Resumen de Photo-Induced Energy or Electron Transfer in Supramolecular Systems:: Applications to Molecular Wires and Light-Harvesting Sensors
A synthetic protocol is summarized that provides access to various multi-site ligands (bipyridines, terpyridines...) bridged by alkyne spacer comprising one to four ethynyl subunits. These ditopic ligands have been used to prepare luminescent transition-metal complexes in which long-range electronic coupling between remote units has been observed. Intramolecular triplet energy transfer, photon migration and light-induced electron transfer occur by way of extremely rapid superexchange involving energetic states localized on the bridge. Very long triplet-energy excited-state have been measured in the terpyridine complexes resulting from a selective decoupling of the MLCT triplet state and higher-energy metal-centered (MC) and ligand-centered excited states (LC). The level of electronic communication along the molecular wire can be modulated by insertion of "Pt(PnBu3)2" insulating groups into the bridge. These metallo-insulating groups provide further means to manipulate the stereochemistry around the central subunit and to control the efficiency of triplet energy transfer. A photochemical molecular device consisting of a light conversion process, via an absorption/energy-transfer/emission (A/ET/E) sequence of photochemical events is realized in photoactive lanthanide complexes of calix[4]arenes podands bearing three to four pendant bipyridine arms.
