Photosensitization of thin SnO2 nanocrystalline semiconductor film electrodes with electron donor-acceptor metallodiporphyrin dyad

A electron donor-acceptor porphyrin dyad (PZn-P) was synthesized by linking an electron acceptor porphyrin; 5,15-bis(4-carboxyphenyl)-10,20-bis(4-nitrophenyl) porphyrin (P) and an electron donor porphyrin; Zn(II) 5-(4-aminophenyl)-10,15,20-tris(4-methoxylphenyl) porphyrin (PZn) by amide bond. PZn-P dyad - thin SnO2 nanocrystalline semiconductor film electrodes show higher spectral sensitized photocurrent quantum yield compared to the electrodes sensitized with either PZn or P monomers. Fluorescence analysis of dyad and the P moiety adsorbed on both, SnO2 semiconductor and SiO2 insulator, shows that the charge injection yields (Φinj) from the excited dyes to the SnO2 are similar in both cases. Thus photocurrent enhancement is interpreted in terms of intramolecular electron transfer and preferential spatial orientation of the dyad on the SnO2 surface that preclude back electron transfer.