Photoinduced energy transfer, supramolecular assemblies

Ward, M. D. Photoinduced electron and energy transfer in noncovalently bonded supramolecular assemblies ,... 

Electron, energy and proton transfer or molecular rearrangements are the most important events that occur in interfacial supramolecular assemblies. In this chapter, the general theories of electron transfer, both within ISAs and across the film/electrode interface, are described. Moreover, photoinduced electron, energy and proton transfer processes are discussed. As this book focuses on supramolecular species, the treatment is restricted to intramolecular or interfacial processes without the requirement for prior diffusion of reactants. 

The study of photoinduced ET in covalently linked donor-acceptor assemblies began with comparatively simple dyad systems which contain a transition metal center covalently linked to a single electron donor or acceptor unit [26]. However, work in this area has naturally progressed and in recent years complex supramolecular assemblies comprised of one or more metal complexes that are covalently linked to one or more organic electron donors or acceptors have been synthesized and studied [27-36]. Furthermore, several groups have utilized the useful photoredox properties of transition metal complexes to probe electron and energy transfer across spacers comprised of biological macromolecules such as peptides [37,38], proteins [39,40], and polynucleic acids [41]. 

Hunter C. A. and Hyde R. K. Photoinduced Energy and Electron Transfer in Supramolecular Porphyrin Assemblies. Angew. Chem., Int. Ed. Engl. 35 (1996) pp. 1936-1939. 

IV. FUNCTIONAL ASPECTS OF SUPRAMOLECULAR ASSEMBLIES A. Photoinduced Electron and Energy Transfer... 

As already mentioned, the supramolecular assemblies can lead to new properties and photoinduced processes which have been studied in great details in solution (see previous section). On the contrary, only few cases of intermolecular photoinduced processes, and in particular, energy transfer, involving transition metal complexes in pure crystalline phases have been reported and will be now discussed. Here, relative orientation and distance between interacting species can be more precisely determined by means of single-crystal X-ray difiractometric analysis. 

Irradiation of 1,4,8,11,15,18,22,25-octabutoxyphthalocyanine or its copper derivatives in degassed ethanol containing triethanolamine causes its reduction by a mechanism which involves a higher excited state of the substrate,and a plot of the log of the rate constants for the photoinduced intramolecular electron transfer in a supramolecular assembly of Zn and Au porphyrins bridged by diphenylphenanthroline has been found to decrease linearly with diminishing energy difference between the HOMO and LUMO of the participating orbitals. ... 

Recently, we have shown that the supramolecular approach (a non-covalent two-fold extra-ligation in conjunction with Zn-porphyrin chemical dimers and trimers) can be successfully employed to create a variety of multiporphyrin structures capable of the fast effective intra-complex energy migration and photoinduced electron transfer [5]. Following this self-assembly principle we have succeeded to anchor in pyridyl substituted porphyrin molecules on CdSe/ZnS QD surfaces. In this case, CdSe/ZnS QDs show luminescence quenching induced by dynamic and/or static interactions between QD and porphyrins depending critically on sample stability, temperature and solvent polarity [6]. The general focus of this contribution is devoted to demonstrate the... 

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