| Abstract
| - Nanocrystalline (anatase) titanium dioxide films have been sensitized to visible light with K4[Fe(CN)6] and Na2[Fe(LL)(CN)4], where LL = bpy (2,2‘-bipyridine), dmb (4,4‘-dimethyl-2,2‘-bipyridine), or dpb (4,4‘-diphenyl-2,2‘-bipyridine). A model is proposed wherein sensitization of TiO2 occurs by metal-to-particle (intervalence) and metal-to-ligand charge-transfer pathways, the quantum yield for the latter being dependent on environment. The solvatochromism of the materials allows the reorganization energies associated with charge transfer to be quantified. The photocurrent efficiencies of the sensitized materials are also reported.
- Nanocrystalline (anatase) titanium dioxide films have been sensitized to visible light with K4[Fe(CN)6] and Na2[Fe(LL)(CN)4], where LL = bpy (2,2‘-bipyridine), dmb (4,4‘-dimethyl-2,2‘-bipyridine), or dpb (4,4‘-diphenyl-2,2‘-bipyridine).Coordination of Fe(CN)64- to the TiO2 surface results in the appearance of a broad absorption band (fwhm ∼ 8200cm-1) centered at 23800 ± 400 cm-1 assigned to an Fe(II) → TiO2 metal-to-particle charge-transfer (MPCT) band.The absorption spectra of Fe(LL)(CN)42- compounds anchored to TiO2 are well modeled by a sum of metal-to-ligand charge-transfer (MLCT) bands and a MPCT band. Pulsed light excitation (417 or 532 nm, ∼8 ns fwhm,∼2−15 mJ/pulse) results in the immediate appearance of absorption difference spectra assigned to an interfacialcharge separated state [TiO2(e-), FeIII], kinj> 108 s-1. Charge recombination is well described by a second-orderequal concentration kinetic model and requires milliseconds for completion. A model is proposed wherein sensitizationof Fe(LL)(CN)42-/TiO2 occurs by MPCT and MLCT pathways, the quantum yield for the latter being dependent onenvironment. The solvatochromism of the materials allows the reorganization energies associated with chargetransfer to be quantified. The photocurrent efficiencies of the sensitized materials are also reported.
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