Abstract
Vibrational properties of the biphenyl at around the melting transition temperature are investigated by Raman scattering. Nearly all the vibrational modes exhibit anomalous changes on the frequency, width, and intensity at around the melting temperature. The librational modes disappear at above the melting temperature. The energy separations between the 1220 and 1280 cm−1 modes and between the modes at around 1600 cm−1, as well as the intensity ratio of the last two modes, all show anomalous changes at around the melting transition temperature.
Highlights
Biphenyl is the shortest POP with only two phenyl rings in one molecule
The transition temperature of the crystalline biphenyl is about 45 K and the melting temperature is about 343 K.24
In order to analyze the vibrational properties of the biphenyl, we normalize the Stokes Raman intensities by I(ω) = I0(ω)/[n(ω, T)+1]
Summary
P-Oligophenyls (POPs) always attract plenty of attention due to the versatile physical and chemical properties. The POP molecules are composed of certain numbers of phenyl rings connecting at the para positions. Such a typical molecular conformation generates two opposite internal forces: One is the steric repulsion stems from the neighbouring four hydrogen atoms, the other is the conjugation which is responded to the delocalized π-electrons.. Plenty of works have been performed to study the vibrational properties of the POPs at low temperature. Due to the reemergence of the twist angles below the transition temperature, all the vibrational modes exhibit anomalous changes. Few works have been performed to study the vibrational properties at high temperatures, especially at around the melting temperature. This work provides a method to confirm the melting point of organic materials
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