Molecular meccano, 57 - Template-directed syntheses, spectroscopic properties, and electrochemical behavior of [n]catenanes

Catenanes composed of two, three, five, or seven interlocked macrocycles ha ve been synthesized in yields ranging from 1 to 30%. Their template-directe d syntheses rely on a series of cooperative noncovalent bonding interaction s between pi-electron rich 1,5-dioxynaphthalene ring systems and pi-electro n deficient bipyridinium units which are incorporated within the macrocycli c components. The interlocked structure associated with one of the [3]caten anes was demonstrated unequivocally by single crystal X-ray analysis which also revealed the formation of polar stacks stabilized by intermolecular [p i...pi] interactions. The number of interlocked components of each catenane was determined by Liquid secondary ion, matrix-assisted laser desorption i onization/time-of-flight, and/or electrospray mass spectrometries. The abso rption spectra, emission spectra, and electrochemical properties of the mac rocyclic components and of the catenanes have been investigated. Two kinds of charge-transfer absorption bands (intramolecular in the cyclophanes cont aining electron-donor and electron-acceptor units, intercomponent in the ca tenanes) have been found. Such charge-transfer excited states are responsib le for the quenching of the potentially fluorescence units of the cyclophan es, and of the crown ethers in the catenanes. Charge-transfer electronic in teractions are also evidenced by the electrochemical behavior. Correlations among the redox potentials of the various compounds are reported and discu ssed.