Self-assembling formation of a [2] catenane consisting of cyclobis(4,4"-azopyridinium-p-phenylene) and bis-p-phenylene-34-crown-10

A [2]catenane consisting of a pi-electron-accepting tetracationic cyclophane of cyclobis(4,4'-azopyridinium-p-phenylene) and a pi-electron-donating macrocyclic polyether of bis-p-phenylene-34-crown-10 was synthesized via a template-directed synthesis in 68% yield. The [2]catenane exhibited charge transfer bands with lambda(max) = 526 nm and 566 nm in CH3CN. A precursor of the cyclophane, bis[4-(4-pyridylazo)pyridinium], spontaneously formed a charge transfer complex with the macrocyclic polyether. The investigation of the charge transfer complex using UV-visible and H-1 NMR spectroscopy revealed that the complex had a pseudo-rotaxane structure with a stability constant (K-a) of 120 dm(3) mol(-1) at 25 degrees C in CH3CN. The highly efficient catenation of 68% yield was attributable to cooperative self-assembling processes derived from the strongly pi-electron deficient 4,4'-azopyridinium and 4-(4-pyridylazo)pyridinium units. These results suggested that there was a new formation mechanism of the catenated structure through preorganization of the charge transfer complex. (C) 1998 Elsevier Science Limited.