Photoconductivity of Nanofilaments That are Self-Assembled from a Porphyrin with Long Alkyl-Chain Substituents

Abstract

Photoelectronically active nanostructures that are self-assembled from organic molecules hold the promise of tailored functionality with simple and inexpensive production. Comparison of nanowires assembled from related compounds can give important insights into the details of self-assembly and the conduction mechanisms. We report the photoconductivity of nanofibers that are self-assembled from a porphyrin with long alkyl substituents. In contrast to previously studied porphyrin nanowires, the photoconductivity increases as atmospheric O2 is increased. This can be explained using the same model as used in the previous studies, by assuming a different line-up of the bands of the nanofilaments with the electrode Fermi level. However, this model does not explain our observation that, at O2 concentrations above 1%, the conduction increases with continued illumination; this may be due to photoactivation of shallow O2 adsorption sites. The overall conduction level is low even at high O2 concentration, because th...