Selective chiral handedness induced in spin-coated polyaramide films

Abstract

Supramolecular structures are formed by noncovalent interactions such as electrostatic interactions, hydrogen bonding, van der Waals contacts and p-p interactions. Therefore, controlling these noncovalent bonds is an efficient approach to the construction of precise chiral structures. Usually, chiral supramolecular assemblies have been built from chiral molecules or building blocks. 1,2 In specific cases, chiral assemblies can also be obtained from achiral molecules through noncovalent interactions. 3,4 In recent studies, vortices showing a macroscopic chirality have also been regarded as sources of chirality. 5 In fact, electrostatic J-aggregation of a 4-sulfonatophenylporphyrin in aqueous media has demonstrated that the sense of optical activity can be selected using the direction of rotary stirring. [6][7][8][9] The optical activity of a helical ribbon reflected the direction of the chirality induced in a stirred solution. 9 Furthermore, a hydrogen-bonded dendritic porphyrin wire gives a selective and reversible optically active solution, suggesting that rotational stirring is a potential tool for chiral induction. 10,11 The dendritic porphyrin derivatives form optically active films whose enantiometric form is determined by the spinning direction. 11 The noncovalent interaction of these porphyrin systems and hydrodynamic effects has an important role in selecting chiral handedness.We investigated the possibility of a selective induction of optical activity using an artificial polymer system (Figure 1a), which exhibits a lyotropic liquid crystalline (LLC) phase in water. As mentioned above, achiral porphyrin derivatives have successfully formed optically active assemblies from fluid vortexes and spin-coated solutions by controlling their J-aggregation through p-stacking interactions. 12 Herein, we found that the polyaramide films fabricated by spin-coating show optical activity and that their handedness is selected by the spinning direction. Spinning the films changes the direction of the hydrogen bonds that form between the polymers. The simple chemical structure of the polyaramide obtained through a short synthetic procedure makes it useful as a chiral template material.The sulfonated polyaramide (PPSA) used in this study was synthesized by polycondensation between 2-sulfoterephthalic acid and 1, 4-phenylenediamine. 13 Despite a rigid structure composed of mainchain aromatic and amide groups, PPSA was dissolved in water because of the hydrophilic inverted sulfonic acid. The solutions became viscous over 2.0 wt% of PPSA and changed into gels when the concentration of solution reached 3.0 wt% (Figure 1b). When viewed with polarizing optical microscopy, the sample solutions showed typical LC (liquid crystal) textures (Figure 1c) for concentrations exceeding the critical value of 0.6 wt%. The gelled samples also showed an LC phase, suggesting that hydrogen bonding participates in the construction of a highly ordered LC phase.We used circular dichromism (CD) spectroscopy to probe the degree of optical activity ...

Formation of Chiral Environments by a Mechanical Induced Vortex Flow

“…Based on this knowledge, we investigated the possibility of a selective induction of optical activity, using an artificial oligomer 5 (Figure 11), which exhibits a lyotropic LC phase in water. [24] As expected, films prepared from the aqueous lyotropic LC phase (>1.0wt %) were optically active, whereas the ones prepared from isotropic solutions (0.5 wt %) were silent. [24] As expected, films prepared from the aqueous lyotropic LC phase (>1.0wt %) were optically active, whereas the ones prepared from isotropic solutions (0.5 wt %) were silent.…”

“…The spin-coated films were analyzed by CD spectroscopy to probe the degree of optical activity and their handedness ( Figure 12). [24] As expected, films prepared from the aqueous lyotropic LC phase (>1.0wt %) were optically active, whereas the ones prepared from isotropic solutions (0.5 wt %) were silent. To further support these results, the statistical distribution of direction was evaluated.…”

“…The films were obtained from different aqueous concentrations: a) 3.0 wt %; b) 2.0 wt %; c) 1.0 wt % and d) 0.5 wt %. Reproduced with permission from ref [24]…”

Outstanding Chiroptical Features of Thin Films of Chiral Oligothiophenes

“…found two enantiomeric supramolecular architectures, resulting in opposite ECD spectra, for film samples of dendritic zinc porphyrin J ‐aggregates depending on spinning direction . More recently, the same behaviour was found for spin‐coated polyaramide films, when the original solution would consist in a lyotropic liquid crystalline phase, although no ECD was recorded upon spin coating an isotropic solution . Unfortunately, in most of the cases cited above, the simple test of sample flipping was not reported.…”

“…[37] More recently, the same behaviour was found for spin-coated polyaramide films, when the original solution would consist in a lyotropic liquid crystalline phase, although no ECD was recorded upon spin coating an isotropic solution. [38] Unfortunately, in most of the cases cited above, the simple test of sample flipping was not reported.…”