城田 秀明

We have investigated the interionic vibrational dynamics of 1-butyl-3-methylimidazolium cation ([BMIm] ) based ionic liquids with the anions of [PF ] , [AsF ] , and [SbF ] as well as the static physical properties, such as shear viscosity and liquid density. Shear viscosity for the ionic liquids becomes lower with the heavier atom anion: [BMIm][PF ] > [BMIm][AsF ] > [BMIm][SbF ]. This tendency for heavy atom substitution for the anion results from weaker interionic interaction caused by larger anion volume. Femtosecond optically heterodyne-detected Raman-induced Kerr effect spectroscopy has been used to observe the interionic vibrational dynamics of ionic liquids. The interionic vibration in the frequency region of less than 50 cm clearly shows the heavy atom substitution effect; that is, the heavy atom substitution of [XF ] critically affects the interaction-induced motion. The forthcoming paper will further provide the molecular-level insights of the heavy atom substitution effect of the [XF ] anion on the interionic dynamics and interaction for the three ionic liquids by a molecular dynamics simulation approach. © 2009 American Chemical Society. + - - - - - - 6 6 6 6 6 6 6 6

In this study, we have compared the interionic/intermolecular vibrational dynamics of ionic liquids (ILs) and concentrated electrolyte solutions measured by femtosecond optically heterodyne-detected Raman-induced Kerr effect spectroscopy. A typical anion in ILs, bis(trifluoromethanesulfonyl)amide ([NTf ] ), has been chosen as the anion for the sample ILs and concentrated electrolyte solutions. ILs used in this study are 1-butyl-3-methylimidazolium, 1-butylpyridinium, N -butyl- N,N,N -triethylammonium, and 1-butyl-1-methylpyrrolidinium with [NTf ] . Li [NTf ] solutions (∼3.3 M) of water, methanol, propylene carbonate, and poly(ethylene glycol) have been selected as control samples. Kerr transients of the ILs and electrolyte solutions show intra- and interionic/intermolecular vibrational dynamics followed by slow picosecond overdamped relaxation. Fourier transform Kerr spectra have shown a difference in the relative intensities of intraionic vibrational bands of [NTf ] (280-350 cm ) between the ILs and electrolyte solutions. The origin of the difference is attributed to the change in the conformational equilibrium between cisoid and transoid forms of [NTf ] , which is caused by a favorable stabilization of dipolar cisoid form due to Li and dipolar solvent molecules in the electrolyte solutions. Low-frequency Kerr spectra (0-200 cm ) exhibit unique features with the variation of cation and solvent species. The aromatic ILs have a prominent high-frequency librational motion at about 100 cm-1 in contrast to the case for the nonaromatic ones. The common structure of the spectra observed at about 20 cm-1 likely comes from an interionic motion of [NTf ] . The nonaromatic ILs allow a fair comparison with the electrolyte solutions of propylene carbonate and poly(ethylene glycol) because of the structural similarities. The comparison based on the first moment of the interionic/intermolecular vibrational spectrum suggests the stronger interionic/intermolecular interaction in the concentrated electrolyte solutions than the ILs. © 2009 American Institute of Physics. 2 2 2 2 2 2 - - - -1 - + -1 -

We have studied the ultrafast dynamics of forty aprotic molecular liquids by femtosecond optical heterodynedetected Raman-induced Kerr effect spectroscopy. Some physical properties such as shear viscosity, density, and surface tension of the molecular liquids have also been measured. From the Fourier transform Kerr spectra in the frequency range of about 0200 cm , we have found that the first moment of the low-frequency intermolecular vibrational spectrum is moderately correlated with the root of the value of surface tension divided by density. This fact indicates that the microscopic intermolecular interaction is related to the macroscopic physical property of intermolecular force in molecular liquids. On the other hand, a correlation between the first moment of the intermolecular vibrational spectrum and the interaction energy of two identical molecules is almost nonexistent. The difference between the two relations suggests that the many-body interaction effect takes a hand in the intermolecular vibrational dynamics in molecular liquids. We have also found that the shapes of the broad low-frequency vibrational spectra for aromatic molecular liquids show a clearer bimodal feature than those for non-aromatic molecular liquids. Picosecond Kerr transients for most of the molecular liquids are non-exponential. The slowest relaxation time is qualitatively explained by the StokesEinsteinDebye model. © 2009 The Chemical Society of Japan. -1

Ionic liquids can simultaneously assume multiple solvent roles, because they are strongly polar and polarizable solvents and binary solutions and frequently contain very hydrophobic components. When the cation and anion functional groups are tuned appropriately, ionic liquids can be used as designer solvents for a broad range of applications. In this Account, we discuss our spectroscopic studies on the intermolecular interactions, dynamics, solvation, transport, and friction in ionic liquids, as compared with information obtained from macroscopic experiments including viscometry and calorimetry. © 2007 American Chemical Society.

Trimethylsilylmethyl (TMSiM)-substituted imidazolium bis(trifluoromethylsulfonyl)imide (NTf ), and tetrafluoroborate (BF ) ionic liquids (ILs) have lower room-temperature viscosities by factors of 1.6 and 7.4, respectively, than isostructural neopentylimidazolium ILs. In an attempt to account for the effects of silicon substitution in imidazolium RTILs and to investigate the ion dynamics, we report nuclear magnetic resonance (NMR) measurements of H (I = 1/2) and F (I = 1/2) spin-lattice relaxation times (T ) and self-diffusion coefficients (D) as a function of temperature for ILs containing the TMSiM group and, for comparison, the analogous neopentyl group. The H and F nuclei probe the dynamics of the cations and anions, respectively. The low-temperature line shapes were determined to be Gaussian, and the onset of the rigid lattice line width is correlated with the measured glass transition temperature. The spin-lattice relaxation data feature a broad T minimum as a function of inverse temperature for both nuclear species. The Arrhenius plots of the diffusion data for both nuclear species are found to exhibit Vogel-Tammann-Fulcher curvature. Analysis of the η and D data generally show fractional Stokes-Einstein behavior D ∝ (T/η) . This is most prominent in the neopentylimidazolium BF IL with m ≈ 0.66. © 2007 American Chemical Society. 2 4 1 1 4 - - 1 19 1 19 m -

The intermolecular interactions and dynamics of novel ionic liquids with alkylsilyl and alkylsiloxy substitutions on the cations are studied by measuring the intermolecular vibrational spectra and reorientational dynamics using femtosecond Kerr effect methods. The new ionic liquids include 1-dimethylphenylsilylmethyl-3-methylimidazolium (PhSi-mim ), and 1-methyl-3-pentamethyldisiloxymethylimidazolium (SiOSi-mim ) cations paired with the bis(trifluoromethylsulfonyl)imide (NTf ) anion. Measured ionic liquid viscosities are surprisingly low for such bulky cation substituents. DFT electronic structure calculations on the isolated ions provide additional information about the electrostatic interactions. © 2007 American Chemical Society. + + - 2

Ultrafast excited-state structural dynamics of [Cu (dmp)2] (dmp = 2,9-dimethyl-1,10-phenanthroline) have been studied to identify structural origins of transient spectroscopic changes during the photoinduced metal-to-ligand charge-transfer (MLCT) transition that induces an electronic configuration change from Cu(I) (3d ) to Cu(II) (3d ). This study has important connections with the flattening of the Franck-Condon state tetrahedral geometry and the ligation of Cu(II)* with the solvent observed in the thermally equilibrated MLCT state by our previous laser-initiated time-resolved X-ray absorption spectroscopy (LITR-XAS) results. To better understand the structural photodynamics of Cu(I) complexes, we have studied both [Cu (dmp)2] and [Cu (dpp) ] (dpp = 2,9-diphenyl-1,10-phenanthroline) in solvents with different dielectric constants, viscosities, and thermal diffusivities by transient absorption spectroscopy. The observed spectral dynamics suggest that a solvent-independent inner-sphere relaxation process is occurring despite the large amplitude motions due to the flattening of the tetrahedral coordinated geometry. The singlet fluorescence dynamics of photoexcited [Cu (dmp) ] were measured in the coordinating solvent acetonitrile, using the fluorescence upconversion method at different emission wavelengths. At the bluest emission wavelengths, a prompt fluorescence lifetime of 77 fs is attributed to the excited-state deactivation processes due to the internal conversion and intersystem crossing at the Franck-Condon state geometry. The differentiation between the prompt fluorescence lifetime with the tetrahedral Franck-Condon geometry and that with the flattened tetrahedral geometry uncovers an unexpected ultrafast flattening process in the MLCT state of [Cu (dmp) ] . These results provide guidance for future X-ray structural studies on ultrafast time scale, as well as for synthesis toward its applications in solar energy conversion. © 2007 American Chemical Society. I + 10 9 I + I + I + I + 2 2 2

We have investigated the dynamics of polyvinylpyrrolidone solutions (PVP, M = 10 000) on time scales from 20 fs to 42 ps using femtosecond optically heterodyne-detected Raman-induced Kerr effect spectroscopy. To compare the dynamics of polymer solutions with those of the analogous monomer, we also characterized solutions of 1-ethyl-2-pyrrolidone (EP). Dynamics of both PVP and EP solutions have been characterized for sample concentrations of 6.4, 12.7, 24.5, 33.3, and 40.7 wt %. The longest time scale relaxations observed in the Kerr transients for these solutions occur on the picosecond time scale and are best fit to triexponential functions. The intermediate and slow relaxation time constants for PVP and EP solutions are concentration dependent. The time constants for the PVP solutions are not consistent with the predictions of hydrodynamic models, while the analogous time constants for the EP solutions do display hydrodynamic scaling. The predominant relaxation of the polymer is assigned to reorientations of the pyrrolidone side group or torsional motions of the constitutional repeat unit, with additional relaxation pathways including hydrogen bond reorganization in aqueous solution and segmental motion of multiple repeat units. The vibrational dynamics of PVP and EP solutions occur on the femtosecond time scale. These dynamics are analyzed with a focus on the additional degrees of freedom experienced by EP relative to PVP that result from the absence of the tether from the pyrrolidone group on the main chain backbone. The intermolecular Kerr spectra of PVP in H O and CH Cl differ because H O can donate a hydrogen bond to the carbonyl acceptor group on the pyrrolidone ring, while CH Cl cannot. © 2006 American Institute of Physics. w 2 2 2 2 2 2

We have prepared novel room temperature ionic liquids (RTILs) with trimethylsilylmethyl (TMSiM)-substituted imidazolium cations and compared the properties of these liquids with those for which the TMSiM group is replaced by the analogous neopentyl group. The ionic liquids are prepared with both tetrafluoroborate (BF ) and bis(trifluoromethylsulfonyl) imide (NTf ) anions paired with the imidazolium cations. At 22 °C, the TMSiM-substituted imidazolium ILs have shear viscosities that are reduced by a factor of 1.6 and 7.4 relative to the alkylimidazolium ILs for the NTf - and BF - anions, respectively. To understand the effect of silicon substitution on the viscosity, the charge densities have been calculated by using density functional theory electronic structure calculations. The ultrafast intermolecular, vibrational, and orientational dynamics of these RTILs have been measured by using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The intermolecular dynamical spectrum provides an estimate of the strength of interactions between the ions in the RTILs, and provides a qualitative explanation for the observed reduction in viscosity for the silicon-substituted RTILs. © 2005 American Chemical Society. 4- 2 2 4 -

In this study, we address the following question about room-temperature ionic liquids (RTILs). Are the properties of a RTIL more dependent on the charges of the molecular ions or on the fact that the liquid is a complex mixture of two species, one or both of which are asymmetric? To address this question and to better understand the interactions and dynamics in RTILs, we have prepared the organic ionic liquid 1-methoxyethylpyridimum dicyanoamide (MOEPy /DCA ) and compared this RTIL with the analogous isoelectronic binary solution, comprised of equal parts of 1-methoxyethylbenzene (MOEBz) and dicyanomethane (DCM). In essence, we have created a RTIL and a nearly identical neutral pair in which we have effectively turned off the charges. To understand the intermolecular interactions in both of these liquids, we have characterized the bulk density and shear viscosity. Using femtosecond optical Kerr effect spectroscopy, we have also characterized the intermolecular vibrational dynamics and diffusive reorientation. To verify that the shape, polarizability, and electronic structure of the RTIL ions and the components of the neutral pair are truly quite similar, we have carried out density functional theory calculations on the individual molecular ion and neutral species. © 2005 American Chemical Society. + -

We have investigated the ultrafast molecular dynamics of five pyrrolidinium cation room temperature ionic liquids using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The ionic liquids studied are N -butyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P 14 + NTf2-), N -methoxyethyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P 1EOE + NTf2-), N -ethoxyethyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P 1EOE + NTf2-), N -ethoxyethyl- N -methylpyrrolidinium bromide P 1EOE +, and N -ethoxyethyl- N -methylpyrrolidinium dicyanoamide P 1EOE + DCA-). For comparing dynamics among the five ionic liquids, we categorize the ionic liquids into two groups. One group of liquids comprises the three pyrrolidinium cations P 14 +, P 1EOM +, and P 1EOE + paired with the NTf2- anion. The other group of liquids consists of the P 1EOE + cation paired with each of the three anions NTf2-, Br-, and DCA-. The overdamped relaxation for time scales longer than 2 ps has been fit by a triexponential function for each of the five pyrrolidinium ionic liquids. The fast (~2 ps) and intermediate (~20 ps) relaxation time constants vary little among these five ionic liquids. However, the slow relaxation time constant correlates with the viscosity. Thus, the Kerr spectra in the range from 0 to 750 cm-1 are quite similar for the group of three pyrrolidinium ionic liquids paired with the NTf2- anion. The intermolecular vibrational line shapes between 0 and 150 cm-1 are fit to a multimode Brownian oscillator model; adequate fits required at least three modes to be included in the line shape. © 2005 American Institute of Physics.

Ultrafast molecular dynamics of liquid poly(ethylene glycol)s, tetra(ethylene glycol), penta(ethylene glycol), and poly(ethylene glycol) with the molecular weight of 600, and crown ethers, 12-crown-4 and 15-crown-5, have been investigated by means of femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy. Picosecond Kerr transients of polyethylene glycol)s and crown ethers are characterized by a biexponential function with the time constants of about 2 and 20 ps. Both the faster and slower time constants do not vary much among the five oligo(ethylene oxide)s. Femtosecond dynamics is discussed based on the Kerr (depolarized Raman) spectra obtained by Fourier transform deconvolution analysis of the high time resolution Kerr transients. The broad low-frequency band (0-200 cm ) in the Kerr spectrum is analyzed by two Brownian oscillators. The spectral shapes of linear poly(ethylene glycol) and cyclic crown ether are very different. Both the low- and high-frequency Brownian oscillators for crown ethers show lower frequency and broader spectral features than those for poly(ethylene glycol)s. The comparison of the low-frequency spectra of poly(ethylene glycol)s and crown ethers shows that the low-frequency spectrum of 15-crown-5 is closer to that of polyethylene glycol)s than that of 12-crown-4 is. The difference of the low-frequency spectra between poly(ethylene glycol) and crown ether is discussed with the concepts of molecular conformation and liquid density. The features of the observed intramolecular vibrational bands are also correlated with the molecular conformations. © 2005 American Chemical Society. -1

Solvation dynamics of the fluorescence probe, coumarin 102, in anionic surfactant, sodium alkyl sulfate (C H SO Na; n = 8, 10, 12, and 14), and cationic surfactant, alkyltrimethylammonium bromide (C H N(CH ) Br; n = 10,12,14, and 16), micelle solutions have been investigated by a picosecond streak camera system. The solvation dynamics in the time range of 10 -10 s is characterized by a biexponential function. The faster solvation time constants are about 110-160 ps for both anionic and cationic micelle solutions, and the slower solvation time constants for sodium alkyl sulfate and alkyltrimethylammonium bromide micelle solutions are about 1.2-2.6 ns and 450-740 ps, respectively. Both the faster and the slower solvation times become slower with longer alkyl chain surfactant micelles. The alkyl-chain-length dependence of the solvation dynamics in both sodium alkyl sulfate and alkyltrimethylammonium bromide micelles can be attributed to the variation of the micellar surface density of the polar headgroup by the change of the alkyl chain length. The slower solvation time constants of sodium alkyl sulfate micelle solutions are about 3.5 times slower than those of alkyltrimethylammonium bromide micelle solutions for the same alkyl-chain-length surfactants. The interaction energies of the geometry optimized mimic clusters (H O-C H SO and H O-C H N(CH ) have been estimated by the density functional theory calculations to understand the interaction strengths between water and alkyl sulfate and alkyltrimethylammonium headgroups. The difference of the slower solvation time constants between sodium alkyl sulfate and alkyltrimethylammonium bromide micelle solutions arises likely from their different specific interactions. © 2005 American Chemical Society. n 2n-1 4 n 2n+1 3 3 2 2 5 4 2 2 5 3 3 -10 -8 - -

The ultrafast molecular dynamics of liquid aromatic molecules, benzene, toluene, ethylbenzene, cumene, and 1,3-diphenylpropane, and the mixtures with CCl have been investigated by means of femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The picosecond Kerr transients of benzene, toluene, ethylbenzene, and cumene and the mixtures with CCl show a biexponential feature. 1,3-Diphenylpropane and the mixtures with CCl show triexponential picosecond Kerr transients. The slow relaxation time constants of the aromatic molecules and the mixtures with CCl are qualitatively described by the Stoke-Einstein-Debye hydrodynamic model. The ultrafast dynamics have been discussed based on the Kerr spectra in the frequency range of 0-800 cm obtained by the Fourier transform analysis of the Kerr transients. The line shapes of the low-frequency intermolecular spectra located at 0-180 cm frequency range have been analyzed by two Brownian oscillators (∼11 cm and ∼45 cm peaks) and an antisymmetric Gaussian function (∼65 cm peak). The spectrum shape of 1,3-diphenylpropane is quite different from the spectrum shapes of the other aromatic molecules for the low magnitude of the low-frequency mode of 1,3-diphenylpropane and/or an intramolecular vibration. Although the concentration dependences of the low- and intermediate-frequency intermolecular modes (Brownian oscillators) do not show a significant trend, the width of high-frequency intermolecular mode (antisymmetric Gaussian) becomes narrower with the higher CCl concentration for all the aromatics mixtures with CCl . The result indicates that the inhomogeneity of the intermolecular vibrational mode in aromatics/CCl mixtures is decreasing with the lower concentration of aromatics. The intramolecular vibrational modes of the aromatic molecules observed in the Kerr spectra are also shown with the calculation results based on the density functional theory. © 2005 American Institute of Physics. 4 4 4 4 4 4 4 -1 -1 -1 -1 -1

We have compared the picosecond to nanosecond solvation dynamics of coumarin 153 in liquid poly(ethylene glycol)s to that in the deuterated analogues. The observed solvation dynamics in the poly(ethylene glycol)s shows a biexponential feature. Deuterium substitutions of the end hydroxyl groups on the poly(ethylene glycol)s do not affect on the faster solvation time constant of about 130 ps, but the slower solvation process in the deuterated poly(ethylene glycol)s is about 1.2 times slower than that in the undeuterated poly(ethylene glycol)s. In contrast to the solvation dynamics, the fluorescence anisotropy decay of coumarin 153 in poly(ethylene glycol)s shows no deuterium isotope effect. The retardation of the slower solvation component in deuterated poly(ethylene glycol)s in comparison with the undeuterated poly(ethylene glycol)s may be due to an indirect motion of the end groups of poly(ethylene glycol)s. © 2004 Elsevier B.V. All rights reserved.

We have studied the surfactant concentration dependence and solvent isotope effect on the slow solvation dynamics and orientational dynamics of solvatochromic coumarin dyes in the aqueous sodium dodecyl sulfate (SDS) micelle solutions using picosecond fluorescence spectroscopy. The solvation time constants for SDS micelle H O solutions are about 130 ps and 2.5 ns. Both the faster and slower solvation time constants do not depend on the SDS concentration in the range 16.2-810 mM, though the observed solvation component becomes larger with increasing of SDS concentration. The solvation dynamics in SDS micelle D O solutions is about 1.2 times slower than that in SDS micelle H O solutions. The retardation of the solvation dynamics in micelle solutions could be due to the slower process of the hydrogen bond dynamics in the hydration layer around the micelle, as well as simple hydrogen-bonding liquids. The surfactant concentration dependence and solvent isotope effect on the orientational dynamics of the fluorescence probe is correlated with those on the solvation dynamics in SDS micelle solutions. 2 2 2

Deuterium isotope effects on swelling kinetics and volume phase transition in typical polymer hydrogels (poly(N-isopropylacrylamide) and polyacrylamide gels) are discussed. Deuterium substitutions affect on the swelling kinetics and volume phase transition of the polymer hydrogels. The slower swelling kinetics of hydrogels in D O than in H O arises mainly from the high viscosity of the medium. The deuterium isotope effect on the swelling-shrinking curve of hydrogels would come from the different polymer-solvent interaction. The microenvironments of hydrogels studied by solvatochromic fluorescence probe are compared with the bulk state. The zipper-type hydrogen-bonding inter-polymer complexes (poly(acrylic acid)-polyacrylamide and poly(acrylic acid)-poly(N-acryloylglycineamide)) are also investigated and show the huge isotope effect on the phase separation temperature. 2 2

We have investigated the solvation dynamics and reorientation of coumarin 153 (C153) in liquid poly(ethylene glycol)s with molecular weights of 150, 194, 238, 300, 400, and 600 and liquid crown ethers 12-crown-4 and 15-crown-5 using picosecond time-resolved emission spectroscopy. The observed subnanosecond solvation dynamics is characterized by a biexponential function. The faster solvation time constant is about 130 ps, and this time constant is insensitive to the molecular weight and the molecular geometric structures. The time constant for slower solvation dynamics (0.5-1.6 ns range) varies with the change of the molecular weight and the different molecular geometric structures of the macromolecules. The features of the orientational dynamics of C153 in poly(ethylene glycol)s and crown ethers are similar to those of the solvation dynamics. Both the slower solvation and reorientation time constants of coumarin 153 in poly(ethylene glycol)s are linearly correlated with the bulk viscosity.

Steady-state and time-resolved fluorescence spectroscopies were used to investigate the local environments of coumarin 102 (C102) probe molecules when encapsulated within an amphiphilic starlike macromolecule (ASM). ASMs are promising surfactant-type nanoscale transporters of hydrophobic drug molecules. They consist of a hydrophobic core, in which small, hydrophobic molecules such as C102 can be encapsulated, and a hydrophilic shell that makes the whole assembly water-soluble. Steady-state fluorescence spectroscopy revealed that C102 molecules sense a very polar environment when encapsulated in ASMs. Both time-correlated single-photon counting and fluorescence upconversion techniques indicated that the solvent reorganization and diffusive reorientation of the C102 solvatochromic fluorescent probe are significantly slowed compared to the rates in aqueous solutions. These results provide insight into the dynamics of drugs encapsulated within ASMs.

The measurement of the intra- and inter-molecular dynamics of aqueous dimethyl sulfoxide (DMSO) solutions using optical heterodyne-detected Raman-induced Kerr effect spectroscopy were presented. The longer diffusive relaxation time constant τ was assigned to DMSO reorientation. The starter time constant τ/ was assigned to water reorientation. Results showed that polarizabilities of DMSO permit to estimate the anisotropic Kerr signal for an isolated DMSO molecule. 2 1

We have investigated the ultrafast dynamics of aqueous polyacrylamide ([-CH CH(CONH )-] , or PAAm) solutions using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The observed aqueous PAAm dynamics are nearly identical for both M = 1500 and 10 000. Aqueous propionamide (CH CH CONH , or PrAm) solutions were also studied, because PrAm is an exact model for the PAAm constitutional repeat unit (CRU). The longest time scale dynamics observed for both aqueous PAAm and PrAm solutions occur in the 4-10 ps range. Over the range of concentrations from 0 to 40 wt %, the picosecond reorientation time constants for the aqueous PAAm and PrAm solutions scale linearly with the solution concentration, despite the fact that the solution shear viscosities vary exponentially from 1 to 264 cP. For a given value of solution concentration in weight percent, constant ratios of measured reorientation time constants for PAAm to PrAm are obtained. This ratio of PAAm to PrAm reorientation time constants is equal to the ratio of the volume for the PAAm constitutional repeat unit (-CH CHCONH -) to the molecular volume of PrAm. For these reasons, we assign the polymer reorientation dynamics to motions of the entire constitutional repeat unit, not only side group motions. Simple molecular dynamics simulations of H[-CH CH(CONH )-] H in a periodic box with 180 water molecules support this assignment. Amide-amide and amide-water hydrogen-bonding interactions lead to strongly oscillatory femtosecond dynamics in the Kerr transients, peaking at 80, 410, and 750 fs. 2 2 n w 3 2 2 2 2 2 2 7

We have investigated the deuterium isotope effect on phase separation in aqueous zipper-type hydrogen-bonding polymer solutions. The phase separation temperature of poly(acrylic acid)-poly(acrylamide) in heavy water is about 16°C higher than that in water. This large isotope effect in the aqueous zipper-type macromolecular system arises from the polymer-polymer interaction due to cooperative hydrogen bonds in the polymer-polymer complex.

We have investigated the deuterium isotope effects on the microenvironment of the swelling-shrinking state of typical aqueous polymer gels (poly(N-isopropylacrylamide) gel and polyacrylamide gel) in aqueous binary solutions (methanol/water and acetone/water) by using a fluorescence probe. For comparison, we have also investigated the microenvironment of the linear polymers in the binary mixtures by using a fluorescence probe. Interestingly, the deuterium isotope effects in the bulk changes of poly(N-isopropylacrylamide) gel and polyacrylamide gel in the low organic-solvent composition region show opposite behaviour to each other, but the deuterium isotope effects in the microenvironment changes of (poly(N-isopropylacrylamide) gel and polyacrylamide gel display similar characteristics. © Wiley-VCH Verlag GmbH, 2000.

We have investigated the anomalous behavior of aqueous 1-propanol binary solutions using a typical fluorescence probe molecule, coumarin 153. We present data on the fluorescence lifetimes, fluorescence anisotropies, and solvent reorganization dynamics, as well as the steady-state absorption and emission spectra of coumarin 153 in the binary solutions. The rotational diffusion and solvation time constants depend strongly on the content of 1-propanol, especially at low 1-propanol mole fractions. Spectroscopic results presented here are consistent with prior light scattering [G. H. Großmann and K. H. Ebert, Ber. Bunsenges. Phys. Chem. 85, 1026 (1981)], small angle x-ray scattering [H. Hayashi, K. Nishikawa, and T. Iijima, J. Phys. Chem. 94, 8334 (1990)], and dielectric relaxation [S. Mashimo, T. Umehara, and H. Redlin, J. Chem. Phys. 95, 6257 (1991)] data. The anomalous dynamics features likely arise from the effect of the preferential solvation due to the 1-propanol clustering. © 2000 American Institute of Physics.

The deuterium isotope effects on the volume phase transition of a typical temperature-sensitive polymer gel (poly(N-isopropylacrylamide) (PNIPAM) gel) and the phase separation of the linear polymer (PNIPAM) have been investigated. For the comparison between the bulk change and the microenvironment change, the deuterium isotope effects of PNIPAM gel and linear PNIPAM solution have also been investigated by using a fluorescence probe. Both the transition temperature of the polymer gel and the phase separation temperature of the linear polymer in heavy water are about 0.7°C higher than those in water. However, the deuterium isotope effects on the difference of the transition temperatures in the heating process and the cooling process in the microenvironments of PNIPAM gel and linear PNIPAM solution are not observed. © 1999 American Chemical Society.

Ultrafast intermolecular electron transfer (ET) from orthomethoxyaniline (orthoanisidine, ANS) to a number of excited (S ) 4-trifluoromethyl-1,2-benzopyrones (coumarins) having differently substituted 7-amino group has been investigated by femtosecond fluorescence up-conversion technique. The ET dynamics in the present systems are nonsingle-exponential and occur faster than the diffusive solvation dynamics. The ET rates are largely dependent on the nature of the substituents at the 7-amino group of the coumarins. This dependence is well correlated with the free energy changes (ΔG ) for the ET reactions. The ET dynamics become slower on using deuterated ANS as the donor, where the amino group hydrogens of ANS are substituted by deuterium. The deuterium isotope effect, however, gradually reduces as the ET dynamics becomes faster. Conventional ET theories can not explain all the observations. The results are explained on the basis of the two-dimensional ET model, which considers the solvent coordinate and the intramolecular coordinate separately to depict the ET process. It is seen that in coumarin-ANS systems the ET occurs much faster than the coumarin-aniline systems. It is indicated that the electronic coupling matrix element, a parameter which determines the extent of interaction between the reactant and the product states in the ET process, is much larger in the present systems than for the coumarin-aniline systems. The deuterium isotope effect on the ET dynamics is explained in terms of the changes in the ΔG values on isotopic substitution of the solvent donors. © 1999 American Institute of Physics. 1 0 0

Ultrafast photoinduced electron transfer between excited oxazine-1 (OX1) dye and electron donating solvents aniline (AN) and N,N-dimethylaniline (DMA) has been studied with the femtosecond fluorescence up-conversion technique. Ultrafast and highly nonexponential fluorescence decay of OX1 is observed in AN and DMA. The fastest component observed is about 60 fs in DMA and assigned to fluorescence quenching due to an electron transfer reaction. Fluorescence decays are observed to be strongly dependent on the wavelength of observation in DMA and moderately dependent in AN. The wavelength dependence is assigned to fluorescence from different configurations of OX1 and solvent molecules. The energy parameters for electron transfer are estimated and discussed. © 1999 American Chemical Society.

The deuterium isotope effects on the swelling process of typical aqueous polymer gels (poly(N-isopropylacrylamide) gel and polyacrylamide gel) have been investigated in this study. The swelling times of both the poly(N-isopropylacrylamide) gel and the polyacrylamide gel in heavy water are longer than those in water. The deuterium isotope effect in the swelling process of gels is mainly arising from the higher viscosity in heavy water than in water. The additional deuterium isotope effect on the diffusion coefficient related to the swelling process should be due to the larger microscopic friction arising from the stronger polymer-solvent interaction in heavier water than in water. We also discuss in this paper the deuterium isotope effects on the size of the aqueous gels in the equilibrium state. Interestingly, the size in the equilibrium state of poly(N-isopropylacrylamide) gel in heavy water is larger than that in water. In contrast to poly(N-isopropylacrylamide) gel, the size in the equilibrium state of polyacrylamide gel in heavy water is smaller than that in water.

We have investigated the solvation dynamics of methanol and acetonitrile in reverse micelles for the first time. The solvation dynamics of both methanol and acetonitrile in reverse micelles show nonexponential features and unusual slow solvation components (from a few hundreds of picosecond to several nanoseconds). Interestingly, the solvation dynamics of methanol in reverse micelles becomes faster with a larger ratio of polar solvent to surfactant (w = [polar solvent]/[Aerosol OT]) of micelles. However, the w dependence of the solvation dynamics of acetonitrile in reverse micelles is not observed. The different w dependence of solvation dynamics in methanol and acetonitrile within reverse micelles should be arising from the presence of the intermolecular hydrogen-bonding network. © 1999 American Chemical Society.

We have investigated the deuterium isotope effect on the volume phase transition of a temperature-sensitive polymer gel (poly(N-isopropylacrylamide) gel). The transition temperature of poly(N-isopropylacrylamide) gel in heavy water is about 1°C higher than that in water. From the simulation based on a simple modified Flory-Rehner model, the deuterium isotope effect on the volume phase transition of poly(N-isopropylacrylamide) gel is arising from the difference in the polymer-solvent interactions in water and heavy water.

Ultrafast intermolecular electron transfer (ET) from electron-donating solvents to excited coumarin dyes has been investigated by the femtosecond fluorescence up-conversion technique. In this work we have used hydrazine derivatives as an electron-donating solvent to investigate the effects of very low oxidation potentials of electron-donating solvents on the ET dynamics. The ET rate with the aromatic hydrazines is much faster (sub-picoseconds) than that with the aliphatic hydrazine (a few tens of picoseconds), although the oxidation potential of the aliphatic hydrazine is lower than that of the aromatic hydrazine. However, the coumarin-hydrazine systems used in this study are not in the so-called Marcus inverted region. The results are discussed in light of the theoretical prediction from the two-dimensional ET model. We find that the electronic matrix element should be largely different between the aromatic and aliphatic hydrazine cases, which may result from the different molecular orbitals of these molecules.