Porphyrins thiophene-functionalized

Redox molecules are particularly interesting for an electrochemical approach, because they offer addressable (functional) energy states in an electrochemically accessible potential window, which can be tuned upon polarization between oxidized and reduced states. The difference in the junction conductance of the oxidized and the reduced forms of redox molecules may span several orders of magnitude. Examples of functional molecules used in these studies include porphyrins [31,153], viologens [33, 34,110,114,154,155], aniline and thiophene oligomers [113, 146, 156, 157], metal-organic terpyridine complexes [46, 158-163], carotenes [164], nitro derivatives of OPE (OPV) [165, 166], ferrocene [150, 167, 168], perylene tetracarboxylic bisimide [141, 169, 170], tetrathia-fulvalenes [155], fullerene derivatives [171], redox-active proteins [109, 172-174], and hydroxyquinones [175]. 

Although commercial applications are still future goals, much progress has been made in the design of potential molecular wires. Molecules so far studied have included organic molecules with conjugated alkyne functionalities, porphyrins connected by alkyne units, chains of connected thiophenes, and a number of organometallic complexes. Examples of the latter are shown below ... 

It is also possible to improve the ion-exchange properties of polypyrrole by its functionalization with alkyl ammonium. In the polymer obtained, it is then easy to incorporate, simply by ion exchange, species such as metallic porphyrins [91,92] or heteropolyanions [93]. Heteropolyanions can also be incorporated into polyaniline [86], polybutyl-thiophene layer [94], or polyamino-naphtol [95]. 

Schaferling, M. and P. Bauerle (2001). Electrochemical properties of porphyrin-functionalized poly thiophenes. Syn. Met. 119, 289-290. 

Efforts towards the preparation of porphyrin-functionalized polythiophenes have centered on complexes 38-41, in which thiophenes are tethered to porphyrin cores (Chart 5.9) [50], The syntheses employed either porphyrin formation using MacDonald-type conditions (38-40) or Wittig coupling to produce 41. No electronic properties of these materials have yet been reported. 

Metal cyciam and porphyrin complexes may function as catalysts or electrocatalysts and electrode surfaces may be modified with such complexes by covalently attaching them to conjugated polythiophene backbones. Electropolymerization of a thiophene bearing a tethered Ni(II) tetramacrocycle (48, Chart 5.14) resulted in... 

When larger aromatic surfaces are involved, CH-n or van der Waals interactions controlled by alkyl chains may not be enough to prevent face-on deposition. In the two previous examples, archetypal aromatic structures such as porphyrins were shown to interact face-on with both metallic and hydrophobic surfaces. To obtain surface-tuned assemblies like those observed in alkyl substituted thiophenes with large aromatic structures, a much stronger interaction must be developed between the periphery of the porphyrin and the surface. The self-assembly of a cyano-functionalized porphyrin into extended ID structures on a KBr(OOl) surface, under ultra high vacuum, is one such example (Figure 38). ... 

Polymers with porphyrin units in the main chain and fuUerene side groups are described as electroactive [113], as well as polymers with azo-groups in the main chain [114] and triarylamines in the side chain [115-118]. By proper functionalization and architecture, even poly(thiophene) [119] and oligoaniline [120-122] and derivatives [123] become soluble in different solvents. Also, electroactive polymers derived from 2,2,6,6-tetramethyl piperidinyloxyl (TEMPO) have drawn attention, especially with respect to energy storage apphcations [124—127]. 

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