Self-Metalation of 2H-Tetraphenylporphyrin on Cu(111) Studied with XSW: Influence of the Central Metal Atom on the Adsorption Distance

Abstract

We present a systematic X-ray standing wave (XSW) study of the π-conjugated organic compound 2H-tetraphenylporphyrin (2HTPP) and copper(II)-tetraphenylporphyrin (CuTPP) on Cu(111) at room and low temperatures. We exploit the feature of thermally activated self-metalation of 2HTPP to CuTPP to study the influence of the central metal atom on the bonding distance of the molecule to the substrate surface. Comparison between the average adsorption distances of the carbon and nitrogen atoms of 2HTPP reveals a distorted molecule with the nitrogen atoms being closer to the surface than the carbon ones on average. Additionally, the measured positions of the two chemically inequivalent types of nitrogen atoms (iminic and aminic) of 2HTPP indicate a distorted porphyrin ring. After the chemical reaction from 2HTPP to CuTPP at 500 K, no change of the adsorption distance of the carbon skeleton is seen, but the entire molecule becomes flattened. Despite the changes upon metalation, adsorption distances for both molecule...