Nanoscopic imaging of meso-tetraalkylporphyrins prepared in high yields enabled by Montmorrilonite K10 and 3A molecular sieves.

We have developed a high-yielding synthesis of meso-tetraalkylporphyrins, which previously have been obtained only in lower yields. By employing Montmorrilonite K10 as the acid catalyst and 3 Å molecular sieves as the dehydrating agent, yields that reached 70 % could be achieved with some aliphatic aldehydes. The free-base porphyrins with decyl (C10) or longer chains were imaged at the single-molecule level at the solvent/surface interface. Highly oriented pyrolytic graphite (HOPG) was used as a π-stacking surface, whereas 1-phenyloctane and 1-phenylnonane were used as solvents. An odd-even effect was observed from C13 to C16. For C13 a single-crystal X-ray structure allowed an unprecedented insight into how packing from two dimensions is expanded into a three-dimensional crystal lattice.