Solvent-Independent Anharmonicity for Carbonyl Oscillators

Abstract

The physical origins of vibrational frequency shifts have been extensively studied in order to understand noncovalent intermolecular interactions in the condensed phase. In the case of carbonyls, vibrational solvatochromism, MD simulations, and vibrational Stark spectroscopy suggest that the frequency shifts observed in simple solvents arise predominately from the environment’s electric field due to the vibrational Stark effect. This is contrary to many previously invoked descriptions of vibrational frequency shifts, such as bond polarization, whereby the bond’s force constant and/or partial nuclear charges are altered due to the environment, often illustrated in terms of favored resonance structures. Here we test these hypotheses using vibrational solvatochromism as measured using 2D IR to assess the solvent dependence of the bond anharmonicity. These results indicate that the carbonyl bond’s anharmonicity is independent of solvent as tested using hexanes, DMSO, and D2O and is supported by simulated 2D spectra. In support of the linear vibrational Stark effect, these 2D IR measurements are consistent with the assertion that the Stark tuning rate is unperturbed by the electric field generated by both hydrogen and non-hydrogen bonding environments and further extends the general applicability of carbonyl probes for studying intermolecular interactions.

Energy Level Modification with Carbon Dot Interlayers Enables Efficient Perovskite Solar Cells and Quantum Dot Based Light‐Emitting Diodes

“…Figure 3c reveals that the elemental ratios of C:N are 4.5:1 and 8.8:1 in the CD 0.33 and CD 5 samples, respectively. C 1s high-resolution XPS spectra of CD 0.33 and CD 5 (Figure 3d) show presence of CC bonds (≈285 eV), CN bonds (≈286 eV), and CN/CO coordination (≈288 eV), [21] with CD 0.33 possessing a higher CN bond content than CD 5 , which is well consistent with the decrease in the amount of −NH 2 groups. N 1s high-resolution…”

Electric Fields and Enzyme Catalysis

“…In those works, vibrational frequency red-shifts were interpreted to imply that the bond probed is destabilized from strain (mechanically or electrostatically) imposed onto it by the enzyme. In contrast, data from our laboratory accrued over the past few years have supported the view that most vibrational frequency variation (in carbonyls, at least) can be explained through a static electric field–difference dipole effect (53, 91), not by bond weakening or strain (i.e., changes in the force constant) (103, 104). This represents a departure from how vibrational measurements (both infrared and Raman) have traditionally been interpreted in enzymology (105–107), and efforts are ongoing to reinterpret this corpus of biochemical data within this physical framework (108, 109).…”

“…In other words, the recorded frequency shifts report on the electrostatic environment experienced by the ground state (as the excited state will not cause the environment to reorganize in any appreciable way). Second, |Δ μ⃗ | tends to be insensitive to the probe’s environment (another consequence of small Δ α ) (54, 91). Third, vibrations can be confined to as few as two atoms (to a good level of approximation), so the experiment provides a more local, higher-resolution description of electric fields (88, 92).…”

Discovery of a Multinary Noble Metal–Free Oxygen Reduction Catalyst

“…Comparison of intrinsic activity of sputtered NPs using the i ss method. [32] a) Voltammograms of all sputtered NPs (Pt, binary, quaternary, and quinary Cr-Mn-Fe-Co-Ni) using an i ss normalized scale for activity comparison. "I" and "II" refer to repetition with same suspension, "new" to analysis of a sample prepared with an alloy target.…”

“…Hence, we hypothesize that catalytic activity cannot be solely predicted based on the properties of the constituent elements, and superior multinary catalysts do not uniquely rely on the position of their elements in such volcano plots [26,27] alone. Strain effects [28][29][30] or interparticle distance [31,32] were shown to affect electrocatalytic activity. Strain effects can be strongly modulated in multinary solid solutions; however, more importantly, the homogeneous distribution of all elements induces a numerous amount of new active site configurations with different constitutions of neighboring atoms electronically interacting with each other.…”