Evidence for Kinetic Nucleation in Helical Nanofiber Formation Directed by Chiral Solvent for a Perylene Bisimide Organogelator

Abstract

The self-assembly behavior of an achiral perylene bisimide (PBI) organogelator that bears two 3,4,5-tridodecyloxybenzoylaminoethyl substituents at the imide positions has been investigated in chiral solvents (R)- and (S)-limonene in great detail by circular dichroism (CD) spectroscopy and atomic force microscopy (AFM). CD spectroscopic studies on dilute solutions revealed a preferential population of one-handed helical assemblies in chiral solvent with an enantiomeric excess close to 100 %, whereas AFM images of more than 100 nanofibers of the organogel obtained from more concentrated solutions were found to consist of both handed helices with an enantiomeric excess of only 20 %. This discrepancy is attributed to the fast gelation process at high dye concentration that evidently proceeds through non-equilibrated nuclei in a kinetic rather than thermodynamic self-assembly process. Under these conditions the chiral induction from the homochiral solvent may not be adequate in effectively populating only one-handed helices.

Chiral Perylene Diimides: Building Blocks for Ionic Self‐Assembly

“…These conditions can be used to establish non‐equilibrium conditions, thus enabling control over kinetic or thermodynamic pathways of self‐assembly to obtain structures of desired helicity 48. Factors that promote a fast aggregation rate, such as rapid cooling and high concentration, can lead to self‐assembly processes that occur by a kinetically controlled pathway 49. This behaviour has been demonstrated recently by investigations in which tuneable helicity of PDI materials was achieved by employing non‐equilibrium conditions using solvent,17 ultrasound,36b, 50 and concentration 51.…”

Size evolution of highly amphiphilic macromolecular solution assemblies via a distinct bimodal pathway

“…cooperative self-assembly). Cooperative self-assembly processes have been reported in numerous systems including proteins 49 , peptide-based molecules 50 , small molecules 49,51 , and nanoparticles 52 and are characterized by a bimodal distribution of small oligomers and larger aggregates. In our system, the small micelles may fuse to form metastable intermediates, which then rapidly fuse with additional smaller micelles to produce a bimodal size distribution.…”

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

“…[267] More rigid columnar PBI aggregates were envisioned by enforcing a particular arrangement by additional hydrogenbonding connectivities (Figure 19). [268] Whilst a multitude of such PBI dyes has been synthesized and investigated particularly with regard to their gelator properties, [269,270] PBIs 3-6 are sufficient to illustrate the concept. PBI 3 and PBI 4 comprise the parent core-unsubstituted PBIs, while in PBI 5 and PBI 6 tetraphenoxy-bay-substituted PBI scaffolds are utilized.…”