Abstract
Porphyrin molecules are chemical analogs of the photoactive part of chlorophyll. Using AFM, we have found1 that the diacid form of the porphyrin tetrakis(4-sulfonatophenyl) porphine self-assembles into straight, rod-like aggregates, with a well-defined height of 3.8 pm 0.3 nm, and with lengths of up to 5 mu m. We summarize our studies of the mechanism of rod formation and growth in solution, using UV/Vis spectroscopy and dynamic light scattering. Spectroscopy suggests significant intermolecular electronic interaction along the rods. We have performed DC conductivity measurements on parallel arrays of the nanorods, with contact pad spacing of 0.4 mu m (much smaller than the typical nanorod length). Without light, the rods are insulators. We find significant photoconductivity that turns on immediately upon illumination, then slowly grows. After the light is removed, the conductivity persists for several minutes. We discuss possible models for this behavior.