Temperature Dependence of Local Density Augmentation for Acetophenone N,N,N‘,N‘-Tetramethylbenzidine Exciplex in Supercritical Water

Aizawa, Takafumi; Kanakubo, Mitsuhiro; Hiejima, Yusuke; Ikushima, Yutaka; Smith, Richard L.

doi:10.1021/jp051389l

Cited by 11 publications

(7 citation statements)

References 34 publications

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“…[The critical temperature ( T C ) and pressure ( P C ) of water are 647 K and 22.1 MPa, respectively.] Mostly the solvatochromic method has been used to probe the hydrogen bonding between solute and solvent. − Recently, our group developed a high-pressure and high-temperature optical cell available for various spectroscopic experiments and studied solute–solvent hydrogen bonding in SCW and supercritical alcohols using the Raman spectroscopic method. − In these works, the effects of solute–solvent hydrogen bonding on the NO 2 and NH 2 stretching vibrations of p -nitroaniline (pNA) and the CN stretching vibration of p -aminobenzonitrile were revealed. However, the relation of the changes in solute–solvent hydrogen bonding with basic chemical reactions in SCW such as electron transfer and proton transfer is still not clear.…”

Section: Introductionmentioning

confidence: 99%

Study of the Excited-State Proton-Transfer Reaction of 5-Cyano-2-naphthol in Sub- and Supercritical Water

2012

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The excited-state proton-transfer (ESPT) reaction of 5-cyano-2-naphthol (5CN2) has been investigated in sub- and supercritical water using time-resolved fluorescence measurements. Under ambient conditions, a very fast decay of the fluorescence from the excited state of normal 5CN2 (ROH*) and a simultaneous increase of the fluorescence from the excited state of the anion species (RO(-)*) were observed, as reported previously. The very high ESPT rate was evaluated as 0.12 ps(-1). With increasing temperature at a constant pressure of 39.0 MPa, the proton transfer became slow. At 615 K and 39.0 MPa, another fluorescence from a new unknown chemical species appeared, which was assigned to the contact ion pair (CIP) of RO(-)* and the hydronium ion. With decreasing pressure at 664 K, the fluorescence from RO(-)* disappeared, and the fluorescence from ROH* and CIP was observed. At the very low density of supercritical water, only the fluorescence decay of ROH* was detected. The reaction dynamics was analyzed with the help of singular value decomposition and spectral decomposition using model functions. The ESPT rate was correlated with the solvent dielectric constant and/or the hydrogen-bonding ability.

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Section: Introductionmentioning

confidence: 99%

Study of the Excited-State Proton-Transfer Reaction of 5-Cyano-2-naphthol in Sub- and Supercritical Water

2012

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“…Supercritical water and supercritical alcohols have been attracting much attention for their unique properties for chemical applications. − To understand chemical processes occurring in these media, knowledge of intermolecular interactions such as solute−solvent hydrogen bonding is quite important. Among various kinds of spectroscopic methods utilized to investigate the properties of these fluids, − Raman spectroscopy is a powerful tool to understand the local solvent effect on the solute molecule such as hydrogen bonding. In our previous work, we have applied resonance and nonresonance Raman spectroscopic methods to p -nitroaniline (PNA) in supercritical water and supercritical alcohols .…”

Section: Introductionmentioning

confidence: 99%

Raman Spectroscopic Study on the Solvation of p-Aminobenzonitrile in Supercritical Water and Methanol

et al. 2009

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Raman spectra of the C[triple bond]N stretching vibration of p-aminobenzonitrile (ABN) have been investigated in water, methanol, and cyclohexane under sub- and supercritical conditions, and in acetonitrile under subcritical condition. In all solvent fluids covering the supercritical region, the vibrational frequency of the C[triple bond]N stretching mode decreased with increasing solvent density from the gaseous region to the medium density region rho(r) approximately = 2, where rho(r) is the reduced density by the critical density of the solvent. However, from the medium density region to the higher density region, the vibrational frequency turned to increase with the solvent density. The temperature-induced low frequency shift of the C[triple bond]N stretching Raman band was also ascertained by the measurement of the temperature dependence of Raman spectrum of ABN vapor above 543 K. The electronic absorption spectra in the UV region of ABN were also measured under the same experimental conditions. The absorption peak energies decreased with an increase of the solvent density, except in water above rho(r) = 2.8. The vibrational frequency shift in cyclohexane was explained by a sum of contributions of the repulsive interaction, the mean field attractive interaction, and the pure temperature effect probably due to the hot-band contribution. The residual frequency shift after the subtraction of the repulsive and temperature effects in water and methanol showed the low frequency shift with increasing solvent density from rho(r) congruent with 0 to 2.8. However, above rho(r) congruent with 2.8 in water, the residual shift showed a high frequency shift with increasing solvent density. The electronic state calculations based on the PCM model using the density functional theory (DFT) indicated that the solvent polarity change caused the low frequency shift of the C[triple bond]N stretching mode, which was also correlated with the shift of the electronic absorption spectrum. The results of the DFT calculations on the cluster of ABN with water molecules and the molecular dynamics simulations indicated that the high frequency shift of the C[triple bond]N stretching mode in water above rho(r) congruent with 2.8 could be due to the hydrogen bonding between water and ABN.

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“…Most studies to date have used absorption or fluorescence measurements of solvatochromic probe molecules to examine the local environment of the solute. [14][15][16][17][18] The main discussion has concentrated on the clustering of solvent molecules around the solute in the supercritical phase, the so-called "local density enhancement", which is a unique phenomenon occurring close to the critical point as a result of the solute-solvent attractive interaction and enhanced inhomogeneity in SCFs. 19,20 The dielectric continuum model has been a useful model to estimate the local density enhancement qualitatively.…”

Section: Introductionmentioning

confidence: 99%

Solvent Effects on the Local Structure of p-Nitroaniline in Supercritical Water and Supercritical Alcohols

2008

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Raman spectra of p-nitroaniline in supercritical water and supercritical alcohols were measured, and the effects of solvents on the NO 2 and NH 2 stretching modes were investigated. The intensity and frequency of the NO 2 stretching mode significantly changed as a function of the solvent density and temperature. The frequency of the NO 2 stretching mode correlated with the absorption peak energy of the S 1<--S 0 transition. On the other hand, the vibrational frequency of the NH 2 stretching mode did not correlate with the absorption peak shift, although it had a large frequency shift as a function of the density. The correlation between the NO 2 frequency and absorption peak energy suggested that the solvent effects of supercritical water and supercritical alcohols were similar to those for nonpolar solvents. The density functional calculation using the polarizable continuum model and p-nitroaniline-water clusters qualitatively reproduced the density dependence of the NO 2 stretching mode as well as the solvent polarity dependence. Detailed vibrational analysis revealed that the coupling between the NO 2 and C-NH 2 vibrational motions at the harmonic level has an important effect on the intensity and frequency shift of the NO 2 stretching mode. The frequency shift of the NH 2 stretching mode correlated with the degree of hydrogen bonding between the solvent molecules estimated from NMR measurements [Hoffmann M. M.; Conradi, M. S. J. Phys. Chem. B. 1998, 102, 263]. The existence of intermolecular hydrogen bonding around the NH 2 group was demonstrated even at low-density conditions.

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Temperature Dependence of Local Density Augmentation for Acetophenone N,N,N‘,N‘-Tetramethylbenzidine Exciplex in Supercritical Water

Cited by 11 publications

References 34 publications

Study of the Excited-State Proton-Transfer Reaction of 5-Cyano-2-naphthol in Sub- and Supercritical Water

Study of the Excited-State Proton-Transfer Reaction of 5-Cyano-2-naphthol in Sub- and Supercritical Water

Raman Spectroscopic Study on the Solvation of p-Aminobenzonitrile in Supercritical Water and Methanol

Solvent Effects on the Local Structure of p-Nitroaniline in Supercritical Water and Supercritical Alcohols

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