Supramolecular polymerization and gel formation of bis(merocyanine) dyes driven by dipolar aggregation.
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 pi-conjugated tube is jacketed by the tridodecyloxy groups.
Yao
Sheng
S
Institut für Organische Chemie, Universität Würzburg, Am Hubland, D-97070 Würzburg, Germany.
Beginn
Uwe
U
Gress
Tobias
T
Lysetska
Marina
M
Würthner
Frank
F
D004396:Coloring Agents / Q000138:chemical synthesis* / Q000737:chemistry; D005782:Gels; D006860:Hydrogen Bonding; D007700:Kinetics; D046911:Macromolecular Substances; D008956:Models, Chemical; D015394:Molecular Structure; D011744:Pyrimidinones / Q000138:chemical synthesis* / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D014783:Viscosity
D004396:Coloring Agents; D005782:Gels; D046911:Macromolecular Substances; D011744:Pyrimidinones; C003954:merocyanine dye