Cooperative Supramolecular Polymerization: Comparison of Different Models Applied on the Self‐Assembly of Bis(merocyanine) Dyes

Three new molecular building blocks 1 a – c for supramolecular polymerization are described that feature two dipolar merocyanine dyes tethered by p‐xylylene spacers. Concentration‐ and temperature‐dependent UV/Vis spectroscopy in chloroform combined with dynamic light scattering, capillary viscosimetry and atomic force microscopy investigations were applied to elucidate the mechanistic features of the self‐assembly of these strongly dipolar dyes. Our detailed studies reveal that the self‐assembly is very pronounced for bis(merocyanines) 1 a , b bearing linear alkyl chains, but completely absent for bis(merocyanine) 1 c bearing sterically more bulky ethylhexyl substituents. Both temperature‐ and concentration‐dependent UV/Vis data provide unambiguous evidence for a cooperative self‐assembly process for bis(merocyanines) 1 a , b , which was analyzed in detail by the Meijer–Schenning–Van‐der‐Schoot model (applicable to temperature‐dependent data) and by the Goldstein–Stryer model (applicable to concentration‐dependent data). By combining both methods all parameters of interest to understand the self‐assembly process could be derived, including in particular the nucleus size (8–10 monomeric units), the cooperativity factor (ca. 0.006), and the nucleation and elongation constants of about 10³ and 10⁶ M ^?1 in chloroform at room temperature, respectively.