Photon-harvesting polymers

Webber has surveyed the photophysics of photon harvesting polymers. Electronic energy transfer and the role of intracoil excimer formation are aspects of the subject which are discussed in this review. 

For other distributions and/or dimensionalities the donor decay becomes more complex with assuming values equal to 1/6 and 1/3 for one and two dimensional systems, respectively [85, 86]. In many cases, such as photon-harvesting polymer systems, where a distribution of relaxation times is expected, due to intrachain donor-acceptor energy transfer steps, either the distributions and/or the dimensionality are difficult to define a priori. Thus the use of a stretched exponential (Eq. 15.61, where 0 < / < 1 is an empirical parameter) has been proposed. 

Bai F, Chang CH, and Webber SE. Photon-harvesting polymers Singlet energy transfer in anthracene-loaded alternating and random copolymers of 2-vinyInaphthalene and methacrylic acid. Macromolecules 1986 19 2484-2494. 

Photocurrent response in the near-infrared region up to 1600 nm, related to absorption features of semiconducting SWNTs in blends with MEH-PPV and P30T, offers principally the operation of infrared sensitive photodetectors with these materials [318]. To enable the photon harvesting in this spectral region, the SWNTs needed to be finely dispersed within the polymer matrices, thereby switching off the excitation quenching observed within CNT bundles. 

Winder C, Saridftci NS (2004) Low bandgap polymers for photon harvesting in bulk heterojunction solar cells. J Mater Chem 14 1077... 

Energy migration in polymer films via triplet or singlet excitons is potentially applicable to "photon harvesting". Unfortunately many polymers possess pendent chromophores that absorb only in the UV. Experiments at 77K on poly(2-vinylnaphthalene)... 

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. 

High absorption cross section for photon harvesting. Ideally, the electronic structure of conjugated polymers is that of a one-dimensional semiconductor in which the absorption coefficient increases steeply above the band gap absorption. The absorption coefficient of the frequently used poly(p-phenylene vinylene) polymer MDMO-PPV (Figure 10.2.) reaches 10 cm just... 

Figure 47 Schematic layout of organic fullerene/polymer solar cell, (a) Phase segregation on the nanoscale creates bulk heterojunction in the active layer, which allows for efficient photon harvesting and charge generation and (b) molecular structures of classical fullerene-based and pol3mer-based materials most widely investigated in organic bulk heterojunction solar cells. (Reproduced from Ref. 156. American Chemical Society, 2004.)...

Photoexcited electronic energy migration and transfer phenomena in polymers are important if one is to understand photodegradation and photostabilization of polymers from a practical perspective. The phenomena are also critical in the photon-harvesting system for natural photosynthesis. For both practical and scientific interests, the energy migration and its transfer in... 

New natural polymers based on synthesis from renewable resources, improved recyclability based on retrosynthesis to reusable precursors, and molecular suicide switches to initiate biodegradation on demand are the exciting areas in polymer science. In the area of biomolecular materials, new materials for implants with improved durability and biocompatibility, light-harvesting materials based on biomimicry of photosynthetic systems, and biosensors for analysis and artificial enzymes for bioremediation will present the breakthrough opportunities. Finally, in the field of electronics and photonics, the new challenges are molecular switches, transistors, and other electronic components molecular photoad-dressable memory devices and ferroelectrics and ferromagnets based on nonmetals. 

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