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Novel Au nano-particle catalysts immobilized on both titanium(IV)- and alkylthiol-functionalized SBA-15 type ordered mesoporous silicate supports were developed. The bi-functionalized SBA-15 type support could be synthesized by a one-pot method. To the synthesized supports, Au was immobilized by the reaction of the alkylthiol groups on the supports with AuCl4−, following reduction with NaBH4. The immobilized amount and the formed structures and the electronic property of the Au species depended on the loading of alkylthiol. The moderate size (2–3 nm) nano particulate Au sites formed on Ti(0.5)-SBASH(0.5) were negatively charged. The aerobic alcohol oxidation activity of the catalysts depended on the loading of alkylthiol and the structure of the Au nano-particles. The non-thiol-functionalized catalyst (Au/Ti(0.5)-SBASH(0)) composed of the large (5–30 nm) and the higher thiol-loaded catalyst (Au/Ti(0.5)-SBASH(8)) composed of the small cationic Au species were almost inactive. The most active catalyst was Au/Ti(0.5)-SBASH(0.5) composed of the electron-rich Au nano-particles formed by the electron donation from the highly dispersed thiol groups. Styrene oxidation activity in the presence of 1-phenylethanol with O2 depended on the loadings of titanium(IV) on the Au/Ti(x)-SBASH(0.5). The titanium(IV) sites trapped the H2O2 generated through the alcohol oxidation reaction, and also contributed to the alkene oxidation by activating the trapped H2O2.

Cationic BN-embedded polycyclic aromatic hydrocarbons (BN-PAH+ s) were synthesized from a nitrogen-containing macrocycle via pyridine-directed tandem C-H borylation. Incorporating BN into PAH+ resulted in a remarkable hypsochromic shift due to an increase in the LUMO energy and the symmetry changes of the HOMO and LUMO. Electrophilic substitution or anion exchange of BN-PAH+ possessing tetrabromoborate as a counter anion (BN+ [BBr4- ]) afforded air-stable BN-PAH/PAH+ s. Of these, BN+ [TfO- ] allowed reversible two-electron reduction and the formation of two-dimensional brickwork-type π-electronic ion pair with 1,2,3,4,5-pentacyanocyclopentadienyl anion, demonstrating the potential application of BN-PAH+ as electronic materials.

Various counteranions of the thiaporphyrin–NiII complex as a p-electronic cation were exchanged for preparing stable ion pairs. The ion-pairing assembling modes, and properties depended on the geometries and electronic states of the counteranions.

In this study, charged π-electronic species are observed to develop stacking structures based on electrostatic and dispersion forces. iπ–iπ Interaction, defined herein, functions for the stacking structures consisting of charged π-electronic species and is in contrast to conventional π–π interaction, which mainly exhibits dispersion force, for electronically neutral π-electronic species. Establishing the concept of iπ–iπ interaction requires the evaluation of interionic interactions for π-electronic ion pairs. Free base (metal-free) and diamagnetic metal complexes of 5-hydroxy-10,15,20-tris(pentafluorophenyl)porphyrin were synthesized, producing π-electronic anions upon the deprotonation of the hydroxy unit. Coexisting cations in the ion pairs with porphyrin anions were introduced as the counter species of the hydroxy anion as a base for commercially available cations and as ion-exchanged species, via Na+ in the intermediate ion pairs, for synthesized π-electronic cations. Solid-state ion-pairing assemblies were constructed for the porphyrin anions in combination with aliphatic tetrabutylammonium (TBA+) and π-electronic 4,8,12-tripropyl-4,8,12-triazatriangulenium (TATA+) cations. The ordered arrangements of charged species, with the contributions of the charge-by-charge and charge-segregated modes, were observed according to the constituent charged building units. The energy decomposition analysis (EDA) of single-crystal packing structures revealed that electrostatic and dispersion forces are important factors in stabilizing the stacking of π-electronic ions. Furthermore, crystal-state absorption spectra of the ion pairs were correlated with the assembling modes. Transient absorption spectroscopy of the single crystals revealed the occurrence of photoinduced electron transfer from the π-electronic anion in the charge-segregated mode., π-Electronic ion pairs comprising porphyrin-based π-electronic anions have exhibited characteristic assembling modes and resulting electronic properties such as solid-state absorption and photoinduced electron transfer.

Stimulus-responsive supramolecular architectures have become an attractive alternative to conventional ones for many applications in sensing, drug-delivery and switchable memory systems. Herein, we used an anion receptor (H: host) as a hydrostatic-pressure-manipulatable fluorescence foldamer and halide anions as chiral (binaphthylammonium) and achiral (tetrabutylammonium) ion pairs (SS or RR·X and TBA·X; X = Cl, Br), and then investigated their (chir)optical properties and molecular recognition behavior under hydrostatic pressures. The conformational changes and optical properties of H in various organic solvents were revealed by UV/vis absorption and fluorescence spectra and fluorescence lifetimes upon hydrostatic pressurization. The anion-recognition abilities of H upon interactions with SS or RR·X and TBA·X at different pressure ranges were determined by hydrostatic-pressure spectroscopy to quantitatively afford the binding constant (Kanion) and apparent reaction volume changes . The results obtained indicate that hydrostatic pressure as well as solvation plays significant roles in the dynamic control of the present supramolecular system in the ground and excited states. This work will provide a new guideline for further developing hydrostatic-pressure-responsive foldamers and supramolecular materials., Hydrostatic pressure can control interactions of chiral countercations with helical receptors containing anions, causing remarkable chiroptical changes.

The introduction of a carboxy unit onto dipyrrolyldiketone skeletons was achieved by complexation with arylfluoroboron moieties bearing an acid group. Carboxylate-appended anion-responsive π-electronic molecules, formed upon deprotonation, provided anion-binding self-assemblies, as anionic supramolecular polymers, resulting in ion-pairing assemblies.

Two-photon-excited fluorescent probes are important for two-photon microscopy for biomedical studies. In contrast to the many examples of probes for cationic species, such as metal ions, there have been fewer reports on the control of two-photon optical properties by anions because in such systems it is difficult to control the associated π-electronic states. This Minireview summarizes anion-responsive molecules that exhibit changes in two-photon optical properties and describes their molecular design and anion-response mechanisms, which are driven by changes in covalent bonds and noncovalent interactions. Results from a recent study of two-photon systems, where geometries and optical properties are modulated by anion binding, are also discussed.

Organic radicals consisting of light elements exhibit a low spin-orbit coupling and weak hyperfine interactions with a long spin coherence length, which are crucial for future applications in molecular spintronics. However, the synthesis and characterization of these organic radicals have been a formidable challenge due to their chemical instability arising from unpaired electrons. Here, we report a direct imaging of the surface chemical transformation of an organic monoradical synthesized via the monodehydrogenation of a chemically designed precursor. Bond-resolved scanning tunneling microscopy unambiguously resolves various products formed through a complex structural dissociation and rearrangement of organic monoradicals. Density functional theory calculations reveal detailed reaction pathways from the monoradical to different cyclized products. Our study provides unprecedented insights into complex surface reaction mechanisms of organic radical reactions at the single molecule level, which may guide the design of stable organic radicals for future quantum technology applications.

In this study, the diverse derivatives of dipyrrolyldiketone boron complexes as anion-responsive π-electronic systems were synthesized via the Huisgen cycloaddition of an ethynyl-substituted anion receptor and azide derivatives. The obtained triazole-substituted anion receptors showed effective anion-binding behaviors and ion-pairing assemblies comprising receptor-anion complexes and countercations. Solid-state ion-pairing structures were modulated according to the introduced azide moieties along with coexisting bulky and π-electronic cations.

Modified curved π-electronic systems, dipyrrolylbenzodiazepines, exhibited modulated electronic properties and assemblies, including C60complexation by a hydrogen-bonding cyclic hexamer, which induces solid-state photo-induced electron transfer.

Anion-responsive photofunctional materials have been extensively studied because anions are important for biotic activity and constitute the building blocks of elegant supramolecular architectures. A number of fluorescent anion receptors that can probe anions in their environments have been reported, but the excited states of many of these molecules remain elusive. Studies on excited-state dynamics provide fruitful information for optimizing the emission properties, minimizing the photodegradation and photorelease of anions, and exploring novel photofunctions. In this study, we investigated the excited-state dynamics of an aryl-substituted dipyrrolyldiketone difluoroboron complex, a π-conjugated anion receptor, by time-resolved visible and infrared absorption spectroscopy and emission decay measurements combined with quantum chemical calculations. Anion binding was found to alter the radiative and nonradiative rate constants and the excited-state absorption of the anion receptor. In contrast, the molecular structures and binding abilities were similar in the S

Ion-pairing assemblies consisting of appropriately designed charged π-electronic species afford various functional supramolecular assemblies, including crystals and soft materials; they are formed by the anisotropic arrangement of charged π-electronic species through electrostatic and other weak noncovalent interactions. The design, synthesis and combination of charged π-electronic species (ion-pair formation) are crucial for the preparation of functional dimension-controlled assemblies. This article includes the prologue and progress of ion-pairing assemblies comprising π-electronic ions. Synthesis of π-electronic ions, preparation of ion pairs, fabrication of assemblies as crystals, gels and liquid crystals and their characteristic properties are summarized.

Phenyl groups were introduced at the β-positions proximal to the meso-hydroxy moiety in hydroxyporphyrin NiII complexes by oxidized BINAP PdII complexes. Ion-pairing assemblies of deprotonated π-electronic anions, anionic site of which was stabilized by the introduced phenyl moieties with a bulky cation, were formed. They showed charge-by-charge assemblies, assembly modes of which were modulated by the anionic building units.

Dipyrrolylnitrophenols (DPPhs) afforded various hydrogen-bonding-stabilized π-electronic anions upon deprotonation. Through ion-pair metathesis, π-electronic cations were introduced as a counter species to provide π-electronic ion pairs that occurred as tightly bound states in solution while resulting in solid-state charge-by-charge assemblies. The assembling modes were modulated according to the geometries and electronic states of the positively charged constituents along with the substituents of the DPPh anions.

Pyrrole-based zwitterionic π-electronic systems including a phenylcarboxylate (benzoate) anionic site and an N-methyl pyridinium cation unit were synthesized. Spectroscopic and theoretical examinations revealed the intermolecular hydrogen-bonding interactions of the pyrrole NH group and the 3-pyridinium and 3-benzoate ortho-CH moieties of zwitterions with a carboxylate anion to form self-assembled dimers. The self-assembled dimers were found to exist in equilibrium with the corresponding monomers in DMSO, whose dimerization ability was examined by concentration-dependent measurements.