Highly Regioselective Cyclodehydrogenation of Diphenylporphyrin on Metal Surfaces

Exploring the effect of porphin tautomerism on the regioselectivity of its derivatives is a big challenge, which is significant for the development and application of porphyrin drugs. In this work, we demonstrate the regioselectivity of 2H-diphenylporphyrin (H₂-DPP) in the planarization reaction on Au(111) and Ag(111) substrates. H₂-DPP monomer forms two configurations (anti- and syn-) via a dehydrogenation coupling, between which the yield of the anti-configuration exceeds 90%. Using high-resolution scanning tunneling microscopy, we visualize the reaction processes from the H₂-DPP monomer to the final two planar products. Combined with DFT calculations of the potential reaction pathway and comparative experiments on Au(111) and Ag(111) substrates. Using M-DPP (M = Cu and Fe), we confirm that the regioselectivity of H₂-DPP is derived from the reaction energy barrier during the cyclodehydrogenation reaction of different tautomers. This work reveals the regioselectivity mechanism of H₂-DPP on the atomic scale, which holds great significance for understanding the chemical conversion process of organic macrocyclic molecules.