Photo-functional molecular assemblies

In this chapter, we describe three different systems with which to construct electro- and photo-functional molecular assemblies on electrode surfaces. The first is the bottom-up fabrication of redox-conducting metal complex oligomers on an electrode surface and their characteristic redox conduction behavior, distinct from conventional redox polymers.11-13 The second is a photoelectric conversion system using a porphyrin and redoxconducting metal complex.14 The third is the use of a cyanobacterial photosystem I with molecular wires for a biophotosensor and photoelectrode.15 16 These systems will be the precursors of new types of molecular devices working in electrolyte solution. 

While molecular assembly has proven to be effective for a photoelectric conversion system, coordination reactions are possibly a simple approach for connecting such functional molecules, as presented in the previous section. We applied the stepwise coordination method to prepare a photoelectric conversion system. Since the molecular wire exhibits redox conduction through the wire,11,13 efficient photo-electron transport through the redox sites in the wire is also expected. In this section, we demonstrate the fabrication of a photoelectric conversion system using ITO electrodes modified with M(tpy)2 (M = Co, Fe, Zn) complex wires with a terminal porphyrin moiety as a photosensitizer. The behavior of photo-electron transfer from porphyrin to ITO through the molecular wire was investigated by changing the metal element in the M(tpy)2 moieties.14... 

Tetrad 10 illustrates the clear advantage of multistep ET pathways in enhancing the lifetime and quantum yield of the separated state at the molecular level [40]. The multifunctional tetrad 10 combines the functionalities of the two triads D-S-A and S-Aj-Aj discussed earlier, and can be considered as a D-S-A,-Aj assembly. The porphyrin acts as the photo-... 

Supramolecular dendrimers that contain photo- and/or redox-active functions have attracted a great deal of interest due to their potential apphca-tions in molecular recognition, catalysis and hght harvesting [121-123]. Dye molecules are assembled into dendritic superstructures through metal-ligand mediated coordination for serving as photoactive materials. 

Molecular opto-electronic assemblies, which consist of a functionalized gold electrode with a photo-isomerizable redox-activated monolayer, enables amperometric transduction of the photonic information recorded by the interface. On-off operation of superstructure formation of hermaphroditic cyclodextrin derivatives is brought about by disturbing the monomer/dimer equilibrium of -azobenzene structures by photoisomerization. When the structures have the Z-form, the dimer dissociates. The thermal Z— isomerization can be enhanced by heating in favor of the dimer formation (Figure 89.8). ... 

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