Terahertz spectroscopy has proven itself to be an excellent non-contact probe of charge injection and conductivity with sub-picosecond time resolution.  I will describe the charge injection time scale and efficiency for a selection of high-potential photoanodes (HPPAs) for photo-electrochemical cells.  The anodes consist of bis- and tris-pentafluorophenyl free-base and metallo-porphyrin sensitizers anchored to TiO2 and SnO2 nanoparticles.  Photoelectrochemical measurements demonstrate that the photosensitizers extend the absorption of the bare anode well into the visible region.  THz spectroscopic studies demonstrate the sensitizers used in these HPPAs are capable of injecting electrons into the conduction band of the metal-oxide materials in those cases where the energies of the donor (excited state dye) and acceptor (metal oxide conduction band minimum) components are appropriate.  The time scales and efficiencies are interpreted in terms of the identities (singlet vs. triplet) and energetics of excited electronic states. We have also investigated axially complexing bis-pentafluorphenyl Zn-porphyrin sensitizers to an isonicotinic acid anchor or variants thereof rather than binding them directly to the metal oxide surface.  I will compare their binding stability in water, as well as their photoexcited interfacial electron transfer efficiency when using carboxylic acid, hydroxamate, acetylacetonate and phosphonate the anchoring group.

Carrier injection and dynamics from photoexcited transition metal containing porphyrins

245th National Meeting (2013)

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