Photon harvesting

CQDs can be efficient chromophores for photon harvesting and photoconversion [55] and it was shown that photogenerated electrons could be transferred to gold or platinum nanoparticles for the photocatalytic conversion of carbon dioxide and splitting of water for hydrogen generation [55,56], In both cases, CQDs similar to titania... 

Figure 38. Emission spectra (Aex = 450 nm) of the photon-harvesting assembly having an electronreceiving PVT-MV-+ layer. Reprinted with permission from D.M. ICaschak, J.T. Lean, C.C. Waraksa, G.B. Saupe, H. Usami and T.E. Mallouk, J. Am. Chem. Soc. 1999, 121, 3435. Copyright 1999 American Chemical Society.

Reaction (16) is the sum of reactions (17) and (18). Clearly, if each photon harvested by the system can lead to the transfer of one electron, then a minimum of four photons are required for the conversion of each CO2 molecule. Experimental measurements of the quantum yield indicate that eight photons are actually needed, suggesting that two photons are used for each electron transfer and that a two-step process is taking place with long-lived intermediates coupling the steps. 

Penmans P., Bulovic V. and Forrest S. R. (2000), Efficient photon harvesting at high photon intensities in ultra-thin organic double-heterostructure photovoltaic diodes , Appl. Phys. Lett. 76, 2650-2653. 

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... 

Scheme 16 Dendrimer system reported by Jiang and Aida to exhibit low-energy photon harvesting [80-82]...

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. 

Morrison have used model systems specially synthesised to test the efficiency of different aryl antenna groups for photon harvesting and examined effectiveness of singlet-singlet energy transfer to target ketone acceptors. 

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. 

Scheme 1.2 Mechanism of photon harvesting. Illustration of the transport of excitation energy by self-transfer through donor moieties (naphthalene) to an acceptor trap (anthracene).

Chart 1.3 Chemical structures of repeating units bearing naphthalene and anthracene groups contained in copolymers employed in photon-harvesting studies [13]. 

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... 

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