Dication-type amino acid ionic liquids have been prepared and their physicochemical properties, such as viscosity, glass transition temperature, Kamlet-Taft parameter, ionic conductivity, and refractive index, have been examined. Comparing these properties of the dication-type amino acid ionic liquids with those of corresponding monocation-type ones, we have investigated the effects of the cation-bridging. In addition, the comparison of aliphatic amino acid ionic liquids and aromatic ones has been also examined. By examining lyotropic liquid-crystalline behavior of an amphiphile in these ionic liquids, we have examined how these modifications of ionic liquids make changes in the potential utility of ionic liquids as self-organization media of amphiphiles. It has been found that critical concentrations of lyotropic liquid-crystalline amphiphiles in ionic liquids are successfully reduced by bridging their cations with covalent bonding and/or introducing aromatic-structures into their anions.
Lanthanide (Ln3+) complexes composed of luminescent Eu3+ complex and joint metal blocks (Al3+, Zn2+ and Pd2+ complexes) are reported. The Eu3+ complexes [Eu(hfa)3(dppy)2PdCl2]n (Eu-Pd), [Eu(hfa)3(dppy)2ZnCl2]n (Eu-Zn) and [Eu(hfa)3(dppy)4AlCl3]n (Eu-Al) (hfa: hexafluoroacetylacetonato, dppy: 4-pyridyldiphenylphosphine oxide) were synthesized by the complexation of [Eu(hfa)3(H2O)2] with [MCln(dppy)m] (M = Pd2+, Zn2+ and Al3+). These predicted structures were estimated using single-crystal X-ray structural analyses and DFT calculations. Photophysical properties of these complexes were evaluated based on the emission lifetimes and emission quantum yields. The emission quantum yields are dependent on the moiety of the joint metal blocks. Eu-Al complex shows the largest emission quantum yield (Φff = 72%). In contrast, the emission quantum yield of Eu-Pd is found to be 1.3%. The structures and photophysical properties of Eu3+ complexes linked with joint metal blocks are demonstrated.
In this work, the synthesis and solid-state structure of a lithium borate with 2,2-dipropylglycolato (GlyPr2) ligand has been described. The desired lithium borate as well as previously reported borates with methyllactato (ML) and mandelate (Man) ligands could be synthesized rapidly and cleanly by using LiBH4 as a reagent in THF. The solid-state structures of the THF- and glyme-solvates of LiB(GlyPr2)2 (3 and 4) were determined by XRD analysis. Both these structures, except DME-solvate 4a, have one dimensional aggregate (AGG) form (1D-chain) that contains a µ2-borate fragment. In contrast, the THF-solvates with other borates derived from MLH2 and (S)-ManH2 (1 and 2) are less soluble in THF and have tighter AGG (2D-layer) with the µ3-borate fragment in the solid state.
The ability to manipulate the behavior of electrons at organic–inorganic interfaces is of crucial importance in the development of future molecular devices. It has been shown that interface dipoles, created by the chemisorption of a self-assembled organic monolayer (SAM) on a solid surface, induce carrier injection effects. This means that the interface electronic properties can be manipulated by designing the molecular dipoles and arrangements in the SAMs. In this study, a novel strategy to photo-control molecular dipoles through the use of photochromic SAMs is proposed, and a number of photo-controllable molecular devices have been developed based on this strategy. This account provides a review of the basic concept of the photo-control of interface dipoles and the recent advances in the development of photo-controllable molecular devices.
The efficient catalytic conversion of lignocellulose is a formidable issue, but it is worth studying in terms of the high potential as renewable chemical feedstock. In this account, we describe our approach to convert solid cellulose with solid catalysts. We found that carbons bearing weak acid sites were active for the hydrolysis of cellulose. The catalyst produced glucose in up to 88% yield after the formation of good solid–solid contact, due to selective enhancement of the solid–solid interfacial reaction. We also developed a cyclic system to efficiently convert real lignocellulosic biomass. Mechanistic study has revealed that polycyclic carbon aromatics attract cellulose by CH–π interactions mainly consisting of dispersion forces and hydrophobic interactions. The adsorbed cellulose molecules diffuse on the surface, rapidly penetrate even micropores, and undergo hydrolysis by weak acid sites such as carboxylic acids. Phenolic or carboxylic groups adjacent to the weak acid increase the frequency factor by forming hydrogen bonds. The combined functions of carbon derived from both polar and non-polar groups achieve the hydrolysis of cellulose. Finally, we comment on future perspective to apply these findings.
Imide- or amide-based π-systems, as represented by naphthalenediimides (NDIs), perylenediimides (PDIs), or diketopyrrolopyrroles (DPPs), have been extensively studied owing to their characteristic optical properties, their electronic structures, and so forth. Here, we present syntheses of NDIs, a PDI, and a DPP with ethynyl substituents, and their use as new building blocks for the synthesis of amino-functionalized electron-accepting π-conjugated systems. The reaction between the ethynyl group of the electron acceptor and an amine proceeds almost quantitatively, without a catalyst, to give a Michael-addition-type product that shows remarkable changes in its optical properties, redox properties, and dipole moment. The progress of the reaction can be visually monitored in various media. On the basis of a kinetic analysis of the amine-addition reaction, various amino-functionalized asymmetric and symmetric π-systems were obtained in a designed manner.
Derivatives of malachite green, a well-known triphenylmethine dye, have been adapted for third-generation photovoltaic applications as dye-sensitized solar cells (DSSC). The solar cells were developed based on a concentrated Br3−/Br− liquid electrolyte coupled to different trifluoroacetate (TFA−), triflate (TfO−), bromide (Br−) and tetrafluoroborate (BF4−) malachite green salts as dye sensitizers and mesoporous TiO2 anatase as electron collector, and their optoelectronic properties were characterized. The adsorption patterns of such salts at the TiO2 nanoparticle surface were studied by zeta (ζ) potential measurements on colloidal suspensions under neat conditions, and compared to the desorption rates of the dyes when exposed to the DSSC electrolyte. The different affinities of the ionic pairs for the oxide surface and the bulk were found crucial for the stability of the self-assembled monolayer of carboxylic acid-anchored chromophores at the surface, and for the photoconversion efficiency associated therewith. This study aimed at depicting the behavior of the ionic pairs at the surface and gave insights for their physical and chemical stabilization in the DSSC environment.
A simple and efficient cascade synthesis was achieved to produce chloro substituted 9-phenyl-6H-benzo[c]chromenes under mild and additive-free reaction conditions via chlorination followed by benzannulation. This would be a green alternative approach to introduce a chlorine atom on poly hetero aromatic rings without use of other toxic and malodorous chlorinating agents. The core structure is a part of several biological active compounds, and this new protocol allows design of new polyheterocyclic frameworks using an alternative to traditional cross-coupling strategies.
Anion-mixed iron(II) assembled complexes using NCS and NCBH3 as anionic ligand and bridged by 1,2-bis(4-pyridyl)ethane (bpe) are synthesized under several conditions for various ratios of NCS to NCBH3. Elemental analysis showed that the experimentally observed fractions of NCS tend to be more than those in the preparation. Some structures are determined by using single crystal X-ray structural analysis. Powder X-ray diffraction patterns are compared among the anion-mixed crystals. 57Fe Mössbauer spectroscopy reveals that a new doublet appears and it is different from the doublets of Fe(NCS)2 and Fe(NCBH3)2 units and the relative area of this new doublet reaches maximum when the fraction of NCS is around 1.0 per each iron, suggesting that the new doublet is ascribed to an Fe(NCS)(NCBH3) unit. Corresponding anion-mixed complexes enclathrating p-dichlorobenzene (p-DCB) are synthesized. Superconducting quantum interference device (SQUID) measurement and Mössbauer spectroscopy reveal that the complexes show spin-crossover (SCO) phenomenon and the relative area of the low-spin state is more than the expected value. The existence of Fe(NCS)(NCBH3) is supported by the results of SQUID measurement and density functional theory (DFT) calculation. Ligand field splitting strength of Fe(NCS)(NCBH3) unit is estimated to be intermediate between Fe(NCS)2 and Fe(NCBH3)2 units. Complexes enclathrating p-DCB display propeller conformation of bpe around the iron atom, while complexes without a guest molecule have distorted propeller conformation of bpe around the iron atom. It is suggested that such difference determines whether the SCO is on or off.
The stereoselectivity for the addition of an organometallic reagent to an aldehyde or ketone possessing a Lewis basic atom at the α-position can be predicted according to the well-known Chelation Model. Herein we discuss stereoselective reactions of bis(iodozincio)methane, which can coordinate to a heteroatom containing substrate with two zinc atoms in the reagent. Zinc atom coordination in a face-to-face manner to the substrates containing two heteroatoms enables specific molecular recognition, realizing novel molecular transformations.
The optical properties of polycyclic aromatic hydrocarbon fluorophores, such as pyrene and perylene, are controlled by confined spaces of meso- and supermicropores in a silica matrix. The quantum yield of fluorescence from monodispersed pyrene and perylene increases with limitation of the excimer formation in 1 nm supermicropores. When the pore diameter is close to the molecular size, solid-state fluorescence having a high quantum yield is achieved via the fluorophores in the confined spaces by suppressing the aggregation, the interaction with charge-transfer sites and the stabilization of the excited state.
Two diastereomers of d-limonene-derived five-membered cyclic carbonates were prepared from the corresponding isomers of d-limonene oxide with CO2. Their syntheses were catalyzed by commercially available tetrabutylammonium chloride with high stereoselectivity. The reaction behavior dependent on the reaction conditions such as CO2 pressure was clarified.
The host-guest complexes between commercially available fluorescence dyes and cucurbit[n]urils (CB[n], n = 6, 7 and 8) were exploited as multiple sensor elements to provide arrays for sensing biogenic amines using principal component analysis (PCA). Since the sensor elements respond differently to each amine, the array generates distinct patterns of fluorescence changes for each amine. We analyzed these results using PCA to allow precise discrimination of individual biogenic amines. This result demonstrated the great potential of these host-guest complexes as useful sensor elements for biogenic molecules, which may be useful to develop a diagnostic tool for diseases including cancers.
Self-assembly is a viable approach to create soft functional materials with architectural diversity and property variations. Among the large number of different chromophores used, borondipyrromethene (Bodipy) dyes find a unique space because of their promising photophysical properties such as high molar absorptivity, fluorescent quantum yield and excellent photostability along with the associated synthetic ease. Recently, research on Bodipy dyes has experienced a surge of activities in view of favorable self-assembling properties. In this review, recent developments in self-assembled Bodipy dyes and their significance in various applications are discussed.
Development of novel π-conjugated building blocks that can be integrated into molecular or macromolecular systems is key to the evolution of new superior organic semiconductors utilized as the active materials in organic electronics devices such as organic field-effect transistors (OFETs), organic photovoltaics (OPVs), and organic thermoelectric (TE) devices. This review affords a brief overview of thiophene-fused naphthalene diimide (NDI), namely naphtho[2,3-b:6,7-b′]dithiophene diimide (NDTI) and naphtho[2,3-b]thiophene diimide (NTI), recently developed as novel electron deficient building blocks for n-type and ambipolar organic semiconductors. These thiophene-fused NDI building blocks had not been known until 2013 owing to their synthetic difficulty; more precisely, the difficulty in attaching fused-thiophene ring(s) on the NDI core. We have successfully established a thiophene-annulation reaction on ethyne-substituted NDI derivatives, which allows us to elaborate various NDTI and NTI derivatives. The key features of these building blocks are low-lying energy levels of lowest unoccupied molecular orbitals (LUMO, 3.8–4.1 eV below the vacuum level) and easy functionalizability of the thiophene α-positions, which allows their derivatives and polymers to conjugate efficiently with additional π- and co-monomer units. These features make the NDTI- and NTI-derivatives and polymers promising n-type and ambipolar materials for OFETs and acceptors for OPVs. In fact, various useful materials have already been derived from the NDTI and NTI building blocks: air-stable n-type small molecules and polymers with high electron mobility (∼0.8 cm2 V−1 s−1), ambipolar oligomers and polymers with well-balanced hole and electron mobilities, doped n-type semiconductors affording bulk conductors applicable to n-type TE materials, and electron acceptor molecules and polymers for OPVs showing promising power conversion efficiencies of up to 9%. These impressive and diversified device performances testify the usefulness of thiophene-fused NDI building blocks in the development of new electron deficient π-functional materials.