Photochemistry intermolecular electron transfer reactions

Imides. Although the photochemistry of imides is quite diverse (203), there exists solid reason to believe that electron transfer can control the reactivity of some imide/olefin pairs. For example, addition reactions analogous to those discussed above for iminium salts can also be observed for imides, either in an intermolecular sense, eq. 67 (204),... 

Natui al photosynthesis undoubtedly represents an exemplary system for supramolecular photochemistry. In a series of irreversible electron transport processes in bacterial photosynthesis, an electron was ejected from bacteriochloro-phyll dimer (specif pair) [43S-438] and transferred to quinone [439-441] via bacteriopheophytin [442-444]. Ferrocytochrome c supplies an electron to the hole of a special pair [445]. The charge separation and each electron transfer have been supposed to proceed at almost 100% efficiency. Those postulates were actually verified in a series of elegant works on structural analyses of reaction center from Rhodopseudomonas (Rps.) viridis and Rb. sphaeroides by Deisen-hofer et al. [428-430]. In 1984 they fotmd that the special pair and bacteriopheophytin were beautifully aligned and oriented with each other in the system [428]. The intermolecular center-to-center distance within the special pair was revealed to be 7.0 A and the distances between the two molecular planes were 3.0 A for Rps. and 3.5 A for Rb., respectively [428-434,446-450] (Fig. 39). 

In this chapter, we have described the fundamental parameters that should be obtained when characterising an electronic, singlet or triplet, excited state and how to determine them experimentally including methodologies and required equipment. These characteristics include electronic energy, quantum yields, lifetimes and number and type of species in the excited state. Within this last context, i.e., when excited state reactions give rise to additional species in the excited state we have explored several excited state kinetic schemes, found to be present when excimers, exciplexes are formed and (intra and intermolecular) proton transfer occurs. This includes a complete formalism (with equations) for the steady-state and dynamic approaches for two and three-state systems, from where all the rate constants can be obtained. Additionally, we have explored additional recent developments in photophysics the competition between vibrational relaxation and photochemistry, and the non-discrete analysis (stretched-exponential) of fluorescence decays. 

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