title: Loading pentapod deca(organo)[60]fullerenes with electron donors: from photophysics to photoelectrochemical bilayers.
abstract: A pentapod deca(aryl)[60]fullerene, C(60)(C(6)H(4)CO(2)H)(5)(C(6)H(4)Fc)(5)Me(2) (4; Fc = ferrocenyl), bearing five carboxylic acid and five ferrocenyl groups was synthesized through top and bottom functionalization of [60]fullerene by means of copper-mediated penta-addition reactions. For electrochemical measurements (i.e., E(ox) = 0.08 V, five-electron oxidation of the ferrocenyl groups; E(red) = -1.89 and -2.28 V for the fullerene part vs Fc/Fc(+)), we used an ester-protected compound, C(60)(C(6)H(4)CO(2)Et)(5)(C(6)H(4)Fc)(5)Me(2) (2), and 4 was probed by performing femtosecond flash photolysis experiments in a variety of organic solvents. Importantly, the formation of a radical ion pair state was corroborated with lifetimes of up to 333 ps in toluene. In complementary studies, penta(carboxylic acid)-penta(ferrocenyl) compound 4 was deposited on indium-tin oxide (ITO) electrodes with a surface coverage (i.e., 0.14 nmol/cm(2)) that corresponded to a unique bilayer structure. Decisive for the bilayer motif is the presence of five ferrocenyl groups, which are assembled with a merry-go-round-shaped arrangement on the [60]fullerene. The novel 4/ITO photoelectrode gave rise to a cathodic photocurrent with a 12% quantum yield in the presence of methyl viologen, whereas an anodic photocurrent was generated in the presence of ascorbic acid for a C(60)(C(6)H(4)CO(2)H)(5)(C(6)H(5))(5)Me(2) (5)/ITO photoelectrode. Photophysical investigations revealed that the difference in photocurrent, that is, cathodic versus anodic photocurrents, is related to the nature of the excited state feature in 4 (i.e., charge separated state) and 5 (i.e., triplet excited state). The unique molecular architecture of 4, in combination with its remarkable donor-acceptor properties, validates the use of the pentapod deca(aryl)[60]fullerene in photoelectrochemically active molecular devices.
authors.affiliation: Department of Chemistry, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. matsuo@chem.s.u-tokyo.ac.jp
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Matsuo
authors.forename: Takahiko
authors.initials: T
authors.lastname: Ichiki
authors.forename: Shankara Gayathri
authors.initials: SG
authors.lastname: Radhakrishnan
authors.forename: Dirk M
authors.initials: DM
authors.lastname: Guldi
authors.forename: Eiichi
authors.initials: E
authors.lastname: Nakamura
mesh_terms: D004563:Electrochemistry; D004566:Electrodes; D004579:Electron Transport; D005296:Ferrous Compounds / Q000737:chemistry; D037741:Fullerenes / Q000737:chemistry*; D000075163:Metallocenes; D008958:Models, Molecular; D008968:Molecular Conformation; D055668:Photochemical Processes; D017971:Tin Compounds / Q000737:chemistry
chemical_list: D005296:Ferrous Compounds; D037741:Fullerenes; D000075163:Metallocenes; D017971:Tin Compounds; C109984:indium tin oxide; C069837:fullerene C60; C004998:ferrocene