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The regulation of intramolecular vibrational energy redistribution (IVR) to influence energy flow within molecular scaffolds provides a way to steer fundamental processes of chemistry, such as chemical reactivity in proteins and design of molecular diodes. Using two-dimensional infrared (2D IR) spectroscopy, changes in the intensity of vibrational cross-peaks are often used to evaluate different energy transfer pathways present in small molecules. Previous 2D IR studies of para-azidobenzonitrile (PAB) demonstrated that several possible energy pathways from the N3 to the cyano-vibrational reporters were modulated by Fermi resonance, followed by energy relaxation into the solvent [Schmitz et al., J. Phys. Chem. A 123, 10571 (2019)]. In this work, the mechanisms of IVR were hindered via the introduction of a heavy atom, selenium, into the molecular scaffold. This effectively eliminated the energy transfer pathway and resulted in the dissipation of the energy into the bath and direct dipole–dipole coupling between the two vibrational reporters. Several structural variations of the aforementioned molecular scaffold were employed to assess how each interrupted the energy transfer pathways, and the evolution of 2D IR cross-peaks was measured to assess the changes in the energy flow. By eliminating the energy transfer pathways through isolation of specific vibrational transitions, through-space vibrational coupling between an azido (N3) and a selenocyanato (SeCN) probe is facilitated and observed for the first time. Thus, the rectification of this molecular circuitry is accomplished through the inhibition of energy flow using heavy atoms to suppress the anharmonic coupling and, instead, favor a vibrational coupling pathway.

The sluggishness of the O 2 reduction reaction (ORR) is the most significant challenge to fuel cell commercialization. Cu-based ORR catalysts are promising non-precious metal alternatives to Pt. In this study, we synthesize four different Cu 2+ complexes of tripeptides (Cu−GSHAmide, Cu−NCG, Cu−ECG, and Cu−QCG) and analyze the relationships between their electrocatalytic activities and physicochemical properties. Rotating ring-disk electrode experiments indicate that the catalytic current densities and selectivities vary widely as a function of pH and peptide identity. Through Fourier transform infrared spectroscopy, we describe the nature of the intermolecular forces between the peptides studied along with those of the corresponding Cu 2+ complexes. This analysis allows us to quantify the degree of peptide aggregation in the ORR electrocatalysts. Combined with the Cu 2+ −peptide binding constants, we develop models that accurately predict how peptide aggregation dictates catalyst current density and selectivity for the four-electron reduction of O 2 to water. These models indicate that Cu 2+ −peptide ORR electrocatalysts with relatively strong binding constants and weak peptide aggregation exhibit increased selectivity and enhanced kinetics. This central finding highlights an important set of design rules for the development of future highperformance Cu ORR electrocatalysts.

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