Thermally Activated on‐Surface Self‐Metalation of Pd‐Phthalocyanines

Phthalocyanines (Pcs) are essential organic molecules with wide-ranging applications in fields such as catalysis and optoelectronics, owing to their stable aromatic structure and exceptional thermal stability. Equally important is their versatility, which can be achieved by modifying the central metal atom. In this context, metalation-the process by which a central metal atom is incorporated into the macrocycle-plays a critical role in tailoring both the electronic and structural properties of Pcs. In this work, we investigate the thermally activated on-surface synthesis of palladium phthalocyanine (PdPc) by depositing metal-free phthalocyanine ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>H</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>Pc</mml:mi></mml:mrow> <mml:annotation>${\rm H}_2{\rm Pc}$</mml:annotation></mml:semantics> </mml:math> ) onto a Pd(001) surface in ultra-high vacuum (UHV) conditions. Using temperature-dependent X-ray photoemission spectroscopy (XPS), we analyze the evolution of the N <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mn>1</mml:mn> <mml:mi>s</mml:mi></mml:mrow> <mml:annotation>$1s$</mml:annotation></mml:semantics> </mml:math> core level signal, confirming the successful formation of PdPc. The appearance of a secondary peak in the Pd <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mn>3</mml:mn> <mml:mi>d</mml:mi></mml:mrow> <mml:annotation>$3d$</mml:annotation></mml:semantics> </mml:math> core level, attributed to Pd atoms coordinated within the phthalocyanine molecule after metalation, provides further evidence for the PdPc synthesis. Additionally, near-edge X-ray absorption fine structure (NEXAFS) reveals that no desorption or chemical degradation occurs during the process. We believe this study represents a significant step forward in the scalable synthesis of PdPc, which, like other Pd-containing organic molecules, holds great potential for applications in catalysis and cancer therapy.