synthesis of amphiphilic π-conjugated acyclic oligopyrroles and the formation of solvent-assisted aggregates are reported. We have prepared various types of BF2 complexes of 1,3-dipyrrolylpropane-1,3-diones bearing aryl rings substituted with hydrophilic polyethyleneglycol (PEG) chains, both as acyclic anion receptors and as building subunits for organized architectures based on π-π stacking. The formation of supramolecular H-type assemblies of these "amphiphilic" derivatives in aqueous solution was suggested by UV/Vis and fluorescence spectroscopy and further supported by 1H NMR and dynamic light scattering (DLS) analyses. Cryogenic transmission electron microscopy (cryo-TEM) analyses of the aqueous solutions suggest that the fabrication of nanoscale network structures and vesicles depends on the peripheral substituents. The H-aggregates in aqueous solution are sensitive to the conditions required for transformation into monomers through replacement with miscible solvents such as alcohols and into J-type aggregates by water evaporation and freeze-drying procedures. However, they are fairly stable and sustainable to anion binding, whereas on CH2Cl2 extraction they are transformed into other assembled modes but remain in the aqueous solution. The metastable states of affairs for distributions between two immiscible solvents are controlled by the orders of solution preparation; this also suggests that the formation of stable assemblies is assisted by water molecules. Furthermore, assemblies in which the stacking modes depend on the aliphatic side chains are also observed in a nonpolar hydrocarbon solvent.
All Science Journal Classification (ASJC) codes
- Organic Chemistry