Intermolecular Association and Supramolecular Organization in Dilute Solution. 2. Light Scattering and Optical Activity of Poly(p-biphenylylmethyl l-glutamate)

Investigations of the Alignment Process of PBPMLG: 2 H NMR Analysis Reveals a Thermoresponsive 90° Flip of the Polymer

The application of anisotropic parameters in NMR-spectroscopy enables the acquisition of spatial and angular information, complementary to those from conventional isotropic NMR-measurements. The use of alignment media is a well-established method for inducing anisotropy. PBPMLG is a recently discovered polyglutamate-based alignment medium, exhibiting thermoresponsive behavior in the lyotropic liquid crystalline (LLC) phase, thus offering potential for deeper understanding of the alignment process. We present one approach for investigating the thermoresponsive behavior by synthesizing specifically deuterated PBPMLG-isotopologues and their subsequent analyses using 2 H NMR-spectroscopy. It was possible to relate the observed thermoresponsive behavior to a flip of the polymer with respect to the external magnetic field-an effect never observed before in glutamate-based polymeric alignment media. Furthermore, a solvent-induced temperature dependent gelation was verified in THF, which might provide yet another opportunity to manipulate the properties of this alignment medium in the future.

Large-Scale Supramolecular Structure in Solutions of Low Molar Mass Compounds and Mixtures of Liquids. III. Correlation with Molecular Properties and Interactions

The presence of a large-scale supramolecular structure is evidenced in a large variety of electrolyte solutions, nonelectrolyte solutions, and mixtures of liquids. This structure comprises submicron-sized domains with different solute concentration from that in the rest of solution. While the first paper of this series [J. Phys. Chem. B 2006, 110 (9), 4329-4338] dealt with a detailed characterization of the supramolecular structure and the second paper [J. Phys. Chem. B 2006, 110 (9), 4339-4345] dealt with the kinetics of the formation of this structure and its long-time stability, the present work contains a detailed classification of systems with respect to the capability of formation of the supramolecular organization. Around 100 different solute-solvent pairs were investigated in total, covering most common inorganic and organic electrolytes, nonionic solid compounds, and a large variety of liquids. The main experimental techniques used were static and dynamic light scattering, which are very effective techniques in observing and characterizing association. Light scattering data were complemented by osmotic pressure data obtained by vapor pressure osmometry, which reflects association on a different principle. The presence and intensity of the supramolecular domain organization was correlated with properties and interactions between constituent molecules and ions. The most plausible explanation of the observed effect of the large-scale supramolecular structure at this stage of our knowledge is that domains form due to directional attractive interactions between solute molecules via hydrogen bond bridges formed by one or several solvent molecules, which are themselves hydrogen bonded.

Poly(thiaheterohelicene): A Stiff Conjugated Helical Polymer Comprised of Fused Benzothiophene Rings

A novel helical aromatic polymer comprised of fused benzothiophene rings, poly(thiaheterohelicene), was synthesized via an intramolecular ring-closing reaction with a controlled helicity to one-sided bias. The synthetic helicity control involved the induction of the helical conformation and its fixation. The ladder polymer showed both an extended pi-conjugation and planarity and a very stiff helical structure. [structure: see text]

Solvent and temperature effects on the chiral aggregation of poly(alkylarylsilane)s bearing remote chiral groups

Novel switchable chiroptical characteristics of poly(alkylarylsilane) microaggregates, controllable by the choice of good/poor solvent ratio (solvent polarity), solvent addition order, and sample temperature are described. The formation of stable chiral aggregates depends critically on the polysilane structure and stereochemistry. Poly[n-hexyl-(p-(S)-2-methylbutoxyphenyl)silane] (1), optically inactive in molecularly dispersed THF solution due to the existence of dynamically equivalent amounts of right (P)- and left (M)-handed screw sense helical main chain domains, shows a marked bisignate CD signal due to the formation of chiral aggregates in good/poor cosolvent systems. The sign and magnitude of the CD signals are dependent on solvent polarity, solvent addition order, and thermal effects. The less sterically hindered poly[methyl-(p-(S)-2-methylbutoxyphenyl)silane] (2) exhibits a weak, bisignate, nonswitchable CD signal in only the toluene/acetonitrile system, and no CD signals are evident in pure toluene or THF due to masking of the helicity. In contrast, although the even less sterically hindered, less polar poly[methyl-(m-(S)-2-methylbutoxyphenyl)silane] (3) does show optical activity in pure THF or toluene (negative CD signal at 310 nm), the CD signal disappears on formation of aggregates in good/poor cosolvent systems.