Structure and dynamics of gas-phase molecules and their clusters formed in a supersonic jet has been a great interest to many researchers. Studies on these simple systems provide us with the fundamental concept of many physical and chemical phenomena observed in bulk systems. These studies are also important for the verification of theoretical prediction and quantum chemical calculations. Especially molecular clusters have been thought to be a good model for molecular level understanding of intermolecular interaction and relaxation in condensed phase. However, until the beginning of 1990, studies of molecular clusters mainly concentrated on electronic spectroscopy and very few studies were reported for vibrational spectroscopy. On the other hand, vibrational spectroscopy is essential in condensed phase, and there has been a gap between cluster science and condensed phase science. In 1993 we first reported infrared (IR)–ultraviolet (UV) double resonance spectroscopy of the OH stretching vibration of phenol and its hydrated clusters in a supersonic jet. The observed vibrational spectra showed a characteristic feature of the H-bonding, that is a larger frequency shift as well as broadening of the OH stretching band, and the structures were unambiguously determined with the aid of quantum chemical calculation. It is not too much to say that the combination of double resonance vibrational spectroscopy and quantum chemical calculation has become a very popular method in cluster science. In this paper, we describe various double resonance vibrational spectroscopies in frequency domain. Typical examples of application are shown; determination of H-bonded clusters of benzonitrile, conformer selective vibrational spectroscopy for L-phenylalanine and its hydrated cluster, and study of the encapsulation structure of guest atom and molecules by functional molecules, calixarene and crown ether. Finally, time-domain studies for the dynamics of the vibrations are described. Picosecond IR–UV pump–probe spectroscopy is applied to study the vibrational energy relaxation (VER) of the OH stretching vibration of isolated aromatic molecules and the H-bonded clusters.
Development of double resonance vibrational spectroscopy and its application to molecular clusters and functional molecules are described. Conformer and size-selective vibrational spectroscopic study in frequency and time domain reveals the detailed structures as well as the dynamics of the clusters.
This account reviews the chemical synthesis of inorganic nanoparticles stabilized by an organic shell layer and the investigation of their specific characteristics. Consideration of design and construction of organic–inorganic hybrid nanoparticles by wet process is indispensable in order to exploit the unprecedented nature resulting from the fusion of both organic and inorganic traits. In a series of studies, two synthetic parameters were the center of focus: physical construction of the inorganic core and the chemical constituents introduced. External stimuli such as electric fields or solvent polarity can be utilized to transform the characteristics of nanoparticles when redox active or liquid crystalline molecules as an organic shell are attached to the surface of an inorganic nano-core. In another case, the catalytic activities of nanoparticles are controllable by modifying the crystal faces and the surface area of the inorganic cores in connection with shape and size. Novel nanomaterial has also been fabricated by choosing a metal coordination polymer as a core, leading to the first isolation of alkyl chain-stabilized metal coordination nano-polymers (MCNPs). The compounds are listed as Pt nano-cubes, size-selected Au nanoparticles, metal hexacyanoferrate MCNPs, and metal nanoparticles functionalized by biferrocene, anthraquinone, and triphenylene derivatives. Synthetic procedures and remarkable characteristics are demonstrated.
This account reviews the synthesis of inorganic nanoparticles stabilized by organic layers with electronic, optical, catalytic, and magnetic properties. The compounds are Pt nano-cube, size-selected Au nanoparticles, metal coordination nano-polymers, and metal nanoparticles functionalized with biferrocene, anthraquinone, and triphenylene derivatives.
This account describes the redox behaviors of endohedral metallofullerenes having remarkable electron-accepting and -donating abilities, which accompany the transformation between their paramagnetic and diamagnetic states. A convenient method of isolating endohedral metallofullerene by means of selective reduction from carbon soot extracts is also developed. Successful isolation in large amount by utilizing this method allows examination of the construction of a supramolecular system based on endohedral metallofullerenes with azacrown ethers, unsaturated thiacrown ethers, and organic donor molecules. Consequently, endohedral metallofullerenes are revealed to form an inclusion complex with the crown compounds by electron transfer, and a stimuli-responsive reversible electron transfer system is constructed by using endohedral metallofullerenes and organic donors. These electron transfers proceed readily even in the ground state, which is a specific phenomenon for endohedral metallofullerenes.
Endohedral metallofullerenes are revealed to form an inclusion complex with azacrown ethers and unsaturated thiacrown ethers by electron transfer between them, and a stimuli-responsive reversible electron transfer system is constructed by using endohedral metallofullerenes and organic donors.
9,9′-Bianthryl formed an inclusion compound with chlorocycloheptane in a 2:1 ratio. X-ray analysis revealed that two guest molecules were accommodated in a cavity surrounded by eight host molecules. The guest molecules were conformationally fixed in each cavity into either of two twist-chair forms that differed in the position of the chloro group. These conformations were compared with the calculated ones for chlorocycloheptane itself by DFT calculation. When the inclusion compound was prepared from a concentrated solution of 9,9′-bianthryl in chlorocycloheptane, the gelation was followed by crystallization. This phenomenon is unusual for relatively small molecules lacking strong intermolecular interactions.
9,9′-Bianthryl formed an inclusion compound with chlorocycloheptane in a 2:1 ratio, where two guest molecules are accommodated in each cavity in either of two twist-chair forms. Under certain conditions, the gelation was followed by crystallization.
The sugar–base correlation of cytosine (base) and deoxyribose (sugar) moieties of cytidine is investigated based on their inner-shell electronic structural information. A recently developed density functional theory (DFT) model, CV-B3LYP, with a Gaussian-type basis set of 6-311G**, and the DFT-LB94 model with a Slater-type basis set of TZ2P are employed to calculate inner shell ionization energies. The results reveal that the corresponding geometry of cytidine is not significantly different from its fragments, i.e., cytosine and deoxyribose. Changes in charge distribution of cytidine with respect to cytosine and deoxyribose concentrate on the local C sites in the base pyrimidine ring and sugar ring, as indicated by the atomic Hirshfeld charges. The O-K, N-K, and C-K spectra of cytidine inherit the aromatic signature in cytosine, suggesting that the role of the aromatic ring is a buffer to diffuse the changes brought in by the addition of the deoxyribose moiety. Formation of cytidine, however, substantially changes the C-K spectra of the deoxyribose moiety. In general, the correlated O-K, N-K, and C-K sites of cytidine exhibit small red shifts with respect to the cytosine base, whereas the O-K and C-K sites of cytidine show blue shifts in comparison with those of deoxyribose.
Hexakis(3-O-methyl)-α-cyclodextrin (3α) bound to m- and p-nitrophenolate ions more strongly, whereas hexakis(2-O-methyl)-α-cyclodextrin (2α) bound less strongly than native α-cyclodextrin. ROESY spectra showed that the 3-O-methyl groups of 3α interact with the guest protons, whereas 2-O-methyl groups of 2α do not. 3α accelerated and 2α decelerated the cleavage of m-nitrophenyl acetate in an alkaline solution, suggesting that the C(2)–OH of α-cyclodextrin is more catalytic than the C(3)–OH. However, the catalytic effect of 3α was much smaller than that of native α-cyclodextrin. Loss of hydrogen bonding between the C(3)–OH and C(2)–OH by 3-O-permethylation is responsible for the small catalytic effects of 3α. Similar results were obtained for β-cyclodextrin analogs.
Stability of a conductive state of iodine-doped poly(3-octyloxythiophene) (P3OOT) was compared with that of poly(3-octylthiophene) (P3OT). Temporal decay in the electric conductivity of P3OOT after the doping was much slower than that of P3OT. The cation of P3OOT was stable and an increase in the spin concentration was not observed. The results support the mechanism of dedoping of poly(3-alkylthiophene)s proposed by the authors [J. Phys. Chem. B2005, 109, 15288]: the dedoping proceeds through deprotonation of the cation, which results in the formation of a stable polyenyl radical. The deprotonation of the cation of P3OOT occurs with difficulty since deprotonation gives an unstable radical. The conductive state of P3OOT is hence stable.
Intermolecular distance dependence on ferromagnetic interactions in organic-radical assemblies was deduced by using molecular orbital methods. It was shown that non-bonding molecular orbitals (NBMOs) were subject to orbital mixing to form localized NBMOs. The high-spin stabilities had maxima when magnitude of intra- and intermolecular resonance integrals was nearly equal. From amplitude pattern analysis of NBMOs, the origin of the maxima was attributed to itinerant character of the non-bonding electrons in the proper intermolecular distance regions. Our analysis was supported by theoretical calculations.
A study of the kinetics of the proton-transfer reaction in flavonoid in ethanol solution by means of stopped-flow spectroscopy indicated that proton tunneling plays an important role in the antioxidant reaction.
(+)-(18-Crown-6)-tetracarboxylic acid (18C6H4) is used as a chiral selector for various amino acids, where the L-isomer is usually eluted prior to the D-isomer in HPLC using 18C6H4-linked column. To clarify the structural scaffold of (+)-18C6H4 responsible for chiral separation of amino acids, we have previously investigated the interaction mode between (+)-18C6H4 and amino acids using X-ray analysis. However, no conclusive results could be obtained to explain the reverse elution order in the case of serine and to establish a general separation rule of chiral amino acid by (+)-18C6H4 in HPLC. Thus, to clarify the exceptional result obtained with serine and to set a general separation rule, interaction between (+)-18C6H4 and α-amino-n-butyric acid, valine, and alanine, as methyl substitutes of the methyl groups for the hydroxy groups of serine and threonine, and the simplest chiral amino acid, respectively, was investigated both in solution and solid states. Consequently, it was found that an asymmetric bowl-like conformation of (+)-18C6H4 is necessary for chiral separation. This conformation is constructed by chiral-specific interaction between the Cα–H groups of the amino acid and the polar oxygen atoms of (+)-18C6H4. It was also found that the exceptional reverse elution observed with serine is due to additional interaction between the polar groups of the amino acid side chain and (+)-18C6H4.
Structures and spectral properties have been investigated for nickel(II) mixed-ligand complexes, [Ni(Me4en)(acac)(NO3)] (1), [Ni(EtMe3en)(acac)(NO3)] (2), [Ni(asym-Et2Me2en)(acac)(NO3)] (3), [Ni(Et3Meen)(acac)(NO3)] (4), and [Ni(Et4en)(acac)(NO3)] (5) (Me4en = N,N,N′,N′-tetramethylethylenediamine, EtMe3en = N-ethyl-N,N′,N′-trimethylethylenediamine, asym-Et2Me2en = N,N-diethyl-N′,N′-dimethylethylenediamine, Et3Meen = N,N,N′-triethyl-N′-methylethylenediamine, Et4en = N,N,N′,N′-tetraethylethylenediamine, acac = acetylacetonate). The crystal structures of complexes 2 and 3 have been determined. These complexes have 6-coordinated octahedral (Oh) structure with a bidentate nitrate in the solid state as well as in 1,2-dichloroethane or acetone solution, while the nitrate partially dissociates in nitromethane to establish an equilibrium with square-planar (Sp) form [Ni(acac)(diam)]+ where diam represents a diamine. The degree of dissociation of NO3− increases in the order of diam: Me4en < EtMe3en < asym-Et2Me2en < Et3Meen < Et4en, indicating that the bulkier diamine more favors the Sp form. This relative stabilization of the Sp form can be attributed to relief of the steric strain in the Oh species. Effects of bulky substituents in the diamine on the ligand-field strength are also discussed.
Tropolone-terminated oligomeric fluorophores (Tp2OP, Tp2OPV, and Tp2OPE) were prepared by palladium-catalyzed coupling reactions. A phenylene-type Tp2OP showed an emission maximum in the blue fluorescent region and the fluorescence quantum yield was relatively low. Tp2OPV and Tp2OPE, which included vinylene and ethynylene units as connecting groups, respectively, had emission maxima at longer wavelength regions than Tp2OP. The UV spectra of Tp2OP gradually red shifted as the dielectric constant of solvent increased. Tp2OP exhibited positive solvatofluorochromic behavior, which related to an increase of the dipole moment due to the charge-transfer characteristics of the emitting state. The fluorescence quantum yields (QYs) of fluorophores exponentially fell with increasing MeOH content in THF solution. Upon addition of CuCl2 to Tp2OP until the ratio of [Cu2+]/[Tp2OP] reached 1, the UV spectra exhibited a red-shift. The emission maximum wavelength of Tp2OP blue shifted and a remarkable decrease of the PL intensity was observed. Tp2OP showed metal ion-response, especially in PL spectra.
Water-soluble naphthalene dendrimers WN1, WN2, and WN3, together with the lipophilic compounds N1, N2, and N3 were prepared and their photochemical properties were examined. Whereas lipophilic dendrimers N1, N2, and N3 gave monomer emission peaking at 330–340 nm, water-soluble dendrimers WN1, WN2, and WN3 gave not only the monomer emission at 330–340 nm but also excimer emission peaking at 400 nm in aqueous solution under considerably diluted conditions. The relative intensity of the excimer fluorescence at longer wavelengths compared to the monomer emission depended on the dendrimer generation and the concentration of dendrimer and added salt (KCl). In particular the excimer emission of the second generation dendrimer is considerably higher than those of the first and the third generation dendrimers. Based on these experimental results, the aggregation and the excimer formation of water-soluble naphthalene dendrimers in aqueous solution depending on the generation and the conditions were discussed.
The reactions of aryl halides with 2,3,3-trimethyl-4-penten-2-ol in the presence of a palladium catalyst result in prenyl transfer from the alcohol to aryl halides via retro-allylation, yielding prenylarenes. Other multisubstituted allyl groups such as the 2,3-dimethyl-2-butenyl group are introduced to aromatic rings.
Substituent effects on the acetolysis rates of 2-aryl-1-cyano-1-(trifluoromethyl)ethyl trifluoromethanesulfonates (α-OTf) and 2-aryl-2-cyano-2-(trifluoromethyl)ethyl trifluoromethanesulfonates (β-OTf) were investigated by using LArSR equation. The obtained ρ and r+ values were ρ = −3.28, r+ = 0.98 and ρ = −3.48, r+ = 0.93 for the acetolysis of α-OTf and β-OTf, respectively. The obtained ρ values are comparable to those for typical aryl-assisted solvolyses, but the r+ values are much larger. The large r+ values suggest that the ester bond cleavages in the deactivated aryl-assisted solvolyses are assisted by the strong participation of the β-aryl group.
A series of water-soluble dendritic ligands with a phosphine core was synthesized through the coupling of tris(4-hydroxyphenyl)phosphine oxide with poly(benzyl ether) dendron having tri(ethylene glycol) units, followed by reduction. By employing the corresponding water-soluble phosphine–gold(I) dendrimers as a catalyst, the hydration of alkynes proceeded smoothly. Furthermore, by membrane separation based on the nano-order size of the dendritic catalyst, the gold(I) catalyst was recycled without deactivation.
Chlorophyll and bacteriochlorophyll derivatives possessing a trifluoroacetyl group at the 3-position were synthesized as new colorimetric sensors for amine detection. α-Amino alcohol formation of the free-base chlorin and metallochlorins showed visual color changes from brown to purple and from green to blue, respectively. On the other hand, bacteriochlorin derivative showed large blue-shifts of the Qy peak in the near-infrared region (775 → 724 nm) and the Qx peak in the visible region (549 → 520 nm), which are advantageous points for amine sensing. Clear color change was observed from pink to turquoise by the formation of α-amino alcohol adduct.
Ab initio MO calculations were carried out at the MP2/6-311++G(d,p) level to investigate the Gibbs energy of conformational isomers of cyclohexanes cyclo-C6H11X 3 and cyclohexanones cyclo-C6H9OX 4. In 3, it has been found that the conformer bearing an oxygen or halogen atom (X = OCH3, F, Cl, and Br) at the axial orientation is relatively stable as compared to corresponding alkyl cyclohexanes; the result is consistent with documented experimental data. For X = CCH and CN, the axial conformer has been suggested to be slightly more stable. In 4, the axial conformer has been found to be more stable than the equatorial conformer, except for X = OH. Short non-bond distances have been disclosed in every axial conformer of 3 and 4, between axial CHs of the cyclohexane ring and X. The reason for the relative stability of the axial conformers has been sought in the context of the CH/n and CH/π hydrogen bonds. We suggest that a considerable part of the relative stability of the axial conformation is attributed to intramolecular CH/n and CH/π hydrogen bonds. Natural bonding orbital charges of the relevant atoms are consistent with the above suggestion.
The photochemical removal of NO, NO2, and N2O was investigated in N2 using a 146 nm Kr2 (25 mW cm−2) excimer lamp. The results obtained were compared with those obtained using 172 nm Xe2 (50 or 300 mW cm−2) excimer lamps. The removal rates of NO and NO2 at 146 nm were 11 and 36% slower than those at 172 nm, respectively. On the other hand, the removal rate of N2O at 146 nm was 21 times faster than that at 172 nm. The differences in the removal rates are discussed in terms of the absorption coefficient at each wavelength and effects of photoabsorption by N2 at 146 nm. By the addition of a small amount of O2 into an N2O/N2 mixture, the removal rate of N2O at 146 nm decreased greatly. On the basis of these facts, it was concluded that the 146 nm excimer lamp is especially useful for the N2O removal in N2 at atmospheric pressure.