Photoconductivity of Nanotapes Self-assembled from meso-Tri(4-sulfonatophenyl)monophenylporphine

We have shown$^{1}$ that meso-Tetra(4-sulfonatophenyl)porphine (TPPS$_{4})$ forms well-defined nanorods in acidic solution. Experiments on related molecules provide insight into the mechanisms for self-assembly and photoconduction. Meso-Tri(4-sulfonatophenyl)monophenylporphine (TPPS$_{3})$ has one fewer sulfonate group than TPPS$_{4}$, but is otherwise identical. Previous work$^{2}$ has shown that, when deposited onto substrates by rotary evaporation, it forms folded nano-ribbons. We have found that, when deposited via immersion and spin-drying, it forms tape-like aggregates of two distinct heights. The larger width of these nanotapes (compared to TPPS$_{4}$ nanorods) is expected from the smaller in-solution charge of the monomer. The TPPS$_{3}$ aggregates exhibit photoconductive properties very similar to those of TPPS$_{4}$. The aggregates ordinarily form in solution, but can also be surface-catalyzed. $^{1}$ A.D. Schwab \textit{et al.}, Nano Letters \textbf{4}, 1261 (2004). $^{2}$ J. Crusats \textit{et al.,} Chem Commun. 1588 (2003).