Gold Nanoparticle Enhanced Charge Transfer in Thin Film Assemblies of Porphyrin−Fullerene Dyads

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 approximately 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 AuNP|PF 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 AuNP|PF 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.

Photosensitisation studies of silicone polymer doped with methylene blue and nanogold for antimicrobial applications

“…25 It is also possible that the polymer can also act as an electron donor to the MB triplet state to form MB radicals. However, as discussed above, the steady-state levels of the MBc radicals are likely to be low owing to rapid electron-transfer to O 2 .…”

Photoinduced processes in chromophore–gold nanoparticle assemblies

“…[11,13,19,33,34] are acknowledged for their participation in the presented work. In addition, the authors acknowledge the whole photochemistry group at Tampere University of Technology.…”

“…Dyad molecules with hydrophilic groups are able to organize at the air-water interface, allowing deposition of monolayers, where photoinduced, vectorial electron transfer takes place between the porphyrin and fullerene planes [18]. The electron transfer of such a porphyrinfullerene monolayer is enhanced by a GNP monolayer deposited adjacent to the porphyrin moieties [11,19], as shown in Fig. 2B.…”

“…The GNP layer was combined with monolayers of a porphyrin derivative, a fullerene derivative, and a conducting polymer, polyhexylthiophene (PHT). The photovoltage signals indicated electron transfer from the particles to porphyrin or fullerene [11] and electron transfer from PHT to the particles [12]. From these bilayer structures, the one with porphyrins and GNPs was chosen for more detailed studies.…”

“…This is the highest photovoltage observed for GNP-containing film structures. More detailed analysis of the photovoltage results indicates that creation of the photovoltage requires excitation of the dyad [11]. A possible scheme for charge transfer would be intramolecular charge separation of the dyad followed by hole transfer from the porphyrin to the GNPs.…”