This study concerns development of a non-destructive method to control conduction and magnetism of molecular solids such as single crystals of charge-transfer complexes. The method is named “optical doping”, where appropriate irradiation is utilized under ambient conditions. Owing to this feature, it can be applied to a wide range of substances while measuring the properties during the control. In addition, the method adds unique conduction and magnetic properties to common insulators. Unlike other doping methods, optical doping only affects the properties and/or structures of the irradiated part of a sample while leaving the rest of the sample unchanged. There are two patterns in the optical doping. Irreversible optical doping produces junction-structures on the single molecular crystals, which exhibit characteristic behavior of semiconductor devices such as diodes and varistors. Reversible optical doping produces “giant photoconductors” and “photomagnetic conductors” by realizing unprecedented metallic photoconduction. In the latter case, localized spins are also excited to produce a Kondo system, where carriers and localized spins interact with each other. Not only the control of conduction and magnetism, the optical doping has realized the observation of physical properties in molecular crystals hardly observed under any thermodynamic condition.
Multiactive site catalysts have been developed for conducting one-pot synthesis and highly efficient reactions based on the principle of concerted catalysis. Ru-grafted hydrotalcite containing both Ru and base sites on its outer surface exhibits high catalytic activity for the one-pot synthesis of dinitrile compounds. A reaction system consisting of a strong acid, base, and Pd species is capable of catalyzing a one-pot process consisting of five successive reactions, esterification, deacetalization, aldol reaction, hydrogenation, and Michael reaction, to produce a final product, 2,4-dicyanoester, from starting materials containing cycnoacetic acid and acetal, with excellent overall yield. Immobilization of an amine base onto a solid acid surface affords an acid–base bifunctional catalytic surface with controlled acid–base interactions. Various nucleophilic addition reactions including the one-pot synthesis of dinitroalkane derivatives proceeds effectively by acid–base concerted catalysis. The concept of concerted catalysis on solid surfaces can be extended to synergistic/double-activation catalysis between a metal complex and organic base immobilized on a surface. Further, the concept of multiactive site catalysis can also be applied to a homogeneous catalyst system. For example, a Cu-bisphosphine complex exhibits excellent catalytic performance for the transformation of CO2 to valuable chemicals, such as cyclic carbonate, silyl formate, and formamides.
Layered double hydroxide (LDH)/anionic fluorescein dye (AFD)/1-butanesulfonate (C4S) hybrid thin solid films prepared by immersing LDH thin films in aqueous solutions of AFD and C4S were investigated as sensing materials for relative humidity (RH) and/or various organic vapors. The basal spacing, i.e., the d003 value, of the LDH/AFD/C4S hybrid films under wet conditions became larger than that under dry conditions when water was adsorbed into the interlayer space. The intensity of photoluminescence (PL) from the AFD incorporated into the hybrid also increased upon water adsorption. This PL intensity exhibited a maximum value at 10% RH and was constant when the RH exceeded 20%. This behavior is explained by an increase in the population of dianionic AFD caused by water adsorption. The PL intensity of the LDH/AFD/C4S hybrid thin solid films also increased in the presence of alcohol vapor and became larger than under wet conditions. Moreover, the PL intensity also depended on the species of alcohol. Specifically, the PL intensity decreased in the presence of nonpolar organic solvent vapors. Therefore, the present hybrid materials can be used as a sensor for relative humidity and polar organic solvent vapors.
A complex of α-cyano-4-hydroxycinnamic acid (CHCA) and zeolite was used as the matrix for the analysis of drugs and their metabolites in urine by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). It was found that acetaminophen (AAP) and its metabolites could be detected in urine without any pretreatment or separation process. It was also found that the hydrolysis of one of the metabolites, glucuronide, was promoted when a mixture of urine and the developed matrix was heated at 343 K for 15 minutes. Because of the homogeneous distribution of CHCA on the zeolite surface, high reproducibility of the analyte peak intensity was achieved. By using isotope-labeled acetaminophen (D4-AAP) as the internal standard, quantitative analysis of AAP in urine from a donor who took 300 mg of AAP four hours before was performed, and 5.29 ± 0.19 mg of AAP was detected in 1.00 g of urine.
Gold nanorods and gold-silver core-shell nanorods were colloidally dispersed in polar organic solvents, acetonitrile, dimethylsulfoxide, and dimethylformamide, and their water mixtures. The gold nanorods showed narrow longitudinal surface plasmon bands in 100% dimethylformamide, 25% dimethylsulfoxide, and 25% acetonitrile solutions, indicating that the gold nanorods were well dispersed in these solutions. For the core-shell nanorods, acetonitrile and its water mixtures gave well-dispersed colloidal solutions. Amphiphilic molecules in the dispersions did not influence the systems; however, thiol-terminated poly(ethylene glycol) (PEG-SH) strongly stabilized the colloidal dispersions. The nanorods in the organic dispersions with the addition of PEG-SH could be redispersed in phosphate buffer saline (PBS) solutions. The zeta potentials of the gold nanorods in 1/10 PBS solutions ranged from −7.5 to +3.3 mV. Steric effects of the bulky PEG chains attached to the nanorod surfaces stabilized their colloidal dispersions in PBS.
The unusual magnetic/spectroscopic properties of Cytochrome c′ (Cyt c′) have been discussed, especially concerning the possibility of a quantum mechanically mixed-spin configuration of heme Fe(III). Here, four unique-spin species were identified from the magnetic circular dichroism (MCD) spectra of Cyt c′ from Alcaligenes xylosoxidans (AxCyt c′). The electrospray ionization mass spectrometric (ESI-MS) and circular dichroism (CD) spectroscopic data showed the overall conformation of AxCyt c′ was unchanged, in complete contrast to the drastic changes in the heme MCD spectra over the range of pH 3.5 and 11.8. The pH dependency of ESI-MS, electronic absorption, MCD, and CD spectroscopic properties of AxCyt c′ enabled us to reveal the undiscovered correlation between the protein-folding state and the electronic structure of the active site as a function of pH. The mechanism of alkaline spin-state transition through the rearrangement of the hydrogen-bonding linkage between Helix C and D is also proposed on the basis of atomic resolution crystal structure analyses (A. Takashina, M. Unno, T. Kohzuma, Chem. Lett. 2015, 44, 268).
Treatment of 4,6-di(substituted)amino-1,2-dihydro-1,3,5-triazine derivative (5) with sodium chloride in a bilayer system consisting of toluene and water gave its hydrochloride (6) in the toluene layer and sodium hydroxide in the aqueous layer. Similarly, treatment of 5, 8 and 9 with an aqueous sodium acetate solution in organic solvents resulted in the formation of their corresponding acetates, 7, 12 and 13, respectively.
New well-lubricated ILs including ammonium sulfonate having a long alkyl chain have been developed. The materials based on ammonium sulfonate have a higher ΔpKa between the Brønsted acid and the Brønsted base of the salts and do not decompose even at 300 °C, making them more thermally stable than the perfluoropolyether (PFPE). Therefore, octadecyl ammonium sulfonates have a lower frictional coefficient on the carbon overcoat film even after heat treatment at high temperatures. The ILs are adsorbed on the media surface with high orientation. The alkyl chains of the C16 and C18 sulfonates in the bulk have a trans conformation, nevertheless, the films have a gauche conformation. A sufficient length of the hydrocarbon chain leads to both macro and micro-friction reductions. Dimethyl ammonium sulfonate has sufficient solubility in fluorinated solvent, which may make commercial applications possible.
Development of host materials is crucial for organic electroluminescent devices. In order to generalize the way to molecular design the host materials, we here present a guideline to design effective host materials for blue phosphorescent devices based on 4,4′-bis(9-carbazolyl)-1,1′-biphenyl (CBP) derivatives, comparing some theoretical parameters of seven CBP derivatives with experimental ones in terms of thermal stability, T1 energy level, and band gap. Although our computation at the density functional theory level could not reproduce the absolute values and phenomena that were experimentally obtained, theoretical relative correlations between different molecules agreed with experimental ones. Indeed, both experimental and theoretical approaches predicted that the same molecule (1,1-bis(4-(9-carbazolyl)-phenyl)cyclohexane) was viable as blue host material among the target molecules in terms of thermal stability, the T1 state with the LE character within carbazole moieties and T1 energy 3.00 eV higher than that of blue emitters. The qualitative guideline we proposed would be potentially helpful to save experimental work to design other hole- or electron-transporting materials.
The preparation of polyhedral oligomeric silsesquioxane (POSS) derivatives possessing different types of alkyl substituents and their application as a molecular filler for simultaneously lowering refractive indices and enhancing thermal and mechanical properties of poly(methyl methacrylate) (PMMA) are described. The modified POSS derivatives were prepared in situ through sol–gel reactions in the presence of two types of alkylsilanes. The products had molecular distributions originating from the formation of cubic and pentagonal prism structures and variable introduction ratios of alkyl substituents. Owing to the reduction of symmetry, the POSS fillers showed high miscibility with PMMA. From optical and thermal measurements, it was demonstrated that the POSS fillers with dual types of substituents can lower refractive indices (RIs) of PMMA matrices and enhance thermal and mechanical properties.
A ZSM-5 zeolite molecular sieve was prepared by using a new type of double long-alkyl-chain organosilane template. The structure of the acquired zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption–desorption measurement, which showed a piled circular sponge crystal morphology and contained mesopores around 4 nm in it.
The miscibility of chiral molecules to unimodal side-chain nematic liquid crystalline (LC) polymers was studied to generate chiral nematic phases. Chiral dopants, a phenyl benzoate derivative S-811 and an isosorbide dibenzoate derivative ISO-(6OBA)2 were miscible to the nematic LC polymer PMA(4OPB) tethering phenyl benzoate moieties as side-chain mesogens by preparing mixtures in solutions rather than directly melting the powders together. Nematic LC random copolymers containing non-LC side chains were designed to promote the interaction between mesogens and chiral molecules. The introduction of hexyl chains as side chains randomly into nematic LC polymers improved the miscibility of chiral molecules of an isosorbide dibenzoate derivative with hexyl tails. The hexyl chains of the polymer provided spaces for the chiral molecules and caused alkyl–alkyl interactions. We demonstrated that the randomly introduced hexyl chains promoted the interaction of chiral molecules with LC mesogens to generate chiral nematic phases.
The AREC (alkoxy radical elimination capacity) assay was developed to observe the DMPO (5,5-dimethyl-1-pyrroline N-oxide) spin adducts of free radicals produced by thermal decomposition of AAPH (2,2′-azobis(2,4-amidinopropane) dihydrochloride) using a flow-injection ESR (FI-ESR) system. The γ50 value is defined as [DMPO]0/ID50 = kS/k1, where k1 is the rate constant of spin-trapping of the alkoxy radical by DMPO, kS, that of alkoxy radical-elimination by the substrate, and ID50, 50% inhibition of the alkoxy radical by the substrate, and the AREC value is the ratio of γ50 value of the substrate to that of Trolox (6-hydroxy-2,5,7,8-tetramethyl-chroman-2-carboxylic acid, TRX). The γ50 and AREC values show fairly wide variations and can be determined for most biosubstances. The highest AREC values were observed for sinapic acid, l-glutathione, caffeic acid, and chlorogenic acid, followed by TRX, syringic acid, trans-ferulic acid, and homogentisic acid. Little correlation is observed between the AREC values and the hydroxy and superoxide radical-elimination abilities. The AREC values of 4-hydroxycinnamic acid derivatives (HCAs) are linearly related to the aryloxy radical-elimination abilities, which indicate that the alkoxy radical-elimination by HCAs is mainly caused by hydrogen-atom transfer. The newly defined AREC value is applicable for various biosubstances, and is far superior and a more reliable indicator than the oxygen radical absorption capacity (ORAC) value determined by the ORAC-fluorescein assay. Thus, the AREC value is an excellent indicator to characterize the antioxidant activities of a wide range of biologically important antioxidants present in fruits, vegetables, and beverages.
Thermally activated delayed fluorescence (TADF) emitters consisting of a xanthone acceptor unit and a para-, meta-linked tercarbazole donor unit were developed. The influence of the regioisomeric donor–acceptor structures on their photophysical and TADF properties was studied. Blue organic light-emitting diodes employing these TADF emitters showed high external electroluminescence quantum efficiencies of up to 14.4% with suppressed roll-off characteristics.
An orthorhombic form of polymorphs of mixed-valence trinuclear iron pentafluorobenzoate containing dichloromethane as a crystal solvent molecule, [Fe3O(C6F5COO)6(C5H5N)3]·CH2Cl2 (o-1), was newly prepared and confirmed by single crystal X-ray analysis at 123 and 300 K. Three bond lengths of Fe–O in the central Fe3O moiety are not identical, which is in contrast to our previously reported hexagonal form (h-1) having D3h local symmetry.1 57Fe Mössbauer spectra of o-1 showed a valence-trapped state consisting of high-spin Fe(III) and high-spin Fe(II) atoms with an area ratio of 2/1 to 3/1 between 78 and 300 K, being in complete contrast to those of h-1 with the valence-detrapped (averaged) state above ∼90 K. The present findings are consistently explained from the viewpoints of the crystal and molecular structures.
Continuous rapid-flow electron spin resonance (ESR) was used to detect poly(vinyl alcohol) (PVA)-derived carbon-centered radicals, in order to characterize the short-lived intermediate radicals in the initial stage of the graft polymerization of PVA. ESR spectra were recorded by mixing PVA, hydrogen peroxide, and Ti2(SO4)3 at pH 2.0. The observed spectrum indicated three paramagnetic species: a minor species A, and two major species B1, and B2. Based on the observed proton hyperfine coupling constant (hfcc) values, species A was assigned to the carbon-centered radical of PVA produced by hydrogen atom abstraction from the methine carbon bearing a hydroxyl group. Species B1 and B2 were ascribed to two structural isomers of the PVA-derived, carbonyl-conjugated radical produced by acid-catalyzed radical reaction at the vicinal diol moiety (i.e., head-to-head structure) of PVA. Spin-trapping ESR measurements were performed at 80 °C using a water-soluble spin-trapping reagent 3,5-dibromo-4-nitroso-benzenesulfonate sodium salt (DBNBS). Based on the hfcc values observed for the spin-adducts, species B1 and B2 were confirmed to be the major PVA main-chain-derived radicals produced under the graft reaction conditions. These findings demonstrated that the PVA-derived, carbonyl-conjugated radicals are one of the intermediate radicals in the initial stage of the graft polymerization reaction under acidic conditions.