Antenna effect in polymers

Nowakowska, M., Foyle, V.R, and GuiUet, J.E., Studies of the antenna effect in polymer molecules. 24. Solar photosynthesis of previtamin D3 in aqueous solutions of poly(sodium styrenesulfonate-co-2-vinylnaphthalene),/. Am. Chem. Soc., 115, 5975-5981,1993. 

The phenomenon of excitonlc energy transport in polymer films has been studied actively for the past decade (2 ). This photophysl-cal process is relevant to photodegradation and photoconductivity in polymers, but in this contribution we wish to emphasize the potential application of polymer films as photon "harvesters" with subsequent transfer of energy to a reaction center, analogous to the so-called "antenna effect" in chloroplasts. 

ABSTRACT. Intramolecular excimer formation in synthetic polymers is reviewed. The antenna effect in macromolecules is examined and evidence for singlet energy migration and trapping is discussed. 

The overall yield and the kinetics of photoinduced electron transfer (ET) for a polyelectrolyte-bound chromophore are modified by steric effects arising from hydrophobic interactions between the polymer and chromophore [43-45] these are termed hydrophobic protection. Partially sulfonated poly(vinylnaphthalene)s form a hypercoiled structure in water, and photoexcitation energy migrates through naphthalene units in the hypercoil [46]. Such antenna polyelectrolytes, with photochemically reactive molecules incorporated inside the hypercoil, exhibit efficient photosensitized reactions owing to the antenna effect, and are termed photozymes [46]. Hydrophobic protection and photozymes are based on the same principles as compartmentalization. 

Fig. 4. Detection of single molecules by near-field techniques, (a), (b) SNOM images of single molecules embedded in a polymer film with random orientations, from [29]. (c) Sketch of the field distribution in the near field of the aperture, (d) Comparison of measured field distributions to calculated, once for both fundamental orientations, from [27]. (e) Effect of an optical antenna on the emission of a single emitter [36].

Applications that have received attention, and the material properties that enable them, are shown in Figure 27.1. These applications are reviewed in detail in Waser and Ramesh. Decoupling capacitors and filters on semiconductor chips, packages, and polymer substrates (e.g., embedded passives ) utilize planar or low aspect ratio oxide films. These films, with thicknesses of 0.1 to 1 J,m, are readily prepared by CSD. Because capacitance density is a key consideration, high-permittivity materials are of interest. These needs may be met by morpho-tropic phase boundary PZT materials, BST, and BTZ (BaTi03-BaZr03) solid solutions. Phase shifters (for phase array antennas) and tunable resonator and filter applications are also enabled by these materials because their effective permittivity exhibits a dependence on the direct current (DC) bias voltage, an effect called tunability. 

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