Showing papers by "Jacky Wing Yip Lam published in 2009"

Twisted Intramolecular Charge Transfer and Aggregation-Induced Emission of BODIPY Derivatives

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 ro...

Functionalized Siloles: Versatile Synthesis, Aggregation‐Induced Emission, and Sensory and Device Applications

Abstract: The synthesis of functionalized siloles has been a challenge because of the incompatibility of polar functional groups with the reactive intermediates in the conventional protocols for silole synthesis. In this work, a synthetic route for silole functionalization is elaborated, through which a series of functionalized siloles are successfully prepared. Whereas light emissions of traditional luminophores are often quenched by aggregation, most of the functionalized siloles show an exactly opposite phenomenon of aggregation-induced emission (AIE). The siloles are nonemissive when dissolved in their good solvents but become highly luminescent when aggregated in their poor solvents or in the solid state. Manipulation of the aggregation–deaggregation processes of the siloles enables them to play two seemly antagonistic roles and work as both excellent quenchers and efficient emitters. The AIE effect endows the siloles with multifaceted functionalities, including fluorescence quenching, pH sensing, explosive detection, and biological probing. The sensing processes are very sensitive (with detection limit down to 0.1 ppm) and highly selective (with capability of discriminating among different kinds of ions, explosives, proteins, DNAs, and RNAs). The siloles also serve as active layers in the fabrication of electroluminescent devices and as photosensitive films in the generation of fluorescence patterns.

Aggregation-induced Emission of Silole Molecules and Polymers: Fundamental and Applications

Abstract: Aggregation generally quenches the light emissions of chromophoric molecules. In this review, we demonstrate that 1,1-disubstituted 2,3,4,5-tetraphenyl siloles and 2,5-difunctionalized siloles as well as their polymers exhibit the opposite behaviors. Instead of quenching, aggregation has greatly boosted their photoluminescence quantum yields by up to two orders of magnitude, turning them from faint fluorophores into strong emitters. Such “abnormal” phenomenon of “aggregation-induced emission (AIE)” is attributed to restricted intramolecular rotations of the peripheral phenyl rings against the central silole core, which block the nonradiative channel via the rotational energy relaxation processes and effectively populate the radiative decay of the excitons. Utilizing such a novel effect, siloles and their polymers find an array of applications as: sensors for chemicals, explosives, pH, and biomacromolecules (proteins, DNAs and RNAs), indicators for determining CMC and monitoring layer-by-layer self-assembling, biocompatible fluorogens for cell imaging, visualizing agent for DNA gel electrophoresis, biolabels for immunoassay, stimuli-responsive organic nanomaterials, magnetic fluorescent nanoparticles for potential bio-imaging and -separation, and outstanding materials for efficient OLEDs and PV cells.

Polytriazoles with Aggregation-Induced Emission Characteristics: Synthesis by Click Polymerization and Application as Explosive Chemosensors

Abstract: The copper-catalyzed 1,3-dipolar cycloaddition of alkynes with azides is a typical example of “click” reaction. Since the reaction enjoys the advantages of high efficiency and regioselectivity and requires mild reaction conditions and simple purification procedures, it has become a versatile synthetic tool with applicability in diverse areas including bioconjugation and surface modification. The click reaction has also been utilized in polymer science with emphasis on the functionalization of preformed polymers through postpolymerization approaches. The effort of developing the reaction into a new polymerization technique, however, has met with only limited success. The polymerization reactions of arylene diazides and arylene diynes catalyzed by copper(I) species were sluggish, taking as long as 7-10 days to finish. The products often precipitated from the reaction mixtures even at the oligomer stage or became insoluble in common organic solvents after purification, unless very long alkyl chains, such as n-dodecyl groups, were attached to the arylene rings. The prepared polytrizoles were nonluminescent in the solid state, although their dilute solution emitted UV light, suggesting that the polymer emission has been quenched by the aggregate formation. If the polytriazoles are to be utilized as light-emitting materials, this issue must be properly tackled because luminophores are commonly used as solid films in their practical applications. We have recently discovered an intriguing phenomenon of aggregation-induced emission (AIE): a series of nonemissive molecules such as tetraphenylethene (TPE) and hexaphenylsilole as well as their derivatives are induced to emit efficiently by aggregate formation. The AIE effect greatly boosts the fluorescence quantum yields (ΦF) of the molecules by up to 3 orders of magnitude, turning them from faint luminophores into strong emitters. Thanks to their unique AIE characteristics, the molecules have been found to serve as chemosensors, bioprobes, stimuli-responsive nanomaterials, and active layers in the construction of efficient organic light-emitting diodes. Among the AIE luminophores, the TPE system has received much attention because of its facile preparation, ready functionalization, good photostability, and high photoluminescence (PL) efficiency. For practical applications, these low molecular weight luminophores have to be fabricated into solid films by expensive techniques such as vacuum vapor deposition processes, which are not well suited to the manufacture of large-area, flat-panel devices. One way to surmount this processing disadvantage is to synthesize high molecular weight polymers, which can be readily fabricated into large-area films by simple macroscopic processing techniques such as spin coating and static casting. However, polymers with efficient light emissions in the aggregate or solid state are rare because aggregation of the polymer chains commonly quenches light emission. In this paper, we report a group of new TPE-containing polytriazoles (P3) synthesized from the click polymerization of diyne (1) with diazides (2; Scheme 1). The light emission of the polymers is dramatically enhanced, instead of being quenched, by aggregate formation. The diyne and diazide monomers, namely 1,4-bis(propargyloxy)benzene (1), 1,2-bis[4-(azidohexyloxy)phenyl]-1,2-diphenylethene (2a), and 1,2-bis[(4-azidomethyl)phenyl]-1,2-diphenylethene (2b), were synthesized according to Scheme S1. The reactions proceeded smoothly, and the desired monomers were obtained in good yields. The monomer structures were confirmed by spectroscopic analyses (see Supporting Information for detailed characterization data). We attempted to transform the monomers to their polymers by 1,3-dipolar polycycloaddition. We have previously succeeded in the catalyst-free polycycloaddition of bis(aroylacetylene)s with diazides by simple heating. No high molecular weight polymers, however, were obtained when 1 and 2 were refluxed in THF for 110 h (Table 1, no. 1). This is due to the low reactivity of diyne 1 because it contains no election-withdrawing groups. Although the monomers could be polymerized by

Metal-Free Click Polymerization: Synthesis and Photonic Properties of Poly(aroyltriazole)s

Abstract: Regioselective 1,3-dipolar polycycloadditions of tetraphenylethene (TPE). containing diazides 1―3 and bis(aroylacetylene) 4 are initiated by simple heating, affording poly(aroyltriazole)s (PATAs) PI-PIII with high molecular weights in high yields. The PATAs are completely soluble in common organic solvents and stable at temperatures up to 358 °C. Thanks to their TPE units, the polymers show aggregation-induced emission and work as explosive sensors with high sensitivity. The PATAs are optically transparent in the whole visible spectral region. Their refractive indexes can be tuned to a great extent (Δn ≈ 0.08) by simply changing their alkyl spacer lengths. The modified Abbe numbers of the PATAs are very high (up to 273), indicative of very low optical dispersions in the telecommunication-important wavelength region. UV irradiation through a photomask quenches the light emissions of the polymers, enabling the generation of two-dimensional fluorescent images without development. The polymers can be readily photo-crosslinked, yielding three-dimensional patterns with high resolutions.

Luminogenic Polyacetylenes and Conjugated Polyelectrolytes: Synthesis, Hybridization with Carbon Nanotubes, Aggregation-Induced Emission, Superamplification in Emission Quenching by Explosives, and Fluorescent Assay for Protein Quantitation

Abstract: Phenylacetylene and 1-pentyne derivatives containing aminated tetraphenylethene (TPE) units 1 and 2 are synthesized. The TPE-functionalized luminogens are nonemissive in dilute solutions but luminescent as solid aggregates, showing a novel behavior of aggregation-induced emission (AIE). The monomers are polymerized to their corresponding polymers P1 and P2 with an E conformation by organorhodium catalysts, although Rh-catalyzed polymerizations normally yield Z-rich polyacetylenes. Whereas P1 fluoresces faintly in THF, its light emission is enhanced by aggregation in aqueous media, exhibiting an aggregation-induced emission enhancement (AIEE) effect. On the other hand, P2 is AIE active: the emission of its nanoaggregates suspended in 90% aqueous mixture is ∼57-fold stronger than that of its solution in THF. A novel superamplification effect is observed in the emission quenching of P2 nanoaggregates by picric acid (PA): the quenching constant (KSV) is nonlinearly increased with the quencher concentration an...

Pyrazine luminogens with “free” and “locked” phenyl rings: Understanding of restriction of intramolecular rotation as a cause for aggregation-induced emission

Abstract: Nitrogen-containing heterocyclic pyrazine luminogens with “free” (1) and “locked” (2) phenyl rings were readily prepared in high yields. The propeller-shaped luminogen 1 shows aggregation-induced emission feature, whereas the disk-shaped chromophore 2 shows conventional aggregation-caused quenching effect, offering a direct evidence to support our hypothesis that restriction of intramolecular rotation is the main cause for the AIE phenomenon.

Crystallization-induced emission enhancement in a phosphorus-containing heterocyclic luminogen.

Abstract: Whereas aggregation often quenches luminescence, the emission of a heterocyclic luminogen, 10-[2,5-bis(4-pentyloxyphenylcarbonyloxy)phenyl]-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (3), is greatly enhanced by aggregate formation. Crystallization further boosts the emission of 3, turning it from a weak emitter in the solution state to a strong emitter in the crystalline state. The emission of 3 is changed in response to the exposure to vapors of volatile organic compounds (VOCs). The morphology of the thin film of 3 is reversibly and repeatedly modulated between amorphous and crystalline phases by simple fuming−heating and heating−cooling cycles, leading to an emission switching between bright and dark states. The novel attributes of the crystallization-induced emission enhancement, the VOC-responsive emission change, and the morphology-tunable emission switching of 3 could enable it to find applications in an array of technological areas, including chemosensing, optical display, and rewritable i...

Synthesis of an AIE-active fluorogen and its application in cell imaging

Abstract: A fluorogen named 1-decyl-1-methyl-2,5-bis{4-[(N,N-diethylamino)methyl]phenyl}-3,4-diphenylsilole (3) was synthesized. It emitted weakly as isolated molecule but strongly as supramolecular aggregate, showing a characteristic behavior of aggregation-induced emission (AIE). The molecules of 3 formed highly emissive nanoparticles in aqueous media, which quickly and selectively marked cytoplasm of HeLa cells and posed no toxicity to the living cells. The fluorogen is thus a promising candidate mate-rial for cell imaging as a sensitive, selective and cytocompatible biosensor.

Chiral Poly(4‐ethynylbenzoyl‐L‐valine)‐Induced Helical Self‐Assembly of Alkynylplatinum(II) Terpyridyl Complexes with Tunable Electronic Absorption, Emission, and Circular Dichroism Changes

Abstract: A chiral amino acid-containing polyacetylene, poly(4-ethynylbenzoyl-L-valine), was found to induce the aggregation and self-assembly of square-planar alkynylplatinum(II) terpyridyl complexes by electrostatic binding of the positively charged metal complexes to the anionic sites of the polyacetylene, as revealed by the appearance of new UV/Vis absorption and emission bands upon mixing under basic conditions. The induced complex self-assembly was found to be influenced by the polyacetylene and/or base concentration, and the effect of pH on the reversibility of the aggregate/monomer interconversion was also studied. The conformational changes of the polyacetylene were probed by circular dichroism (CD) spectroscopy, in which the chirality signal of the corresponding chain helicity in the presence of the base was enhanced and stabilized upon addition of the platinum(II) complexes. The induced complex aggregation was dependent on the structural properties of the polyacetylene, while the chirality of the polyacetylene was strongly influenced by the introduction of the complex.

A New Disubstituted Polyacetylene for the Detection of α-Amino Acids.

Abstract: New imidazole-functionalized disubstituted polyacetylene was synthesized by utilizing the postfunctional strategy. In addition, its ability to sense copper ions and α-amino acids by fluorescence quenching has been studied. The quenching of the fluorescence of the imidazole-functionalized disubstituted polyacetylene was observed at a very low level of Cu(2+) (7.0 × 10(-7) mol · L(-1) ). The fluorescent intensity decreased rapidly upon the increase of the concentration of the added solution of Cu(2+) . It was expected that the addition of α-amino acids to the solution of the polyacetylene/Cu(2+) complex could turn on the fluorescence of the polyacetylene, if α-amino acids could remove the copper ions from the complex. Glycine, was used for testing: upon the addition of glycine the quenched fluorescence of P1 turned on immediately. The detection limit was as low as 6.0 × 10(-5) mol · L(-1) .

Functional Polyacetylenes Carrying Mesogenic and Polynuclear Aromatic Pendants : Polymer Synthesis, Hybridization with Carbon Nanotubes, Liquid Crystallinity, Light Emission, and Electrical Conductivity

Abstract: Multifunctional polyacetylenes and their nanohybrids with liquid crystallinity, light emission, and electrical conductivity are developed in this work. New acetylene monomers containing biphenyl mesogens and polynuclear chromophores, namely 4-[3-(1-pyrenyl)propylcarbonyloxy]-4′-biphenylyl 11-(4-ethynylphenoxy)undecanoate (1), 4-[3-(1-pyrenyl)propylcarbonyloxy]-4′-biphenylyl 10-undecynoate (2), and (9-fluorenyl)methyl-4-[(9-decynyl)-carbonyloxy]-4′-biphenylyloxycarbonylmethyl carbamate (3), were synthesized and transformed to their corresponding polymers (P1−P3) by the polymerization reactions catalyzed by organorhodium complexes of Rh+(nbd)[C6H5B−(C6H5)3] and [Rh(diene)Cl]2. Whereas none of the monomers were mesomorphic, P1 and P2 were liquid crystalline. The pyrene pendants enabled P1 and P2 to function as dispersants for short (s)- and long (l)-multiwalled carbon nanotubes (MWNTs). P1 assisted the dissolution of s- and l-MWNTs in THF, with respective solubilities as high as 723 and 625 mg/L. The resulta...

Exploration of Effective Catalysts for Diyne Polycyclotrimerization, Synthesis of an Ester-Functionalized Hyperbranched Polyphenylene, and Demonstration of Its Utility as a Molecular Container with Implication for Controlled Drug Delivery

Abstract: We present the first examples of a group of effective ruthenium catalysts for polycyclotrimerization. The polymerization reactions of an arylene bipropiolate monomer initiated by the Ru(II−IV) complexes of CpRu(PPh3)2Cl, Cp*Ru(PPh3)2Cl, [Cp*RuCl2]n, and [Ru(η3:η3-C10H16)(μ-Cl)Cl]2 (Cp = cyclopentadienyl, Cp* = pentamethyl-Cp, and C10H16 = 2,7-dimethylocta-2,6-diene-1,8-diyl) produce ester-functionalized poly(aroxycarbonylphenylene) (PACP) with high molecular weights (Mw up to 200 × 103) in good yields (up to 90%). Topological structure of the polymer product can be hyperbranched or cross-linked, tunable by the extent of triple-bond conversion. The degree of branching (DB) of the PACP is ∼0.76, much higher than those of the “conventional” hyperbranched polymers (DB ∼ 0.5). The PACP exhibits high transparency in the visible spectral region. It works as a molecular container, effectively trapping small molecules in its cavities with the aid of hydrogen-bond interaction. The polymer undergoes a bursting hydro...

Cobalt-Containing Hyperbranched Poly(silylenearylene)s

Abstract: A group of hyperbranched poly(silylenearylene)s are synthesized by homopolycyclotrimerizations of A2-type silylenediynes. The polymers can be readily metallized by complexations of their periphery triple bonds with cobalt octacarbonyls Co2(CO)8. Pyrolysis of these organometallic polymers gives magnetic ceramics in good yields. Analyses by SEM, TEM, XPS, EDX, and XRD demonstrate that the ceramics comprise ferromagnetic Co and paramagnetic Co2Si nanocrystallites wrapped by carboneous shell. The ceramics show high magnetic susceptibilities (M s up to ~50 emu/g) and near-zero coercivity (H c down to ~0.14 kOe), suggesting that they are good soft magnetic materials with low hysteresis loss.

Preparation of Functional Poly(aroyltriazole)s by Metal‐Free Click Polymerization

Abstract: Functional poly(aroyltriazoles) (PATAs) were synthesized by heating mixtures of bis(aroylacetylene)s and diazides in polar solvents such as DMF/toluene at a moderate temperature of 100 °C with high molecular weights (M w up to 17200) and regioregularities (1,4-regioisomeric ratio up to ∼95%) in high yields (up to ∼95%). The obtained polymers are soluble in common organic solvents and are thermally stable. The PATAs containing triphenylamine units emit visible light and show unique solvatochromism, exhibiting large two-photon absorption cross sections due to the intramolecular charge transfer between their electron-donating triphenylamine and electron-accepting aroyltriazole units. The tetraphenylethene (TPE)-functionalized polymer shows intriguing aggregation-induced emission phenomenon, that is, the polymer is weakly emissive in its solution state but emit strongly in its aggregate/solid state with quantum yield of ∼7.1%.

Synthesis and properties of poly(1-phenyl-1-octyne)s containing stereogenic and chromophoric pendant groups

Abstract: Poly(1-phenyl-1-octyne)s containing different stereogenic and chromophoric pendants {-[(C6H13)C= C(C6H4-p-CO2-R)] n -R = [(1S)-endo]-(−)-borneyl (P3), (1R,2S,5R)-(−)-menthyl (P4), -C6H4-p-(1R,2S,5R)-(−)-menthyl (P5), 2-napthyl (P6), 4-biphenylyl (P7)} have been designed and synthesized. The polymers are prepared in moderate yields by WCl6-Ph4Sn and possess high molecular weights (M w up to 64000). The structures and properties of the polymers are characterized and evaluated by NMR, TGA, UV, CD, PL, and EL analyses. All the polymers are thermally stable and their temperatures for 5% weight loss locate in the range of 300 to 416°C under nitrogen. The energy band gaps of all the polymers are ∼3.0 eV. Polymers P4 and P5 show CD absorptions associated with the helicity of the polymer segments. Excitation of the THF solutions of P3–P7 by UV irradiation gives strong blue lights of ∼485 nm with quantum yields higher than 20%. The thin films of the polymers also emit in the same spectral region, indicative of little aggregation-caused quenching of light emission. Multilayer EL devices with a configuration of ITO/Polymer:PVK/BCP/Alq3/LiF/Al are constructed, which emit blue lights of ∼487 nm. The maximum luminance and external quantum efficiency vary with the pendant groups, with P6 exhibiting the highest external quantum efficiency of 0.16%. The spectra stability of the EL devices is outstanding and the EL peak maximum experiences little change with the applied voltage.

Improvement of the solubility of multiwalled carbon nanotubes with disubstituted polyacetylenes bearing different side-chains: improvement of the solubility of multiwalled carbon nanotubes with disubstituted polyacetylenes bearing different side-chains

Abstract: Disubstituted polyacetylenes are fluorescent polymers,and they are more stable than their monosubstituted counterparts.In comparison with the reports about those monosubstituted polyacetylenes,there is only one example showing the dispersing effects of disubstituted polycetylenes on carbon nanotubes.In this letter we demonstrated the fabrication of the composites of multiwalled carbon nanotubes(MWNTs) and different disubstituted polyacetylenes,and the polymer chains wrapped onto the MWNTs via π-π interactions,leading to the improved solubility of MWNTs in organic solvents.This methodology is scatheless to MWNTs.Meanwhile,the disubstituted polyacetylenes encapsulating the MWNTs exhibited their unique photoluminescence properties.