Influence of the Solvent and the Enantiomeric Purity on the Transition between Different Supramolecular Polymers

• Published in: Chemistry : a European journal 2012-11, Vol.18 (47), p.15057-15064
• Main Authors: Wolffs, Martin, van Velthoven, Juliën L. J., Lou, Xianwen, Bovee, Ralf A. A., Pouderoijen, Maarten, van Dongen, Joost L. J., Schenning, Albertus P. H. J., Meijer, E. W.
• Format: Article
• Language: English
• Subjects: Chemistry; Chromatography; cooperative effects; Macromolecular Substances - chemical synthesis; Macromolecular Substances - chemistry; majority rules; Molecular Structure; Polymerization; Polymers - chemical synthesis; Polymers - chemistry; self-assembly; size exclusion chromatography; Solvents - chemistry; Stereoisomerism; supramolecular chemistry; Thermodynamics
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201200984

The self‐assembly of two enantiomerically pure hexa(oligo (p‐phenylene vinylene))‐substituted benzenes having 24 stereocenters was studied in pure methylcyclohexane (MCH) and in a mixture of MCH/toluene (4:1). Irrespective of the solvent a cooperative supramolecular polymerization mechanism was determined for these star‐shaped molecules by using temperature‐dependent CD and UV/Vis spectroscopy. Quite remarkably, a transition from one helical supramolecular state (A) to a second more thermodynamically stable supramolecular helical assembly (B) was observed. The rate of the A→B transition was strongly dependent on the nature of the solvent; being faster in the solvent mixture than in pure MCH. By using size exclusion chromatography we could relate the increased rate to a decreased stability of the supramolecular A state in the solvent mixture. Next, we mixed the two enantiomerically pure hexa‐substituted benzene derivatives in a so‐called majority‐rules experiment, which lead to the anitcipated chiral amplification in the A state. More importantly it appeared that the A→B transition was significantly hampered in these mixed systems. Furthermore, the absence of chiral amplification in the B state revealed the formation of separated enantiomerically pure assemblies. Therefore, by using a wide variety of spectroscopic and chromatographic techniques we determined the influence of solvent and enantiomeric purity on the transition between different supramolecular states. Phase separation in supramolecular assemblies: The use of star‐shaped oligo(p‐phenylene vinylene) (OPV) derivatives with 24 stereocenters allowed the design of a system in which the high mismatch penalty between the enantiomers results in demixing in the self‐assembled state. Furthermore, a transition between different self‐assembled structures has been observed, in which the rate of the transition has been found to depend both on the solvent and the enantiomeric purity (see figure).