Mio Kondo

Molecular decoding using luminescence from an entangled porous framework

Chemosensors detect a single target molecule from among several molecules, but cannot differentiate targets from one another. In this study, we report a molecular decoding strategy in which a single host domain accommodates a class of molecules and distinguishes between them with a corresponding readout. We synthesized the decoding host by embedding naphthalenediimide into the scaffold of an entangled porous framework that exhibited structural dynamics due to the dislocation of two chemically non-interconnected frameworks. An intense turn-on emission was observed on incorporation of a class of aromatic compounds, and the resulting luminescent colour was dependent on the chemical substituent of the aromatic guest. This unprecedented chemoresponsive, multicolour luminescence originates from an enhanced naphthalenediimide–aromatic guest interaction because of the induced-fit structural transformation of the entangled framework. We demonstrate that the cooperative structural transition in mesoscopic crystal domains results in a nonlinear sensor response to the guest concentration. Distinguishing closely related molecules using chemosensor materials is a continuing challenge. Here, an entangled porous coordination polymer is developed, which confines volatile organic compounds, and allows photoluminescence-based distinction of structurally similar aromatic molecules.

Shape-Memory Nanopores Induced in Coordination Frameworks by Crystal Downsizing

Size Affects Shape Porous molecular framework materials can adopt a different phase when guest molecules absorb and uniformly distort the framework. Usually the framework returns to its original shape when the guests desorb. Sakata et al. (p. 193) noted that because surface stress drives this process, it might be avoided in smaller crystals. Indeed, a flexible porous coordination polymer, [Cu2(dicarboxylate)2(amine)]n, could retain the structure induced by guest molecules such as methanol if crystallites were made sufficiently small (submicrometer scale) and did so to a greater degree as the crystallite dimensions decreased. A porous material retains its framework shape after guest molecules desorb if its crystallites are sufficiently small. Flexible porous coordination polymers change their structure in response to molecular incorporation but recover their original configuration after the guest has been removed. We demonstrated that the crystal downsizing of twofold interpenetrated frameworks of [Cu2(dicarboxylate)2(amine)]n regulates the structural flexibility and induces a shape-memory effect in the coordination frameworks. In addition to the two structures that contribute to the sorption process (that is, a nonporous closed phase and a guest-included open phase), we isolated an unusual, metastable open dried phase when downsizing the crystals to the mesoscale, and the closed phase was recovered by thermal treatment. Crystal downsizing suppressed the structural mobility and stabilized the open dried phase. The successful isolation of two interconvertible empty phases, the closed phase and the open dried phase, provided switchable sorption properties with or without gate-opening behavior.

Heterogeneously Hybridized Porous Coordination Polymer Crystals: Fabrication of Heterometallic Core–Shell Single Crystals with an In-Plane Rotational Epitaxial Relationship†

MOF on MOF: Core-shell porous coordination polymer (PCP) crystals are fabricated at the single-crystal level by epitaxial growth in solution. Synchrotron X-ray diffraction measurements unveiled the structural relationship between the shell crystal and the core crystal, where in-plane rotational epitaxial growth compensates the difference in lattice constant.

Sequential Functionalization of Porous Coordination Polymer Crystals

Crystal extractor: heterostructured porous coordination polymer crystals fabricated using epitaxial growth have two contradictory porous functions, namely size selectivity and high storage. The crystals not only extract linear petroleum molecules from a mixture with its branched isomer, even at very low concentrations of linear isomer (1 wt %), but also shows improved accumulation of the molecules in its pores.

A pentanuclear iron catalyst designed for water oxidation

Although the oxidation of water is efficiently catalysed by the oxygen-evolving complex in photosystem II (refs 1 and 2), it remains one of the main bottlenecks when aiming for synthetic chemical fuel production powered by sunlight or electricity. Consequently, the development of active and stable water oxidation catalysts is crucial, with heterogeneous systems considered more suitable for practical use and their homogeneous counterparts more suitable for targeted, molecular-level design guided by mechanistic understanding. Research into the mechanism of water oxidation has resulted in a range of synthetic molecular catalysts, yet there remains much interest in systems that use abundant, inexpensive and environmentally benign metals such as iron (the most abundant transition metal in the Earth’s crust and found in natural and synthetic oxidation catalysts). Water oxidation catalysts based on mononuclear iron complexes have been explored, but they often deactivate rapidly and exhibit relatively low activities. Here we report a pentanuclear iron complex that efficiently and robustly catalyses water oxidation with a turnover frequency of 1,900 per second, which is about three orders of magnitude larger than that of other iron-based catalysts. Electrochemical analysis confirms the redox flexibility of the system, characterized by six different oxidation states between FeII5 and FeIII5; the FeIII5 state is active for oxidizing water. Quantum chemistry calculations indicate that the presence of adjacent active sites facilitates O–O bond formation with a reaction barrier of less than ten kilocalories per mole. Although the need for a high overpotential and the inability to operate in water-rich solutions limit the practicality of the present system, our findings clearly indicate that efficient water oxidation catalysts based on iron complexes can be created by ensuring that the system has redox flexibility and contains adjacent water-activation sites.

Porous coordination polymer hybrid device with quartz oscillator: effect of crystal size on sorption kinetics.

A new strategy to synthesize monodispersed porous coordination polymer (PCP) nanocrystals at room temperature was developed and utilized for the formation of PCP thin films on gold substrates with fine control over the crystal sizes using the coordination modulation method. Hybridization of these PCP thin films with an environment-controlled quartz crystal microbalance system allowed determining the adsorption properties for organic vapors (methanol and hexane). In the case of high sensitivity (at the low-concentration dosing of analytes), the sensor response depended on the crystal size but not on the type of analyte. In contrast, at the high-concentration dosing, a clear dependence of the sorption kinetics on the analyte was observed due to significant sorbate-sorbate interaction.

Localized cell stimulation by nitric oxide using a photoactive porous coordination polymer platform

Functional cellular substrates for localized cell stimulation by small molecules provide an opportunity to control and monitor cell signalling networks chemically in time and space. However, despite improvements in the controlled delivery of bioactive compounds, the precise localization of gaseous biomolecules at the single-cell level remains challenging. Here we target nitric oxide, a crucial signalling molecule with site-specific and concentration-dependent activities, and we report a synthetic strategy for developing spatiotemporally controllable nitric oxide-releasing platforms based on photoactive porous coordination polymers. By organizing molecules with poor reactivity into polymer structures, we observe increased photoreactivity and adjustable release using light irradiation. We embed photoactive polymer crystals in a biocompatible matrix and achieve precisely controlled nitric oxide delivery at the cellular level via localized two-photon laser activation. The biological relevance of the exogenous nitric oxide produced by this strategy is evidenced by an intracellular change in calcium concentration, mediated by nitric oxide-responsive plasma membrane channel proteins.

Control over the nucleation process determines the framework topology of porous coordination polymers

In this contribution, we present a method to selectively synthesize crystal polymorphs of [Zn2(bdc)2(dabco)]n (1) and [Zn2(bdc)2(bpy)]n (2), either the pillared 2D square-grid nets (1sql or 2sql) or the pillared 2D Kagome nets (1kgm or 2kgm) by simply changing the crystallization temperature.

Targeted functionalisation of a hierarchically-structured porous coordination polymer crystal enhances its entire function

Spatiospecific functionalisation of a shell crystal was performed in a core-shell crystal of a porous coordination polymer (PCP) via post-synthetic modification (PSM). The shell crystal allowed the core crystal to selectively accumulate N,N-dimethylaniline (DMA) and afford the intense exciplex fluorescence.

Hybrid Catalysis Enabling Room-Temperature Hydrogen Gas Release from N-Heterocycles and Tetrahydronaphthalenes

Hybrid catalyst systems to achieve acceptorless dehydrogenation of N-heterocycles and tetrahydronaphthalenes-model substrates for liquid organic hydrogen carriers-were developed. A binary hybrid catalysis comprising an acridinium photoredox catalyst and a Pd metal catalyst was effective for the dehydrogenation of N-heterocycles, whereas a ternary hybrid catalysis comprising an acridinium photoredox catalyst, a Pd metal catalyst, and a thiophosphoric imide organocatalyst achieved dehydrogenation of tetrahydronaphthalenes. These hybrid catalyst systems allowed for 2 molar equiv of H2 gas release from six-membered N-heterocycles and tetrahydronaphthalenes under mild conditions, i.e., visible light irradiation at rt. The combined use of two or three different catalyst types was essential for the catalytic activity.