Photoexcitation center

As for the photoexcitation center, dye sensitizers, small bandgap semiconductors or dye-sensitized large bandgap semiconductors are candidates... 

Figure 13-3. Artificial photosynthesis [9] that combines a water oxidation catalyst (C2), a photoexcitation center (sensitizer) and a proton reduction catalyst (C ) through mediators (M2 and Ml).

In this chapter, the discussion will center on the reactions of excited states, rather than on the other routes available for dissipation of excess energy. The chemical reactions of photoexcited molecules are of interest primarily for three reasons ... 

Using a variety of transient and CW spectroscopies spanning the time domains from ps to ms, we have identified the dominant intrachain photoexcitations in C )-doped PPV films. These are spin-correlated polaron pairs, which are formed within picoseconds following exciton diffusion and subsequent dissociation at photoinduced PPV+/Cw> defect centers. We found that the higher-energy PA band of polaron pairs is blue-shifted by about 0.4 eV compared to that of isolated polarons in PPV. 

In addition, the results indicated that the efficiency of cis —> trans increased as the initial cis double bond configuration is shifted from the center of the polyenic chain, consistent with the 7j, triplet excited state potential curve that has a very shallow minimum at the 15-cis position compared to the deep minima at the all-trans position. The results strongly suggest that isomerization takes place via the 7j state of the carotenoid even in the case of direct photoexcitation, with their photosensitized process because of the very low intersystem crossing quantum yield, isc ([Pg.246]

In this chapter, the effect of preexcitation with the light of band-gap energy on trapping and thermal generation is examined in selenium and selenium-rich As-Se alloy films by several techniques. Results suggest that excess carrier trapping and dark-carrier generation are controlled by deep defect centers whose population can temporarily be altered by photoexcitation. 

It is often the goal of photoconductivity studies to measure the photoexcitation cross sections, i.e., the crvni and avpi. Although it is hard to determine the magnitudes of these cross sections, because of the other terms in Eq. (44) that are unknown, it is often easy to determine their energy dependences. The reason is that none of the other terms are usually very energy dependent. In 1965, Lucovsky published an oft-quoted equation for [Pg.101]

Cyclic photophosphorylation in purple bacteria. QH2 is eventually dehydrogenated in the cytochrome bc1 complex, and the electrons can be returned to the reaction center by the small soluble cytochrome c2, where it reduces the bound tetraheme cytochrome or reacts directly with the special pair in Rhodobacter spheroides. The overall reaction provides for a cyclic photophosphorylation (Fig. 23-32) that pumps 3-4 H+ across the membrane into the periplasmic space utilizing the energy of the two photoexcited electrons. 

Figure 54. Sampling of TOF spectra for He + Ne. Time t0 is flight time from beam excitation region to collision center e, expected elastic flight time derived from Newton diagram of Fig. 53, and numbered times those for Ne in various final states (notation as in Fig. 53). Number zero corresponds to beam neon photoexcited by far-UV photons produced as result of energy transfer (see Section III.A.7).

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