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

Abstract

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 10(3) and 10(6) M(-1) in chloroform at room temperature, respectively.

Spacer‐Modulated Differentiation Between Self‐Assembly and Folding Pathways for Bichromophoric Merocyanine Dyes

“…As expected based on our previous work on the aggregation of simple ATOP merocyanine dyes,13 for the reference dyes 1 a , b the spectral changes could appropriately be described with the dimerization model (Figure 4), while the isodesmic model was not applicable to describe their aggregation process. On the other hand, it is surprising that the concentration‐dependent spectral changes observed for bis(merocyanine) dye 1 c could also be nicely fitted with the dimerization model, although our previous work on another class of bis(merocyanine) dyes bearing p ‐xylylene spacer unit afforded supramolecular polymers28 as depicted in Scheme (on the right). This illustrates that subtle changes in conformational preferences and sterical demands have a strong impact on the formation of preferred self‐assembly product…”

H‐Aggregates of Oligophenyleneethynylene (OPE)‐BODIPY Systems in Water: Guest Size‐Dependent Encapsulation Mechanism and Co‐aggregate Morphology

“…For both solvents, the fact that the size distribution is dependent on the scattering angle strongly suggests the formation of anisotropic one‐dimensional aggregates 15a. 28…”

Anti-cooperative supramolecular polymerization: a new K2–K model applied to the self-assembly of perylene bisimide dye proceeding via well-defined hydrogen-bonded dimers

“…Remarkably, while a broad variety of cooperative self-assembly processes ( σ < 1) have been characterized in great detail in the meanwhile, work demonstrating the opposite case of anti-cooperative growth ( σ > 1) is scarce. 14 , 19 , 23 , 24 This is even more surprising because a large number of molecules are known to self-assemble into dimers for instance by hydrogen bonding, 25 – 27 or electrostatically driven π-stacking of dipolar dyes. 28 , 29 …”