Interaction induced transition in the nanoporous Tio2/Pd-porphyrin system

M. FUNES, P. ZABEL, T. DITTRICH, E. DURANTINI, L. OTERO

La Plata

Encuentro; Cuarto Encuentro de Física y Química de Superficies; 2009

Porphyrins and their metal complexes are of great interest for sensing, for energy conversion as light receptors and for spectral sensitization of wide band gap semiconductors. For all of these applications, the interaction of porphyrin molecules with a metal oxide surface plays an important role. The central metal atom of metal centred porphyrins has a strong influence on the electronic transitions in porphyrins, especially on the Q-band and should also play an essential role for the molecule – metal oxide surface interaction. Specific interactions will lead to the formation of new electronic states at or near the surface of the metal oxide. Molecules of Pd(II) 5-(4-carboxyphenyl)-10,15,20-tris(4-methylphenyl) porphyrin were adsorbed from highly diluted dichloromethane solution on ultra-thin layers of nanoporous TiO2 and investigated by modulated surface photovoltage (SPV) spectroscopy.  The most striking feature of the PV spectra of Pd-porphyrin deposited at surfaces of sintered TiO2 nanoparticles is the appearance of an additional transition with a maximum at 2.03 eV for the Q band at lower energy after annealing. As remark, a similar new transition did not appear for porphyrins with other central atoms. Therefore we suspect that a specific interaction (formation of a new charge transfer complex) between a Pd atom in the Pd-porphyrin and a Ti surface atom is the reason for the new transition. The optical density of the new charge transfer complex was similar to that of the Q-band of Pd-porphyrin.