The Impact Of Temperature On Molecular Structural Order Of β-carotene

The polyenes linear Biological molecule which containπelectronic conjugation play an important role on nanometer material, optoelectronic devices and so on.β-carotene is the polyenes linear Biological molecule which have nine C=C, and it have special optocal property. Our study indicate thatβ-carotene have largely Raman active, and its Raman cross section (RCS) can reached 10-23-10-20 cm2molecule-1Sr-1 by 514.5 laser excitation, and the RCS of normal molecular is 10-30 cm2 molecule-1Sr-1.This result mainly from molecular structural order besides resonance Raman. Whenβ-carotene have large molecular structural order, it can produce strong RCS in the effect of laser due to coherent weakly damped CC vibrations. External conditions such as temperature, electromagnetic field, van der waals force have important influence on molecular structure and motion state. In the study, in the solution ofβ-carotene dissolved dimethyl sulfoxide(DMSO), the range of the temperature is from 73℃to 25℃. We found the temperature has great effect on molecular structural order ofβ-carotene. Due to the temperature decreases, the molecular structural order ofβ-carotene increases which lead to the weak of coherent weakly damping CC bond vibration, the CC bond length changs longer. Because the CC bond length is slightly different, the Raman scattering cross section increases about 0.6×10-23cm2 molecule-1 Sr-1. And the frequency shifts towards lower frequencies, the frequency components of vibration decrease, and the Raman linewidth becomes narrow. Due to the temperature decreases, the UV-visible spectra of P-caroten caused slightly red shift(about 6 nm). The observed phenomenon is explained by a mechanism involving decrease ofβ-carotene thermally disorder, increase of molecule structural order, expansion ofπ-electron delocalization with the decreasing of temperature. The width of the electronic gap become narrow, which leads to slight shift of absorption spectra to longer wavelengths.This article is very useful for the study of the structure, property and it also provides valuable information of the polyenes linear biological molecule in solution.