On-surface transmetalation of metalloporphyrins self-assembled monolayers.

J. M. LOMBARDI; D. HÖTGER; P. ABUFAGER; C. MORCHUT; P. ALEXA; D. GRUMELLI; J.DREISER; S. STEPANOW; H. F. BUSNENGO; M. ETZKORN; R.GUTZLER; K. KERN

Santa Fe (Argentina)

Conferencia; VI San Luis Conference on Surfaces, Interfaces and Catalysis; 2018

Metalation of free-base porphyrins is a standard procedure for the synthesis of metalloporphyrins in solution as well as on surfaces. In recent years, metal insertion into free-base porphyrins at the vacuum/solid interface has been thoroughly studied, providing detailed insight into the mechanisms at play. A standard procedure to metalate free-base porphyrins is through the uptake of metal atoms at the vacuum/solid interface and the resultant simultaneous release of H2.1. The mechanism by which the two pyrrolic hydrogens are expelled and replaced by a metal atom is well understood.1,2 However, the metal exchange, in which an existing metal cation is replaced by a second metal, is rarely investigated in surface-supported porphyrins3-5. Herein, we have investigated the transmetalation of metal porphyrin monolayer networks self-assembled on Au(111) using Density Functional Theory calculations, X-ray absorption and scanning tunneling microscopy. When depositing Co on the networks formed by Fe-porphyrines at room temperature, we find strong evidence of an efficient metal cation exchange. The process is unidirectional as we find no signs of transmetalation for Fe deposited on Co-porphyrines. The role of the peripheral functional group in the exchange mechanism is analyzed. Our findings have important implications for the fabrication of porphyrin layers on surfaces when subject to the additional deposition of metals.