Nano-scale self-assembly impeded by CH⋯π interaction in block selective solvents in the case of oligostyrene-perylenediimide-oligostyrene (coil-rod-coil) molecule
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 7.08 ppm. 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.
|Keywords||C-H⋯π interaction, Inverse surfactant, Nano-scale self-assembly, Oligostyrene, Perylenediimide|
|Journal||European Polymer Journal|
Islam, M.R. (Molla Rafiquel), & Sundararajan, P. (2013). Nano-scale self-assembly impeded by CH⋯π interaction in block selective solvents in the case of oligostyrene-perylenediimide-oligostyrene (coil-rod-coil) molecule. In European Polymer Journal (Vol. 49, pp. 2042–2051). doi:10.1016/j.eurpolymj.2013.04.037