Effect Of Temperature And Pressure On Raman Spectra Of Conjugated Molecule

Carbon-conjugated molecules in industrial production and research in thefield of organic chemistry plays an important role, such as benzene is animportant raw material production of plastics, rubber, fiber and other，carotenoid molecules play a significant role in photosynthesis in plants,in the human body β-carotene is a precursor of vitamin A and is essentialfor human. In this paper, we the use the Raman spectroscopy and electronabsorption spectroscopy techniques to research the following work. Weinvestigated binary CH/π interaction in different volume ratio of as wellas the effect of high-pressure and low-temperature for this interaction.We measured the Raman spectra of β-carotene at different temperaturesand analyze the influence of the relative intensity of spectral lines by thetemperature. We obtained the high pressure Raman spectra of p-terphenyland analyzed the molecular structure change of pressure.We got thefollowing innovative achievements:1. CH/π interaction plays an important role in organicchemistry, biology and materials science system. Based on thedifferent volume ratio of chloroform and benzene solution Ramanspectroscopy we obtain CH/π interaction strength will change withthe dual solution volume ratio, when the mixed solution volume ratioof chloroform and benzene reach3:4, this interaction force reachessaturation. Temperature also has some influence on this interaction, when the condition from room temperature to210K CH/πinteraction with a small margin enhancement, but less than210K, theeffect of temperature on this interaction becomes very small. Whenthe pressure is less than1.5GPa, pressure has a slight effect for CH/πinteraction, with pressure increases, when the pressure is greater than1.5GPa, CH/π interaction effect at atmospheric pressure not bereflected in a high pressure Raman spectrum.2. The resonance Raman spectra of the fundamental,combination and overtone modes around the C-C and C=C stretchesof all-trans-β-carotene in1,2-dichloroethane solution are obtainedfrom the293K to83K temperature range. β-carotene solution ofnon-phase transition as the temperature decreases the carbon-carbonstretching vibration of the fundamental modes, combinations modesline intensities have increased, during a phase transition thefundamental modes spectrum weakened, and combinations modescontinued to improve. This is because the temperature decreases,β-carotene molecular structural order to improve, π electrondelocalization extended conjugated polyene molecule effectivelylength increasing, greatly enhances the Raman-active. During a phasetransition, the molecular structure order decline, reducing theeffective conjugation length, resulting in phase transition of thefundamental modes of the spectral intensity unusual. But decreases with temperature, electron-phonon coupling strength continued toimprove, and this has led to combinations modes increases withtemperature decrease.3. We obtained the high pressure Raman spectra ofp-terphenyl up to5GPa. We analyzed the Raman actives change ofdifferent molecular symmetry using group theory, and obtainedp-terphenyl molecular structure change from a twist C2to planar D2hsymmetry through the disappearing of certain Raman modes. A phasetransition of p-terphenyl was obtained at around1.3GPa based on thefrequency–pressure relationships. This report provided a new methodfor judging planar structure of polyphenyl materials.