Reactivity of porphyrin- and phthalocyanine-based assemblies at surfaces from UHV to near-ambient pressure

Metal-organic materials represent a promising alternative to traditional technologies, minimizing the consumption of rare metals and production costs. Furthermore, their properties can be tuned through chemical functionalization or by tailoring the electronic structure, making them extremely versatile. This thesis is dedicated to the growth and experimental characterization of porphyrin- and phthalocynine-based biomimetic materials, focusing on their reactivity at surfaces. Two different Pd-heterostructures are investigated in the first part of this work, PdTPP on Cu(100) and 2HPc on Pd(001). We focus on Pd-based molecular tectons since they demonstrated drug delivery capabilities, relevant for cancer therapy research. The electronic and conformational properties of PdTPP/Cu(100) are studied through a combination of multiple spectroscopic and microscopic techniques, revealing their instability upon deposition on the metallic copper termination. The strong interaction with the surface induces a thermally-enhanced redox metal exchange between Pd and Cu surface atoms, paralleled by dehydrogenation reactions, ultimately leading to a reconstruction of the organic structure. We finally demonstrate that PdTPP can be decoupled and stabilized by exploiting an oxygen buffer layer. Starting from the non-metalated precursor, we show instead that PdPcs are easily obtained by self-metalation of 2HPcs deposited on Pd(001), promoted by a mild annealing. The second part of this work presents the growth and characterization of MnTPyP and MnTPyP-Co on inert substrates, Gr/Ir(111) and Au(111). Previous studies predicted and demonstrated the catalytic abilities of Co and Mn organic compounds towards oxygen evolution and reduction reactions, regulating the operation of metal-air batteries. Our investigation of these model catalysts, with stronger focus on the Gr/Ir(111) support, extends from ultrahigh vacuum to near-ambient pressure conditions in order to tackle their catalytic properties in situ. The coordination of Co to a MnTPyP layer leads to a dramatic non-local electronic and vibronic structure modification, allowing to tune the oxidation state of the metal sites and to modify the frontier molecular orbitals. Additionally, the peripheral coordination of a second metal induces a rearrangement of the tectons supramolecular ordering. The comparison between the properties of these systems on Gr/Ir(111) and Au(111) reveals some differences associated to the surface trans-effect originating from the different molecule-substrate interaction. The chemical activity of the MnTPyP-Co/Gr/Ir(111) system towards CO and O2 is investigated by complementary in situ spectrocopies. CO reversibly ligates to Co, where the adsorbate coverage is determined by the equilibrium between the adsorption and desorption processes. We also find that anti-cooperative mechanisms arise between neighbouring Co sites, mediated by the organic matrix, revealed by means of a pressure uptake from ultra-high vacuum to near-ambient pressure. Finally, the pressure-dependent results of the O2 reactivity study are presented. At low pressure, molecular oxygen reversibly ligates to Co in equilibrium the O2 background. At high pressure instead the activated O-O bond is cleaved, leading to a non-reversible oxidation of the framework and graphene. Oxygen dissociation is the preliminary step of oxygen reduction reactions, thus its activation at room temperature is an extremely promising result. Indeed, this property can be exploited to oxidise other gases, preventing the catalyst poisoning.