Nano-scale self-assembly impeded by CH⋯π interaction in block selective solvents in the case of oligostyrene–perylenediimide–oligostyrene (coil–rod–coil) molecule

Abstract

Self-assembly of surfactants and block copolymers is normally facilitated by block-selective solvents, i.e., one of the blocks being soluble and the insoluble block self-assembling. In contrast to this phenomenon, we present the case of oligostyrene–perylenediimide–oligostyrene coil–rod–coil molecule, which does not show self-assembly of the perylene segment in solvents that are selective for oligostyrene. We attribute the preclusion of self-assembly to the C–H⋯π interaction that develops between the phenyl side groups of the oligostyrene segment and the perylene π system. In the oligostyrene-selective solvents, the chain would be extended, facilitating such C–H⋯π interaction. With the ring current of perylene shielding the chemical environment of phenyl CH in solution, the chemical shift of phenyl –CH in 1H NMR showed a small shift from 7.15 (for the amino-PS) to 7.08ppm. It is known that the C–H⋯π interaction is very weak. While such a C–H⋯π interaction generally promotes self-assembly and plays a role in host–guest complexes, the opposite effect is seen in the present case. It was found that collapsing the oligostyrene chain by the addition of a non-solvent leads to the self-assembly of the perylene segment.