Loading Pentapod Deca(organo)[60]fullerenes with Electron Donors: From Photophysics to Photoelectrochemical Bilayers

摘要

Abstract: A pentapod deca(aryl)[60]fullerene, C60(C6H4CO2H)5(C6H4Fc)5Me2 (4;Fc ferrocenyl), bearingnfive carboxylic acid and five ferrocenyl groups was synthesized through top and bottom functionalization ofn[60]fullerene by means of copper-mediated penta-addition reactions. For electrochemical measurementsn(i.e., Eox 0.08 V, five-electron oxidation of the ferrocenyl groups; Ered 1.89 and 2.28 V for the fullerenenpart vs Fc/Fc ), we used an ester-protected compound, C60(C6H4CO2Et)5(C6H4Fc)5Me2 (2), and 4 was probednby performing femtosecond flash photolysis experiments in a variety of organic solvents. Importantly, thenformation of a radical ion pair state was corroborated with lifetimes of up to 333 ps in toluene. Inncomplementary studies, penta(carboxylic acid) penta(ferrocenyl) compound 4 was deposited on indium tinnoxide (ITO) electrodes with a surface coverage (i.e., 0.14 nmol/cm2) that corresponded to a unique bilayernstructure. Decisive for the bilayer motif is the presence of five ferrocenyl groups, which are assembled withna merry-go-round-shaped arrangement on the [60]fullerene. The novel 4/ITO photoelectrode gave rise tona cathodic photocurrent with a 12% quantum yield in the presence of methyl viologen, whereas an anodicnphotocurrent was generated in the presence of ascorbic acid for a C60(C6H4CO2H)5(C6H5)5Me2 (5)/ITOnphotoelectrode. Photophysical investigations revealed that the difference in photocurrent, that is, cathodicnversus anodic photocurrents, is related to the nature of the excited state feature in 4 (i.e., charge separatednstate) and 5 (i.e., triplet excited state). The unique molecular architecture of 4, in combination with itsnremarkable donor acceptor properties, validates the use of the pentapod deca(aryl)[60]fullerene innphotoelectrochemically active molecular devices.