Carotenoids energy diagram

Fig. 15. (A) Absorption, fluorescence and phosphorescence spectra of BChl a in vitro at 77 K spectra scaled for convenient presentation also note break of horizontal scale (B) Phosphorescence spectrum of quinone-depleted (-Q) and quinone-containing (+Q) Rb. sphaeroides reaction centers in polyvinyl-alcohol film at 22 K (C) Energy diagram for the components involved in triplet-triplet energy transfer with carotenoids. (A) and (B) and numerical values for the triplet-state energies of BChls a and b and the primary-donors of Rb. sphaeroides and Rp. viridis, i.e., [BChl a and [BChl bjj, respectively, are taken from Takiff and Boxer (1987) Phosphorescence spectra ofbacteriochlorophylls. J Am Chem Soc 110 4425.

Figure 4-9. Energy level diagram indicating the principal electronic states and some of the transitions of chlorophyll. Straight vertical lines represent the absorption of light wavy lines indicate radiationless transitions, for which the energy is eventually released as heat and broken lines indicate those deexcitations accompanied by radiation. In the literature, for chlorophyll is also referred to as S0, as Slt S H as S2, and T sfj as Tt (similar symbols occur for carotenoids).

Figure 5-7. Energy level diagram including vibrational sublevels, indicating the principal electronic states and some of the transitions for carotenoids. The three straight vertical lines represent the three absorption bands observed in absorption spectra, the wavy lines indicate possible radiationless transitions, and the broad arrows indicate deexcitation processes (see Fig. 4-9 for an analogous diagram for chlorophyll).

The triplet-state energies of the BChl a and BChl b derived from the phosphorescence spectra are summarized for chromophores of Rb. sphaeroides and Rp. viridis at the appropriate levels in the diagram in Fig. 15 (C), together with those for the respective carotenoids, spheroidene (in Rb. sphaeroides) and l,2-dihydroneurosporene(inRp. viridis). Singlet oxygen is also shown. 

The connection between experiment and the energy level diagram summarized in Fig. 1 is illustrated by the low temperature absorption and fluorescence spectra of aZZ-rra s-hexadecaheptaene (Fig. 3). The vibronic structure exhibited in these spectra generally is broadened in spectra of carotenoids, particularly for molecules such as /3-carotene where nonplanarities between the central polyene chain and terminal cyclohexenylidene rings result in a distribution of absorbing and emitting species (Christensen and Kohler, 1973 Hemley and Kohler,... 

Schematic diagram of the surface of a photosystem in the thylakoid membrane. It contains a patch-like mosaic of several hundred chlorophyll and carotenoid antenna molecules oriented in the membrane. An exciton absorbed by an antenna molecule quickly migrates via the pigment molecules to the reaction centre, P700 its path is shown by the coloured arrows. Although all the antenna molecules can absorb light, only the reaction centre molecule can convert the excitation energy into electron flow.

Figure 5. Schematic energy level diagram of a carotenoid.

Fig. 4. (A) Scheme of possible molecular arrangement of a chloroplast extract membrane containing chlorophyll, carotenoid and phospholipid as essential components. Ch, chromophore portion of chlorophyll Pht, phytol tail of chlorophyll C, carotenoids P, phospholipid. (B) The corresponding energy barrier diagram for the membrane (M)-water (W) system. The broken line in the membrane represents the reduced energy barrier level due to carotene. The solid lines in the potential wells represent the ground and first excited states of chlorophyll. The dotted line at the right of the membrane solution energy barrier represents the lowering of the energy barrier due to excited biliprotein (phy-cocyanin). The 4 A width is the distance of closest approach between the redox species in water and the chromophore in the membrane.

Figure 4.19 illustrates the use of this approach to calculate transition matrix elements for fm 5-butadiene, which provides a useful model for carotenoids and retinals. Panels A-D show the two highest filled molecular orbitals and the two lowest unoccupied orbitals ( 0i to in order of increasing energy). The vector diagram in panel E shows the direction and relative magnitude of the matrix... 

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