Convergent synthesis of alternating fluorene-p-xylene oligomers and delineation of the (silver) cation-induced folding.

Convergent synthetic routes for the preparation of hitherto unknown fluorene-p-xylene oligomers (containing up to 10 fluorene moieties) from readily available starting materials are described. The conformationally adaptable monomeric receptor (which is made of a pair of fluorene and one p-xylene ring, i.e., Z1) undergoes a simple C-C bond rotation in the presence of silver cations to produce a pi-prismand-like receptor which binds a single silver cation with remarkable efficiency (i.e., K approximately 15,000 M(-1)). The data on 1H NMR spectroscopic titrations with Ag+ together with the density functional theory and AM1 calculations allows us to establish that various oligomers of Z1 (i.e., Z2-Z9) also undergo ready folding into the structures that contain multiple pi-prismand-like receptor sites in the presence of silver cations. The multiple cavities in Z3-Z9 accommodate a single silver cation per cavity with efficiency similar to that of Z1.