Ruthenium( 11) and osmium( 11) complexes of 2,2'bipyridyls (bipy) and 1,lO-phenanthrolines (phen) are identified as feasible dyes for use in luminescent solar collectors. Twenty-seven Ru"( bipy) 3 2 + complexes are prepared and the absorption and emission spectra of their solutions in EtOH-MeOH at room temperature are reported. Quantum efficiencies, which are sensitive to oxygen quenching, vary between 0.002 and 0.306 depending upon substituents. The effect of the medium on the spectral properties of selected compounds has also been investigated. Measured quantum yields of non-aqueous solutions are higher than those for aqueous solutions but lower than for doped plastic films.

The absorption characteristics, emission spectra, luminescent quantum yields, and lifetimes are reported for 24 ruthenium(ii) tris-1 ,1 0-phenanthroline complexes in EtOH-MeOH solution. Quantum yields fall between 0.01 9 and 0.403, the highest values being recorded for complexes substituted at the 4,7-sites with aryl groups. Incorporation of these derivatives into poly(viny1 chloride) film raises the quantum yields leading to values ranging from 0.40 to 0.75.

E , values for 21 tris-complexes of substituted 2,2'-bipyridyls and 1,lO-phenanthrolines with Ru"-Ru"' in acetonitrile have been measured using cyclic voltammetry. A linear correlation exists between E, and the Hammett G constant for data obtained from complexes of 4,4'-and 5,5'-disubstituted 2,2'-bipyridyls. The reduction potential for the couple Ru ( ligand),3 +-• Ru( ligand) 32+, where * refers t o the excited state, have been calculated from the €+ values and a combination of data collected from luminescence and magnetic circular dichroism measurements.Ru" tris-2,2'-bipyridyl complex, Ru(bipy),' +, absorbs light in the visible region at about 450 nm to yield a set of metal-ligand charge-transfer excited states' denoted * Ru(bipy),'', equation(1). These species are strong reducing agents, losing an electron to oxidizing substrates and generating Ru"' tris-2,2'-bipyridyl, R ~( b i p y ) , ~ +, equation ( 2). The latter, being a relatively strong oxidizing agent, may then be reduced to ground state Ru-(bipy),", equation (3). The three equations constitute a photodriven cycle which it may be possible to exploit within schemes for the photochemical cleavage of water3 and for the conversion of solar energy into electrical energy within a photogalvanic cell., Ru(bipy),'+ * R u(biPY)32 + (1) Ru(bipy),,+ + e * R ~( b i p y ) , ~+ E+ (2) Ru(bipy),,+ + e e Ru(bipy),'+ E* (3) Recently, we have prepared and investigated the absorption

A three-state model is presented to explain the variations in the quantum efficiencies within a series of complexes formed from 26 2,2'-bipyridyl ligands with ruthenium( 11). The radiative rate constants are shown to vary with the molar absorptivity for the singlet dn ' transitions. Ln k, (non-radiative rate constant) for complexes bearing +M -I and +M +I groups at the 4and 4,4'-positions of the ligands vary with the energy gap. A parallel is noted between the metal-to-ligand charge-transfer process and the charge-transfer transition from a metal ion impurity to the conducting band of a semiconducting lattice.

We have observed nonlinear absorption in spin-coated poly(4,6-decadiyne-1, 10-diolbis {[(n-butoxycarbonyl)methyl]urethane}) [poly(3BCMU)] polydiacetylene channel waveguides at different wavelengths in the near-infrared. Intensity dependent absorption coefficients, α2 and α3, have been determined by measurements of the intensity dependent transmission. The implications of nonlinear absorption for all-optical device applications in this material are discussed.