Photocurrent generation in noncovalently assembled multilayered thin films

Multilayered photocurrent generating thin films were fabricated by templated noncovalent assembly via stepwise assembly of molecular components. Each of films I-IV contained an underlying self-assembled monolayer (SAM) consisting of an alkanethiol linked covalently to a 2,6-dicarboxypyridine ligand that served as a binding site for attaching additional molecular components. The SAM subsequently was functionalized by sequential deposition of Cu(II), Co(II), or Fe(III) ions followed by a variety of substituted 2,6-dicarboxypyridine ligands as a means to incorporate one or more layers of pyrene chromophores into the film. The films were characterized by contact angle measurements, ellipsometry, grazing incidence IR, cyclic voltammetry, and impedance spectroscopy after deposition of each layer, confirming the formation of ordered, stable layers. Following incorporation into a three-electrode system, photoexcitation resulted in the generation of a cathodic photocurrent in the presence of methyl viologen and an anodic photocurrent in the presence of triethanolamine. Using this strategy, systems were fabricated that produced up to 89 nA/cm(2) of reproducible photocurrent.