Lycopene absorption spectrum

FIGURE 12.4 Lycopene photodegradation in 0.02 M Triton X-100 aqueous solutions illuminated with a 150 W (> 380 nm) filament lamp. Inset evolution of the difference absorption spectrum (AA). 

Fig. 3. Pump-deplete-probe spectroscopy on lycopene in hexane, a) Experimental setup After excitation and depletion of Car S2 with a delay of r=50fs, a white-light probe pulse at delay tprob<.=2ps measures the transient absorption spectrum, b) Spectra without (solid curve) and with depletion pulse (dotted) and their difference (shaded area). Only the Car Si state is depleted the ground state bleach (S0-S2) and positive absorption feature on its low energy side (hotSo-S2) are unaffected.

Figure 23-10 The absorption spectrum of lycopene (plotted vs wavelength). Note the vibrational structure, which has a spacing of 1200-1500 cm-1. The solid line is for alltranslycopene while the dashed line is that of the sample after refluxing 45 min in the dark. The new peak at 360 nm arises from isomers containing some cis double bonds.

Many organic compounds such as lycopene are colored because their HOMO-LUMO energy gap is small enough that X ax appear s in the visible range of the spectrum. All that is required for a compound to be colored, however, is that it possess some absorption in the visible range. It often happens that a compound will have its in the UV region but that the peak is broad and extends into the visible. Absorption of the blue-to-violet components of visible light occurs, and the compound appears yellow. 

Upon exposure to thermal energy, absorption of light, or involvement in specific chemical reactions, interconversion of lycopene isomers is known to take place. The cis isomers of lycopene, formed by rotation around any of its conjugated double bonds, have chemical and physical characteristics distinctly different from their all-frans counterparts. Some of the differences resulting from trans-to-cis isomerization include lower melting point, decreased color intensity, a shift in the lambda max, smaller extinction coefficients, and the appearance of a new maximum in the ultraviolet spectrum. ... 

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