Adsorption, Ordering, and Metalation of Porphyrins on MgO Nanocube Surfaces: The Directional Role of Carboxylic Anchoring Groups

Abstract

The understanding of porphyrin adsorption on oxide nanoparticles including knowledge about coverages and adsorbate geometries is a prerequisite for the improvement and optimization of hybrid materials. The combination of molecular spectroscopies with small-angle X-ray scattering provides molecular insights into porphyrin adsorption on MgO nanocube dispersions in organic solvents. In particular, we address the influence of terminal carboxyl groups on the adsorption of free base porphyrins, on their chemical binding, on the metalation reaction as well as on the coverage and orientation of adsorbate molecules. We compare the free base form 5,10,15,20-tetraphenyl-21,23H-porphyrin (2HTPP) with the carboxyl-functionalized 5,10,15,20-tetrakis(4-carboxyphenyl)-21,23H-porphyrin (2HTCPP) and show that without carboxylic anchoring groups the free base form metalates on the nanocube surface and adopts a flat-lying adsorbate geometry. The saturation limit for flat-lying adsorption on nanocubes with an average edge len...