The quadruply hydrogen-bonded duplexes based on an imide-urea structure preorganized by three-center hydrogen bonds were found to associate via bifurcated hydrogen bonds. (1)H NMR dilution experiments revealed the high stability of the homodimer in apolar solvent (K(dim) > 10(5) M(-1) in CDCl(3)) and enhancement of association ability due to electron-withdrawing substituent effects. The ready synthetic availability and adjustable association affinity via electronic effects may render these association units potentially applicable in constructing supramolecular architectures.