| The yields and dynamics for energy transfer from the metal-to-ligand charge-transfer excited states of Ru(deeb)(bpy)2(PF6) 2, Ru2+, and Os(deeb)(bpy)2(PF6) 2, Os2+, where deeb is 4,4'-(CH3CH2CO 2)2-2,2'-bipyridine, anchored to mesoporous nanocrystalline (anatase) TiO2 thin films were quantified. Lateral energy transfer from Ru2+* to Os2+ was observed, and the yields were measured as a function of their relative surface coverages and the external solvent environment (CH3CN, THF, CCl4, and hexanes). Excited-state decay of Ru2+*/TiO2 was well described by a parallel first- and second-order kinetic model, whereas Os2+* /TiO2 decayed with first-order kinetics within experimental error. The first-order component was assigned to the radiative and non-radiative decay pathways (tau = 1 mus for Ru2+*/TiO2 and tau = 50 ns for Os2+*/TiO2). The second-order component was attributed to intermolecular energy transfer followed by triplet-triplet annihilation. An analytical model was derived that allowed determination of the fraction of excited-states that follow the two pathways. The fraction of Ru2+*/TiO2 that decayed through the second-order pathway increased with surface coverage and excitation intensity. Monte-Carlo simulations were performed to estimate the Ru2+* → Ru 2+ intermolecular energy transfer rate constant of (30 ns) -1.; The initial studies on the energy transfer rates on TiO2 thin films raised the question of the effects of solvent on other properties of the surface bound sensitizers. A more thorough study was performed to investigate the effect of solvent on the absorption, photoluminescence, steady-state photoluminescence, excited state lifetime, and transient absorption spectra of [Ru(bpy) 2(deeb)]2+, [Os(bpy)2(deeb)]2+, [Ru(deeb)3]2+ and [Ru(bpy)2(phen-E-Aryl-Si(CH 2CO2CH2CH3)3)]2+ anchored to ZrO2 thin films. The energy of the most intense MLCT absorption bands were found to vary linearly with the optical dielectric constant and refractive index of the solvent. The emission energies were seen to vary linearly with solvent polarity. A Franck-Condon line shape analysis was used to determine spectral parameters of the four sensitizers. These included the emission energy, E0, the electron-vibrational coupling constant or Huang-Rhys parameter, S, and the full width at half-maximum, Delta nu0,1/2. These parameters allowed the determination of the outer sphere solvent reorganizational energy, lambdao. The time-resolved photoluminescence, similar to the steady-state photoluminescence, was dependent on solvent polarity. As the polarity of the solvent was increased the lifetime of the excited state increased. In general, the ligand upon which the excited state was localized determined the extent of the solvent effects. When the excited state was localized upon a ligand that could be easily accessed by the solvent the observed effects follow predictions based on classical theories.; The compounds Re(CO)3(pphos)Cl, Re(CO)3(Opphos)Cl, [Re(CO)3Cl(pphos)-Re(CO)2(bpy)(PPh3)]OTf, Re(CO)2(bpy)(dppeneO)2+, Ru(bpy) 2(Opphos)2+, and Ru(Opphos)32+, where pphos is 5-(diphenylphosphino-oxide)-1,10-phenanthroline, its oxidation product Opphos is 5-(diphenylphosphino)-1,10-phenanthroline, and dppeneO 2 is the monophosphine oxide of trans-1,2-bis(diphenylphosphino)ethylene were synthesized and characterized. Re(CO)3(Opphos)Cl, Re(CO) 2(bpy)(dppeneO)2+, and Ru(Opphos)3 2+ were anchored to TiO2 using a new linkage through the phosphine oxide ligands. This allowed for surface characterization of the three compounds' absorbance, redox, and photoelectrochemical properties. The calculated absorbed photon-to-current efficiency (APCE) were 0.28, 0.65 and 0.07 respectively. Transient absorption difference spectra for the three compounds were collected in neat acetonitrile, and a surface bound transient absorption spectrum was collected for Ru(Opphos)32+. Ru(Opphos) 32+ exhibited an immediate bleach of the MLCT absorption band assigned as electron inje... |
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