Electron Transfer Systems

Abstract

We have seen in Chaps. 5 and 6 that π-conjugated oligomers are the most promising candidates for molecular wires. They provide efficient electronic coupling between two electroactive units, i.e. donor and acceptor. Among the variety of π-conjugated systems, oligo(para-phenylenevinylene)s (oPPVs) have emerged as particularly interesting in terms of their molecular-wire behavior due to their outstanding conduction properties. Above, it has been demonstrated that when connecting oPPV-bridges of different length to an electron-accepting C₆₀ and an electron-donating exTTF moiety, the oPPV moieties promote wirelike behavior for donor–acceptor distances of $40\,\mathring{\hbox{A}}$ and beyond. The exTTF–oPPV _n –C₆₀ conjugates met all the requirements rendering it an ideal molecular wire:

• energetic matching between the donor (acceptor) and bridge levels,

• sufficient electronic coupling between the donor and acceptor units induced by the bridge orbitals,

• small attenuation factor β, namely $\beta=0.01\pm0.005\,\mathring{\hbox{A}}^{-1}.$

Further, the investigation of the conduction behavior as a function of distance revealed nearly distant-independent charge-transfer characteristics [1]. These findings were corroborated by probing analogous systems containing porphyrins as electron donors instead of exTTF [2, 3].