Antenna molecules

Ge, P., and Selvin, P.R. (2004) Carbostyril derivatives as antenna molecules for luminescent lanthanide chelates. Bioconjugate Chem. 15, 1088-1094. 

Figure 1. Schematic representation of the artificial photosynthetic reaction center by a monolayer assembly by A-S-D triad and antenna molecules for light harvesting (H), lateral energy migration and energy transfer, and charge separation across the membrane via multistep electron transfer (a) Side view of mono-layer assembly, (b) top view of a triad surrounded by H molecules, and (c) energy diagram for photo-electric conversion in a monolayer assembly.

Amphiphilic compounds and other chemicals used are shown in Figs. 5 [3,4] and 6 [36] together with their abbreviations. The synthetic procedures for A-S-D triad, A-S dyad, and H light harvesting antenna molecules in Fig. 5 were described previously [3,37,38]. A cationic cyanine dye with two long alkyl chains (CD) in Fig. 5 was purchased from Japanese Research Institute for Photosensitizing Dyes,... 

FIGURE 19-46 Exciton and electron transfer. This generalized scheme shows conversion of the energy of an absorbed photon into separation of charges at the reaction center. The steps are further described in the text. Note that step (T) may repeat between successive antenna molecules until the exciton reaches a reaction-center chlorophyll. The asterisk ( ) represents the excited state of an antenna molecule. 

Light excites an antenna molecule (chlorophyll or iccessory pigment), raising an electron to a higher energy level. 

The excited antenna molecule passes energy to a neighboring hlorophyll molecule (resonance energy transfer), exciting it. 

Figure 11. Mau water-splitting scheme. The xanthene dyes serve as the antenna molecules collecting the solar energy, transferring it to aa , which reduces methyl viologen (mv), which in turn reduces H+. EDTA reduces the oxidized aa to complete the cycle.

Ruthenium(II) polypyridyl complexes are employed as antenna molecules [311, 333-337] for a variety of reasons [338, 339] Ruthenium(II) polypyridyl complexes (i) are photostable under illumination, (ii) have strong metal-to-ligand-charge-transfer absorption (MLCT) in the visible, (iii) have high lying MLCT excited states (ii°o 2.0 eV), and (iv) are powerful electron donors in the MLCT excited state E 2 ( [Ru(bpy)3] +/[Ru(bpy)3] +) = -0.63 V relative to the SCE in di-chloromethane). Thus, the latter should be able to generate the one-electron reduced fullerene r-radical anion [E i2 = -0.41 V relative to the SCE in dichloro-methane) [338, 339]. 

The design of a dinuclear ruthenium chromophore, in which the mononuclear [Ru(bpy)3] + antenna molecule was replaced by a dinuclear ](bpy)2Ru(BL)Ru(bpy)2] complex (BL = 2,3-bis-(2-pyridyl)quinoxaline) led to a red-shift of the MLCT transition from 460 nm to 625 nm [311]. The luminescence quantum yield of the dinuclear dyad 16 gives rise to a very inefficient intramolecular... 

The energy conversion process begins with the excitation of the special pair of bacteriochlorophyll (Bchl) molecules which are located near the periplasmic side of the membrane. These Bchl species are in van der Waals contact with one another. The excitation may, of course, occur by direct absorption of a photon. More usually it is achieved via singlet-singlet energy transfer from antenna molecules. These antennas have been optimized for maximal absorption of sunlight under the environmental conditions experienced by the organism, and hence vary from species to species. They will be discussed in more detail in Section III. 

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