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

Photoelectronically active nanostructures that are Self-assembled from organic rnolecules hold the prortu se of tailored functionality.with simple and inexpensive production. Comparison of nanoWires assembled from related componnds can give important insightS into the details of self-assembly and the,conduction meehanisms. 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 atthospheric O-2 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 O-2 concentrations above 1%, the conduction increases with continued- illunation; this may be due to photoactivation of shallow O-2 adsorption sites. The overall conduction level is low even at high O-2 Concentration, because the alkyl substituents form an insulating sheath around the rianofibers. Such inSulation could be valuable in applications where it would prevent cross-talk between signal S darried in different nanofilaments. Schottky barriers at the interface between- organic nanostructures and electrodes strongly affect conduction and photoconduction, and are strongly influenced by atmospheric gases such, as O-2.
Funding Agencies|National Science Foundation [CHE-0616615, BMAT-1306170]; Nano/Bio Interface Center at the University of Pennsylvania through the National Science Foundation [NSEC DMR08-32802]; MINECO (Spain) [CTQ2010-16339, MAT2013-47869-C4]; IBM Ph.D. Fellowship; NSF IGERT program [DGE02-21664]; SeRC (Swedish e-Science Research Center)