Electrostatic barriers in rotaxanes and pseudorotaxanes.

摘要: The ability to control the kinetic barriers governing relative motions of components in mechanically interlocked molecules is important for future applications these compounds molecular electronic devices. In this Full Paper, we demonstrate that bipyridinium (BIPY^(2+)) dications fulfill role as effective electrostatic controlling shuttling and threading behavior rotaxanes pseudorotaxanes aqueous environments. A degenerate [2]rotaxane, composed two 1,5-dioxynaphthalene (DNP) units flanking a central BIPY^(2+) unit dumbbell component encircled by cyclobis(paraquat-p-phenylene) (CBPQT^(4+)) tetracationic cyclophane, has been synthesized employing threading-followed-by-stoppering approach. Variable-temperature ^(1)H  NMR spectroscopy reveals barrier CBPQT^(4+) ring over BIPY2+ excess 17 kcal mol^(−1) at 343 K. Further information about nature an was gleaned from related supramolecular systems, utilizing threads either DNP moiety or flanked moiety. dethreading processes with compounds, which were investigated spectrophotometric techniques, reveal responsible affecting both thermodynamics kinetics pseudorotaxane formation means intramolecular self-folding (through donor–acceptor interactions unit), addition Coulombic repulsion. particular, free energy (Δequation image) case thread found be high 21.7 kcal mol^(−1) room temperature. These results can effectively employ serve water order gain systems.