Study on the Effect of Pressure on the Molecular Structure and π-Electron Delocalization of β-Carotene by Raman Spectroscopy

In the present paper, studies on in-situ Raman spectra at high pressure up to 12.85 Gpa were performed on p-carotene using a diamond anvil cell (DAC), and the effects of pressure on the characteristic peaks and pi-electron delocalization of beta-carotene were discussed. The results showed that Raman frequencies of the main characteristic peaks of p-carotene shifted to high wavenumber with the increase in pressure. The relation between pressure and the three main characteristic peaks of beta-carotene was given as follows: nu(1)(C=C) = 4. 74P+1 511.4, nu(2)(C-C) = 2. 55P+1 157.6 and nu(3) (CH3) = 2. 25P+1 011.3. Under the pressure of 5.38 GPa, Raman spectrum of nu(1) +nu(2) sum frequency of p-carotene was subjected to cleavage. Fuethermore, the degree of pi-electron decolization was reduced with the increase in pressure, leading to C=C double bond more compressible than C-C bond on the main chain of beta-carotene.