| Laser flash photolysis/transient diffuse reflectance spectroscopy was used to study electron transfer in simple, self-assembling, nonlinked diads consisting of tris(2,2{dollar}spprime{dollar}-bipyridine)ruthenium(II) (Ru(bpy){dollar}sb3sp{lcub}2+{rcub}rbrack,{dollar} methylviologen (MV{dollar}sp{lcub}2+{rcub}rbrack,{dollar} and their derivatives compartmentalized at the interface between zeolite interior volume and external surface. Quantum yields for formation of photoproducts were calculated. The photochemistry of a sensitizer-acceptor-secondary acceptor complex, consisting of a covalently linked tris(bipyridine)ruthenium(II)-N,N{dollar} spprime{dollar}-dialkyl-2,2{dollar}spprime{dollar}-bipyridinium (RuL{dollar}sb3sp{lcub}2+{rcub}{dollar}-nDQ{dollar}sp{lcub}2+{rcub}rbrack{dollar} supramolecular diad and benzylviologen (BV{dollar}sp{lcub}2+{rcub}rbrack,{dollar} which organizes spontaneously at the surface of a zeolite L particle, was also studied.; Laser flash photolysis/transient absorbance and emission spectroscopy were used to probe the nature of the reductive quenching of ruthenium polypyridyl sensitizers by cyanometalate electron donors in aqueous solution. Quenching rate constants and approximate cage escape efficiencies were measured for a number of donor/sensitizer pairs; octacyanometalates Mo(CN){dollar}sb8sp{lcub}4-{rcub}{dollar} and W(CN){dollar}sb8sp{lcub}4-{rcub}{dollar} exhibit much higher cage escape efficiencies, typically 40 to 80%, than do hexacyanometalates Fe(CN){dollar}sb6sp{lcub}4-{rcub}{dollar} and Os(CN){dollar}sb6sp{lcub}4-{rcub}.{dollar} Cage escape efficiencies vary with the overall charge of the sensitizer; geminate ion pair recombination competes most efficiently with cage escape when the electron donor and acceptor have 4+ and 4{dollar}-{dollar} overall charges, respectively. No dependence of cage escape efficiency on thermodynamic driving force for the back-electron-transfer reaction was observed. Little or no dependence on ionic strength or counterion was observed.; Two integrated systems for light-induced vectorial electron transfer are described. Both utilize photosensitized semiconductor particles grown in linear channel zeolites as components of the electron transfer chain. One system consists of internally platinized zeolites L and mordenite containing TiO{dollar}sb2{dollar} particles and methylviologen ions, with a size-excluded photosensitizer, tris(2,2{dollar}spprime{dollar}-bipyridyl-4,4{dollar}spprime{dollar}-dicarboxylate) ruthenium (RuL{dollar}sb3sp{lcub}2+{rcub}rbrack,{dollar} adsorbed on the external surface of the zeolite/TiO{dollar}sb2{dollar} composite. In the other system, Nb{dollar}rmsb2Osb5{dollar} replaces TiO{dollar}sb2.{dollar} The kinetics of photochemical electron transfer reactions and charge separation were studied by diffuse reflectance flash photolysis. Despite very efficient initial charge separation, the TiO{dollar}sb2{dollar} system does not generate hydrogen photochemically in the presence of an electrochemically reversible, anionic electron donor, methoxyaniline-N,N{dollar}spprime{dollar}-diethylsulfonate (MDESA{dollar}sp{lcub}2-{rcub}rbrack.{dollar} Only the {dollar}rm Nbsb2Osb5{dollar}-containing composites evolve hydrogen photochemically under these conditions. These results are interpreted in terms of semiconductor band energetics and the irreversibility of electron transfer from Nb{dollar}rmsb2Osb5{dollar} to intrazeolitic platinum particles. |
