Molecular Shuttles Based on Tetrathiafulvalene Units and 1,5-Dioxynaphthalene Ring Systems

摘要

Six different degenerate [2]rotaxanes were synthesized and characterized.The rotaxanes contained either two tetrathiafulvalene (TTF)units or two 1,5-dioxynaphthalene (DNP)ring systems,both of which serve as recognition sites for a cyclo-bis(paraquat-p-phenylene)(CBPQT~(4+))ring.Three different spacer units were incorporated into the dumbbell components of the [2]rotaxanes between the recognition sites.They include a poly-ether chain,a terphenyl unit,and a di-phenyl ether linker,all of which were investigated in order to probe the effect of the spacers on the rate of the shuttling process.Data from dynamic ~1!H NMR spectroscopy revealed a relatively small difference in the DELTAG~+values for the shuttling process in the [2]rotaxanes containing the three different spacers,in contrast to a large difference between the TTF-containing rotaxanes (18 kcalmol~(-1))and the DNP-containing rotaxanes (15 kcalmol~(-1)).This 3 kcalmol~(-1)difference is predominantly a result of a ground-state effect,reflecting the much stronger binding of TTF units to the CBPQT~(4+)ring in comparison with DNP ring systems.An examination of the enthalpic (DELTAH)and entropic (DELTAS)components for the shuttling process in the DNP-contain-ing rotaxanes revealed significant differences between the three spacers,a property which could be important in designing new molecules for incorporation into molecular electronic and nanoelectromechanical (NEMs)devices.