Recognition of naphthoflavones by calix[4]pyrrole[2]phenanthrene

Abstract

Here we report the synthesis of a new kind of expanded calix[4]pyrrole named calix[4]pyrrole[2]phenanthrene 1, containing two phenanthrene subunits in lieu of two of the four acetone bridging elements. This macrocycle exists in a planar structure and four pyrrole units adopt the 1,3-alternate conformation in the solid state. Moreover, host 1 exhibits selective recognition against naphthoflavone as confirmed by ¹H NMR, ESI-MS and X-ray analysis experiments. Interestingly, the conformation of 1 changed from a planar to a wing-like conformation after complexation with β-naphthoflavone, and noncovalent interactions played an important role in the formation of the complex.