Electrochromism of a Fused Acceptor–Donor–Acceptor Triad Covering Entire UV–vis and Near-Infrared Regions

A novel fused acceptor–donor–acceptor (A–D–A) type panchromatically electrochromic compound was synthesized. It exhibited intensive absorption bands covering entire UV–vis and near-infrared regions upon reduction to the radical anionic state, owing to the simultaneous presence of π*−π* transitions and intervalence charge transfer

Planar-to-Axial Chirality Transfer in the Polymerization of Phenylacetylenes

A pair of enantiomerically pure planar chiral phenylacetylenes, <i>R</i>- and <i>S</i>-2′-ethynyl-1,10-dioxa­[10]-paracyclophane, were prepared and polymerized under the catalysis of Rh­(nbd)­BPh₄ and MoCl₅, respectively. The resultant polymers had high <i>cis</i>-structure contents and took dominant <i>cis</i>–<i>transoid</i> helical conformations with an excess screw sense as revealed by ¹H NMR, Raman, polarimetry, circular dichroism spectroscopy, and computational simulation, manifesting the effective guidance of the planar chirality of monomers to the growth of the polymer main chains. The rigid <i>ansa</i>-structure of monomer unit made the helical structure of polymer backbone stable toward grinding and thermal treatments. The stereoselective interactions between these chiral polymers and the enantiomers of racemic ethynyl-1,10-dioxa[10]-paracyclophane and cobalt­(III) acetylacetonate were observed. This work demonstrated the first planar-to-axial chirality transfer in the polymerization of acetylenes and offered a new strategy to prepare chiral materials based on optically active helical polymers

Reversible <i>Cis-Cisoid</i> to <i>Cis-Transoid</i> Helical Structure Transition in Poly(3,5-disubstituted phenylacetylene)s

A series of novel 3,5-disubstituted phenylacetylenes, <b>rM-1</b>, <b>sM-1</b> to <b>sM-5</b>, bearing an achiral methoxy­carbonyl pendant group and various chiral <i>N</i>-alkylamide pendant groups, were synthesized. They were converted to the corresponding polymers, <b>rP-1</b>, <b>sP-1</b> to <b>sP-5</b>, with high <i>cis</i>-structure contents under the catalysis of [Rh­(nbd)­Cl]₂, aiming to understand how the environmental variation and the structure of pendant group influence the chiroptical properties of polymers. <b>sP-1/rP-1</b> were soluble in CHCl₃ and THF at the molecular level and exhibited much larger optical rotations with opposite signs to those of <b>sM-1/rM-1</b> and displayed the intense Cotton effects centered at 360 nm in the circular dichroism (CD) spectra, ascribed to the one-handed, contracted <i>cis-cisoid</i> helical polyene backbone. The reversible conformation transition between the contracted <i>cis-cisoid</i> helix and the frustrated, extended <i>cis-transoid</i> helix was achieved by alternately adding trifluoro­acetic acid (TFA) and triethyl­amine into the hydrogen bond donating solvent (i.e., CHCl₃), as evidenced by UV–vis absorption and CD spectroscopy, dynamic and static laser light scattering, DSC, and WAXD results. However, the addition of TFA into the <b>sP-1</b> solution in the hydrogen bond accepting solvent (i.e., THF) caused no discernible halochromism. The competing interaction of THF with TFA was considered to account for the observed difference in acid-induced chromism. The small modification in the chiral alkylamide pendant group was found to remarkably affect the solubility and helical conformation of the polymer. <b>sP-2</b> was insoluble in all the solvents tested, <b>sP-3</b> and <b>sP-4</b> dissolved in polar DMF, while <b>sP-5</b> dissolved in both polar and apolar solvents. Depending on the nature of solvents and additives, <b>sP-3</b> and <b>sP-4</b> took either contracted or frustrated helical conformation, whereas <b>sP-5</b> took only a stretched helical conformation due to the highly branched alkyl group

<i>Cis-Cisoid</i> Helical Structures of Poly(3,5-disubstituted phenylacetylene)s Stabilized by Intramolecular n → π* Interactions

A pair of enantiomeric <i>cis</i>-poly­(phenylacetylene)­s (PPAs) substituted at the <i>meta</i>-positions of pendant phenyl rings by an achiral methoxy­carbonyl group and a chiral 1-methylpropyl­oxycarbonyl group (i.e., <b>sP-Me-C4/rP-Me-C4</b>) as well as two <i>cis</i>-PPAs bearing either just a methoxy­carbonyl (i.e., <i><b>m</b></i><b>-aP-Me</b>) or a 1-methylpropyl­oxycarbonyl (i.e., <i><b>m</b></i><b>-sP-C4</b>) meta substituent were synthesized under the catalysis of [Rh­(nbd)­Cl]₂ (nbd = norbornadiene). Various techniques including ¹H NMR, FTIR, Raman, UV–vis, CD, DSC, STM, DLS/SLS, and computer calculation were applied to characterize the helical structures of these polymers in both solution and solid states. <b>sP-Me-C4</b>/<b>rP-Me-C4</b> adopted contracted <i>cis-cisoid</i> helical conformations in THF, toluene, CH₂Cl₂, and ClCH₂CH₂Cl but <i>cis-transoid</i> ones in CHCl₃ and Cl₂CHCHCl₂. The <i>cis-cisoid</i> helices were considered to be stabilized by the existence of six n → π* interaction bands along the polyene backbones between vicinal carbonyl groups. Such interactions were insensitive to the dielectric constant and polarity of solvent but sensitive to the hydrogen bond donating ability of solvent and temperature. In hydrogen bond accepting solvent, the <i>cis-cisoid</i> helical structures were thermal stable, whereas the <i>cis-cisoid</i> to <i>cis-transoid</i> helix transition could be triggered by raising temperature in the hydrogen bond donating solvent. The stronger the hydrogen bondings between solvent molecules and carbonyl groups, the lower the temperature required to maintain <i>cis-cisoid</i> helix. Moreover, the <i>cis-cisoid</i> helices stabilized by intramolecular n → π* interactions had better tolerance to the polarity of solvent and faster recovery than those stabilized by intramolecular hydrogen bonds. No matter whether methoxy­carbonyl or 1-methylpropyl­oxycarbonyl group was removed, only a <i>cis-transoid</i> helix was observed, implying the weak nature of n → π* interaction and the need for a delicate macromolecular design. This work provided an unusual strategy to build <i>cis-cisoid</i> PPAs

Chiroptical and Thermotropic Properties of Helical Styrenic Polymers: Effect of Achiral Group

Six novel chiral bulky styrenic monomers, (+)-2-[4′-((<i>S</i>)-2″-methylbutyloxy)­phenyl]-5-phenylstyrene <b>(A-1)</b>, (+)-2-[4′-((<i>S</i>)-2″-methylbutyloxy)­phenyl]-5-(4′-fluorophenyl)­styrene <b>(A-2)</b>, (+)-2-[4′-((<i>S</i>)-2″-methylbutyloxy)­phenyl]-5-(4′-<i>tert</i>-butylphenyl)­styrene <b>(A-3)</b>, (+)-2-phenyl-5-[4′-((<i>S</i>)-2″-methylbutyloxy)­phenyl]­styrene <b>(B-1)</b>, (+)-2-(4′-fluorophenyl)-5-[4′-((<i>S</i>)-2″-methylbutyloxy)­phenyl]­styrene <b>(B-2)</b>, and (+)-2-(4′-<i>tert</i>-butylphenyl)-5-[4′-((<i>S</i>)-2″-methylbutyloxy)­phenyl]­styrene <b>(B-3)</b>, were synthesized and radically polymerized to yield the corresponding polymers, <b>PA-1</b>–<b>PA-3</b> and <b>PB-1</b>–<b>PB-3</b>. All of them consisted of laterally attached <i>p-</i>terphenyl pendants terminated by an identical (+)-(<i>S</i>)-2-methylbutyloxy end and an achiral end with various size. The first three differed the others by the position of vinyl group relative to chiral motifs. Evidenced by the results of NMR, polarimetry, circular dichroism spectroscopy, computer simulation, thermal properties, and X-ray diffractions, the chiral <i>p</i>-alkoxyphenyl group <i>ortho</i> to the vinyl group induced the helical conformation of polymer backbone with an excess screw sense as in <b>PA-1</b>–<b>PA-3</b>, whereas that <i>meta</i> to the vinyl group failed to dictate the growth of polymer backbone. The achiral end of the side group had a great effect on the optical rotation of polymer. The specific optical rotation of <b>PA-3</b> that bore tertiary butyl groups was over 3 times larger than <b>PA-1</b> and <b>PA-2</b> terminated with hydrogen and fluorine atoms. Accompanied by the existence of helical structure with a predominant screw sense, stable liquid crystalline phases were generated by <b>PA-1</b>–<b>PA-3</b> at above glass transition temperatures but not by <b>PB-1</b>–<b>PB-3</b>. An unusual glass transition temperature and structure relationship was also revealed

Synthesis and Stereospecific Polymerization of a Novel Bulky Styrene Derivative

A novel vinylbiphenyl monomer, 2-methoxy-5-phenyl­styrene (MOPS), was designed and efficiently synthesized to investigate the stereospecific polymerization of bulky and polar styrenic derivative. Regardless of its large side group and electron-donating <i>o</i>-methoxy substituent, this compound showed a high polymerizability and was readily converted to the corresponding polymers with moderate to high molecular mass through radical, anionic, and coordination polymerizations. The resultant polymers were characterized by a combination of ¹H/¹³C NMR spectrometry, thermal analysis, and wide-angle X-ray diffraction. Radical polymerization initiated by AIBN in toluene at 60 °C produced a syndiotactic-rich (<i>rr</i> = 0.37) polymer as most bulky vinyl monomers, whereas anionic polymerizations induced by <i>n</i>-BuLi yielded only isotactic-rich polymers no matter if polar tetrahydrofuran (−78 °C, <i>mm</i> = 0.54) or apolar toluene (−40 °C, <i>mm</i> = 0.78) was employed as the solvent. The isotactic-rich microstructure obtained by anionic polymerization in polar solvent at low temperature, the condition that usually leads to syndiotactic-rich polymer, manifested the strong interactions between the <i>o</i>-methoxy groups of the growing chain end and the penultimate unit with the lithium counterion. Highly isotactic (<i>mm</i> = 0.95) and perfect syndiotactic (<i>rr</i> > 0.99) polymers were obtained via coordination polymerizations in toluene at ambient temperature with the β-diketiminato­yttrium precursor (<b>I</b>) and the heterocyclic-fused cyclo­pentadienyl­scandium complex (<b>III</b>) as the catalytic precursor, respectively. All the polymers were thermally stable with 5% weight loss temperatures above 360 °C. They underwent glass transitions in the temperature range of 124–140 °C depending on the tacticity, much higher than polystyrene, implying the dominant role of congestion effect of large side groups on the segment movement restriction of polymer chain. Both isotactic and syndiotactic polymers were crystalline and had melting points higher than 300 °C, although the atactic and less stereoregular polymers were amorphous. The facile synthesis in conjunction with stereostructure tailorability, high thermal stability, glass transition temperature, and melting point makes the polymer a promising candidate for not only helical functional material but also engineering plastics

Morphology Evolution of Stimuli-Responsive Triblock Copolymer Modulated by Polyoxometalates

Polyoxometalate (POM) H₃PMo₁₂O₄₀ was coassembled with stimuli-responsive triblock copolymer poly­(ethylene oxide)-<i>block</i>-polystyrene-<i>block</i>-poly­(2-(dimethylamino)­ethyl methacrylate) (PEO-<i>b</i>-PS-<i>b</i>-PDMAEMA) by electrostatic interactions. Depending on the POM contents, the hybrid complexes can self-assemble into a series of morphologies: micelles, rods, toroids, and vesicles. Unlike traditional morphology transition of amphiphilic block copolymer derived from a broad range of hydrophobic volume fractions, POM-induced morphology transitions just occurred in a narrow range of volume fractions. The length of rod micelles exponentially decreased with solvent compositions (tetrahydrofuran/H₂O). The hybrid assemblies showed acid–base responsibility due to the PDMAEMA block. Rod micelles could further assemble and disassemble reversibly upon adding acid/base. Fluorescent polyoxometalate Na₉EuW₁₀O₃₆ was also complexed with PEO-<i>b</i>-PS-<i>b</i>-PDMAEMA to prepare fluorescent vesicles. The vesicles showed off–on switchable fluorescence behavior accompanied with reversible vesicle-to-micelle transformation in response to pH stimuli

Helical Conformations of Poly(3,5-disubstituted phenylacetylene)s Tuned by Pendant Structure and Solvent

A series of novel <i>cis</i> poly­(phenylacetylene)­s (PPAs) substituted at the <i>meta</i>-position(s) by both achiral alkoxycarbonyl and chiral alkylamide groups, i.e., <b>rP-I</b>, <b>sP-I</b> to <b>sP-V</b>, or by just a chiral alkylamide group, i.e., <b>rP-VI</b>, were synthesized under catalysis of [Rh­(nbd)­Cl]₂. The dependence of the elongation, screw sense, and stimuli response of helical polyene backbone on the structure and number of substituent was systematically investigated in both solution and solid states. Stretched <i>cis–transoid</i> helices with opposite signs coexisted in the DMF solution of either <b>sP-I</b> or <b>rP-I</b>, but a single handed, contracted <i>cis–cisoid</i> one formed in the mixture of DMF/THF (10/90, v/v). Increasing the substituent size made the polymers <b>sP-III</b>, <b>sP-IV</b>, and <b>sP-V</b> to take only single handed stretched <i>cis–transoid</i> helical conformations regardless of the solvent polarity. The <i>N</i>-methylation of the amide group in <b>sP-II</b> caused a similar effect. With the removal of achiral methoxycarbonyl substituent, <b>rP-VI</b> took just a stretched <i>cis–transoid</i> helical conformation in polar DMF, whereas it existed as a mixture in equilibrium of stretched <i>cis–transoid</i> and contracted <i>cis–cisoid</i> helices with identical screw sense in less polar solvents such as dioxane, THF, and chloroform. The twisting directions of substituent array and polyene backbone were found to be coincident in a dynamic, contracted helix, but the opposite in a less dynamic, stretched helix. These results suggested that the 3,5-disubstitution, strong intramolecular hydrogen bonding, and small substituent favored the formation of contracted <i>cis</i>–<i>cisoid</i> helices for PPAs

Validation of FGG in individual whole serum samples from 20 PD patients and 20 control subjects.

<p>(A) Representative panel of Western blots. (B) The frequency (14/20) of FGG detected in the serum of PD patients. None was detected in controls. Each number in the panels corresponds to an individual normal control or PD patient. Total protein concentration in each sample was determined by Bradford assay. Protein loadings were approximately equal for all samples (20 µg/lane). The immunoglobulin (IgG) was used as a loading control.</p