Impact of Surface Adsorption on Metal–Ligand Binding of Phenanthrolines

Abstract

Phenanthrolines are a class of ligands known to bind with many different metal cations to form complexes. The aromatic backbone of phenanthroline also allows for preferential adsorption on few-layer graphene (FLG) films via π–π stacking. Here we investigate the effects of adsorption and the resulting steric restrictions on the binding ability of four different phenanthroline derivatives: phenanthroline, neocuproine, bathophen­anthroline, and bathocuproine. In solution, a wide range of metal cations tested formed complexes with these ligands, but only Cu2+ and Ag+ showed evidence of binding to ligands adsorbed onto FLG, as measured by the chemiresistive response of the films. The substituents present on each ligand affected the magnitude of the response in different ways. Raman and X-ray photoelectron spectroscopy (XPS) were used to study two different systems in more detail: iron with phenanthroline, which shows a response in solution (ferroin) but not on the FLG surface (purported monoligand complex), and copper with neocuproine, which responds both in solution (bis­[neocuproine]­copper­(I)) and on the FLG surface (monoligand complex). Raman and XPS data indicate complexing of copper by surface-bound ligands. Theoretical calculations show that the copper–neocuproine monocomplex has a higher adsorption energy and binding energy to a graphene surface than the iron–phenanthroline monocomplex. The reduction of copper­(II) to copper­(I) by the surface-bound neocuproine further results in a stronger charge transfer response from the sensor. The results of this study provide insights into the mechanisms of solid-state sensing of metal cations for water quality detection based on steric and electrochemical restrictions induced by surface adsorption.

Alkynyl Boosted High‐Performance Lithium Storage and Mechanism in Covalent Phenanthroline Framework

“…The Raman spectra of Alkynyl‐CPF, TEB, and DBPhen are displayed in Figure S3. The characteristic peaks at ≈715 and ≈2430 cm −1 are assigned to the stretching vibration of C−Br and ≡C−H from TEB and DBPhen reactants, respectively [11] . For the Alkynyl‐CPF product, the new characteristic peak (≈2210 cm −1 ) which belongs to the vibration of C≡C bonds appears, [12] and the C−Br bonds (≈715 cm −1 ) of DBPhen and ≡C−H bonds (≈2430 cm −1 ) of TEB disappear, suggesting the successful condensation between ≡C−H and C−Br units.…”

“…The characteristic peaks at � 715 and � 2430 cm À 1 are assigned to the stretching vibration of CÀ Br and �CÀ H from TEB and DBPhen reactants, respectively. [11] For the Alkynyl-CPF product, the new characteristic peak ( � 2210 cm À 1 ) which belongs to the vibration of C�C bonds appears, [12] and the CÀ Br bonds ( � 715 cm À 1 ) of DBPhen and �CÀ H bonds ( � 2430 cm À 1 ) of TEB disappear, suggesting the successful condensation between �CÀ H and CÀ Br units. In addition, the characteristic peak that appears at � 1615 cm À 1 is attributed to the pyridinic N, while the obvious peaks in the range of 1600-1400 cm À 1 correspond to the aromatic ring of Alkynyl-CPF, which gives more evidence to the successful occurrence of the condensation reaction.…”

Tuning the Chemical and Mechanical Properties of Conductive MoS2 Thin Films by Surface Modification with Aryl Diazonium Salts

“…When the surface of a pristine or functionalized two-dimensional (2D) material interacts with an aqueous solution containing metal cations, there will be an impact on the electronic structure of the material that can be observed as a result of surface doping or field effects as a result of its interactions with its chemical environment. , These chemical changes can be probed in a chemiresistive thin-film format. Two different mechanisms are commonly invoked to explain chemiresistive responses: (a) an electrostatic gating mechanism as a result of changes in the electrochemical double layer (EDL) and (b) a surface charge transfer mechanism that modulates the dopant concentration of the conductive layer, e.g., as a result of complexation .…”

“…In solution phase, the nitroso group (as it is present in 4-NB) has been reported to form a complex with iron selectively compared to the other three metal ions. 39 The surface geometry, however, restricts the formation of multiligand complexes, 30 reducing the thermodynamic favorability of an iron complex with 4-NB groups anchored to c-MoS 2 . If a complex of the nitro group with any of the cations was formed at all, the resulting change in the electronic structure is not transmitted to the MoS 2 surface (Figure 5c and Figure S5 of the Supporting Information).…”

“…Chemiresistive devices were fabricated using our previously reported procedure. , Briefly, two terminal devices were fabricated on glass slides, which were cleaned by sonication in acetone, followed by methanol and water for at least 15 min during each step. Two parallel pads were drawn on the frosted end of the glass slide using a 9B pencil with a 1 cm gap.…”