Photochemical reactivity of halogen-containing ruthenium-dcbpy (dcbpy=4,4 '-dicarboxylic acid-2,2 '-bipyridine) compounds, trans(Br)-[Ru(dcbpy)(CO)(2)Br-2] and trans(I)-[Ru(dcbpy)(CO)(2)I-2]

The ruthenium mono(dcbpy) (dcbpy=4,4'-dicarboxylic acid-2,2'-bipyridine) co mplexes, trans(Br)-[Ru(dcbpy)(CO)(2)Br-2] and trans(I)-[Ru(dcbpy)(CO)(2)I-2 ], have been synthesized and structurally characterized. Both compounds sho w strong photochemical activity. Under illumination in acetonitrile the col our of the dye solutions changes and infrared spectra indicate an irreversi ble change, with two CO stretching bands disappearing from the spectra with concomitant appearance of a new CO stretching band, an indication of a los s of a CO ligand. Changes in the proton NMR spectra suggest that the releas e of the CO ligand is followed by reorganization of the halogen ligands and attachment of one solvent molecule leading to formation of the cis(X)-Ru(d cbpy)(CO)(CH3CN)X-2] (X=Br, I) isomer. In the visible spectra, a new absorp tion band appears under illumination at 510 nm allowing observation of the kinetics of the reaction. The quantum yields of the reactions are 0.68 and 0.34 for the bromine and iodine complexes, respectively. The trans(I)-[Ru(d cbpy)(CO)(2)I-2] compound shows a temperature dependent luminescence spectr um in the temperature range 77 to 116 K, with an activation energy of 850 c m(-1). We assign this dependence to a thermal population of a secondary tri plet size, slightly above the emitting state, that is capable of initiating the photochemical reaction and/or a non-radiative relaxation to the ground state. The redox properties of the starting materials and the photoreactio n products were studied with cyclic voltammetry and the results are discuss ed with reference to the reaction mechanisms.