Mateusz Woźny

An electrochemically switchable foldamer - a surprising feature of a rotaxane with equivalent stations

A novel, mechanically interlocked molecular device was obtained from unique supramolecular tectons – π-deficient tetraazamacrocyclic complexes of copper(II) and nickel(II). We present the synthesis of the first rotaxanes based on donor–acceptor interactions involving transition metal complexes. While spontaneous shuttling manifests itself in the variability of the NMR spectra, voltammetric experiments reveal a surprising mode of potential-controlled molecular switching, which does not employ common co-conformational changes. Significantly, it relies on reversible folding/unfolding of the rotaxane. The process is driven by the interplay between electrostatic repulsion and cohesive π–π interaction – a tug of war with a critical point at 1.31 V. Although rotaxanes with equivalent stations are considered degenerate molecular shuttles, we show that this is not the case when an unusual mechanism of switching is involved.

Neutral Nickel(II) and Copper(II) Tetraazamacrocyclic Complexes as Molecular Rods Attached to Gold Electrodes

New dithiolated derivatives of neutral Cu(II) and Ni(II) tetraazamacrocyclic complexes have been synthesized and characterized by spectroscopic and diffractional methods. These rod-shaped molecules were assembled in monocomponent and mixed monolayers on gold electrodes. In the mixed monolayers, the active molecules were embedded in a hexanethiol matrix. The dithiolated complexes are oriented perpendicularly to the electrode, and reveal faster kinetics of electron transfer than those assembled in a single-component monolayer. They appear as protrusions, which are easily addressed by using the STM method. In the presence of a suitable electron acceptor in the solution, the donor properties of the anchored Cu complex were weakened, which revealed donor-acceptor interactions with the monolayer. The peak position in the voltammogram indicates a stronger interaction of the solution-based acceptor with the reduced Cu(II) form than with the Cu(III) complex. This suggests the possibility of switching the association on or off by applying an appropriate potential.

Rotaxanes composed of dibenzo-24-crown-8 and macrocyclic transition metal complexing tetraimine units

We present the structures of new rotaxanes. They are composed of dibenzo-24-crown-8 and an axle containing two tetraazamacrocyclic units coordinating the same, or different, metal ions (Ni or/and Cu). These units are linked with the m- and p-xylylene bridges. The structures of these compounds were confirmed by single crystal X-ray diffraction, NMR, and other spectroscopic methods. Rigid linkers between the macrocyclic units allow control of the axle length and geometry of the final compounds. The rotaxanes adopt one of two conformations: folded or extended. Rotaxanes are formed by simultaneous interactions of electron rich benzene rings with electron deficient six membered chelate rings and formation of hydrogen bonds between the secondary amino group and crown ether oxygens. Variable temperature 1H NMR studies of diamagnetic di-Ni-rotaxanes confirm that shuttling of the dibenzo-24-crown-8 moiety takes place along the p-xylylene linked axle, while folding of the axle in the m-xylylene linked rotaxane stabilizes the bent geometry of the whole compound and prevents shuttling of the crown ether moiety. In the case of rotaxanes containing the p-xylylene linkers, at elevated temperatures we observe a translocation of the crown ether unit between the metal coordinating macrocycles, which is well supported by electrochemical results for heteronuclear (Cu/Ni) systems but such translocation was not observed in the m-xylylene bridges. Electrochemical results suggest that an unfolding of the axle takes place upon oxidation of the metal centre in the di-Ni-rotaxane but not in heteronuclear m-xylylene linked rotaxanes.