Self-complementary tweezer-molecules based on a naphthalenediimide core self-assemble into supramolecular dimers through mutual π-π-stacking and hydrogen bonding. The resulting motif is extremely stable in solution (K(a) = 10(5) M(-1)), and its attachment to one terminal position of a poly(ethylene glycol) chain leads to a doubling of the polymer's apparent molecular weight.