Effect of 1,3-adamantane bridging units within the surrounding macrocycle of squaraine rotaxanes

Abstract

Squaraine rotaxanes with macrocycles containing 1,3-adamantanedicarboxamide bridging units have altered chemical and luminescent properties due to a more loosely held rotaxane co-conformation.

Thermally and Photochemically Induced Dethreading of Fumaramide‐Based Kinetically Stable Pseudo[2]rotaxanes

“…For this study we also assembled rotaxanes 3a – c , bearing two 1,3‐adamantane dicarbonyl moieties on the macrocyclic counterpart instead of the isophthaloyl functions present in 2 (Table , entries 6–8). The obtained yields were generally low, as a consequence of the lesser acidity of the hydrogens of the macrocyclic amides of the intermediate supramolecular complex leading to the interlocked compound . The weakness of these hydrogen bonds interactions in 3a was revealed by variable‐temperature NMR experiments.…”

Guest Back-Folding: A Molecular Design Strategy That Produces a Deep-Red Fluorescent Host/Guest Pair with Picomolar Affinity in Water

“…The squaraine design process was guided by computer-based molecular modeling of threaded [2]­pseudorotaxane complexes for which the starting coordinates were derived from homologous X-ray crystal structures. − The initial threaded structure was a gas-phase truncated model of the prototype complex M ⊃ SQ1 with N , N -dimethyl units at each end of the squaraine (Scheme ). The complex structure was systematically modified to have an increasing number of N -benzyl groups, and in each case the coconformation was optimized using the semiempirical PM7 method followed by further optimization using DFT at the BLYP-gCP-D3/def2-svp level.…”

“…The complex that encapsulates unsymmetric SQ2 has two Nbenzyl groups on one end of the dye, whereas the symmetric The aromatic stacking orientations seen in these computed DFT models are essentially identical to those observed in X-ray crystal structures of related squaraine rotaxanes. 68,69 Additional structural and energetic insight was gained by conducting 100 ns molecular dynamic (MD) simulations of each threaded complex utilizing explicit water solvation. Trajectories suggest that virtually all of the coconformational states allow the squaraine N-benzyl groups to stack against the isophthalamide bridging units of the surrounding cyclophane and/or the anthracene sidewalls (movies of the MD simulations can be found in the Supporting Information, with a statistical analysis of aromatic stacking interactions in Table S5).…”

Cyclization of interlocked fumaramides into β-lactams: experimental and computational mechanistic assessment of the key intercomponent proton transfer and the stereocontrolling active pocket

“…As we mentioned above rotaxane 1i , featuring two adamantyl fragments in the macrocycle, experiences the fastest cyclization. In order to explain that, we considered that the torsional flexibility of the adamantyl core 56 enables the proper orientation of the amidate group, favouring the expeditious deprotonation of the N -benzyl group of the thread. In that vein we computationally studied the conformational preference of a range of structurally simplified monoamidates 6 ( Fig.…”

“…The low yield in 1i could be tentatively explained in terms of the lower acidity of the NH hydrogen atoms of the transient precursors of the macrocycle, thus decreasing the stability of the supramolecular complex previous to the nal interlocked structure. 48,56 2.2 Synthesis of the interlocked b-lactams trans-2d-i…”