The Photoconductivity of Porphyrin Nanorods

Brooks Bond-Watts
Haverford College

The photoelectronic properties of meso-tetra(4-sulfonato-phenyl)porphine aggregates were investigated. The aggregates have previously been shown, via atomic force microscopy (AFM), to be rod shaped with an average height of 3.8 ± 0.3 nm.1 A reliable method of inducing aggregation was developed. In addition, the photoconductivity of the aggregates was analyzed. In an argon atmosphere under normal room lighting, no conductivity was observed; however, upon excitation with a laser at 488 nm conductivity through the aggregate was seen. Four effects have been observed in conductivity experiments; a fast rise in photoconductivity followed by a slow phase, a slow decay of photoconductivity without light excitation, and a short circuit photocurrent. A model is proposed to explain the observed photoconductivity phenomena.

Photoconductivity of thin films of TPPS aggregates was also explored. The thin films were less conductive by two orders of magnitude under argon than in atmospheric conditions. Under argon, the thin films appear to be weakly photoconductive. They also exhibited persistent photoconductivity which is not observed for the nanorod samples.

Work supported by the National Science Foundation, the David and Lucille Packard Foundation, and the Arnold and Mabel Beckman Foundation.