Resonance Raman spectra (5800–40 cm⁻¹) of All‐trans and 15‐cis isomers of β‐carotene in the solid state and in solution. Measurements with various laser lines from ultraviolet to red

Abstract

The Raman spectra (5800–40 cm−1) of the all‐trans and 15‐cis isomers of β‐carotene were observed in the solid state at 77 K and in cyclohexane solutions using laser lines of various wavelengths for excitation. The Raman spectra of the solid samples exhibited not only the well known strong bands but also a great number of sharp bands (mostly weak in intensity) which could not be observed or were observed broadly in solutions at room temperature. The molecules of both isomers in solution seem to have structures slightly different (‘relaxed’) from those in the solid state. All the bands in the region of 5800–1800 cm−1 were satisfactorily accounted for as overtones or combination tones of relatively strong fundamentals. Rough excitation profiles and depolarization degrees measured for cyclohexane solutions gave information on the mechanism of resonance enhancement. The polarized bands of the all‐trans isomer at 1597 and 1525 cm−1 are both resonant with the 1Bu←1Ag absorption around 480 nm. In addition, the 1597 cm−1 band is resonant with the 21Bu←1Ag absorption around 275 nm. The polarized bands at 1597, 1533, 1194, 1156 and 1004 cm−1 of the 15‐cis isomer are resonant with the ‘cis‐peak’ around 340 nm as well as with the 1B1←1A1 absorption around 475 nm. The polarized bands at 1241, 1052 and 953 cm−1 of the 15‐cis isomer are characteristic of this isomer, but these are only slightly resonant with the ‘cis‐peak’. The intensity of the depolarized band at 1564 cm−1 of the 15‐cis isomer is enhanced by the vibronic interaction between the excited 1A 1+ and 1B1 states.

Determination by Raman scattering of the nature of pigments in cultured freshwater pearls from the mollusk Hyriopsis cumingi

“…Raman spectra recorded over a wider wavenumber region exhibit the bands in the overtone and combination spectral range as was previously observed by others for pigments containing polyenic chains. 12,21,25,27 However, these peaks are weaker than the fundamental ones; hence, they are of limited interest for our purpose. Luminescence is observed in the green and blue ranges (Figs 2-3) for some colored samples.…”

Fourier‐transform resonance Raman spectra of cation carotenoid in photosystem II reaction centres

“…Note that a less apparent absorption was seen around 830 nm from the chlorophyll cation, Chl , than for the more intact system at the same temperature [4], although the use of ¢lter paper as a sample support in the present work has resulted in spectra of a much lower quality. 31 which are likely to be overtones and combinations of the lower frequency modes (indicating true resonance conditions: [12]). Shown in Fig.…”

Triplet Excitons of Carotenoids Formed by Singlet Fission in a Membrane

“…A similar downshifted CÀC mode is observed in spectra of solid-state all-trans-b-carotene, and is not an indicator of structural distortion. [30] There are no significant changes in the hydrogen out-of-plane wagging modes, which would otherwise indicate structural distortion of the polyene chain. [12,30,31] The HOOP bands of zeaxanthin at~874 and~959 cm À1 are nearly identical in the fluid and gel phases, and reveal that the carotenoids are not distorted in the bilayers.…”

“…[30] There are no significant changes in the hydrogen out-of-plane wagging modes, which would otherwise indicate structural distortion of the polyene chain. [12,30,31] The HOOP bands of zeaxanthin at~874 and~959 cm À1 are nearly identical in the fluid and gel phases, and reveal that the carotenoids are not distorted in the bilayers. The findings support the conclusion that exciton coupling in the gel phase is the cause of the enhanced blue absorption in the UV/Vis spectrum.…”