ELECTRON-TRANSFER THROUGH NORBORNADIENE AND QUADRICYCLANE MOIETIES ASA MODEL FOR MOLECULAR SWITCHING

The bis(pentaammineruthenium(II)) complex of dicyanonorbornadiene has been prepared and characterized. Its photochemical conversion into a d icyanoquadricyclane complex by irradiation in methanol has been follow ed by UV-visible spectroscopy, IR spectroscopy, H-1 NMR spectroscopy, and cyclic voltammetry. The dicyanonorbornadiene complex exhibits an i ntervalence transition in the 1000-1600 nm range when oxidized to the ruthenium-(II)-ruthenium(III) state. This allows the determination of the effective coupling V-ab through the dicyanonor-bornadiene ligand, which is found as 0.023 eV. No such band is observed in the case of th e dicyanoquadricyclane complex. These results show the possibility to modulate an intramolecular electron transfer process by using a photoi somerizable bridging ligand.