Web Release Date: November 16,
Gold Nanoparticle Enhanced Charge Transfer in Thin Film Assemblies of Porphyrin-Fullerene Dyads
and
Institute of Materials Chemistry, Tampere University of Technology, P.O. Box 541, 33101 Tampere, Finland, Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan, and Fukui Institute for Fundamental Chemistry, Kyoto University, 34-4, Takano-Nishihiraki-cho, Sakyo-ku, Kyoto 606-8103, Japan
Received August 16, 2007
In Final Form: September 26, 2007
Abstract:
Photoinduced vectorial electron transfer in a molecularly organized porphyrin-fullerene (PF) dyad film is enhanced
by the interlayer charge transfer from the porphyrin moiety of the dyad to an octanethiol protected (dcore ~ 2 nm)
gold nanoparticle (AuNP) film. By using the time-resolved Maxwell displacement charge (TRMDC) method, the
charge separation distance was found to increase by 5 times in a multilayer film structure where the gold nanoparticles
face the porphyrin moiety of the dyad, that is, AuNP
PF, compared to the case of the PF layer alone. Films were
assembled by the Langmuir-Blodgett (LB) method using octadecylamine (ODA) as the matrix compound. Atomic
force microscopy (AFM) images of the monolayers revealed that AuNPs are arranged into continuous, islandlike
structures and PF dyads form clusters. The porphyrin reference layer was assembled with the AuNP layer to gain insight
on the interaction mechanism between porphyrin and gold nanoparticles. Interlayer electron transfer was also observed
between the AuNPs and porphyrin reference, but the efficiency is lower than that in the AuNPPF film. Fluorescence
emission of the reference porphyrin is slightly quenched, and fluorescence decay becomes faster in the presence of
AuNPs. The proposed mechanism for the electron transfer in the AuNPPF film is thus the primary electron transfer
from the porphyrin to the fullerene followed by a secondary hole transfer from the porphyrin to the AuNPs, resulting
in an increased charge separation distance and enhanced photovoltage.
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