Matthias Häußler

Fluorescent Bioprobes: Structural Matching in the Docking Processes of Aggregation-Induced Emission Fluorogens on DNA Surfaces

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.

Hyperbranched Poly(ferrocenylene)s Containing Groups 14 and 15 Elements: Syntheses, Optical and Thermal Properties, and Pyrolytic Transformations into Nanostructured Magnetoceramics

A series of hyperbranched poly(ferrocenylene)s containing elements (E) of groups 14 [E=Si (hb-1), Ge (hb-2)] and 15 [E=P (hb-3), Sb (hb-4)] are prepared in good isolation yields (up to 82wt%) by the salt-eliminative polycoupling of dilithioferrocene with tri-(RECl3) or tetrachlorides of the elements (ECl4). While the polymers with no or small R groups are insoluble or partially soluble, those with long alkyl chains (R=CnH2n+1 with n ≥ 8) are completely soluble and film forming. The polymers exhibit solution properties characteristic of hyperbranched macromolecules: e.g. hb-1(18) shows a low intrinsic viscosity ([η]=0.02dL/g) despite its high absolute molecular weight (Mw=5 × 105). Spectroscopic analyses reveal that the polymers possess rigid skeleton structures with extended conjugations, with their absorption spectra tailing into the infrared region (>700nm). The polymers show good thermal stability with Td up to ~400°C and can be graphitized into iron-containing ceramics when pyrolyzed at high temperatures, with char yields up to ~60wt%. While calcinations of the Si-containing polymers (hb-1) at 1000°C under nitrogen give ceramics containing mostly α-Fe nanoparticles, those of Ge-(hb-2) and Sb-containing polymers (hb-4) are completely transformed into their iron-alloys. The ceramics from the P-containing polymers (hb-3) show diffraction patterns of iron phosphides. Iron silicide nanocrystals of “large” sizes are obtained when the pyrolysis of hb-1 is conducted at a high temperature of 1200°C under argon. This ceramic is highly magnetizable (Ms up to ~51emu/g) and shows near-zero remanence and coercivity; in other words, it is an outstanding soft ferromagnet with a high magnetic susceptibility and practically nil hysteresis loss.

Metallized hyperbranched polydiyne : a photonic material with a large refractive index tunability and a spin-coatable catalyst for facile fabrication of carbon nanotubes

A cobalt-containing hyperbranched polydiyne shows refractive indexes (n) as high as 1.713-1.813 in the long wavelength region, which can be tuned to a large extent (Deltan up to approximately 0.048) by UV irradiation; the polymer can also function as a spin-coatable catalyst for the growth of carbon nanotubes.

Novel Linear and Cyclic Polyenes with Dramatic Aggregation-Induced Enhancements in Photoresponsiveness

ABSTRACT A series of new linear and cyclic polyenes including siloles, butadienes, cyclcobutenes, fulvenes, and 4H-pyrans are designed and synthesized. When molecularly dissolved in common organic solvents, all the polyenes are practically nonemissive. Addition of poor solvents induces the polyenes to cluster into nanoaggregates, which turns the emission of the polyenes “on” and boosts their luminescence efficiencies dramatically (hence “aggregation-induced emission” or AIE). The emission color ranges from blue to red, depending on the chromophoric structures. Polyene nanoparticles on TLC plates show bright blue fluorescence which switches off reversibly in an atmosphere of volatile organic compounds. Addition of poor solvents to solution of cyclic polyenes bearing cholsteryl moieties leads to polarized green and anisotropic red emissions dependant on the solvent ratios. The different emissions may be caused by different packing patterns of the polyene crystals under different conditions.

UNUSUAL ELECTRONIC AND PHOTONIC BEHAVIORS OF LINEAR POLY(SILOLYLACETYLENE)S AND HYPERBRANCHED POLY(SILOLYLENEARYLENE)S

A series of dendritic 2,3,4,5-tetraphenylsiloles (1–8) are prepared. Polymerizations of 4-8 are effected by transition-metal catalysts, giving linear (9-12) and hyperbranched polymers (14) in high yields. Whereas the silole polymers are practically nonluminescent when molecularly dissolved, they become emissive when aggregated in poor solvents or cooled to low temperatures. The light-emitting diodes using linear poly(silolylacetylene)s as active layers emit blue and green lights with current efficiency up to 1.45 cd/A. The hyperbranched poly(silolenearylene)s are nonlinear optically active and strongly attenuate the optical power of intense laser pulses, whose optical limiting performances are superior to that of C60, a well-known optical limiter.

Hyperbranched Polymers Containing Transition Metals: Synthetic Pathways and Potential Applications

Incorporation of transition metals into organic monomers and polymers has been thoroughly examined over the past five decades in light of the promising electrical, magnetic, optical, sensing and catalytic properties that these organometallic materials possess [1–4]. Thanks to their intriguing properties, which are often inaccessible by their pure organic parents, these organometallic polymers have found applications in the coating, pharmaceutical, and aerospace industries. Whereas many of these studies focused on the synthesis of linear polymers with either transition metals integrated into the main chain or attached as pendant groups at the side chains, the preparation and study of highly branched three dimensional (3-D) macromolecular architectures—such as dendrimers and hyperbranched polymers containing organometallic complexes—has only recently received greater attention. Depending on their position, metal centers have been shown to act as cores, simulating artificial models of biological systems such as metalloenzymes, as well as connectors, branching points, and terminal (surface) units distributed throughout the whole structure with potential applications in the field of sensors, catalysts, and as light-harvesting antennas [5,6]. Despite their structural beauty, dendrimer synthesis needs to be carried out in a thoughtful manner involving multistep reaction and purification protocols in order to construct the various tree-like generations, which will in many cases restrict their potential applications to academic interests only [7]. Moreover, recent advances in mass spectrometric techniques have revealed depictions of dentrimers showing them to be highly idealized and that the real samples indeed exhibit imperfections and structural defects [8]. 1 Background 21 2 Research and Discussion 22 2.1 Theoretical Background 22 2.2 Synthetic Pathways 23 3 Conclusion and Future Considerations 33 References 33

Aggregation-and crystallization-induced light emission

A group of organic chromophoric molecules including siloles, pyrans, tetraphenylethylenes and fulvenes, are designed and synthesized. Light emissions of conventional luminescent materials are often quenched by aggregate formation. These molecules, however, become stronger luminophors when aggregated although they are practically nonemissive in their dilute solutions. By varying their packing structures in the aggregation states, emission color ranging from blue to red can be achieved. The emission of fulvenes can also be controlled by changing their morphology. While they emit a faint light in the amorphous state, their crystal forms are strongly luminescent. Intermolecular interaction or restriction of intramolecular rotation in different states may be responsible for such behaviors. Thanks to such effects, the molecules can be employed as sensors for the detection of explosives, organic solvent vapors, solution pH, and biomacromolecules. Further modification of their structures by molecular engineering endeavors may generate materials that can find an array of applications in optical display systems and as biological probes.

Synthesis of Hyperbranched Conjugative Polymers and Their Applications as Photoresists and Precursors for Magnetic Nanoceramics

This chapter explains the synthesis of hyperbranched conjugative polymers and their applications as photoresists and precursors for magnetic nanoceramics. Synthesis of hyperbranched polymers is an important research because of the expectation that their unique molecular architectures impart novel properties. Compared to dendrimers, hyperbranched polymers can be prepared by economic one-pot, single-step polymerization procedures, accessible through different synthetic strategies. In this chapter, a group of new hyperbranched poly-arylenes, polyynes, and poly(ferrocenylene)s with high molecular weights are prepared in high yields by polycyclotrimerization and polycoupling of acetylenic monomers, and polycondensation reaction of dilithioferrocene with tri- or tetrachlorides of group 14 and 15 elements. All the polymers possess high thermal stability, losing little of their weights when heated to >400°C. Thin films of hyperbranched polyynes exhibit very high refractive indexes ( n up to 1.86). Ceramizations of ferrocene-containing poly(aroylarylene)s, cobalt-polyyne complexes, and poly(ferrocenylene)s at high temperatures under nitrogen afford soft nanoceramics with magnetic susceptibilities up to ∼118 emu/g and near-zero magnetic losses.

Photo-cross-linkable light-emitting polymers for holographic patterning

Blue light-emitting poly(1-phenyl-1-alkyne)s containing photo-cross-linkable vinyl pendants were synthesized and photophysically characterized. Photoluminescence quantum yields are virtually unchanged for pristine and photo-cross-linked films, showing excellent stability and light-emitting property of the insoluble polymer film after photo-cross-linking process. By using laser interference lithography technique, active submicron two-dimensional photonic crystal structures have been fabricated by exposure to UV light. The obtained high quality nanostructures demonstrate that these polymers are applicable in active photonic devices such as distributed feedback laser. Furthermore, the achievable resolution of these polymers is ∼50nm, implying that these polymers may find potential applications in active nanodevices.

Holographic Nano‐Patterning Based On Photo‐Cross‐Linkable Light Emitting Polyacetylenes

Blue light‐emitting poly(1‐phenyl‐1‐alkyne)s containing photo‐cross‐linkable vinyl pendants were synthesized and photophysically characterized. Photoluminescence quantum yields are virtually unchanged for pristine and photo‐cross‐linked films showing excellent stability and light emitting property of the insoluble polymer film after photo‐cross‐linking process. By using laser interference lithography technique, active submicron two‐dimensional photonic crystal structures have been fabricated by exposure to UV light. The obtained high quality nanostructures demonstrate that these polymers are applicable in active photonic devices such as polymer light emitting diode or distributed feedback lasers.