Antenna effects

The principle of the antenna effect is based on long-range interactions (see Section 5.11) between periphery and core. These make it possible to influence 

Owing to their spheroidal molecular shape, fullerenes represent attractive functional core units for light-harvesting dendritic systems. In fullerene dendrimers of 

Moore et al. used a convergent approach to construct first- to sixth-generation dendrons based on arylacetylene units. These were functionalised at the focal point with a - fluorescent - perylene unit and investigated with regard to their flu- 

The design of dendritic multiporphyrin systems [18] permits energy transfer over longer distances. The outer shell of the dendrimer shown in Fig. 5.14 is made up of eight porphyrin-zinc complexes as energy donor units. Excitation of the units of the outer shell leads to fluorescence emission of the metal-free porphyrin core as a result of energy transfer from the periphery to the energy acceptor [19]. 

The scaffold of the two porphyrin dendrimers used is identical (Fig. 5.16) they differ solely in the functionalisation of their periphery. The dendrimer shown schematically in red in Fig. 5.15 corresponds to this basic scaffold, for example with R = CONH(CH2)2N+Me3 the dendrimer shown in green bears the group R = COCTK+. 

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Kawa M (2003) Antenna Effects of Aromatic Dendrons and Their Luminescene Applications. 228 193-204... 

Luminescence experiments in dichloromethane solution indicated that the fluorescence of the phenylacetylene branches is quenched, whereas intense emission is observed from the binaphthol core. This antenna effect represents the first example of efficient (>99%) energy migration in an optically pure dendrimer. The fluorescence quantum yield increases slightly with increasing generation the values of 0.30,0.32, and 0.40 were obtained, respectively, for 10-12. 

Antenna Effects of Aromatic Dendrons and Their Luminescence Applications... 

Antenna Effect Towards an Organic Photosensitive Moiety... 

Remarkable concentration of the photon energy absorbed by aromatic dendritic scaffold toward the focal point (herein called antenna effects ) is one of the most distinct features of the dendritic macromolecules. Poly(benzyl ether) (PBE) dendron [1] has been studied most extensively as an efficient antenna dendron. Careful studies have revealed the crucial role of the symmetric dendritic structure for the antenna effect. 

The morphological dependence of the antenna effect was quantitatively studied by the comparison of the three focal isomers of benzene-cored 4th-genera-tion dendrimers [7]. The energy of the photon absorbed by the dendron subunits must be dissipated either through radiative (luminescence) or nonradia-... 

Self-assembly of aromatic dendron subunits has been tried by the design of coordination to multivalent metal cations (i.e., metal-cored dendrimer complexes). Several metal-cored dendrimer complexes have successfully exhibited luminescence by antenna effects. 

Poly(ether ketone) dendrons [24] have been observed to show an antenna effect toward lanthanide cations, especially for Eu +. Two focal coordination forms were examined, namely carboxylate [25] and 1,3-diketonate [26]. The use... 

A supramolecular assembly of macromolecules bearing antenna dendron has been reported. Pyrazole-anchored PBE dendrons were synthesized to examine the coordination behavior to transition-metal cations (Cu, Au, Ag) [31]. Self-assembled metallacycles were found. The Cu-metallacycle further formed luminescent fibers about 1 pm in diameter. The luminescence (605 nm) occurred by the excitation of the dendron (280 nm) and the excitation spectrum was coincident with the absorption spectrum of the dendron, suggesting the antenna effect. Interestingly, the luminescence of the Cu-metallacycle fiber disappeared when the fiber was dissociated into the individual metallacycles in C2H2. 

Figure 2.9.11 shows schematically the experimental set-up of the ionic current device. The sample is packed between two electrodes that are shaped meander-like in order to avoid eddy currents due to pulsed field gradients. The high frequency filter is essential to prevent an antenna effect of the electrode cables inside the magnet. 

Kawa, M., and Frechet, J.M.J. (1998) Self-assembled lanthanide-cored dendrimer complexes enhancement of the luminescence properties of lanthanide ions through site-isolation and antenna effects. Chem. Mater. 10, 286-296. 

A. Jorio, A.G.S. Filho, V.W. Brar, A.K. Swan, M.S. Unlu, B.B. Goldberg, A. Righi, J.H. Hafner, C.M. Lieber, R. Saito, G. Dresselhaus, and M.S. Dresselhaus, Polarized resonant Raman study of isolated single-wall carbon nanotubes symmetry selection rules, dipolar and multipolar antenna effects. Phys. Rev. B 65, 121402.1-121402.4 (2002). 

Since the properties of the modular components are known and different modules can be located in the desired positions of the dendrimer array, synthetic control of the various properties can be obtained. It is therefore possible, as schematically shown in Figure 2, to construct arrays where the electronic energy migration pattern can be predetermined, so as to channel the energy created by light absorption on the various components towards a selected module (antenna effect). 

Semi-conductors Antenna Effects and Charge Separation. 44 1... 

Antarctic polar stratospheric clouds, effect on ozone depletion, 17 788-789 Anteiso acids, 5 28 Antenna effect, 8 263... 

The antenna effect is illustrated in Fig. 6. The necessary conditions for its efficient implementation are the high molar absorbance of antenna dyes, efficient energy transfer to acceptor dye, and high quantum yield of emission of the latter. At the same time, while evaluating the highly increased apparent brightness of the... 

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