Temperature Dependence and Desorption Kinetics of Porphyrins at the Solid-Solution Interface

The energetics and kinetics of metal porphyrin adsorption on conducting surfaces from solution are of great importance for the formation of self assembled structures for applications.  In this study variable temperature solid-solution interfacial scanning tunneling microscopy (STM) imaging is used to probe the self assembly of porphyrin adlayers. It will be shown that the adsorption of cobalt octaethylporphyrin (CoOEP) and NiOEP from phenyloctane onto Au(111) is kinetically controlled and essentially irreversible below about 100°C.  Above 100°C slow desorption and re-adsorption processes cause exchange of porphyrin species on the surface.  Analysis of the results from studies conducted with varying concentration and temperature result in the relative free energies and enthalpies of activation for the desorption process.  DFT calculated values of adsorption energy will be compared to the experimental results.