Helical Polysilane Research Articles

Synchronization in Non-Mirror-Symmetrical Chirogenesis: Non-Helical π–Conjugated Polymers with Helical Polysilane Copolymers in Co-Colloids

A curious question is whether two types of chiroptical amplifications, called sergeants-and-soldiers (Ser-Sol) and majority-rule (Maj) effects, between non-charged helical copolymers and non-charged, non-helical homopolymers occur when copolymer encounter homopolymer in co-colloids. To address these topics, the present study chose (i) two helical polysilane copolymers (HCPSs) carrying (S)- or (R)-2-methylbutyl with isobutyl groups as chiral/achiral co-pendants (type I) and (S)- and (R)-2-methylbutyl groups as chiral/chiral co-pendants (type II) and (ii) two blue luminescent π-conjugated polymers, poly[(dioctylfluorene)-alt-(trans-vinylene)] (PFV8) and poly(dioctylfluorene) (PF8). Analyses of circular dichroism (CD) and circularly polarized luminescence (CPL) spectral datasets of the co-colloids indicated noticeable, chiroptical inversion in the Ser-Sol effect of PFV8/PF8 with type I HCPS. PF8 with type IIHCPS showed the anomalous Maj rule with chiroptical inversion though PFV8 with type IIHCPS was the normal Maj effect. The noticeable non-mirror-symmetric CD-and-CPL characteristics and marked differences in hydrodynamic sizes of these colloids were assumed to originate from non-mirror-symmetrical main-chain stiffness of HCPSs in dilute toluene solution. The present chirality/helicity transfer experiments alongside of previous/recent publications reported by other workers and us allowed to raise the fundamental question; is mirror symmetry on macroscopic levels in the ground and photoexcited states rigorously conserved?

Dilated Smectic Liquid Crystal of Polystyrene-block-polysilane-block-polystyrene Copolymer Synthesized by Atom Transfer Radical Polymerization

A polystyrene-block-polysilane-block-polystyrene copolymer was synthesized by atom transfer radical polymerization (ATRP) to show a dilated smectic liquid crystal that has been theoretically well simulated for end-tethered rod-like particles. The Si-H end groups of the rigid rod-like helical polysilane synthesized by Wurtz-type condensation, with a narrow molecular weight distribution, were successfully functionalized with the ATRP initiator, followed by ATRP of the styrene monomer to give a coil-rod-coil triblock copolymer with a well-defined structure.

Infrared emissivity property study and conformational analysis of helical polysilane

ABSTRACTLeft and right single‐handed helical polysilane (L‐HPS and D‐HPS) and racemic helical polysilane (R‐HPS) were synthesized by the Wurtz‐type coupling reaction. The chiral dichloro(methoxycarbonyl ethyl propyl ether)methylsilane monomers applied in copolymerization were derived from methyl d/l‐lactate. The obtained polymers were characterized by 1H and 13C nuclear magnetic resonance, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, circular dichroism spectroscopy, gel permeation chromatography and X‐ray diffraction. Infrared emissivity (IRE) values were also investigated. Compared to R‐HPS, L‐HPS, and D‐HPS, a pair of mirror image, showed higher crystallinity, better thermal stability, and lower IRE (8–14 mm) at the values of 0.592 and 0.576, respectively. The higher regular secondary structure of HPSs was attributed to the formation of intermolecular hydrogen bonds. To further study the configurations of L‐HPS, D‐HPS, and R‐HPS, rotational isomeric state scheme with molecular dynamics simulation have been utilized. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46335.

Helical polysilane coating onto hollow spherical indium oxide: Fabrication, characterization and infrared emissivity property study

A new-type of composite combined by helical polysilane (HPS) and hollow spherical indium oxide (In2O3) was designed and fabricated via solution blending. The hollow spheres constructed by In2O3 particles were synthesized via a facile hydrothermal route where it demonstrated larger surface area, enabling the combination of HPS and In2O3 more easily. Meanwhile, the synergetic effect between functional group of HPS and surface hydroxyl of In2O3 improve the reduction of infrared emission. Consequently, the composite shows a superior low infrared emissivity performance at the value of 0.416 (8–14 μm), and the covering of HPS make the composite disperse well in the polar reagent. This work develops a feasible strategy that utilizes metallic oxide to design and synthesize hollow spherical matrix for preparing the low infrared emissivity materials.

Aggregation-induced scaffolding: photoscissable helical polysilane generates circularly polarized luminescent polyfluorene

An enantiopair of rigid rod-like helical polysilanes as a photoscissible scaffold allowed the production of CPL- and CD-active dioctylpolyfluorene aggregates associated with complete removal by a polysilane-selective photoscissoring reaction at 313 nm.

Helical polysilane wrapping onto carbon nanotube: preparation, characterization and infrared emissivity property study

Morphological, structural and infrared emissivity properties of HPS/f-MWNTs complexes prepared by the solution blending method were investigated.

Novel design, facile synthesis and low infrared emissivity properties of single-handed helical polysilanes

Helical polysilane copolymers, consisting of functional groups, were prepared and exhibited lower infrared emissivity values at wavelengths from 8 to 14 μm. The properties of helical polysilanes were systematically investigated.

Circularly Polarized Light Enhancement by Helical Polysilane Aggregates Suspension in Organic Optofluids

Circularly polarized (CP) light may play key roles in the migration and delocalization of photoexcited energy in optically active macroscopic aggregates of chiral chlorophylls surrounded by an aqueous fluid in the chloroplasts under incoherent unpolarized sunlight. Learning from the chiral fluid biosystem, we designed artificial polymer aggregates of three highly luminescent helical polysilanes, 1-S, 2-S, and 2-R (Chart 1). Under specific conditions (molecular weights and good-and-poor solvent ratio), 1-S aggregates with ∼5 μm in organic fluid generated an efficient circularly polarized luminescence (CPL) with gCPL = −0.7 at 330 nm while retaining a high quantum efficiency (ΦPL) ∼53% at room temperature under incoherent unpolarized photoexcitation at 290 nm. This huge gCPL value was the consequence of the intense bisignate circularly dichroism (CD) signals (gCD = −0.35 at 325 nm and +0.31 at 313 nm) due to coupled oscillators with electric-dipole-allowed-transition origin. Also, 2-S and 2-R aggregates gav...

Mirror Symmetry Breaking in Helical Polysilanes: Preference between Left and Right of Chemical and Physical Origin

From elemental particles to human beings, matter is dissymmetric with respect to mirror symmetry. In 1860, Pasteur conjectured that biomolecular handedness— homochirality—may originate from certain inherent dissymmetric forces existing in the universe. Kipping, a pioneer of organosilicon chemistry, was interested in the handedness of sodium chlorate during his early research life. Since Kipping first synthesized several Si-Si bonded oligomers bearing phenyl groups, Si-Si bonded high polymers carrying various organic groups—polysilanes—can be prepared by sodium-mediated condensation of the corresponding organodichlorosilanes. Among these polysilanes, optically active helical polysilanes with enantiomeric pairs of organic side groups may be used for testing the mirror symmetry-breaking hypothesis by weak neutral current (WNC) origin in the realm of chemistry and material science. Several theoretical studies have predicted that WNC-existing chiral molecules with stereogenic centers and/or stereogenic bonds allow for distinguishing between image and mirror image molecules. Based on several amplification mechanisms, theorists claimed that minute differences, though still very subtle, may be detectable by precise spectroscopic and physicochemical measurements if proper chiral molecular pairs were employed. The present paper reports comprehensively an inequality between six pairs of helical polysilane high polymers, presumably, detectable by (chir)optical and achiral 29Si-/13C- NMR spectra, and viscometric measurements.

First observation of a smectic A–cholesteric phase transition in a thermotropic liquid crystal consisting of a rigid-rod helical polysilane

A smectic A–cholesteric phase transition for a rigid-rod helical polymer, poly[n-decyl-(S)-2-methylbutylsilane] (PD2MBS), with a narrow molecular weight distribution, has been observed for the first time. Polarizing optical microscopy showed that the fan-shaped texture of the smectic A phase turned into the characteristic planar texture of the cholesteric phase upon heating. The positive CD band, which corresponds to the reflection band of the cholesteric phase, gradually decreased in intensity within a range 30°C below the transition temperature on cooling, while the peak maximum shifted towards shorter wavelengths. It was concluded that the system has a very wide temperature region over which the cholesteric–smectic A phase transition occurs and in which the cholesteric pitch varies with temperature.

Small-Angle X-Ray Analysis of Smectic a Cholesteric Liquid Crystal Phase Transition in Rigid-Rod Helical Polysilane

The smectic A Cholesteric liquid crystal phase transition of rigid-rod helical polysilane was studied by means of synchrotron radiation small-angle X-ray scattering (SR-SAXS). The information on the smectic trans-layer electron density distribution was clarified by fitting the model of electron density distribution to the diffraction data. Each of the layers was approximated by the boxlike function to introduce the molecular form factor of the polymer. The distribution of the molecular center of gravity within the layers due to the thermal motion was taken into consideration by convolution with the Gaussian function. The elucidated smectic layer structure was not like the conventional structure with their ends packed into the interlayer space. The layers with bumpy surfaces interdigitate in a key-and-keyhole manner to pack the molecules with different lengths into layers due to their finite molecular weight distribution.

Well-Defined Phase Sequence Including Cholesteric, Smectic A, and Columnar Phases Observed in a Thermotropic LC System of Simple Rigid-Rod Helical Polysilane

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTWell-Defined Phase Sequence Including Cholesteric, Smectic A, and Columnar Phases Observed in a Thermotropic LC System of Simple Rigid-Rod Helical PolysilaneKento Okoshi, Hiroyuki Kamee, Goro Suzaki, Masatoshi Tokita, Michiya Fujiki, and Junji WatanabeView Author Information Department of Polymer Chemistry, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8552, Japan; Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan; and CREST-JST (Japan Science and Technology Corporation), 4-1-8 Hon-cho, Kawaguchi, Saitama 332-0012, Japan Cite this: Macromolecules 2002, 35, 12, 4556–4559Publication Date (Web):May 4, 2002Publication History Received26 November 2001Revised7 March 2002Published online4 May 2002Published inissue 1 June 2002https://doi.org/10.1021/ma012056zCopyright © 2002 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views538Altmetric-Citations53LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (136 KB) Get e-AlertsSUBJECTS:Layers,Liquid crystals,Materials,Molecules,Physical and chemical properties Get e-Alerts

Thermo-driven chiroptical switching polysilane featuring 2-cyclopentylethyl side group

A new rod-like helical polysilane, poly{(S)-3,7-dimethyloctyl-(2-cyclopentylethyl)silane}, was found to undergo a thermo-driven, helix-helix transition at –33 ° C in isooctane associated with the discontinuous changes in the Siσ -Siσ *transition energy and intensity in the transition temperature region. This is the first example of a helix-helix transition polysilane with a cycloalkyl group. A similar rod-like polysilane derivative, poly{(S)-3,7-dimethyloctyl-(1-cyclopentylmethyl)silane}, however, did not undergo any helix-helix transition between –61 and 80 ° C.

First Observation of Thermotropic Cholesteric Liquid Crystal in Helical Polysilane

First Observation of Thermotropic Cholesteric Liquid Crystal in Helical Polysilane

Highly Oriented Langmuir−Blodgett Films of Helical Polysilanes and Their Optical Properties

Thin films of a helical polysilane with chiral substituents were fabricated using a Langmuir−Blodgett (LB) method. The polarized absorption and photoluminescence spectra show the high anisotropy for the LB films with the polymer backbone lying in-plane along the dipping direction. The anisotropy of the lowest exciton absorption band can be enhanced by annealing the LB films. With use of the oriented LB film, we have revealed the one-dimensional exciton structures characteristic of polysilanes with helical conformations by measurements of electroabsorption spectra, compared with those of polysilanes of other conformations such as trans-planar and alternating trans-gauche backbone structures. The large binding energies of the lowest exciton are generic in the one-dimensional regular polysilanes, irrespective of the conformations.

Photoluminescence from pendant dye molecules mediated by exciton transport on helical polysilane chains

We have synthesized helical polysilanes on which the pendant groups are partly substituted by dye molecules. The introduction of a few percent of dye molecules into the substituents enhances the luminescent efficiency of the visible region, by behaving as luminescence centers. We have demonstrated that the excitation energy is transferred efficiently by free excitons on the Si backbones to reach the luminescence centers, where energy transfer occurs from the exciton to the dye molecule, and as a result sensitized luminescence occurs. The exciton transfer is found to occur over 50–100 monomer units on the polysilane backbone. This approach will open the way to fabricating a wavelength-tunable luminous device by utilizing the exciton transport on Si chains.

Near-UV, circular dichroism, and fluorescence spectra of a rigid rodlike helical polysilane bearing trietheral moiety in ethanol/water.

An optically active, rigid rodlike helical polysilane with 6, 9, 12-trioxatetradecyl and (S)-2-methylbutyl substituents (1) was newly obtained as a very high molecular weight polymer of several million. Due to the presence of trietheral substituent, 1 was readily soluble in a polar solvent such as ethanol and a mixture of ethanol and water, but was insoluble in pure water. Polysilane 1 in pure ethanol at room temperature exhibited an intense and narrow ultraviolet (UV) and circular dichroism (CD) absorptions at 323 nm, associated with an almost mirror imaged fluorescence (FL) at 328 nm, that are characteristics of rigid rodlike, single-screw-sense helical polysilanes reported previously. When solution temperature was changed from 60 degrees C to -104 degrees C, a global shape of 1 expanded associated with an increase of segment length, whereas a screw pitch tended to be wound tightly. On the other hand, as a solvent polarity became poor, a global shape of 1 shrunk associated with an decrease of segment length and formed a chiral motif with an M-helicity between two helical segments with a kink. At a ratio of 50% of ethanol/water of 50:50 (v/v), 1 became insoluble and formed aggregates.

Effect of main chain length in the exciton spectra of helical-rod polysilanes as a model of a 5 Å wide quantum wire

Helical polysilane rods were regarded as a soluble, polymeric model of a quantum wire with a ∼5 Å width. Spectral characteristics of the lowest exciton band of the helix located at ∼4 eV in isooctane at 20 °C were first measured as a function of a wire length varying from ∼35 Å to ∼3000 Å. Both the extinction coefficient and the circular dichroism coefficient were found to tend to increase linearly as the logarithm of the wire length increases, whereas the exciton energy and the spectral band width approached limiting values.