Acid‐Base Switchable [2]‐ and [3]Rotaxane Molecular Shuttles with Benzimidazolium and Bis(pyridinium) Recognition Sites

Abstract

For the purpose of developing higher level mechanically interlocked molecules (MIMs), such as molecular switches and machines, a new rotaxane system was designed in which both the 1,2-bis(pyridinium)ethane and benzimidazolium recognition templating motifs were combined. These two very different recognition sites were successfully incorporated into [2]rotaxane and [3]rotaxane molecular shuttles which were fully characterized by H NMR, 2D EXSY, single-crystal X-ray diffraction and VT NMR analysis. By utilizing benzimidazolium as both a recognition site and stoppering group it was possible to create not only an acid/base switchable [2]rotaxane molecular shuttle (energy barrier 20.9 kcal⋅mol ) but also a [3]rotaxane molecular shuttle that displays unique dynamic behavior involving the simultaneous motion of two macrocyclic wheels on a single dumbbell. This study provides new insights into the design of switchable molecular shuttles. Due to the unique properties of benzimidazoles, such as fluorescence and metal coordination, this new type of molecular shuttle may find further applications in developing functional molecular machines and materials.

Translational dynamics of a non-degenerate molecular shuttle imbedded in a zirconium metal–organic framework

“…Furthermore, the enhanced chemical stability of Zr( iv ) MOFs introduces the possibility of controlling the dynamics via external chemical stimuli; 13 for instance, the benzimidazole core of the molecular shuttle featured in this work is particularly sensitive to changes in pH. 14 …”

“…Furthermore, the enhanced chemical stability of Zr(IV) MOFs introduces the possibility of controlling the dynamics via external chemical stimuli; 13 for instance, the benzimidazole core of the molecular shuttle featured in this work is particularly sensitive to changes in pH. 14 Previously reported Zr(IV) MOFs UWDM-8 and UWDM-9 11 contain an H-shaped tetracarboxylate [2]rotaxane ligand that crosslinks the tetrahedral cavity of fcu MOFs of the UiO-68 family (Fig. 1b).…”

Regulation of Macrocycle Shuttling Rates in [2]Rotaxanes by Amino‐Acid Speed Bumps in Organic–Aqueous Solvent Mixtures

“…the EXSY cross peaks (IAB and IBA) at different mixing times (tmix) as described in the literature to obtain a straight line with slope kex. [45,46] Further details and sample spectra are provided in the Supporting Information.…”

“…Rotaxane 1a-WS was obtained upon removal of the volatiles in vacuo as a colourless solid (quantitative yield). Hq), 8.14 (dm, 4H, Ho), 7.70 (t, J = 7.8 Hz, 2H, Hp), 7.16 (s, 8H, Hs), 6.97 (d, J = 15.4 Hz, 1H, Hd or He), 6.91 (d, J = 15.4 Hz, 1H, Hd or He), 5.97 (d, J = 15.0 Hz, 1H, Hd' or He'), 5.83 (d, J = 15.0 Hz, 1H, Hd' or , 169.10, 167.25, 167.18, 167.06, 166.91, 161.35, 137.63, 137.56, 135.42, 134.94, 134.90, 132.80, 132.56, 132 46,. To a solution of valine 3a (199 mg, 0.5 mmol, 1 eq.…”

How Secondary and Tertiary Amide Moieties are Molecular Stations for Dibenzo-24-crown-8 in [2]Rotaxane Molecular Shuttles?

“…Several secondary stations for the DB24C8 have been reported in the literature to date. As a non-comprehensive list of them, we can cite the following positively charged stations: bipyridinium [ 4 , 5 , 6 , 7 , 8 , 9 , 10 ], 1,2-bis-(pyridinium)ethane [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ], triazolium [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ], pyridinium [ 31 , 32 , 33 ], pyridinium amide [ 34 , 35 , 36 , 37 ], imidazolium [ 38 , 39 , 40 , 41 ] moieties, oxidized ferrocene [ 42 ], etc. Some neutral molecular stations are also important to be mentioned, such as urea [ 43 ], thiourea [ 44 ], carbamate [ 45 , 46 , 47 , 48 , 49 , 50 ], isoxazole [ 51 ], and benzylic ester [ 52 ], that usually interact either through π-π stacking with the aromatic rings of the crown ether, or through hy...…”