ZnTPP derivatives are attractive candidates for photoinduced electron-transfer mediators. Using x-ray, UV and inverse photoemission spectroscopies in conjunction with density functional theory (DFT) calculations, we have determined the energy alignment between molecular level and substrate band edges for several ZnTPP derivatives adsorbed on ZnO(11-20) and TiO2(110) surfaces. Similar energy alignment is found for all of these systems but large differences in solar cells efficiencies, likely due to dye/dye interaction, are observed. We have determined the molecular adsorption geometry of several ZnTPP derivatives at these surface using local and area-averaging techniques. By functionalizing the ZnTPP with phenyl groups in different ways, the molecules adsorb with the porphyrin macrocycle either upright or parallel to the surface. Upright adsorption enables molecular stacking that opens exciton delocalization pathways that compete with direct electron transfer to the substrate. Choosing the appropriate chromophore adsorption geometry is thus critical for electronic charge transfer pathway control.

Chromophores at oxide surfaces: Energy alignment, molecular packing, and electronic pathways

245th National Meeting (2013)

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