Programming permanent and transient molecular protection via mechanical stoppering

Chemical protection is an essential tool in synthetic chemistry, which involves blocking reactive sites on a molecule through covalent bonds. Physical approaches, such as encapsulation and host-mediated protection, have emerged as interesting alternatives that use steric bulk to inhibit reactivity. Here, we report the protection of a redox-active viologen through its incorporation into mechanically interlocked molecules (MIMs), namely hetero[4]rotaxanes. The viologen was confined inside a host cavity and flanked by two mechanical stoppers, which allowed for permanent and transient protection. Deprotection occurred on-demand via an unstoppering process, triggered by a proton transfer, polarity effect, or a thermal stimulus. We anticipate that permanent and transient mechanical stoppering could be incorporated into devices to function as molecular probes, transport/delivery systems, or stimuli-controlled degradable materials.

Benzobis(imidazolium) salts as templates for the self-assembly of starburst [24]pseudorotaxanes and their corresponding carbene-based classic [22]pseudorotaxanes

Starburst [2₄]pseudorotaxanes and classic [2₂]pseudorotaxanes were prepared from benzobis(imidazolium) salts and their carbene derivatives, respectively.

Naphthalene containing amino-ether macrocycle based Cu(ii) templated [2]pseudorotaxanes and OFF/ON fluorescence switching via axle substitution

A new naphthalene containing macrocycle, NaphMC, and a new fluorophoric bidentate linear axle derivative of 5,5'-dimethyl-2,2'-bipyridine (L3) along with two other ligands 1,10-phenanthroline (L1) and 5,5'-dimethyl-2,2'-bipyridine (L2) are explored towards the synthesis of Cu(ii) templated [2]pseudorotaxanes. All ternary complexes are well characterized by ESI-MS, UV/Vis, EPR spectroscopy, elemental analysis and emission spectroscopic studies. Single crystal X-ray diffraction studies confirm the geometry around the Cu(ii) center as a distorted trigonal bipyramid via the contribution of [3 + 2] orthogonal motifs of the wheel (NaphMC) and the bidentate chelating ligands L1 and L2 in the cases of pseudorotaxanes, CuPR1 and CuPR2, respectively. Furthermore, the fluorescence "OFF" state of the fluorophoric axle L3 is achieved via threading it to the Cu(ii) complex of NaphMC, whereas fluorescence switching "ON" is demonstrated by the substitution of L3 of CuPR3 with a stronger chelating ligand L1.

Threading of various ‘U’ shaped bidentate axles into a heteroditopic macrocyclic wheel via NiII/CuII templation

The Ni^II/Cu^II templated threading of various terminal group embedded ‘U’ shaped axles into an amido–amine macrocyclic wheel towards the development of a new generation of [2]pseudorotaxanes via [3 + 2] coordination assisted by other non-covalent interactions.