Antenna chromophores

Rapid multistep Coulombic energy transfer takes place as the excitation energy is transferred between the antenna chromophores and the special pair of bacteriochlorophyll molecules (P) in the reaction centre. 

Light-harvesting antenna chromophore, 236 Liposomes, 260 Lippert-Mataga equation, 14 Lumi-F intermediate in Pfr - Pr transformation, 268 Lumi-R intermediate in Pr — Pfr transformation, 250... 

In a related vein antenna chromophores have been developed for the self-sensitized photoreduction of ketones using isopropyl alcohol as a mild reducing agent189. One of the most effective chromophores for reduction of the model ketone 4-hydroxycyclohexanone was found to be the dimethylphenylsilyl group, as illustrated in equation 42. 

Compound 99 was made more hydrophobic by butylation of the 2-OH and 3-OH groups [88], The prepared CD derivative (100) solubilized 9-anthrylmethyl pivalate (AP) much more effectively than 99 or (3-CD. In the presence of AP, the naphthyl emission (Xex = 314 nm) of 100 was efficiently quenched and intense AP emission was observed. Because essentially all of the light is absorbed by the naphthyl chromophores, the strong AP fluorescence demonstrates that energy transfer occurs efficiently. The naphthyl antenna chromophores of 100 were shown to sensitize a selective photoreaction of AP included in the CD cavity (Scheme 2). The photoirradiation of AP in methanol gives 9-neopentylanthracene... 

Another water-soluble (3-CD (105) bearing seven naphthoyl chromophores forms very stable 1 1 complexes with a merocyanine laser dye DCM-OH [90], The energy transfer from the naphthoyl antenna chromophores to the included dye is shown to occur with 100% efficiency (antenna effect) (Scheme 3). 

The formation of luminescent lanthanide complexes relies on a number of factors. The choice of coordinating ligand and the method by which the antenna chromophore is attached to it, as well as the physical properties of the antenna, are important. In order to fully coordinate a lanthanide ion, either a high-level polydentate ligand such as a cryptate 1 or a number of smaller ligands (such as 1,3-diketones, 2) working in cooperation are required. Both 1 and 2 are two of the simplest coordination complexes possible for lanthanide ions. In both cases there are no antennae present. However, the number of bound solvent molecules is decreased considerably from nine (for lanthanide ions in solution) to one to two for the cryptate and three for the 1,3-diketone complexes. 

Fig. 58. Organic dyes used as antenna chromophore in terphenyl-based ligands.

The complexes of general formula [Ln(61)] (Ln = Nd, Er and Yb) (see fig. 60) exhibit the typical NIR luminescence of each Lnm ion upon excitation in the antenna chromophore. The overall quantum yields have been determined in deuterated methanol and by using the Ndm... 

Quantum yields for Er111 are much smaller and no data are reported for /3-dikcto nates. Among the few other quantitative figures reported, we note a quantum yield of 0.02% in deuterated water with fluorescein as the antenna chromophore, while all the other quantum yields are far below 10 3%. As for neodymium, 1,10-phenanthroline and 8-hy-droxyquinolinate are among the best sensitizers. 

To assess the effect of distance between the antenna chromophore and the Eu(III) center on luminescence sensitization, a series of four additional Eu(III) complexes, of ligands 57-60, each having the pendant phenanthridyl group at a different distance from the Eu(III) center, have been synthesized for comparison with [Eu(46)] + (76). 

Here, we will mainly focus on two other important aspects of photosensitization the fundamental role of deeply colored compounds as light-harvesting antenna chromophores for solar energy conversion and the possibility of reaching spectroscopically hidden, but photochemically active excited state levels by means of spectral sensitization. 

Macrocyclic Ligands as Antenna Chromophores 12.2.2.1 Cyclen Ligands... 

Calixarenes are particularly useful as molecular scaffolds for the design of luminescent lanthanide complexes because they can be conveniently functionalized with various chromophores [83]. The introduction of an antenna chromophore can be accomplished by either use of the... 

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