Dynamics and Equilibrium of Heme Axial Ligation in Mesoporous Nanocrystalline TiO2 Thin Films

Surfactant-free hydrothermal synthesis of hierarchical flower-like Bi2WO6 mesosphere nanostructures with excellent visible-light photocatalytic activity

Hierarchical flower-like Bi₂WO₆ mesosphere nanostructures self-assembled with nanosheets were synthesized by hydrothermal treatment of an aqueous suspension of Bi(NO₃)₃·5H₂O and Na₂WO₄·2H₂O without surfactants or mineralizers.

Excited state electron transfer after visible light absorption by the Co(i) state of vitamin B12

The Co(i) form of vitamin B₁₂ was found to undergo excitation wavelength-dependent excited state electron transfer to TiO₂.

Ligand coordination and spin crossover in a nickel porphyrin anchored to mesoporous TiO2 thin films

The coordination and spin equilibrium of a Ni(II) meso-tetra(4-carboxyphenyl)porphyrin compound, NiP, was quantified both in fluid solution and when anchored to mesoporous, nanocrystalline TiO2 thin films. This comparison provides insights into the relative rate constants for excited-state injection and ligand field population. In the presence of pyridine, the spectroscopic data were consistent with the presence of equilibrium concentrations of a 4-coordinate low-spin S = 0 ((1)A1g) Ni(II) compound and a high-spin S = 1 ((3)B1g) 6-coordinate compound. Temperature-dependent equilibrium constants were consistently smaller for the surface-anchored NiP/TiO2, as were the absolute values of ΔH and ΔS. In the presence of diethylamine (DEA), the ground-state 6-coordinate compound was absent, but evidence for it was present after pulsed light excitation of NiP. Arrhenius analysis of data, measured from -40 to -10 °C, revealed activation energies for ligand dissociation that were the same for the compound in fluid solution and anchored to TiO2, Ea = 6.6 kcal/mol, within experimental error. At higher temperatures, a significantly smaller activation energy of 3.5 kcal/mol was found for NiP(DEA)2/TiO2. A model is proposed wherein the TiO2 surface sterically hinders ligand coordination to NiP. The lack of excited-state electron transfer from Ni(II)P*/TiO2 indicates that internal conversion to ligand field states was at least 10 times greater than that of excited-state injection into TiO2.