EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Porphyrins are highly attractive materials toward hydrogen production from solar-assisted water splitting, owing to their outstanding light absorption and charge transport properties. Those features can be potentially improved by the extension of the π-π system through the fusion of multiple porphyrin units. In addition, the metal cation chelated in the porphyrin macrocycle can act as a catalytic active site, boosting the water splitting reactions efficiency. However, the poor solubility of these materials jeopardizes their processability and integration in functional devices. Unlike wet chemistry methods, oxidative chemical vapor deposition (oCVD) enables the one-step formation and deposition of conjugated metalloporphyrin coatings, without solvents or post-treatments needed.
We have investigated the impact of the central metal cation on the gas-phase dehydrogenative coupling reaction of 5,15 diphenyl-metalloporphyrins (MDPP; M=Co, Cu, Mg, Zn, Pd, Pt, Ag, Ru, Ag, Fe) in oCVD and hence, on the optoelectronic properties of the resulting fused metalloporphyrin films. The nature of the central metal cation was proven to strongly affect the intermolecular coupling efficiency between the porphyrin units to lead singly, doubly or triply fused tapes. Moreover, they showed a significant influence on the occurrence of side reactions during the oCVD process, as chlorination, intramolecular coupling, demetallation, re-metallation, and oxidation of the porphyrin core. Those features were reflected on the optoelectronic properties of the conjugated metalloporphyrin films, as evidenced on the light absorption spectra, the energy bands alignment, and the conductivity. This study paves the way toward the engineering and practical implementation of porphyrin-based photo-electrocatalytic systems for efficient and clean solar-assisted hydrogen production.