Prompted by a knowledge of the photoprotective mechanism operating in photosystem supercomplexes and bacterial antenna complexes by pigment binding proteins, we have appealed to a boxlike synthetic receptor (ExBox·4Cl) that binds a photosensitizer, 5,15-diphenylporphyrin (DPP), to provide photoprotection by regulating light energy. The hydrophilic ExBox 4+ renders DPP soluble in water and modulates the phototoxicity of DPP by trapping it in its cavity and releasing it when required. While trapping removes access to the DPP triplet state, a pH-dependent release of diprotonated DPP (DPPH2 2+) restores the triplet deactivation pathway, thereby activating its ability to generate reactive oxygen species. We have employed the ExBox 4+-bound DPP complex (ExBox 4+⊃DPP) for the safe delivery of DPP into the lysosomes of cancer cells, imaging the cells by utilizing the fluorescence of the released DPPH2 2+ and regulating photodynamic therapy to kill cancer cells with high efficiency.

Co-crystallization of K and Li ions with γ-cyclodextrin (γ-CD) has been shown to substitute the K ion sites partially by Li ions, while retaining the structural integrity and accessible porosity of CD-MOF-1 (MOF, metal-organic framework). A series of experiments, in which the K/Li ratio was varied with respect to that of γ-CD, have been conducted in order to achieve the highest possible proportion of Li ions in the framework. Attempts to obtain a CD-MOF containing only Li ions resulted in nonporous materials. The structural occupancy on the part of the Li ions in the new CD-MOF has been confirmed by single-crystal X-ray analysis by determining the vacancies of K-ion sites and accounting for the cation/γ-CD ratio in CD-MOF-1. The proportion of Li ions has also been confirmed by elemental analysis, whereas powder X-ray diffraction has established the stability of the extended framework. This noninvasive synthetic approach to generating mixed-metal CD-MOFs is a promising method for obtaining porous framework unattainable de novo. Furthermore, the CO and H capture capacities of the Li-ion-substituted CD-MOF have been shown to exceed the highest sorption capacities reported so far for CD-MOFs.

Artificial molecular machines can be operated using either physical or chemical inputs. Light-powered motors display clean and autonomous operations, whereas chemically driven machines generate waste products and are intermittent in their motions. Herein, we show that controlled changes in applied electrochemical potentials can drive the operation of artificial molecular pumps in a semi-autonomous manner-that is, without the need for consecutive additions of chemical fuel(s). The electroanalytical approach described in this Communication promotes the assembly of cyclobis(paraquat-p-phenylene) rings along a positively charged oligomeric chain, providing easy access to the formation of multiple mechanical bonds by means of a controlled supply of electricity.

Designing macrocycles with appropriate molecular recognition features that allow for the integration of suitable external stimuli to control host−guest processes is a challenging endeavor which enables molecular containers to solubilize, stabilize, and separate chemical entities in an externally controllable manner. Herein, we introduce photoand thermal-responsive elements into a semi-rigid tetracationic cyclophane, OPVEx 2 Box 4+ , that is composed of oligo(p-phenylenevinylene) pyridinium units and the biphenylene-bridged 4,4-bipyridinium extended viologens and adopts a rectangle-like geometry. It transpires that when the photoactive oligo(p-phenylenevinylene) pyridinium unit is incorporated in a macrocyclic scaffold, its reversibility is dramatically improved, and the configurations of the cyclophane can go back and forth between (EE)-and (EZ)-isomers upon alternating blue light irradiation and heating. When the macrocycle is found in its (EE)-configuration, it is capable of binding various π-electron-rich guestse.g., anthracene and peryleneas well as π-electron-deficient guestse.g., 9,10-anthraquinone and 5,12-tetracenequinonethrough charge-transfer and van der Waals interactions. When irradiated with blue light, the (EE)-isomer of the cyclophane can be transformed successfully to the (EZ)-isomer, resulting in the switching off of the binding affinity for guest molecules, which are bound once again upon heating. The use of light and heat as external stimuli to control host−guest interactions involving a multi-responsive host and various guests provides us with a new opportunity to design and construct more-advanced molecular switches and machines.

A series of donor−acceptor (D-A) naphthalene−viologen-based cyclophanes of different shapes, sizes, and symmetries have been synthesized and characterized. Solution optical studies on these cyclophanes reveal the existence of photoinduced intramolecular charge transfer (CT) at 465 nm from naphthalene (D) to viologen (A) units, resulting in a conformational change in the viologen units and the emergence of an emission at 540 nm. The D-A cyclophanes with box-like and hexagon-like shapes offer an opportunity to control the arrangement within 2D layers where D-A interactions direct the superstructures. While a box-like 2,6-disubstituted naphthalene-based tetracationic cyclophane does not form square tiling patterns, a truncated hexagon-like congener self-assembles to form a hexagonal superstructure which, in turn, adopts a hexagonal tiling pattern. Tessellation of the more rigid and highly symmetrical 2,7disubstituted naphthalene-based cyclophanes leads to the formation of 2D square and honeycomb tiling patterns with the boxlike and hexagon-like cyclophanes, respectively. Co-crystallization of the box-like cyclophanes with tetrathiafulvalene (TTF) results in the formation of D-A CT interactions between TTF and viologen units, leading to tubular superstructures. Cocrystallization of the hexagon-like cyclophane with TTF generates well-ordered and uniform tubular superstructures in which the TTF−viologen CT interactions and naphthalene−naphthalene [π•••π] interactions propagate with 2D topology. In the solid state, the TTF−cyclophane co-crystals are paramagnetic and display dual intra-and intermolecular CT behavior at ∼470 and ∼1000 nm, respectively, offering multi-responsive materials with potential pathways for electron transport.