Self-assembly of coronene bisimides: mechanistic insight and chiral amplification.

The study of the organization of small π-conjugated molecules is imperative to understanding and controlling its properties for various applications. Coronene bisimides (CBIs) are potential candidates for novel liquid-crystalline materials and active n-type semiconductor molecules in organic electronics. To understand the self-assembly of this seldom-studied chromophore, we have designed two derivatives of CBIs bearing chiral and achiral 3,4,5-trialkoxyphenyl groups at the imide position, named as CBI-GCH and CBI-GACH, respectively. CBI-GCH self-assembles mainly through π-stacking and van der Waals interactions in nonpolar methylcyclohexane to result in long 1D fibrillar stacks. The mechanism of supramolecular polymerization was probed by using chiroptical studies, which showed an isodesmic pathway for CBI-GCH. The thermodynamic parameters that govern the self-assembly are detailed. CBI-GACH also shows similar self-assembly behavior as its chiral counterpart. X-ray diffraction studies of both molecules reveals a 2D hexagonal columnar arrangement. The coassembly of CBI-GCH and CBI-GACH shows chiral amplification (sergeant and soldiers experiment) with saturation at 30-50 % of the chiral derivative, which was further used to study the dynamics of the assembly. Thus, this study presents a rare report of chiral amplification in an isodesmic system.

Gallium-containing polymer brush film as efficient supported Lewis acid catalyst in a glass microreactor.

Polystyrene sulfonate polymer brushes, grown on the interior of the microchannels in a microreactor, have been used for the anchoring of gallium as a Lewis acid catalyst. Initially, gallium-containing polymer brushes were grown on a flat silicon oxide surface and were characterized by FTIR, ellipsometry, and X-ray photoelectron spectroscopy (XPS). XPS revealed the presence of one gallium per 2-3 styrene sulfonate groups of the polymer brushes. The catalytic activity of the Lewis acid-functionalized brushes in a microreactor was demonstrated for the dehydration of oximes, using cinnamaldehyde oxime as a model substrate, and for the formation of oxazoles by ring closure of ortho-hydroxy oximes. The catalytic activity of the microreactor could be maintained by periodic reactivation by treatment with GaCl3.

Improved catalytic activity and stability using mixed sulfonic acid- and hydroxy-bearing polymer brushes in microreactors.

Sulfonic acid-bearing polymer brushes were grown on the inner walls of continuous flow glass microreactors and used in the acid-catalyzed hydrolysis of benzaldehyde dimethyl acetal as a test reaction. Randomly 1:1 mixed polymer brushes of poly-3-sulfopropyl methacrylate (PSPM) and poly-2-hydroxyethyl methacrylate (PHEMA) showed a 6-fold increase of the TOF value compared to the solely PSPM-containing microreactor. This remarkable improvement is attributed to the cooperative stabilizing effect of proximal OH groups on the active sulfonic acid moieties within the brush architecture. In fact, the rational mixing of SPM with methyl methacrylate (MMA) as an OH-free comonomer caused a drop in the activity of the resulting catalytic platform. A 5-fold increase of the TON of the 1:1 PSPM-PHEMA versus the PSPM homopolymer brush systems additionally demonstrates the substantial increase in the stability of the mixed brushes catalytic platform, which could be continuously run over 7 days without significant loss of activity. The 1:1 PSPM-PHEMA mixed brush catalytic system also showed a good activity in the deprotection of 2-benzyl tetrahydropyranyl ether.