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 approximate to 15 000 M-1). The data on H-1 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.