Study of alkyl chain length dependent characteristics of imidazolium based ionic liquids [CnMIM]+[TFSA]- by Brillouin and dielectric loss spectroscopy

권현정,김형국,황윤회,서정아,Takashi Iwahashi,Yukio Ouchi,김도석 한국물리학회 2013 Current Applied Physics Vol.13 No.1

This study examined the acoustic phonon mode of ionic liquids consisting of 1-alkyl-3-methyl-imidazolium family (CnMIM) cations with n values ranging from 2 to 10 and bis(trifluoromethylsulfonyl)amide (TFSA) anion in the temperature range from 300 K to 100 K. [CnMIM]þ[TFSA] showed depolarized (VH) components of Brillouin peaks at temperatures below the glass transition temperature when n is larger than 4. On the other hand, in the case of ionic liquids with different anions, such as [C4MIM]þ[BF4], [C4MIM]þ[PF6] and [C8MIM]þ[BF4], the VH component of Brillouin peaks was not observed in the temperature range investigated. The dielectric loss spectra showed that the temperature dependence of alkyl chain domain relaxation of all ionic liquids followed the Arrhenius law and showed an increase in activation energy at the temperature where the VH component of Brillouin peak appeared. These results suggest that the observed depolarized component of Brillouin peak might originate from uniquely induced polarization in the 2nd domain composed of head groups of cations and anions.

Comparative Study of Tetrahydrothiophene and Thiophene Self Assembled Monolayers on Au(111): Structure and Molecular Orientation

Ito, Eisuke,Hara, Masahiko,Kanai, Kaname,Ouchi, Yukio,Seki, Kazuhiko,Noh, Jaegeun Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.8

Surface structure and molecular orientation of self-assembled monolayers (SAMs) formed by the spontaneous adsorption of tetrahydrothiophene (THT) and thiophene (TP) on Au(111) were investigated by means of scanning tunneling microscopy (STM) and carbon K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy. STM imaging revealed that THT SAMs have a commensurate (3 ${\times}\;2\sqrt[]{3}$) structure containing structural defects in ordered domains, whereas TP SAMs are composed of randomly adsorbed domains and paired molecular row domains that can be described as an incommensurate packing structure. The NEXAFS spectroscopy study showed that the average tilt angle of the aliphatic THT ring and $\pi$-conjugated TP ring in the SAMs were calculated to be about $30^o\;and\;40^o$, respectively, from the surface normal. It was also observed that the $\pi$* transition peak in the NEXAFS spectrum of the TP SAMs is very weak, suggesting that a strong interaction between $\pi$-electrons and the Au surface arises during the self-assembly of TP molecules. In this study, we have clearly demonstrated that the surface structure and adsorption orientation of organic SAMs on Au(111) are strongly influenced by whether the cyclic ring is saturated or unsaturated.

Comparative Study of Tetrahydrothiophene and Thiophene Self-Assembled Monolayers on Au(111): Structure and Molecular Orientation

Eisuke Ito,Masahiko Hara,Kaname Kanai,Yukio Ouchi,Kazuhiko Seki,노재근 대한화학회 2009 Bulletin of the Korean Chemical Society Vol.30 No.8

Surface structure and molecular orientation of self-assembled monolayers (SAMs) formed by the spontaneous adsorption of tetrahydrothiophene (THT) and thiophene (TP) on Au(111) were investigated by means of scanning tunneling microscopy (STM) and carbon K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy. STM imaging revealed that THT SAMs have a commensurate (3 × 2√3) structure containing structural defects in ordered domains, whereas TP SAMs are composed of randomly adsorbed domains and paired molecular row domains that can be described as an incommensurate packing structure. The NEXAFS spectroscopy study showed that the average tilt angle of the aliphatic THT ring and π-conjugated TP ring in the SAMs were calculated to be about 30o and 40o, respectively, from the surface normal. It was also observed that the π* transition peak in the NEXAFS spectrum of the TP SAMs is very weak, suggesting that a strong interaction between π-electrons and the Au surface arises during the self-assembly of TP molecules. In this study, we have clearly demonstrated that the surface structure and adsorption orientation of organic SAMs on Au(111) are strongly influenced by whether the cyclic ring is saturated or unsaturated.

Alkyl-chain dividing layer at an alcohol/ionic liquid buried interface studied by sum-frequency generation vibrational spectroscopy

Iwahashi, Takashi,Sakai, Yasunari,Kanai, Kaname,Kim, Doseok,Ouchi, Yukio Royal Society of Chemistry 2010 Physical chemistry chemical physics Vol.12 No.40

<P>We demonstrate for the first time the formation of a non-polar alkyl-chain dividing layer between a room-temperature ionic liquid (RTIL) and an <I>n</I>-alcohol. This newly described non-polar interfacial layer, which should be more hydrophobic than both RTIL and alcohol phases, might find applications in liquid/liquid reaction systems, or serve as a soft nano-functional space.</P> <P>Graphic Abstract</P><P>A non-polar alkyl-chain dividing layer is found to exist between butanol and the room-temperature ionic liquid 1-butyl-3-methyl-imidazolium hexafluorophosphate. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0cp00520g'> </P>

Photoluminescence Characteristics of Merocyanine Dyes in Ionic Liquids

심태규,Doseok Kim,H. H. Yoon,김현성,Jaeho Sung,Kyungbyung Yoon,Yukio Ouchi 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6

The photoluminescence (PL) characteristics of merocyanine dye molecules in ionic liquids of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) with different purity grades were investigated. The absorption spectra for this dye in all the ionic liquid solvents investigated looked very similar while the PL emission spectra differed markedly depending on the type of ionic liquid and the impurity content. In all purity grades of [BMIM]BF4 and the ultrahigh grade of [BMIM]PF6, the PL spectra of these merocyanine solutions showed a single peak around 480 nm. However, when a lower grade of [BMIM]PF6 was used as the solvent, an additional PL peak appeared around 575 nm. The deprotonation from the hydroxyl group of the merocyanine molecule after photoexcitation is proposed to explain the phenomenon in this unique solvent system.n

Liquid/liquid interface layering of 1-butanol and [bmim]PF₆ ionic liquid: a nonlinear vibrational spectroscopy and molecular dynamics simulation study

Iwahashi, Takashi,Ishiyama, Tatsuya,Sakai, Yasunari,Morita, Akihiro,Kim, Doseok,Ouchi, Yukio The Royal Society of Chemistry 2015 Physical chemistry chemical physics Vol.17 No.38

<P>IR-visible sum-frequency generation (IV-SFG) vibrational spectroscopy and a molecular dynamics (MD) simulation were used to study the local layering order at the interface of 1-butanol-d<SUB>9</SUB> and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF<SUB>6</SUB>), a room-temperature ionic liquid (RTIL). The presence of a local non-polar layer at the interface of the two polar liquids was successfully demonstrated. In the SFG spectra of 1-butanol-d<SUB>9</SUB>, we observed significant reduction and enhancement in the strength of the CD<SUB>3</SUB> symmetric stretching (<I>r</I><SUP>+</SUP>) mode and the antisymmetric stretching (<I>r</I><SUP>−</SUP>) mode peaks, respectively. The results can be well explained by the presence of an oppositely oriented quasi-bilayer structure of butanol molecules, where the bottom layer is strongly bound by hydrogen-bonding with the PF<SUB>6</SUB><SUP>−</SUP> anion. MD simulations reveal that the hydrogen-bonding of butanol with the PF<SUB>6</SUB><SUP>−</SUP> anion causes the preferential orientation of the butanols; the restriction on the rotational distribution of the terminal methyl group along their <I>C</I><SUB>3</SUB> axis enhances the <I>r</I><SUP>−</SUP> mode. As for the [bmim]<SUP>+</SUP> cations, the SFG spectra taken within the CH stretch region indicate that the butyl chain of [bmim]<SUP>+</SUP> points away from the bulk RTIL phase to the butanol phase at the interface. Combining the SFG spectroscopy and MD simulation results, we propose an interfacial model structure of layering, in which the butyl chains of the butanol molecules form a non-polar interfacial layer with the butyl chains of the [bmim]<SUP>+</SUP> cations at the interface.</P> <P>Graphic Abstract</P><P>IV-SFG vibrational spectroscopy and MD simulation studies reveal a local polar/nonpolar layering structure at the interface of 1-butanol-d<SUB>9</SUB> and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF<SUB>6</SUB>). <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5cp03307a'> </P>

Structures of ionic liquid–water mixtures investigated by IR and NMR spectroscopy

Cha, Seoncheol,Ao, Mingqi,Sung, Woongmo,Moon, Bongjin,Ahlströ,m, Bodil,Johansson, Patrik,Ouchi, Yukio,Kim, Doseok The Royal Society of Chemistry 2014 Physical chemistry chemical physics Vol.16 No.20

<P>Imidazolium-based ionic liquids having different anions 1-butyl-3-methylimidazolium ([BMIM]X: X = Cl<SUP>−</SUP>, Br<SUP>−</SUP>, I<SUP>−</SUP>, and BF<SUB>4</SUB><SUP>−</SUP>) and their aqueous mixtures were investigated by IR absorption and proton NMR spectroscopy. The IR spectra of these ionic liquids in the CH<SUB><I>x</I></SUB> stretching region differed substantially, especially for C–H bonds in the imidazolium ring, and the NMR chemical shifts of protons in the imidazolium ring also varied markedly for ILs having different anions. Upon the introduction of water to screen the electrostatic forces and separate the ions, both IR and NMR spectra of [BMIM]X (X = Cl<SUP>−</SUP>, Br<SUP>−</SUP>, I<SUP>−</SUP>) showed significant changes, while those of [BMIM]BF<SUB>4</SUB> did not change appreciably. H–D isotopic exchange rates of C(2)–H in [BMIM]X–D<SUB>2</SUB>O mixtures exhibited an order: C(2)–H⋯Cl > C(2)–H⋯Br > C(2)–H⋯I, while the C(2)–H of [BMIM]BF<SUB>4</SUB> was not deuterated at all. These experimental findings, supported by DFT calculations, lead to the microscopic bulk configurations in which the anions and the protons of the cations in the halide ionic liquids have specific, hydrogen-bond type of interaction, while the BF<SUB>4</SUB><SUP>−</SUP> anion does not participate in the specific interaction, but interacts less specifically by positioning itself more above the ring plane of the imidazolium cation. This structural change dictated by the anion type will work as a key element to build the structure–property relationship of ionic liquids.</P> <P>Graphic Abstract</P><P>Imidazolium-based ionic liquids having different anions 1-butyl-3-methylimidazolium ([BMIM]X: X = Cl<SUP>−</SUP>, Br<SUP>−</SUP>, I<SUP>−</SUP>, and BF<SUB>4</SUB><SUP>−</SUP>) and their aqueous mixtures were investigated by IR absorption and proton NMR spectroscopy. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp00589a'> </P>

IV-SFG studies on the effect of Li⁺ in extending the electrochemical window at the Pt|[C₂mim][FSA] interface

Iwahashi, Takashi,Miwa, Yujiro,Zhou, Wei,Sakai, Yasunari,Yamagata, Masaki,Ishikawa, Masashi,Kim, Doseok,Ouchi, Yukio Elsevier 2016 Electrochemistry Communications Vol.72 No.-

<P><B>Abstract</B></P> <P>The effect of Li<SUP>+</SUP> addition at the interface of a 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide ([C<SUB>2</SUB>mim][FSA]) room-temperature ionic liquid (RTIL) and a Pt electrode is investigated by infrared-visible sum-frequency generation (IV-SFG) vibrational spectroscopy. Addition of Li<SUP>+</SUP> to the Pt|[C<SUB>2</SUB>mim][FSA] system results in the extension of the electrochemical window (EW) by >1.0V at its negative edge. The potential dependence of the SF signal reveals that the [FSA]<SUP>−</SUP> anion of neat [C<SUB>2</SUB>mim][FSA] is desorbed at −1.5V while it remains in place even at −2.0V when Li<SUP>+</SUP> is added. The SFG spectra indicate that the [FSA]<SUP>−</SUP> anion at the Pt|[C<SUB>2</SUB>mim][FSA] interface interacts with Li<SUP>+</SUP> at the interface with the negatively-charged Pt electrode. This [FSA]<SUP>−</SUP> anion layer anchored through Li<SUP>+</SUP> suppresses [C<SUB>2</SUB>mim]<SUP>+</SUP> cation adsorption on the negatively-charged Pt electrode, resulting in a wider electrochemical window.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Li<SUP>+</SUP> addition to Pt|[C<SUB>2</SUB>mim][FSA] extends EW by >1V at the negative edge. </LI> <LI> IV-SFG directly probes the presence of [FSA]<SUP>−</SUP> on Pt. </LI> <LI> Without Li<SUP>+</SUP>, [FSA]<SUP>−</SUP> desorbs from Pt at −1.0V. </LI> <LI> Li<SUP>+</SUP> is adsorbed on Pt to anchor [FSA]<SUP>−</SUP> to suppress [C2mim]<SUP>+</SUP> adsorption at −2.0V. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>