Photon redox potentials

The chemical association of the exciplex results from an attraction between the excited-state molecule and the ground-state molecule, brought about by a transfer of electronic charge between the molecules. Thus exciplexes are polar species, whereas excimers are nonpolar. Evidence for the charge-transfer nature of exciplexes in nonpolar solvents is provided by the strong linear correlation between the energy of the photons involved in exciplex emission and the redox potentials of the components. 

Actually, the kinetic study of the cluster redox potential by pulse radiolysis [31] (Section 20.3.2) somewhat mimics the process of the black-and-white photographic development, except that clusters are free in the solution (not fixed on AgBr crystals), and that they are produced by ionizing radiation (as in radiography and not by visible photons but the last choice had been incompatible with the time-resolved optical detection in the visible. Beyond the critical nuclearity, they receive electrons without delay from the developer already present (actually, the photographic development is achieved in a delayed step). 

The LB deposition is one of the best methods to prepare highly organized molecular systems, in which various molecular parameters such as distance, orientation, extent of chromophore interaction, or redox potential can be controlled in each monolayer. We have been studying photophysical and photochemical properties of LB films in order to construct molecular electronic and photonic devices. The molecular orientation and interactions of redox chromophores are very important in controlling photoresponses at the molecular level. Absorption and fluorescence spectra give important information on them. We have studied photoresponses, specific interactions, and in-plane and out-of-plane orientation of various chromophores in LB films [3-11], In addition to the change of absorp-... 

The excited state of a diamagnetic species with a closed-shell ground state is both a better donor and acceptor than its associated ground state. In addition to the ground-state redox potential, the excited state has the additional redox power of the absorbed photon, i.e. hv. Figure 2.15 illustrates this point, whereby ionization potentials (IPs) and electron affinities (EAs) for a ground- and excited-state molecule are compared. Excitation decreases the IP by AEhomo-lumo/ i.e. 

TheP7007P700 couple has a redox potential of+0.45 V [c/. redox-potential scale in Fig. 2]. The of the Aq/Aq" couple is probably less than -1 V if it is consistent with the in vitro redox-potential value of Chl/Chl of < -1.0 V. The initial charge separation into P700 and Ao would store approximately 1.5 eV out of 1.8 eV of energy of the absorbed 700-nm photon. The redox potential ofthe A,/A," couple is probably -0.8 V. The redox potentials ofthe iron-sulfur centers FeS-X, FeS-B and FeS-A have been experimentally determined to be -0.73, -0.58 and -0.53 V , respectively. The final electron acceptor in photosystem 1 is the [2Fe-2S]-type ferredoxin (Fd) present in the stroma region of the chloroplasts and having a redox potential of -0.4 V. Under iron-deficient growth conditions, a flavoprotein called flavodoxin is synthesized as a replacement acceptor for ferredoxin. 

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