Supramolecular polymerization and gel formation of bis (merocyanine) dyes driven by dipolar aggregation

S Yao, U Beginn, T Gress, M Lysetska… - Journal of the …, 2004 - ACS Publications
S Yao, U Beginn, T Gress, M Lysetska, F Würthner
Journal of the American Chemical Society, 2004ACS Publications
Two highly dipolar merocyanine dyes were tethered by a rigid tris (n-dodecyloxy) xylylene
unit that preorganizes the dyes for a supramolecular polymerization process through
intermolecular aggregation of the dyes. UV/vis spectroscopy revealed a solvent dependent
equilibrium between monomeric dyes and two different types of dye aggregates that are
characterized by hypsochromically shifted D-and H-type absorption bands. Taking into
account the ditopic nature of the supramolecular building blocks, the occurrence of the D …
Two highly dipolar merocyanine dyes were tethered by a rigid tris(n-dodecyloxy)xylylene unit that preorganizes the dyes for a supramolecular polymerization process through intermolecular aggregation of the dyes. UV/vis spectroscopy revealed a solvent dependent equilibrium between monomeric dyes and two different types of dye aggregates that are characterized by hypsochromically shifted D- and H-type absorption bands. Taking into account the ditopic nature of the supramolecular building blocks, the occurrence of the D-band indicates the formation of an oligomeric/polymeric supramolecular chain whereas the observation of the H-band suggests a higher order assembly. For the H-aggregated dyes, intrinsic viscosities exceed 0.65 L g-1 in methylcyclohexane, values typically found for macromolecular solutions. At higher concentration, further association of these aggregates takes place by entanglement of the alkyl groups leading to a substantial increase in viscosity and gelation. Rheology studies show linear viscoelastic behavior which was attributed to the formation of an entangled dynamic network. AFM and cryo-TEM studies of the gel reveal long and stiff rod-type assemblies. X-ray diffraction studies for a solid film show columnar mesomorphism. Based on these results, a structural model is proposed in which six helically preorganized strands of the supramolecular polymer intertwine to form a rod with a diameter of about 5 nm. Within these rods all dyes are tightly aggregated in a tubular fashion giving rise to delocalized excitonic states, and the π-conjugated tube is jacketed by the tridodecyloxy groups.
ACS Publications
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