ABSTRACT
Modulating the arrangement of superstructures through noncovalent interactions has a significant impact on macroscopic shape and the expression of unique properties. Constructing π-interaction-driven hierarchical three-dimensional (3D) superstructures poses challenges on account of limited directional control and weak intermolecular interactions. Here we report the construction of a 3D diamondoid superstructure, named π-Diamond, employing a ditopic strained Z-shaped building block comprising a porphyrin unit as bow-limb double-strapped with two m-xylylene units as bowstring. This superstructure, reminiscent of diamond's tetrahedral carbon composition, is composed of double-walled tetrahedron (DWT) driven solely by π-interactions. Hetero-π-stacking between porphyrin and m-xylylene panels drive the assembly of four building blocks predominantly into a DWT, which undergoes extension to create an adamantane unit and eventually a diamondoid superstructure wherein each porphyrin panel is shared by two neighboring tetrahedra through hetero-π-stacking. π-Diamond exhibits a solid-state fluorescent quantum yield 44 times higher than that of tetraphenylporphyrin along with excellent photocatalytic performance. The precise 3D directionality of π-interactions, achieved through strained multipanel building blocks, revolutionizes the assembly of hierarchical 3D superstructures driven by π-interactions.
ABSTRACT
Poly[n]catenanes have exceptional mechanical bonding properties that give them tremendous potential for use in the development of molecular machines and soft materials. Synthesizing these compounds has, however, proven to be a formidable challenge. Herein, we describe a concise method for the construction of twisted polycatenanes. Our approach involves using preorganized double helicates as templates, linked crosswise in a linear fashion by either silver ions or triple bonds. By using this approach, we successfully synthesized twisted polycatenanes with both coordination and covalent bonding employing Ag(I) ions and ethynylene units, respectively, as the linkages and leveraging the same Ag(I)-templated double helicate in both cases. Synthesis with Ag(I) ions formed a single-crystalline one-dimensional (1D) coordination poly[n]catenane, and synthesis using ethynylene units generated 1D fibers which self-assembled with solvents to form a gel. Our results confirm the potential of multi-stranded metallohelicates for creating sophisticated mechanically interlocked molecules and polymers, which could pave the way for exploration in the realms of molecular nanotopology and materials design.
ABSTRACT
Delving into the influence of strain on organic reactions in small molecules at the molecular level can unveil valuable insight into developing innovative synthetic strategies and structuring molecules with superior properties. Herein, we present a molecular-strain engineering approach to facilitate the consecutive [1,2]-aryl shift (formal [1,3]-aryl shift) in molecular bows (MBs) that integrate 1,4-dimethoxy-2,5-cyclohexadiene moieties. By introducing ring strain into MBs through tethering the bow limb, we can harness the intrinsic mechanical forces to drive multistep aryl shifts from the para- to the meta- to the ortho-position. Through the use of precise intramolecular strain, the seemingly impractical [1,3]-aryl shift was realized, resulting in the formation of ortho-disubstituted products. The solvent and temperature play a crucial role in the occurrence of the [1,3]-aryl shift. The free energy calculations with inclusion of solvation support a feasible mechanism, which entails multistep carbocation rearrangements, for the formal [1,3]-aryl shift. By exploring the application of molecular strain in synthetic chemistry, this research offers a promising direction for developing new tools and strategies towards precision organic synthesis.
ABSTRACT
A non-aromatic expanded carbaporphyrinoid, incorporating two built-in 2,7-pyrenylene moieties was synthesized. The intrinsically labile structure was demonstrated by proton-triggered conformational changes between the figure-of-eight and quasi-Möbius conformers. Upon treatment with Pd(OAc)2 , the reaction produces two bis-PdII complexes with distinct coordination modes. Metal coordination serves to fix the macrocyclic frameworks with the net result that both bis-PdII complexes could be resolved by high performance liquid chromatography (HPLC) on a chiral stationary phase. The isolated enantiomers showed persistent chiroptical properties as evidenced by the intense response in the circular dichroism (CD) spectra and the record high absorption dissymmetry factors (gabs of up to 0.038) seen in the near-infrared spectral region. Moreover, the mutual interconversion of these two PdII complexes was found to be stereospecific and to favor the more stable isomers under weakly acidic conditions.
Subject(s)
Circular Dichroism , StereoisomerismABSTRACT
We report a fully organic pyridine-tetrapyrrolic U-shaped acyclic receptor 10, which prefers a supramolecular pseudo-macrocyclic dimeric structure (10)2 in a less polar, non-coordinating solvent (e.g., CHCl3). Conversely, when it is crystalized from a polar, coordinating solvent (e.g., N,N-dimethylformamide, DMF), it exhibited an infinite supramolecular one-dimensional (1D) "zig-zag" polymeric chain, as inferred from the single-crystal X-ray structures. This supramolecular system acts as a potential receptor for strong acids, e.g., p-toluenesulfonic acid (PTSA), methane sulfonic acid (MSA), H2SO4, HNO3, and HCl, with a prominent colorimetric response from pale yellow to deep red. The receptor can easily be recovered from the organic solution of the host-guest complex by simple aqueous washing. It was observed that relatively stronger acids with pKa < -1.92 in water were able to interact with the receptor, as inferred from 1H NMR titration in tetrahydrofuran-d8 (THF-d8) and ultraviolet-visible (UV-vis) spectroscopic titrations in anhydrous THF at 298 K. Therefore, this new dynamic supramolecular receptor system may have potentiality in materials science research.
