Phenanthroline Dicarboxamide-Based Helical Foldamers: Stable Helical Structures in Methanol

A series of new aromatic oligoamides 2−5 based on 1,10-phenanthroline diacid and o-phenylenediamine
have been synthesized through a convergent segment coupling strategy. These oligomers can fold into
well-defined helical structures in solution through intramolecular hydrogen bonds and aromatic stacking
interactions, which has been established by 1H NMR, fluorescence, and UV/vis spectra. In particular, it
was found that the oligomers were more favorable to fold into stable helical structures in methanol than
in chloroform and dichloromethane. The helical foldamers formed in the solid state have been characterized
by single-crystal X-ray diffraction analysis. The results showed that the high curvature of the strands led
to one and a half turns for both 2 and 21, three turns for 4, and nearly four turns for 5.