Cyano-Functionalized Porphyrins on Cu(111) from One-Dimensional Wires to Two-Dimensional Molecular Frameworks: On the Role of Co-Deposited Metal Atoms

Abstract

Metal adatoms play a key role in surface diffusion, adsorption conformation, and self-assembly of porphyrin molecules on metal surfaces. Herein, we study the specific influence of coadsorption of Fe, Co, and Pd atoms on the behavior of 2H-tetrakis­(p-cyano)­phenylporphyrin (2H-TCNPP) on Cu(111) using scanning tunneling microscopy. Upon co-deposition of Fe and Co, the molecules form one-dimensional (1D) linear chains after mild annealing on Cu(111) driven by the interaction of its cyano groups with metal adatoms. A similar behavior has been observed previously on Cu(111), mediated by Cu adatoms, where the functional CN groups were also found to lower the reaction rate of the so-called porphyrin self-metalation reaction with Cu atoms significantly, in comparison to the non-cyano-functionalized porphyrin. Upon co-deposition of Pd and mild annealing, we find a remarkably different behavior, that is, a massive reorganization from 1D molecular chains to a peculiar rectangular 2D (two-dimensional) network. The molecular appearance changes to a clover shape, which is attributed to a Pd-induced dehydrogenation and subsequent ring closure reaction of the phenyl and pyrrole groups.

Reassessing the Adsorption Behavior and on-Surface Reactivity of a Brominated Porphyrin on Cu(111)

“…Finally, Figure a and b also shows that all of the molecules are connected via an organometallic bond (C–Cu–C) where the C–Cu bond length is about 1.96 Å, in good agreement with the value of 1.93 Å predicted by DFT. In Figure b and c we show a high-resolution STM image and simulation, respectively, highlighting the Cu adatom in the organometallic bond, similar to other systems. ,, …”

“…The engineering of functional nanoscale materials has been largely explored in science and industry. In this way, the bottom-up fabrication appears as a remarkable strategy to build complex structures for applications in several areas such as photonics, electronic devices, energy production, and storage. , In this regard, porphyrins appear to be promising building blocks for the bottom-up fabrication of functional nanostructures on well-ordered metallic substrates due to their versatility for selective functionalization at the peripheries and central region of the molecule as well as their high chemical and thermal stability. , One of the most interesting approaches to building such structures is via on-surface synthesis − with the supramolecular order driven by the equilibrium of the molecule–molecule and molecule–substrate interactions. Many different intermolecular interactions can occur such as hydrogen bonding, van der Waals/dispersion forces, dipole–dipole interactions, and metal coordination. ,, …”

“…One of the best known metal-mediated C–C coupling reactions is the Ullmann reaction, , which is a high-efficiency route for building tailored covalently bonded structures from molecular precursors . Generally, the Ullmann-coupling reaction starts with the metal-mediated dehalogenation of the molecular precursors, followed by the formation of organometallic intermediates, and ends with the formation of new C–C covalent bonds between precursors. , In particular, molecules with brominated functional groups have been widely explored as precursors for construction of one-dimensional (1D) and two-dimensional (2D) complex organic and metal–organic frameworks (MOFs) due to their lower dehalogenation energy barrier and C–Br bond enthalpy compared to other halogen species, such as chlorine. ,− Porphyrins functionalized with halogen atoms have been explored as molecular precursor, building on well-ordered metallic surfaces (e.g., Ag, Au, Cu) to grow 2D supramolecular ordered structure. ,, In this way, the free base 5,10,15,20-tetrakis­(4-bromophenyl)­porphyrin (H 2 TBrPP) was explored as a molecular precursor for building ordered nanostructures on Au(111) . In that study, different TPP-based molecules with one, two, and four Br–phenyl substituents were deposited independently on Au(111), and therefore, three different covalently bonded structures (dimers, linear chains, and 2D networks) resulted from dehalogenation of these molecular precursors after heating the sample followed by an Ullmann-coupling reaction. − …”

“…Many different intermolecular interactions can occur such as hydrogen bonding, 8 van der Waals/ dispersion forces, 9 dipole−dipole interactions, and metal coordination. 7,10,11 One of the best known metal-mediated C−C coupling reactions is the Ullmann reaction, 12,13 which is a highefficiency route for building tailored covalently bonded structures from molecular precursors. 4 Generally, the Ullmann-coupling reaction starts with the metal-mediated dehalogenation of the molecular precursors, followed by the formation of organometallic intermediates, and ends with the formation of new C−C covalent bonds between precur-sors.…”

“…11,14−17 Porphyrins functionalized with halogen atoms have been explored as molecular precursor, building on well-ordered metallic surfaces (e.g., Ag, Au, Cu) to grow 2D supramolecular ordered structure. 7,17,18 In this way, the free base 5,10,15,20-tetrakis(4-bromophenyl)porphyrin (H 2 TBrPP) was explored as a molecular precursor for building ordered nanostructures on Au(111). 19 In that study, different TPP-based molecules with one, two, and four Br−phenyl substituents were deposited independently on Au(111), and therefore, three different covalently bonded structures (dimers, linear chains, and 2D networks) resulted from dehalogenation of these molecular precursors after heating the sample followed by an Ullmann-coupling reaction.…”