Adrian Joe Urban

While molecular electrocatalysis for CO ₂ reduction has advanced significantly, a key challenge persists in accurately defining the active site distribution, surface density, and structural organization of heterogenized catalysts at electrode interfaces. In this study, we address this gap by employing self‐assembled monolayers of physisorbed metal porphyrins (Fe and Cu) on graphite electrodes as structurally well‐defined model systems for the electrochemical CO ₂ reduction reaction (CO ₂ RR). High‐resolution scanning tunneling microscopy (STM) revealed crystalline monolayers with uniform active site distribution, offering periodicities of ∼1.5 nm. These monolayers exhibit moderate Faradaic efficiencies (FEs) for CO production, with Fe porphyrin outperforming its Cu analogue. Isotopic labeling experiments were employed to confirm that the product CO originates from added CO ₂ . Bicomponent monolayers comprising Fe porphyrin and catalytically inactive free‐base porphyrin were fabricated to investigate composition–activity relationships. STM imaging enabled direct, quantitative assessment of surface composition, and subsequent CO ₂ RR measurements revealed a systematic decrease in FE with increasing coverage of the catalytically inactive component. These findings demonstrate the utility of molecularly ordered porphyrin monolayers as a powerful platform for probing structure–activity relationships in electrocatalytic CO ₂ reduction with exceptional spatial and compositional precision.

We investigate the roles of molecular vibrations and intermolecular interactions in the mechanism underlying chirality-induced spin selectivity (CISS) in monolayers of helical tetrapyrrole (TPBT) molecules. The spin polarization of photoelectrons emitted from TPBT-functionalized Cu(111) surfaces was measured as a function of the temperature and the surface coverage. We employed DFT calculations to determine the energy and temperature-dependent population of vibrational modes which vary either the molecular pitch and/or the molecular radius. In combination, the data demonstrate that molecular vibrations do not play a significant role for CISS in the TPBT layers. Submonolayer coverages were created by gradual thermal desorption of the molecules from the surface during the spin polarization measurements. While the spin polarization scales nonlinearly with the surface coverage, this behavior can be rationalized entirely through changes of the photoelectron yield upon surface functionalization, and therefore represents no evidence for cooperative effects involved in CISS.

The selective synthesis of nickel and copper complexes of 19‐benzoyl‐5,10,15‐triphenyl‐bilatrien‐1‐one (H₂TPBT) is reported, a molecule which crystallizes as a molecular helix of one‐and‐a‐quarter which turns with a 5.7 Å radius and a 3.2 Å pitch, and all 26 participating atoms are sp²‐hybridized. UV/vis, ECD, ESR and cyclic voltammetry experiments reveal a strong interaction between metal and ligand and partial radical character when copper is coordinated instead of nickel. Strong ECD absorption in the 800 nm range is found which, using TD‐DFT calculations as well as literature spectra, is shown to be highly tunable both by metal coordination and variation of the aryl groups in the TPBT periphery. The radical character of the ligand in Cu(TPBT) enables rapid interconversion between (M)‐ and (P)‐enantiomers, possibly via intermittent breakage of a Cu−N bond. The 19‐benzoyl group kinetically stabilizes enantiopure (M/P)‐Ni(TPBT). The results are interpreted with regard to the application as circularly polarized light (CPL) detectors as well as to the chirality‐induced spin‐selectivity (CISS) effect which is currently lacking a concise theoretical model.