Building photoactive molecular-scale wires

Polyalkynylene groups are known to function as excellent electronic conductors at the molecular level. Such moieties have now been used to interconnect redox and photoactive transition metal oligopyridine complexes so that the efficiency of light-induced energy or electron transfer along the molecular axis can be monitored. The important issues that control the effectiveness of electronic coupling through the alkyne are discussed. In particular, attention is given to separating the effects of electron delocalization within the triplet manifold from the more general decoupling of metal-centered and charge-transfer excited states that occurs upon lowering the triplet energy. The role of the auxiliary ligands :is considered, as is the effect of nuclearity. Similarly, the size of the nuclear reorganization energy has to be taken into account in a proper discussion of the photophysical properties of such systems. A second issue of importance to the design of photoelectronic devices concerns the use of interspersed groups to modulate the electronic coupling properties of the alkyne spacer. Such electron relays may be aryl hydrocarbons or platinum bis-acetylides, both groups being able to curtail electron flow along the molecular axis. (C) 1998 Elsevier Science S.A.