This critical review describes mechanisms by which guest molecules enter and depart molecular capsules. The discussion focuses on presenting gated molecular encapsulation, i.e., trapping and releasing of guest molecules at rates that are controlled by conformational changes in the host's structure. Developing quantitative rules that describe the gating are, at present, a matter of scientific curiosity but could play an important role in building more effective catalysts, drug-delivery devices or membranes (105 references).

Organic rechargeable batteries, composed of redox-active molecules, are emerging as candidates for the next generation of energy storage materials because of their large specific capacities, cost effectiveness, and the abundance of organic precursors, when compared with conventional lithium-ion batteries. Although redox-active molecules often display multiple redox states, precise control of a molecule's redox potential, leading to a single output voltage in a battery, remains a fundamental challenge in this popular field of research. By combining macrocyclic chemistry with density functional theory calculations (DFT), we have identified a structural motif that more effectively delocalizes electrons during lithiation events in battery operations-namely, through-space electron delocalization in triangular macrocyclic molecules that exhibit a single well-defined voltage profile-compared to the discrete multiple voltage plateaus observed for a homologous macrocyclic dimer and an acyclic derivative of pyromellitic diimide (PMDI). The triangular macrocycle, incorporating three PMDI units in close proximity to one another, exhibits a single output voltage at 2.33 V, compared with two peaks at (i) 2.2 and 1.95-1.60 V for reduction and (ii) 1.60-1.95 and 2.37 V for oxidation of the acyclic PMDI derivative. By investigating the two cyclic derivatives with different conformational dispositions of their PMDI units and the acyclic PMDI derivative, we identified noticeable changes in interactions between the PMDI units in the two cyclic derivatives under reducing conditions, as determined by differential pulse voltammetry, solution-state spectroelectrochemistry, and variable-temperature UV-Vis spectra. The numbers and relative geometries of the PMDI units are found to alter the voltage profile of the active materials significantly during galvanostatic measurements, resulting in a desirable single plateau for the triangular macrocycle. The present investigation reveals that understanding and controlling the relative conformational dispositions of redox-active units in macrocycles are key to achieving high energy density and long cycle-life electrodes for organic rechargeable batteries.

In this review, we describe the construction of gated molecular baskets, discuss their mechanism of action in regulating the exchange of guests and illustrate the potential of these concave hosts to act as catalysts for controlling chemical reactions. Importantly, a number of computational and experimental studies have suggested that gated baskets ought to unfold their gates at the rim for permitting the passage of guests to/from their inner space. These dynamic hosts are therefore offered as useful models for investigating the process of gating in artificial systems. Furthermore, gated baskets should permit examining the benefit of controlling the rate by which reactants access a gated catalyst for promoting chemical reactions occurring in its confined space.

Designing small-molecule organic redox-active materials, with potential applications in energy storage, has received considerable interest of late. Herein, we report on the synthesis, characterization, and application of two rigid chiral triangles, each of which consist of non-identical pyromellitic diimide (PMDI) and naphthalene diimide (NDI)-based redox-active units. (1)H and (13)C NMR spectroscopic investigations in solution confirm the lower symmetry (C2 point group) associated with these two isosceles triangles. Single-crystal X-ray diffraction analyses reveal their rigid triangular prism-like geometries. Unlike previously investigated equilateral triangle containing three identical NDI subunits, both isosceles triangles do not choose to form one-dimensional supramolecular nanotubes by dint of [C-H···O] interaction-driven columnar stacking. The rigid isosceles triangle, composed of one NDI and two PMDI subunits, forms-in the presence of N,N-dimethylformamide-two different types of intermolecular NDI-NDI and NDI-PMDI π-π stacked dimers with opposite helicities in the solid state. Cyclic voltammetry reveals that both isosceles triangles can accept reversibly up to six electrons. Continuous-wave electron paramagnetic resonance and electron-nuclear double-resonance spectroscopic investigations, supported by density functional theory calculations, on the single-electron reduced radical anions of the isosceles triangles confirm the selective sharing of unpaired electrons among adjacent redox-active NDI subunit(s) within both molecules. The isosceles triangles have been employed as electrode-active materials in organic rechargeable lithium-ion batteries. The evaluation of the structure-performance relationships of this series of diimide-based triangles reveals that the increase in the number of NDI subunits, replacing PMDI ones, within the molecules improves the electrochemical cell performance of the batteries.

Radical templation centered around a heterotrisradical tricationic inclusion complex DB•+ ⊂DAPQT 2(•+), assembled from an equimolar mixture of a disubstituted 4,4'-bipyridinium radical cation (DB interlocked cyclobis(paraquat-p-phenylene) rings-with 0, 1, and 2 more highly conjugated diazapyrenium dication (DAP 2+ ) units, respectively, a consecutive series of 5, 6, and 7 redox states can be accessed in the resulting SC•7PF 6 (0, 4+, 6+, 7+, and 8+), HC•7PF 6 (0, 2+, 4+, 6+, 7+, and 8+), and AC•7PF 6 (0, 1+, 2+, 4+, 6+, 7+, and 8+), respectively. These unique[2]catenanes present a promising prototype for the fabrication of high-density data memories. ■ INTRODUCTIONEver since the landmark discovery of the triphenylmethyl radical 1 by Moses Gomberg, research on stable organic radicals 2 has attracted attention, not only on account of their exotic electronic properties, but also because of their potential applications as spin-labels 3 and in organic lithium batteries 4 as well as in conductive and magnetic materials. 5 To date, however, most organic radicals experience a fleeting existence and readily undergo dimerization and/or 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 3 oxidation. The synthesis and isolation of persistent radicals in crystalline forms remains a challenge. In addition, molecular systems with adjustable number of accessible redox states are quite difficult to achieve. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 6 complex is indeed the bisradical tetracation ((DB⊂DAPQT) 2•4+ ) rather than a trisradical trication in the solid state. Since the torsional angles of both units A and B are less than 3° and the planeto-plane separation between them is only 3.1 Å, the implication is that both units A and B are in the radical cationic BIPY •+ state and the remaining unit C is in the dicationic DAP 2+ state. The plane-to-plane separation between units B and C is 3.4 Å, a distance which is a typical one for[π···π] interactions. In addition, the complex is further stabilized by multiple [C-H···π] interactions between the p-phenylene rings on the unit B and C-H groups on the DAP 2+ unit.Overall, the superstructure is arranged (Figure 2d) in an infinite stack, driven by intermolecular[Br···π] interactions between adjacent inclusion complexes.Since the hetero trisradical tricationic complex is stable in MeCN, we grasped 18 the opportunity to synthesize (Schemes S1 and S2) AC•7PF 6 and SC•7PF 6 . The in situ formed complex DB •+ ⊂DAPQT 2(•+) was allowed to react with 4,4'-bipyridine and 2,7-diazapyrene, respectively, for two weeks at room temperature to afford both AC•7PF 6 and SC•7PF 6 as purple solids. The 1 H NMR spectra of bo...

A preparative procedure for obtaining a pair of twisted molecular baskets, each comprising a chiral framework with either right ((P)-1syn) or left ((M)-1syn) sense of twist and six ester groups at the rim has been developed and optimized. The racemic (P/M)-1syn can be obtained in three synthetic steps from accessible starting materials. The resolution of (P/M)-1syn is accomplished by its transesterification with (1R,2S,5R)-(-)-menthol in the presence of a Ti(IV) catalyst to give diastereomeric 8(P) and 8(M). It was found that dendritic-like cavitands 8(P) and 8(M), in CD2Cl2, undergo self-inclusion ((1)H NMR spectroscopy) with a menthol moiety occupying the cavity of each host. Importantly, the degree of inclusion of the menthol group was ((1)H NMR spectroscopy) found to be greater in the case of 8(P) than 8(M). Accordingly, it is suggested that different folding characteristic of 8(P) and 8(M) ought to affect the physicochemical characteristics of the hosts to permit their effective separation by column chromatography. The absolute configuration of 8(P)/8(M), encompassing right- and left-handed "cups", was determined with the exciton chirality method and also verified in silico (DFT: B3LYP/TZVP). Finally, the twisted baskets are strongly fluorescent due to three naphthalene chromophores, having a high fluorescence quantum yield within the rigid framework of 8(P)/8(M).

We have developed a novel synthetic method that enables the preparation of functional derivatives of heptiptycene, i.e., cavitands with two juxtaposed cavities. The homocoupling of bicyclic dibromoalkenes is promoted by Pd(OAc)2 (10%) in dioxane (100 °C) to give cyclotrimers in 27-77% yield under optimized reaction conditions (Ph3P, K2CO3, n-Bu4NBr, N2, 4 Å MS). These dual-cavity baskets show a strong π → π* absorption at 241 nm (ε = 939,000 M(-1) cm(-1)), along with a subsequent fluorescence emission at 305 nm.

Up for grabs: A modular receptor comprises a hexaazatriphenylene "platform" and three imide residues on its concave side carrying flexible alkane chains. The chains not only populate the host's cavity but can also extend and can grab an appropriately sized and shaped guest in solution.