Switching of pseudorotaxanes and catenanes incorporating a tetrathiafulvalene unit by redox and chemical inputs

An acyclic polyether la, incorporating a central tetrathiafulvalene (TTF) e lectron donor unit and two 4-tert-butylphenoxy groups at its termini, has b een synthesized. Two macrocyclic polyethers containing two different electr on donors, namely a TTF unit with, in one case, a 1,4-dioxybenzene ring (2a ), and, in the other case (2b), a 1,5-dioxynaphthalene ring system, have al so been synthesized. These two macrocyclic polyethers have been mechanicall y interlocked in kinetically controlled template-directed syntheses with cy clobis(paraquat-p-phenylene) cyclophane (3(4+)) to afford the [2]-catenanes 2a/3(4+) and 2b/3(4+), respectively X-ray crystallography reveals that the [2]-catenane 2b/3(4+) has the TTF unit of 2b located inside the cavity of 3(4+). The spectroscopic (UV/vis and H-1 NMR) and electrochemical propertie s of compounds 1a, 2a, 2b, 2a/3(4+), and 21b/3(4+) and of the [2]pseudorota xane 1a.3(4+) were investigated. The absorption and emission properties of the mono- and dioxidized forms of the TTF unit in these various species hav e also been studied. The results obtained in acetonitrile solution can be s ummarized as follows. (a) Whit TTF2+ exhibits a strong fluorescence, no emi ssion can be observed for the TTF2+ units contained in the polyethers and i n their pseudorotaxanes and catenanes. (b) A donor-acceptor absorption band is observed upon two-electron oxidation of the TTF unit in the macrocyclic polyethers 2a and 2b. (c) The spontaneous self-assembly of la and 3(4+) to give the [2]pseudorotaxane 1a.3(4+) is strongly favored (K-ass = 5 x 10(5) L mol(-1)) but slow (at 296 K, k = 11.3 L mol(-1) s(-1) and Delta G double dagger = 15.9 kcal mol(-1)) because of the steric hindrance associated wit h the bulky end groups of la. (d) In the pseudorotaxane 1a.3(4+), the rever sible displacement of the cyclophane from the TTF unit in the threadlike su bstrate occurs on oxidation/reduction of its electroactive components. (e) Snitching between the two translational isomers of the catenanes 2a/3(4+) a nd 2b/3(4+) occurs by cyclic oxidation and reduction of the TTF unit contai ned in 2a and in 2b, respectively. (f) Addition of o-chloroanil to the pseu dorotaxane 1a.3(4+) and to the catenanes 2a/3(4+) and 2b/3(4+) causes the d isplacement of the TTF unit from the cavity of the cyclophane 3(4+) because of the formation of an adduct between the TTF unit and o-chloroanil.