|Haedler, A.T.; Meskers, S.C.J.; Zha, R.H.; Kivala, M.; Schmidt, H.-W.; Meijer, E.W.: Pathway Complexity in the Enantioselective Self-assembly of Functional Carbonyl-bridged Triarylamine Trisamides, Journal of the American Chemical Society 138(33), 10539–10545 (2016) -- DOI: 10.1021/jacs.6b05184|
Functional supramolecular systems like carbonyl-bridged triarylamine (CBT) trisamides are known for their long-range energy transport at room temperature. Understanding the complex self-assembly processes of this system allows for control over generated structures using controlled supramolecular polymerization. Here, we present two novel CBT trisamides with (S)- or (R)-chiral sidechains which show a two-pathway self-assembly behaviour in solution. Depending on the thermal profile during the self-assembly process, two different stable states are obtained under otherwise identical conditions. A kinetically trapped state A is reached upon cooling to 7° C, via a proposed isodesmic process. In addition, there is a thermodynamically stable state B at 7° C that is induced by first undercooling to -5° C, via a nucleation-elongation mechanism. In both cases, helical supramolecular aggregates comprising H-aggregated CBTs are formed. Additionally, controlled supramolecular polymerization was achieved by mixing the two different states (A and B) from the same enantiomer, leading to a conversion of the kinetically trapped state to the thermodynamically stable state. This process is highly enantioselective, as no conversion is observed if the two states consist of opposite enantiomers. We thus show the importance and opportunities emerging from understanding the pathway complexity of functional supramolecular systems.