Spatial separation between donor

Fig. 8.8 HOMO/LUMO orbital schemes of 5b and 6b representing the spatial separation between donor and acceptor moiety...

The emitted photon energy depends on both the relative positions of donor and acceptor levels in respect to the VBs and CBs (ED and EA, respectively) and the spatial separation between the donor and acceptor sites (r) [33],... 

A similar mean diameter i.e., 170 nm) was found for Ceo-aniline clusters in toluene - acetonitrile (1 3 v/v). This cluster formation exerted an improving impact on the performance of Ceo-based donor-acceptor dyads. For example, in aggregates of a Ceo-aniline dyad the radical pairs have a lifetime of 60 ps, while no detectable charge-transfer intermediates were noted for the isolated dyad. The close and condensed network in the cluster composites fecilitates the hopping of electrons from the parent fullerene to an adjacent one etc., progressively increasing the spatial separation between radical ions of the charge-separated state. 

Examples of electron tunneling reactions on the surface of heterogeneous catalysts have been discussed in Chap. 7. These reactions provide electron transfer between spatially separated donor and acceptor centres on the surface of heterogeneous catalysts as well as between the centres one of which is on the surface of the catalyst and the other is in the subsurface layer. Such processes are expected to be important for photocatalytic reactions, as well as for thermal catalytic reactions proceeding at low temperatures by heterolytic mechanisms. 

Intramolecular charge separation is energetically favoured over intermolecular charge separation because the spatial separation of charges, and hence the Coulomb term, is limited by the fixed distance between donor... 

Since the electrode and the protein redox center may be considered as a donor-acceptor pair, the distance, or spatial, separation of the enzyme redox center from the electrode by means of the protein shell prohibits the direct electrical communication between the redox site and the electrode. Substantial research efforts were directed during the last two decades to overcome the insulating protein barrier surrounding the redox centers and... 

The lifetime of the final charge-separated ion pair, C -P-Q" , is about 300 ns in a dichloromethane solution (and about 2 jus in a butyro-nitrile solution). This lifetime is substantially longer when compared to porphyrin-quinone ion pairs, P -Q (ca. 100 to 200ps). Other D-S-A assemblies containing porphyrins as chromophores are exemplified in structures 3 and 4. In these triad assemblies an aniline residue provides the electron donor component [35], System 3, for example, exhibits structural rigidity, and thus defined spatial orientation between the donor and acceptor components is established. The sequence of ET reactions occurring upon excitation of the porphyrin is summarized by... 

---