Weak noncovalent Si···F?C interactions stabilized fluoroalkylated rod-like polysilanes as ultrasensitive chemosensors

Noncovalent interactions, such as hydrogen bonding, metal coordination, and π-π stacking, are increasingly being utilized to develop well-ordered and self-organized supramolecular materials. Recently, new types of nonclassical weak interactions, such as C H···π, C H···F C, and C H···O, have been exploited in stabilizing the specific conformations of molecules and molecular assemblies in the solid state. These noncovalent interactions play an important role in materials comprised of polymer chains, because cooperative effects from a large number of weak interactions can lead to drastic changes in its conformation, several properties, and functionalities. The programmed design of synthetic helical polymer with well-defined molecular conformation has been the main subject in modern polymer science and engineering. Silicon-catenated polysilane is an ideal helical silicon quantum wire and polymers with unique photophysical properties. The present review highlights the spectroscopic evidences for through-space weak Si···F C interaction in poly(methyl-3,3,3-trifluoropropylsilane) ( 1 ) in noncoordinating and coordinating solvents by means of NMR (²⁹Si and ¹⁹F) and IR spectroscopies, and viscometric measurement. It was found that 1 is applicable for chemosensors with an extremely high sensitivity and selectivity toward fluoride ions in tetrahydrofuran (THF) and with high sensitivity for nitroaromatic compounds, detected by a decrease in the photoluminescence intensity in THF and in thin solid film. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5060–5075, 2006     

Solid-state optical properties of a chiral supramolecular fluorophore consisting of chiral (1R,2R)-1,2-diphenylethylenediamine and fluorescent carboxylic acid derivatives

By using (1R,2R)-1,2-diphenylethylenediamine as a chiral molecule and 2-anthracenecarboxylic acid as a fluorescent molecule, we created a chiral supramolecular organic fluorophore having circularly polarized luminescence properties in the solid-state.     

Control of chiral ordering in aggregated poly[3-(S)-[2-methylbutyl]thiophene] by a doping-dedoping process

The chiral ordering in aggregated poly(3-alkylthiophene) can be controlled by a metal salt-dependent doping-dedoping process. Enhancement or reduction in the chiral anisotropy factor depends on the doping level, such that doping driven by polymer-metal salt interactions, and dedoping driven by aggregate formation must be balanced in order to achieve maximal chiral ordering. This phenomenon provides a new basis to control chiral arrangement in conjugated polymer aggregates, relying solely on doping, and thus avoiding tedious modification of side-chain or main-chain structures.     

Cooperative C-F...Si interaction in optically active helical polysilanes

Cooperative amplification of the C-F...Si weak interaction between side chains and the main chain was found to afford rigid rodlike helical polysilanes with a preferential screw sense.     

Supramolecular chirogenesis in zinc porphyrins: equilibria, binding properties, and thermodynamics

Complexation mechanism, binding properties and thermodynamic parameters of supramolecular chirality induction in the achiral host molecule, syn (face-to-face conformation) ethane-bridged bis(zinc porphyrin), upon interaction with chiral monoamine and monoalcohol guests have been studied by means of the UV-vis, CD, (1)H NMR, and ESI MS techniques. It was found that the chirogenesis process includes three major equilibria steps: the first guest ligation to a zinc porphyrin subunit of the host (K(1)), syn to anti conformational switching (K(S)), and further ligation by a second guest molecule to the remaining ligand-free zinc porphyrin subunit (K(2)), thus forming the final bis-ligated species possessing supramolecular chirality. The validity of this equilibria model is confirmed by the excellent match between the calculated and experimentally observed spectral parameters of the bis-ligated species. The second ligation proceeds in a cooperative manner as K(2) > K(1) for all supramolecular systems studied, regardless of the structure of the chiral ligand used. The binding properties are highly dependent on the nature of the functional group (amines are stronger binders than alcohols) and on the structure of the chiral guests (primary and aliphatic amines have overall binding constant values greater than those of secondary and aromatic amines, respectively).     

Steady-state and nanosecond spectroscopic studies of triplet sensitized reaction of K-region arene oxides

Photorearrangement reactions of K-region arene oxides, 9,10-epoxy-9,10-dihydrophenanthrene (1a), 3-acetyl-9,10-epoxy-9,10-dihydrophenanthrene (1b), and 3,4-epoxy-3,4-dihydropyrene (1c) in dichloroethane (DCE) solution were investigated by steady irradiation and nanosecond transient spectroscopy. Photorearrangements producing substituted oxepins, 2 occur via the singlet excited state of these compounds, while the phenolic products, 9-hydroxyphenanthrene (3a), 3-acetyl-9-hydroxyphenanthrene (3b), and 4-hydroxypyrene (3c) are formed via the triplet state. Phenol 3 formation from the triplet 1 sensitized by the triplet 3 (i.e. product sensitization) is proposed for the photorearrangement reactions of 1a and 1c, and this process is the only way phenol (3a) is formed because of the negligible intersystem crossing probability of 1a. No product sensitization occurs in the photorearrangement reaction of 1b.     

Heteroatom Polysilylenes

Heteroatom polysilylenes with Cl, OR and NR₂ substituents attached to the silicon chain through the heteroatom are described. The relationship between the single crystal X-ray structures of octachlorocyclotetrasilane Si₄Cl₈ and perchloropolysilylene, (SiCl₂)_n, is discussed with reference to possible mechanisms for its phototopochemical synthesis from Si₄Cl₈. Substitution with alcohols yields the bis(alkoxy)polysilylenes, and the origin of the red-shifted UV spectra are discussed in terms of the electronic interaction between oxygen n and silicon orbitals. Substitution with secondary amines yields soluble, yellow polymers with even longer wavelength UV absorption maxima. Effects of the alkyl chain length on hydrolytic stability are considered.