title: Host-guest interactions in the supramolecular incorporation of fullerenes into tailored holes on porphyrin-modified gold nanoparticles in molecular photovoltaics.
abstract: Novel gold nanoparticles modified with a mixed self-assembled monolayer of porphyrin alkanethiol and short-chain alkanethiol were prepared (first step) to examine the size and shape effects of surface holes (host) on porphyrin-modified gold nanoparticles. The porphyrin-modified gold nanoparticles with a size of about 10 nm incorporated C60 molecules (guest) into the large, bucket-shaped holes, leading to the formation of a supramolecular complex of porphyrin-C60 composites (second step). Large composite clusters with a size of 200-400 nm were grown from the supramolecular complex of porphyrin-C60 composites in mixed solvents (third step) and deposited electrophoretically onto nanostructured SnO2 electrodes (fourth step). Differences in the porphyrin:C60 ratio were found to affect the structures and photoelectrochemical properties of the composite clusters in mixed solvents as well as on the SnO2 electrodes. The photoelectrochemical performance of a photoelectrochemical device consisting of SnO2 electrodes modified with the porphyrin-C60 composites was enhanced relative to a reference system with small, wedged-shaped surface holes on the gold nanoparticle. Time-resolved transient absorption spectroscopy with fluorescence lifetime measurements suggest the occurrence of ultrafast electron transfer from the porphyrin excited singlet states to C60 or the formation of a partial charge-transfer state in the composite clusters of supramolecular complexes formed between porphyrin and C60 leading to efficient photocurrent generation in the system. Elucidation of the relationship between host-guest interactions and photoelectrochemical function in the present system will provide valuable information on the design of molecular devices and machines including molecular photovoltaics.
authors.affiliation: Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan. imahori@scl.kyoto-u.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Imahori
authors.forename: Atsushi
authors.initials: A
authors.lastname: Fujimoto
authors.forename: Soonchul
authors.initials: S
authors.lastname: Kang
authors.forename: Hiroki
authors.initials: H
authors.lastname: Hotta
authors.forename: Kaname
authors.initials: K
authors.lastname: Yoshida
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Umeyama
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Matano
authors.forename: Seiji
authors.initials: S
authors.lastname: Isoda
authors.forename: Marja
authors.initials: M
authors.lastname: Isosomppi
authors.forename: Nikolai V
authors.initials: NV
authors.lastname: Tkachenko
authors.forename: Helge
authors.initials: H
authors.lastname: Lemmetyinen