1 research outputs found
Impact of Alkyl Spacer Length on Aggregation Pathways in Kinetically Controlled Supramolecular Polymerization
We
have investigated the kinetic and thermodynamic supramolecular
polymerizations of a series of amide-functionalized perylene bisimide
(PBI) organogelator molecules bearing alkyl spacers of varied lengths
(ethylene to pentylene chains, <b>PBI-1-C2</b> to <b>PBI-1-C5</b>) between the amide and PBI imide groups. These amide-functionalized
PBIs form one-dimensional fibrous nanostructures as the thermodynamically
favored states in solvents of low polarity. Our in-depth studies revealed,
however, that the kinetic behavior of their supramolecular polymerization
is dependent on the spacer length. Propylene- and pentylene-tethered
PBIs follow a similar polymerization process as previously observed
for the ethylene-tethered PBI. Thus, the monomers of these PBIs are
kinetically trapped in conformationally restricted states through
intramolecular hydrogen bonding between the amide and imide groups.
In contrast, the intramolecularly hydrogen-bonded monomers of butylene-tethered
PBI spontaneously self-assemble into nanoparticles, which constitute
an off-pathway aggregate state with regard to the thermodynamically
stable fibrous supramolecular polymers obtained. Thus, for this class
of π-conjugated system, an unprecedented off-pathway aggregate
with high kinetic stability could be realized for the first time by
introducing an alkyl linker of optimum length (C4 chain) between the
amide and imide groups. Our current system with an energy landscape
of two competing nucleated aggregation pathways is applicable to the
kinetic control over the supramolecular polymerization by the seeding
approach