Achiral Polydialkylsilane Aggregates That Record Stirring Direction

Abstract

Achiral polysilane aggregates can recognize the chirality of low-molecular-weight compounds. It was found that they can also record the stirring direction. Poly(n-decyl-2-methylpropylsilane), poly(n-nonyl-2-methylpropylsilane), poly(n-decyl-2-ethylbutylsilane), and poly(n-decyl-(S)-2-methylbutylsilane) aggregates were prepared in a mixture of tetrahydrofuran/isopropanol. Although the optical activity of the aggregates of the polysilane with chiral side chains was not tunable by changing the direction of the vortex flow, that of the aggregates of the optically inactive polysilane had a strong relationship to the direction, time, and rate of the vortex flow. The chiral stacked polysilanes were proposed to exist at the surfaces of the aggregates. The optically inactive polysilanes also exhibited optical activity under shear force with a distinct signal in the linear dichroism (LD) spectra of the achiral aggregates in vortex flows. However, the LD signals did not have a significant influence on the circular dichroism signals.

Outstanding Chiroptical Features of Thin Films of Chiral Oligothiophenes

“…However, a more important aspect to investigate is the influence of deposition technique: on the one hand drop casting is generally performed with a slow solvent evaporation and it hardly produces homogeneous films; on the other hand, spin coating results in a fast deposition, where solution is very quickly spread on a thin layer, from which the solvent immediately evaporates . It is well known that hydrodynamic forces in stirred solutions (i. e. flow vortices) can induce chirality in supramolecular species of J ‐aggregates . Therefore, the spin coating technique can play a fundamental role in generating chiroptical properties of thin films: Aida et al .…”

Symmetry Breaking and Amplification in a Self-Assembled Helix from Achiral trans-3-Nitrocinnamic Acid

“…Homochirality in the biological system, that is, almost all of the amino acids and sugars found in living organisms are of L- and D-type, respectively, is one of the most mysterious phenomena found in life. − It is generally believed that the homochirality evolves in consecutive steps starting from the mirror symmetry breaking of a minute enantiomeric imbalance, subsequent chiral amplification for the enantiomeric enrichment, and chiral transfer. − In the last two decades, symmetry breaking , has been found in crystals and supramolecular assemblies such as liquid crystals, , dye aggregates, − amphiphile assemblies, , Langmuir monolayers as well as two-dimensional assemblies, − and supramolecular gels. ,,, In some of the systems, not only the circular dichroism (CD) spectra but also helical structures could be observed . During the symmetry breaking, the noncovalent bond, in particular, hydrogen bond, plays an important role.…”

Chirality-Driven Parallel and Antiparallel β-Sheet Secondary Structures of Phe–Ala Lipodipeptides

“…However, the precise control of the chirality of supramolecular nanostructures is still of interest. Early research indicated that the chirality of supramolecular aggregates could be finely tuned by alternating the side groups, , changing the solvent (or solvent composition), − modulating the pH value, and controlling the direction of stirring, additives, , ultrasonification, and temperature. , Moreover, in the case of self-assemblies constructed by achiral molecules, the addition of a small number of chiral molecules is known to induce the formation of chiral supramolecular nanostructures. A similar phenomenon has also been observed for artificial polymers. , …”