Pre-organized molecular tweezer stabilized by intramolecular hydrogen bonds: solvent-responsive host–guest complexation

Synthesis, optical properties and self-assemblies of three novel asymmetrical perylene diimides modified with functional hydrogen bonding groups at bay positions

Three new perylene diimides modified with functioned hydrogen bonding groups at bay positions were successfully prepared. Their optical properties and self-assemblies on HOPG were investigated.

High-Yielding Flow Synthesis of a Macrocyclic Molecular Hinge

Many molecular machines are built from modular components with well-defined motile capabilities, such as axles and wheels. Hinges are particularly useful, as they provide the minimum flexibility needed for a simple and pronounced conformational change. Compounds with multiple stable conformers are common, but molecular hinges almost exclusively operate via dihedral rotations rather than truly hinge-like clamping mechanisms. An ideal molecular hinge would better reproduce the behavior of hinged devices, such as gates and tweezers, while remaining soluble, scalable, and synthetically versatile. Herein, we describe two isomeric macrocycles with clamp-like open and closed geometries, which crystallize as separate polymorphs but interconvert freely in solution. An unusual one-pot addition cyclization reaction was used to produce the macrocycles on a multigram scale from inexpensive reagents, without supramolecular templating or high-dilution conditions. Using mechanistic information from NMR kinetic studies and at-line mass spectrometry, we developed a semicontinuous flow synthesis with maximum conversions of 85–93% and over 80% selectivity for a single isomer. The macrocycles feature voids that are sterically protected from guests, including reactive species such as fluoride ions, and could therefore serve as chemically inert hinges for adaptive supramolecular receptors and flexible porous materials.

Conformational Analysis of the Supramolecular Complexation of Diaryl-Substituted Tetrathiafulvalene Vinylogues with Fullerenes

Tetrathiafulvalene vinylogues (TTFVs) functionalized with diaryl substituents (aryl = 1-napthyl, 9-anthryl, and 1-pyrenyl) via click chemistry have been previously synthesized and studied as tweezer-type receptors for binding with C60 and C70 fullerenes. In particular, dianthryl-TTFV exhibits unique selectivity for C70 fullerene, giving rise to effective fluorescence turn-on sensing of C70 in the presence of a large excess of C60 fullerene. This observation indicated that dianthryl-TTFV has a preferential binding affinity for C70 over C60 fullerene, but the reason for such selectivity is unclear. Aiming at addressing this issue, we herein investigated the relative conformational stability of diaryl-substituted TTFVs in complexation with C70 and C60 fullerenes. The dispersion-corrected density functional theory approximation (B3LYP-D3) was employed in our computational analysis to determine binding energies and electronic properties of these supramolecular complexes. It was found that the highest binding energies (and the lowest relative conformational energies) are in pairings when fullerenes are placed around the central TTFV moieties (such as the triazole rings). The results of electronic properties show that the dianthryl-TTFV and dipyrenyl-TTFV conformers have lower highest occupied molecular orbital-lowest unoccupied molecular orbital gaps relative to the ones obtained for dinaphthyl-TTFV, indicating that dianthryl-TTFV, and to some extend dipyrenyl-TTFV, could be good candidates for chemical sensing of fullerenes with fluorescence spectroscopy. We also investigated the effect of the solvent on the interactions of the diaryl-TTFVs with fullerenes using the polarizable continuum model. In general, the presence of a solvent decreases the diaryl-TTFV/fullerene binding energies, presumably because of the interactions of the solvent with individual fullerenes and diaryl-TTFVs.

Multicomponent Assembled Systems Based on Platinum(II) Terpyridine Complexes

Platinum(II) terpyridine complexes have received tremendous attention in recent years because of their square-planar geometry and fascinating photophysics. Bottom-up self-assembly represents an intriguing approach to construct well-ordered supramolecular architectures with tunable optical and electronic properties. Until now, much effort has been devoted to the fabrication of monocomponent platinum(II) terpyridine-based assemblies. The next step is to develop multicomponent coassembled systems via the combination of platinum(II) terpyridine complexes with other π-organic and -organometallic molecules. The implementation of electron/energy transfer processes renders advanced functionality to the resulting coassemblies. For the fabrication of discrete multicomponent architectures, a feasible protocol is to construct preorganized molecular tweezers and macrocycles with the involvement of platinum(II) terpyridine complexes as the panel units. In view of their planar surface and positively charged character, such supramolecular receptors are capable of encapsulating electron-rich polyaromatic hydrocarbons and organometallic guests via donor-acceptor charge-transfer and/or metal-metal interactions. Intermolecular hydrogen bonds can be further incorporated between the molecular tweezers receptor and the polyaromatic hydrocarbon guests, giving rise to the strengthened binding affinity and sensitive stimuli-responsiveness. On this basis, multilayer donor-acceptor stacks have been obtained via the precise control over the number of pincers, which feature enhanced complexation strength and superior functionality. Moreover, platinum(II) terpyridine-based macrocycles are more suitable for guest accommodation than the corresponding molecular tweezers receptors in light of their definite size and constrained environment. Stimuli-responsive elements can be conveniently implemented into the rigid spacers of the molecular tweezers and macrocyclic receptors, facilitating the capture and release of the sandwiched guests in a highly controlled manner. On the other hand, long-range-ordered supramolecular polymers have been successfully fabricated with linear, hyperbranched, and cross-linked topologies by employing platinum(II) terpyridine-based molecular tweezers/guest recognition motifs as the non-covalent connecting unit. The degree of polymerization of the resulting donor-acceptor-type supramolecular polymers can be efficiently modulated by incorporating intermolecular hydrogen bonds between the molecular tweezers receptor and the complementary guest unit. An alternative approach toward extended multicomponent donor-acceptor assemblies is to mimic the structure of Magnus' green salt. A delicate balance of non-covalent driving forces between homo- and heterocomplexation processes and a deeper understanding of thermodynamic and kinetic behaviors play the decisive roles in the final arrangement of the coassembled structures. Overall, multicomponent coassembly of platinum(II) terpyridine complexes into well-ordered nanostructures would open up a new avenue toward functional supramolecular materials that are especially promising for sensing, optoelectronics, and catalytic applications.