Fibril Film Formation of Pseudoenantiomeric Oxymethylenehelicene Oligomers at the Liquid–Solid Interface: Structural Changes, Aggregation, and Discontinuous Heterogeneous Nucleation

Abstract

Oxymethylenehelicene (P)- and (M)-oligomers up to a nonamer were synthesized by a building block method. The oligomers formed dimeric homoaggregates in trifluoromethylbenzene. A mixture of the pseudoenantiomeric (P)-pentamer and (M)-hexamer formed a heteroaggregate, which self-assembled into one-dimensional fibril films at the liquid-solid interface. Discontinuous heterogeneous nucleation occurred, which involved the formation of particles that were 50 nm in diameter and subsequent fibril growth from these particles. The fibril film was formed on the solid surface and the molecules remained dissociated in solution. The fibril film formation was affected by seeding and the solid surface materials.

Equilibrum and Nonequilibrium Chemical Reactions of Helicene Oligomers in the Noncovalent Bond Formation

“…25 The oligomers were sequentially synthesized from monomer, dimer, trimer, and higher oligomers, and their properties were systematically examined with regard to the helicene number, which showed discontinuous phenomena: Above certain numbers of the helicene unit, the oligomers formed dimeric aggregates in solution. The helicene oligomers, except for the amide derivatives, sharply responded to temperature changes, which reversibly associated on cooling and dissociated on heating, being the equilibrium-to-equilibrium chemical reactions.…”

Mechanical Stirring Induces Heteroaggregate Formation and Self‐assembly of Pseudoenantiomeric Oxymethylene Helicene Oligomers in Solution

“…A trifluoromethylbenzene solution (5 mL) of a pseudoenantiomeric 1:1 mixture of ( P )‐ 5 and ( M )‐ 6 (total, 0.5 mM) in a cylindrical glass vial (diameter, 21 mm) was heated at 80 °C for 3 min, and dissociated random coils were obtained . Then, the solution was cooled to 25 °C to produces a metastable solution, which was mechanically stirred in a clockwise direction with an oval‐shaped Teflon magnetic stirring bar (0.4 g weight) at a rate of 2000 rpm.…”

“…In response to mechanical stirring at 25 °C, heteroaggregates were formed by the ( P )‐ 5 /( M )‐ 6 system in solution, followed by self‐assembly. Thus, different molecular and self‐assembled structures were formed in the ( P )‐ 5 /( M )‐ 6 system under different conditions: Mechanical stirring formed heteroaggregates and self‐assembly materials in solution at 25 °C; contact with solid surfaces without mechanical stirring formed heteroaggregates and fibril films on the surface at 5 °C . It was also noted that the heteroaggregates and self‐assembly materials yielded enantiomeric CD spectra indicating enantiomeric structures of the heteroaggregates (Figure S8).…”

“…It was shown that the oligomers with two‐atom linkers such as acetylene, amide, sulfonamide, aminomethylene, and oxymethylene groups exhibited different properties. Among the oligomers, hetero‐double‐helix formed by oxymethylene oligomers ( P )‐ 5 /( M )‐ 6 self‐assembled on the solid surface, which were not observed with other oligomers: surface contact induced the hetero‐double‐helix formation from metastable dissociated random‐coil solution followed by thin film formation. The present study describes a different self‐assembly of the oxymethylene oligomers ( P )‐ 5 /( M )‐ 6 by mechanical stirring.…”

“…Previously, we reported the structural change of oxymethylene helicene oligomers in solution from random coils at high temperatures to homo‐helix‐dimers at low temperatures . It was also shown that 1:1 mixtures of the pseudoenantiomeric oxymethylene helicene ( P )‐pentamer ( P )‐ 5 and ( M )‐hexamer ( M )‐ 6 , being enantiomeric oligomers with different helicene numbers, formed heteroaggregates at the liquid‐solid interface at 5 °C which then self‐assembled to form fibril films on a solid surface (Figure ).…”