High extinction coefficient chromophores and long-lived charge-separated states are both necessary in donor-acceptor systems. Zinc-protoporphyrin IX (ZnP) absorbs across a large portion of the visible spectrum with a maximum extinction coefficient over 200,000 M-1cm-1. ZnP can be covalently attached to a peptide (making ZnPp), by expressing heme c peptides in E. coli and exchanging the iron center with zinc. In this work, single-walled carbon nanotubes (SWNTs) have been used in conjunction with ZnPp derivatives to create bio-nano hetero-junctions capable of photoinduced charge separation. SWNTs are ideal electron acceptors because they are excellent molecular wires, which allows for facile separation of charge over long distances. Using ZnPp derivatives in this work facilitates the noncovalent attachment of ZnP, a chromophore with a low reduction potential in the excited state, to SWNTs in a simple and straightforward manner. Through modification of the amino acid residues in the polypeptide, the strength of this attachment can be varied. ZnPp binding affinity to SWNTs has been evaluated using atomic force microscopy (AFM) and absorption spectroscopy. Photoinduced charge separation has been monitored using fluorescence spectroscopy and photocurrent spectroscopy. Our results demonstrate that photoinduced charge separation can be enhanced by altering the ZnPp/SWNT interaction through modification of the ZnPp amino acid sequence.

Photoinduced charge transfer from zinc protoporphyrin IX peptides to single-walled carbon nanotubes

246th National Meeting (2013)

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