CONSTRUCTION OF ONE-DIMENSIONAL MULTICOMPONENT MOLECULAR ARRAYS - CONTROL OF ELECTRONIC AND MOLECULAR MOTIONS

Transition metals are powerful three-dimensional templates, which can gather various functionalized ligands and orient them in a precise fas hion so that complex multicomponent molecular systems can be obtained without constructing covalently-assembled edifices. The compounds thus prepared exhibit precise chemical or physical functions, which are go verned by the design of the system. The construction of one-dimensiona l molecules around ruthenium(II) or osmium(II), using rigid ligands at tached to the desired electroactive species, leads to systems that are able to undergo charge separation after photonic excitation. In other related compounds, a ruthenium(II)-based chromophore is, for example, connected to an osmium(II) complex by means of rod-like bridging liga nd, thereby ensuring strict control over the Ru...Os distance. By tuni ng the length and the electronic properties of the bridge, one can con trol the efficiency of the electronic energy transfer between the two chromophores. In particular, the use of a bis-cyclometallating ligand is very conducive to energy transfer and allows the observation of thi s process up to a Ru..Os distance of approximate to 20 Angstrom. By co mbining the building blocks of these inorganic systems with appropriat e porphyrins, long-range (centre-to-centre distance between the donor and the acceptor porphyrins approximate to 30 Angstrom) and relatively long-lived photoinduced charge separation has been demonstrated. Fina lly, with copper(I) as the template, compounds of the rotaxane family are obtained, which consist of a coordinating ring threaded by a strin g-like component. If this acyclic fragment is end-functionalized by tw o bulky stoppering groups and if it incorporates two different coordin ation sites (a bi-and a terdentate chelate site), novel dynamic proper ties are observed. The movement of a given fragment of the molecule is triggered by changing the metal oxidation state. This one-dimensional motion of the ring along the string on which it is threaded is contro lled by redox manipulation, resulting in a primitive molecular machine .