Gao Sq

Carbon disulfide assisted polymerization of benzene.

The chemical transformation of benzene (C(6)H(6)) and carbon disulfide (CS(2)) binary solution under high pressure condition is investigated by means of Raman spectroscopy up to 6.8 GPa. On increasing the pressure, all the Raman bands of benzene decrease in intensity, whereas new broad bands start to be observed at 1520 and 1450 cm(-1), indicating that a highly cross-linked polymer is formed. The recovered sample is analyzed through Raman and FT-IR spectroscopy and is identified as a saturated hydrocarbon and element sulfur.

Anharmonic coupling between fundamental modes in tetramethylurea

In situ high pressure Raman spectra of tetramethylurea have been measured up to 25 GPa, liquid-solid and solid-solid phase transitions were detected at 0.2 GPa and 7.4 GPa, respectively. An unprecedented spectral phenomenon is the observation of a Fermi resonance between the fundamental modes. An exponential relationship between the intensity and the frequency difference was concluded. Pressure provides us a new way to study the correlation between Fermi resonance parameters.

Phase-dominant pressure-induced planar molecular conformation of S-trioxane.

In situ high-pressure Raman spectra of S-trioxane have been measured up to 28 GPa. A first-order phase transition was detected at ~3 GPa from the splitting, newly existing and diminishing of the internal modes and from changes in the slope on plots of frequency versus pressure. The vibrational spectra and theoretical simulation indicate that the isolated molecule structure changes from puckered to very puckered structure at the first phase, while at the beginning of the second phase, S-trioxane goes back to its original puckered structure and loses its C3 axis; then, it changes to planar structure at about ~GPa and keeps its flat structure in the second phase up to the highest pressure studied. We believe that phase may be a dominant factor responsible for the pressure-induced planar molecular geometry, providing a reasonable explanation for the experimental observations.

Stiffness tunable molecular spring washers: high-pressure Raman investigations on porphyrin self-assemblies.

The Raman spectra of a series of meso-substituted porphyrin self-assemblies have been measured as a function of pressure up to 13 GPa. In comparison with that for Tpp J-aggregates in our previous investigation [J. Phys. Chem. B, 2008, 112, 15562], a similar phenomenon has been observed in all meso-substituted self-assemblies, such as peaks in the spectrum which show positive linear pressure dependence which provides no evidence of the phase transition and the intensity enhancement of aromatic Psi(3) C-C stretching vibration with pressure. The different slopes of intensity ratios between Psi(3) C-C and C(a)-C(m) stretching vibration to pressure in these meso-substituted porphyrin self-assemblies indicate that the stiffness of molecular spring washers is tunable.

Molecular spring washers: Raman scattering studies on Tpp J-aggregates under high pressure.

High-pressure Raman scattering studies at ambient temperature are performed on Tpp J-aggregates up to 13 GPa. It can be concluded that all the vibrational frequencies upshift linearly with increasing pressure which indicate that no obvious phase transition occurs during compression. In particular, the fact that the relative intensity of phenyl psi3 C-C in-plane stretching vibration shows monotonic enhancement with pressure future indicates that the dihedral angle between the porphyrin ring and phenyl groups decreases with increasing pressure. And all the transformation is reversible during decompression. The combined analysis of scanning election microscopy (SEM) image and the high-pressure behavior of Tpp J-aggregates makes it an ideal candidate for future potential applications as pressure-driven molecular spring washers.