The Effect of Solution Conditions on the Driving Forces for Self-Assembly of a Pyrene Molecule.

Fe(CO){CO(CH2 )5 CH2 -pyrene}(Cp)(PPh3 ) (Fp-pyrene) is soluble in DMSO and THF, but insoluble in water, methanol, and ethanol. The hydrophobic force drives the molecules' assembly into vesicles in THF/water. The π-π interaction of the pyrene groups subsequently occurred within the vesicular membrane. The assembly, however, is driven by the π-π interaction in DMSO/water (water content: 40-80 vol %) into membranes, which is attributed to the relatively higher degree of de-solvation (δ) of pyrene in DMSO. Further increase in δ (DMSO/90 vol % water) suppresses the π-π interaction and spherical particles are formed. On the other hand, the supersaturated solutions were prepared via a cycle of heating and cooling of Fp-pyrene in methanol or ethanol. Fp-pyrene aggregates into particles without the π-π interaction in the solutions with a lower degree of supersaturation (σ). In contrast, a higher σ induces the π-π interaction, which drives the assembly into nanotapes. The π-π interaction is a conditional effect depending on the solution conditions, which can be adjusted for the synthesis of nanostructures assembled from the same aromatic molecule.