ARTICLE pubs.acs.org/JACS
Molecular Photoelectric Switch Using a Mixed SAM of Organic [60]Fullerene and [70]Fullerene Doped with a Single Iron Atom Yutaka Matsuo,* Takahiko Ichiki, and Eiichi Nakamura* Department of Chemistry, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
bS Supporting Information ABSTRACT: We describe a photoswitch fabricated on indium tin oxide (ITO) as a self-assembled monolayer (SAM) of two fullerene molecules, a purely organic [60]fullerene that generates an anodic current and a [70]fullerene doped with a single iron atom. This device generates a bidirectional photocurrent upon irradiation at 340 and 490 nm. The new [70]fullerene iron complex bearing three rigid carboxylic acid legs, Fe[C70(C6H4C6H4COOH)3]Cp, generates only a cathodic current upon photoexcitation between 350 and 700 nm, whereas the organic [60]fullerene absorbs at wavelengths shorter than 500 nm. The quantum efficiency of the photocurrent generation by the mixed SAM is comparable to that of a single-component SAM, indicating that the individual diode molecules on ITO generate photocurrents independently with little cross talk.
’ INTRODUCTION
’ RESULTS AND DISCUSSION
Molecular design and hierarchical structural control of molecular assembly are the major challenges in the study of molecular photoelectronics.16 For instance, a molecular photoswitch first requires two molecular photodiodes that generate photocurrents along the molecules in opposite directions7,8 and then requires these molecules to work independently upon irradiation at two different wavelengths after controlled fabrication on an electrode surface. We previously reported that a [60]fullerene photodiode 1 (part a of Figure 1) on indium tin oxide (ITO) generates only an anodic photocurrent upon irradiation at 500 nm (cf., part d of Figure 1). We report here that a mixed self-assembled monolayer (SAM) made of C60(C6H4C6H4COOH)5Me (1) and Fe[C70(C6H4C6H4COOH)3]Cp* (2) (part b of Figure 1 and Scheme 1; Cp* = η5C5Me5) generates a bidirectional photocurrent of approximately þ8 and 8 nA/cm2 upon irradiation at 340 and 490 nm, respectively (part f of Figure 1). The quantum efficiency of the photocurrent generation by the mixed SAM is on the same order of that of a single-component SAM, and the current density was 10 times larger than those (
