The selective self-assembly of a threadlike tetracation, containing two dialkylammonium (NH2+) centers and a 4,4'bipyridinium (bpym(2+)) unit, with an assortment of macrocyclic polyethers has been investigated. Spectroscopic studies, supported by X-ray crystallographic analyses, have demonstrated the formation of pseudorotaxanes between the thread and the macrocyclic polyethers. In particular, the macrocyclic polyethers dibenzo[24]crown-8 (DB24C8) and bis-p-phenylene[34]crown-10 (BPP34C10) associate selectively with the thread's NH2+ and bpym(2+) units, respectively, to generate novel multicomponent pseudorotaxane and pseudopolyrotaxane superarchitectures as a consequence of hydrogen-bonding and charge-transfer interactions. BPP34C10's preference for bpym(2+) units is shared by several of its dinaphtho-containing crown-l0 congeners, which self-assemble with the tetracationic thread to produce [2]pseudorotoxanes in which the bpym(2+) moiety is encircled by the macrocyclic polyether. The reversible acid - base controlled de/rethreading of [n]pseudorotaxanes based on the multifunctional tetracationic thread has also been studied by H-1 NMR, absorption, and fluorescence spectroscopies. Only one DB24CS macrocycle is ejected from a [3]pseudorotaxane-created from the tetracationic thread and two DB24C8 molecules-when both of its DB24CS-encircled NH; centers are deprotonated with base, leading to a [2]pseudorotaxane whose bpym(2+) unit is associated with the remaining DB24C8 macroring, The [3]pseudorotaxane is reestablished upon reprotonation of the thread with a stoichiometric amount of acid. Treatment of this species with an excess of acid causes protonation of the DB24C8 macrorings, which are completely dethreaded thereafter, Again, the dethreading process can be reversed upon neutralization of the surplus acid with base, Addition of dicyclohexano[24] crown-8 (DCy24C8) to a solution of the [3]pseudorotaxane induces the dethreading of one of the two DB24C8 macrocycles, so that a [4]pseudorotaxane is produced in which the tetracation's NH2+ and bpym(2+) units are encircled by DCy24C8 and DB24C8 macrorings, respectively Reversible acid- base de-/rethreading processes have also been observed for [2]pseudorotaxanes bearing the dinaphtho-containing crown-10s.
