We describe our investigations of the spectroscopic and electrochemical properties of these systems and compare them with those obtained previously5d for 1b and 1b‚34+
Switching of pseudorotaxanes and catenanes incorporating a tetrathiafulvalene unit by redox and chemical inputs
JOURNAL OF ORGANIC CHEMISTRY, no. 7 (2000): 1924-1936
An acyclic polyether la, incorporating a central tetrathiafulvalene (TTF) electron donor unit and two 4-tert-butylphenoxy groups at its termini, has been synthesized. Two macrocyclic polyethers containing two different electron donors, namely a TTF unit with, in one case, a 1,4-dioxybenzene ring (2a), and, in the other case (2b), a 1,5-di...更多
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- It is well-known that tetrathiafulvalene (TTF) can be oxidized reversibly to TTF+ and TTF2+.
- It has been shown that TTF can behave in charge-transfer complexes as a donor in its neutral form and as an acceptor in its 2+ oxidation state.
- For these reasons, TTF is an ideal building block with which to construct
- It is well-known1 that tetrathiafulvalene (TTF) can be oxidized reversibly to TTF+ and TTF2+
- The results obtained in acetonitrile solution can be summarized as follows. (a) While TTF2+ exhibits a strong fluorescence, no emission can be observed for the TTF2+ units contained in the polyethers and in 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 1a and 34+ to give the pseudorotaxane 1a‚34+ is strongly favored (Kass. ) 5 × 105 L mol-1) but slow 11.3 L mol-1 s-1 and ∆Gq ) 15.9 kcal mol-1) because of the steric hindrance associated with the bulky end groups of 1a. (d) In the pseudorotaxane 1a‚34+, the reversible displacement of the cyclophane from the TTF unit in the threadlike substrate occurs on oxidation/reduction of its electroactive components. (e) Switching between the two translational isomers of the catenanes 2a/34+ and 2b/34+ occurs by cyclic oxidation and reduction of the TTF unit contained in 2a and in 2b, respectively. (f) Addition of o-chloroanil to the pseudorotaxane 1a‚34+ and to the catenanes 2a/34+ and 2b/34+ causes the displacement of the TTF unit from the cavity of the cyclophane 34+ because of the formation of an adduct between the TTF unit and o-chloroanil
- It is worth noting that while TTF2+ exhibits a strong fluorescence, no emission can be observed for the TTF2+ units contained in the polyethers
- We have prepared the TTF-containing macrocyclic polyethers 2a and 2b in yields of 49 and 55%, respectively. These macrocyclic polyethers have been used as templates in the kinetically controlled selfassembly of catenanes 2a/3[PF6]4 and 2b/3[PF6]4 which were isolated in yields of 43 and 23%, respectively
- The spectroscopic investigations of these compounds have shown that, while TTF2+ exhibits a strong fluorescence, no emission can be observed for the TTF2+ units contained in the polyethers and in the corresponding pseudorotaxanes and catenanes
- The results obtained in the electrochemical experiments and upon addition of Fe(ClO4)3 or o-chloranil show clearly that oxidation or adduct formation of the TTF unit of the polyethers in 1a‚ 34+ and in 2a/34+ and 2b/34+ and reduction of the cyclophane in 1a‚34+ cause extensive mechanical movements
- Solvents were purified according to literature procedures. The compounds 1b,5d 4,8 5a,14 6[PF6]2,14 5b,34 and 3[PF6]435 were synthesized according to literature procedures.
- Solvents were purified according to literature procedures..
- The compounds 1b,5d 4,8 5a,14 6[PF6]2,14 5b,34 and 3[PF6]435 were synthesized according to literature procedures.
- For reversible processes the same halfwave potential values were obtained from the DPV peaks and from an average of the cathodic and anodic cyclic voltammetric peaks.
- The potential values for not fully reversible processes were estimated from the DPV peaks.
- The experimental error on the potential values for reversible and not fully reversible processes was estimated to be (5 and (10 mV, respectively
- The central [CdC] bond of the TTF unit and the [O‚‚‚O] axis of the 1,5-dioxynaphthalene ring system subtend angles of 74° and 18°, respectively, to the mean plane of the tetracationic cyclophane.
- The catenane molecules pack to form π-donor/π-acceptor stacks (Figure 2b) with an interplanar separation of 3.29 Å between the “alongside” 1,5-dioxynaphthalene ring system of one molecule and the “alongside” bipyridinium unit of another
- The authors have synthesized the TTF-containing polyether 1a which associates (Kass. ) 5 × 105 L mol-1 at 296 K in MeCN) under thermodynamic control with the tetracationic cyclophane 34+ in solution to form the pseudorotaxane 1a‚34+.
- The results obtained in the electrochemical experiments and upon addition of Fe(ClO4) or o-chloranil show clearly that oxidation or adduct formation of the TTF unit of the polyethers in 1a‚ 34+ and in 2a/34+ and 2b/34+ and reduction of the cyclophane in 1a‚34+ cause extensive mechanical movements
- Such rearrangements involve the circumrotation of one ring with respect to the other in 2a/34+ and in 2b/34+ (Figure 9), and the displacement of the ring along the thread, leading to dethreading, in 1a‚34+ (Figure 10).
- The movements can be fully reversed by electrochemical or chemical inputs
- Table1: Electrochemical Dataa for the Molecular Components
- This research was supported by the Engineering and Physical Sciences Research Council in the United Kingdom and by the University of Bologna (Funds for Selected Research Topics) and MURST (Supramolecular Devices project) in Italy, and by the EU (TMR grant FMRX-CT96-0076)