Synthesis and photophysical properties of Zn(II) porphyrin-C60 dyad with potential use in solar cells

Zn(II) porphyrin-C-60 dyad (7) was synthesized by the coupling reaction between Zn(II) 5-(4-aminophenyl)-10,15,20-tris(4-methoxylphenyl)porphyrin (4) and 12-dihydro-1,2-methanofullerene[60]-61-carboxylic acid (6). The electron-donor capacity of the porphyrin moiety in dyad 7 is enhanced by methoxy group substitution on the macrocycle peripheries and complexation with Zn(II). Spectroscopic studies showed only a very weak interaction between the chromophores in the grown state. The emission of the porphyrin moiety in dyad 7 is strongly quenched by the attached fullerene C-60 moiety. Thermodynamically, dyad 7 shows a higher capacity to form a photoinduced charge-separated state than the same dyad with free-base porphyrin. This was confirmed by steady-state photolysis in the presence of methylviologen as electron acceptor and N,N,N',N-tetramethyl-1,1'-naphthidine as electron donor. Dyad 7 sensitizes a tin dioxide (SnO2) electrode and the generation of photoelectrical effect shows that a large photocurrent is generated for the dyad 7 in the region where C60 is mainly responsible for light absorption. Also, dyad 7 produces a higher photoelectric effect than the corresponding amidoporphyrin model. An alternative photoelectric mechanism, other than direct electron injection from the excited porphyrin to SnO2, could be occurring, probably involving a charge-separated state of dyad 7. These results indicate that dyad 7 shows interesting properties for possible application in artificial solar energy conversion devices. Copyright (C) 2002 John Wiley Sons, Ltd.