Photophysics and electron transfer in poly(3-octylthiophene) alternating with Ru(II)- and Os(II)-bipyridine complexes

A series of soluble metal-organic polymers that contain Ru(II)- and Os(II)- polypyridine complexes interspersed within a pi -conjugated poly(3-octylthi ophene) backbone are prepared. Detailed electrochemical and photophysical s tudies:are cairied out on the polymers and two model complexes to determine the extent that the metal-polypyridine units interact with the pi -conjuga ted system. The results indicate that there is a strong electronic interact ion between the metal-based chromophores and the pi -conjugated organic seg ments, and consequently the photophysical properties are not, simply based on the sum of the properties of the individual components. In the Ru(II) po lymers, the metal,to-ligand charge-transfer (MLCT) excited state is slightl y higher in energy than the (3)pi,pi* State of the poly(3-octylthiophene) b ackbone. This state-ordering results in a material that displays only a wea k MLCT luminescence and a long-lived transient absorption spectrum that is dominated by the (3)pi,pi* state. In the Os(II) polymer the MLCT state is l ower in energy than the polythiophene-based (3)pi,pi* state and the "unpert urbed" MLCT emission is observed. Finally, all of the metal-organic polymer s undergo photoinduced bimolecular electron-transfer (ET) reactions with th e oxidative quencher dimethyl viologen. Transient absorption spectroscopy r eveals that photoinduced ET to dimethyl viologen produces the oxidized poly mers, and in most cases, the transient spectra are dominated by features ch aracteristic of a poly(3-octylthiophene) polaron.