eliminate directional scattering effects.
Applied Physics Letters 08/2009; 95(5):051503-051503-3. · 3.84 Impact Factor
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ABSTRACT: We fabricated tetraphenylethylene (TPE)-doped poly(methyl methacrylate) (PMMA) nanowires in the channels of anodic aluminum oxide template. Strong blue photoluminescence from the TPE aggregates in the polymer nanowires was observed. Room temperature ultraviolet lasing can be achieved in as-prepared TPE/PMMA nanowires. Lasing from isolated individual nanowires at 372 nm with emission width of 0.3 nm was also observed at low temperature. Ultrafast emission decay of 34 ps from the 372 nm peak pumped above threshold verified the stimulated emission nature of the lasing process. Our result shows that combining small molecules with highly processable PMMA can result in high-quality polymer nanowires and meanwhile maintain or even enhance the original functionality of the small molecules.
10/2008;
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Juntao Li,
Yikun Liu,
Xiangsheng Xie,
Peiqing Zhang,
Bing Liang,
Li Yan,
Jianying Zhou,
Gershon Kurizki,
Daniel Jacobs, Kam Sing Wong,
Yongchun Zhong
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ABSTRACT: A one-step introduction of functional defects into a photonic crystal is demonstrated. By using a multi-beam phase-controlled holographic lithography, line-defects in a Bragg structure and embedded waveguides in a two-dimensional photonic crystal are fabricated. Intrinsic defect introduction into a 3-dimensional photonic crystal is also proposed. This technique gives rise to a substantial reduction of the fabrication complexity and a significant improvement on the accuracy of the functional defects in photonic crystals.
Optics Express 09/2008; 16(17):12899-904. · 3.59 Impact Factor
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Journal of Polymer Science Part A Polymer Chemistry 02/2008; 46(6):2025 - 2037. · 3.92 Impact Factor
