Surface directed reversible imidazole ligation to nickel(ii) octaethylporphyrin at the solution/solid interface: a single molecule level study

Abstract

Scanning tunneling microscopy (STM) is used to study for the first time the reversible binding of imidazole (Im) and nickel(ii) octaethylporphyrin (NiOEP) supported on highly oriented pyrolytic graphite (HOPG) at the phenyloctane/NiOEP/HOPG interface at 25 °C. The ligation of Im to the NiOEP receptor while not observed in fluid solution is readily realized at the solution/HOPG interface. The coordination process scales with increasing Im concentration and can be effectively modeled by the Langmuir isotherm. At room temperature it is determined that the standard free energy of adsorption is ΔGc = -15.8 kJ mol(-1) and the standard enthalpy of adsorption is estimated to be ΔHc ≈ -80 kJ mol(-1). The reactivity of imidazole toward NiOEP adsorbed on HOPG is attributed to charge donation from the graphite stabilizing the Im-Ni bond. This charge transfer pathway is supported by molecular and periodic modeling calculations which indicate that the Im ligand behaves as a π-acceptor. DFT calculations also show that the nickel ion in the Im-NiOEP/HOPG complex is in a singlet ground state. This is surprising since both our calculations and previous experimental studies find a triplet ground state for the five and six coordinated Im-nickel(ii) porphyrins in the gas-phase or in solution. Both the experimental and the theoretical findings provide information that is useful for better understanding of chemical sensing/recognition and catalytic processes that utilize metal-organic complexes adsorbed on surfaces where the reactivity of the metal is moderated by the substrate.

Structure, Properties, and Reactivity of Porphyrins on Surfaces and Nanostructures with Periodic DFT Calculations

“…PDFT calculations of not porphyrins but porphyrin-based molecules are also studied in the literature. For example, Zhang et al studied the adsorption of Ni(Salophen) molecule on Au(111) surface using vdW-DFT functionals and determined the adsorption energy to be 2.74 eV which is about 2/3 of the adsorption energy of similar porphyrin [96,106] molecules on Au(111). Gurdal et al studied the adsorption of pyrphyrin molecules on Au(111) [107] and Ag (111) [108] surfaces using various GGA and vdW-GGA functionals.…”

“…Nandi et al [106], used PDFT simulations with vdW-DF [43,48] functional to understand the binding mechanism of imidazole (Im) ligand to Ni-octaethylporphyrin (NiOEP) bound on HOPG surface. Using STM, solution-spectroscopy, and molecular DFT calculations the authors reported that Im ligand does not bind to NiOEP in solution or in gas-phase but does bind when NiOEP is on the HOPG surface.…”

“…In the cross-section (A1-D1, top row) the rainbow colors (blue to red) indicate charge with blue being highly negative and red being highly positive. Reproduced from reference [106] published by the PCCP Owner Societies.…”

Sparse‐coding denoising applied to reversible conformational switching of a porphyrin self‐assembled monolayer induced by scanning tunnelling microscopy

“…, , ). Recent publications have been reporting studies about the dynamic behaviour of porphyrins, in particular, conformational manipulations using STM (Zhao et al ., ; Kumagai et al ., ; Nandi et al ., ; Lensen et al ., ) and a recent review paper highlights some of the experiments that involved porphyrin manipulation using STM (Auwarter et al ., ). Most of them, are related to porphryins conformational switching in response to external inputs like temperature, light, atomic force or current.…”

“…These distortions also influence the conductivity of the porphyrins which is an important property for the design of organic electronic systems (Wolfle et al, 2008;Ferreira et al 2014Ferreira et al , 2011Ferreira et al , 2013. Recent publications have been reporting studies about the dynamic behaviour of porphyrins, in particular, conformational manipulations using STM (Zhao et al, 2013;Kumagai et al, 2014;Nandi et al, 2016;Lensen et al, 2012) and a recent review paper highlights some of the experiments that involved porphyrin manipulation using STM (Auwarter et al, 2015). Most of them, are related to porphryins conformational switching in response to external inputs like temperature, light, atomic force or current.…”