Nanoscopic Imaging of meso-Tetraalkylporphyrins Prepared in High Yields Enabled by Montmorrilonite K10 and 3 Å Molecular Sieves

• Published in: Chemistry : a European journal 2013-08, Vol.19 (34), p.11293-11300
• Main Authors: Plamont, Rémi, Kikkawa, Yoshihiro, Takahashi, Mayuko, Kanesato, Masatoshi, Giorgi, Michel, Chan Kam Shun, Anita, Roussel, Christian, Balaban, Teodor Silviu
• Format: Article
• Language: English
• Subjects: Chemical Sciences; clays; graphite; interfaces; porphyrinoids; self-assembly
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201300532

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. 2D or not 2D?­ meso‐Tetraalkylporphyrins were obtained in high yields of up to 70 %. When the alkyl chains are decyl or longer, the porphyrins could be imaged at the liquid/solid interface of n‐phenyloctane or n‐phenylnonane and highly oriented pyrolitic graphite. An odd–even effect is observed, and for a C13 alkyl chain length the 2D lattice is compared to the 3D packing in a single crystal (see figure).