Optical, Redox and Binding Properties of Some Representative Dyes

Optical, Redox and Binding Properties of Some Representative Dyes 

In this review, we restrict ourselves to metal-mediated assemblies of functional 7T-systems, which absorb light in the visible region (i.e. A. 400 nm). Thus, materials whose color arises from metal ions or metal-ligand charge transfer (MLCT) are not included here. Self-assembhes derived from free base porphyrins, metalloporphyrins and perylene bisimide dyes have shown promising applications in artificial LH systems. Therefore, some fundamental properties of a few representative chromophores, namely meso-tetraphenylporphyrin (TPP), zinc tetraphenylporphyrin (ZnTPP), tetra-phenoxy-substituted perylene bisimide (PPBI) and bay area imsubstituted perylene bisimide (PBI), are briefly summarized herein. These properties are essential for the understanding of the photophysical and photochemical behavior of assemblies derived from such dyes. 

The dyes TPP, ZnTPP and perylene bisimides (PPBI, PBI) also show well-defined redox waves in cyclic voltammograms (Table 2). Both TPP and ZnTPP possess two reversible oxidation and two reversible reduction waves. As the data in Table 2 reveal, ZnTPP is somewhat easier to oxidize than TPP. Compared with TPP and ZnTPP, PBI and also the tetraphenoxy-substituted PPBI are electron-deficient chromophores, thus, they can successively accept two electrons to afford radical anionic and dianionic species, respectively, at readily accessible potentials. By contrast, the oxidation waves of PBI and PPBI appear at relatively high potentials. 

In addition to the photo- and electrochemical properties of the representative dyes, we also present the binding constants of some metal-ligand interactions (Table 3) which are of relevance for the coordinative bond formation in the dye assemblies discussed in this review. The binding constants reflect the stability of the assembhes formed and are critically dependent on many factors, including ligands, metals, temperatxne, and solvents as well. In order to get assemblies of considerable stabUity, the varions factors need to be adjusted properly. The binding constant of pyridine (frequently used as 

Ligand donor Ligand acceptor/ metal ion Solvent Ks (M-i) -AG / kj mol Ref. 

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