Probing Ligand Effects on the Ultrafast Dynamics of Copper Complexes via Midinfrared Pump–Probe and 2DIR Spectroscopies

Abstract

The effects of ligand structural variation on the ultrafast dynamics of a series of copper coordination complexes were investigated using polarization-dependent mid-IR pump− probe spectroscopy and two-dimensional infrared (2DIR) spectroscopy. The series consists of three copper complexes [( R 3 P 3 tren)Cu I I N 3 ]BAr 4 F ( 1 P R 3 , R 3 P 3 tren = tris[2-( p h o s p h i n i m i n a t o ) e t h y l ] a m i n e , B A r 4 F = tetrakis-(pentafluorophenyl)borate) where the number of methyl and phenyl groups in the PR 3 ligand are systematically varied across the series (PR 3 = PMe 3 , PMe 2 Ph, PMePh 2 ). The asymmetric stretching mode of azide in the 1 PR3 series is used as a vibrational probe of the small-molecule binding site. The results of the pump−probe measurements indicate that the vibrational energy of azide dissipates through intramolecular pathways and that the bulkier phenyl groups lead to an increase in the spatial restriction of the diffusive reorientation of bound azide. From 2DIR experiments, we characterize the spectral diffusion of the azide group and find that an increase in the number of phenyl groups maps to a broader inhomogeneous frequency distribution (Δ 2 ). This indicates that an increase in the steric bulk of the secondary coordination sphere acts to create more distinct configurations in the local environment that are accessible to the azide group. This work demonstrates how ligand structural variation affects the ultrafast dynamics of a small molecular group bound to the metal center, which could provide insight into the structure−function relationship of the copper coordination complexes and transition-metal coordination complexes in general.

Exploring the Structure and Complexation Dynamics of Azide Anion Recognition by Calix[4]pyrroles in Solution

“…In addition, a small shoulder peak (1985 cm −1 ) on the lower frequency side of the main peak is also observed, which is possibly caused by the bending hot band of the azide anion. 44,45 The FTIR spectrum of N 3 − dissolved in DMSO solution is consistent with previous studies. 44,46 The spectral features shown in Figure 1C indicate that the N 3 − anion is mainly solvated by the DMSO molecules, and the countercation TBA + should stay away from the anion.…”

“…The peak positioned at 2000 cm –1 is assigned to the asymmetric stretching mode of N 3 – . In addition, a small shoulder peak (1985 cm –1 ) on the lower frequency side of the main peak is also observed, which is possibly caused by the bending hot band of the azide anion. , The FTIR spectrum of N 3 – dissolved in DMSO solution is consistent with previous studies. , The spectral features shown in Figure C indicate that the N 3 – anion is mainly solvated by the DMSO molecules, and the countercation TBA + should stay away from the anion. When the host molecule was present in the solution, a new peak at 2033 cm –1 appeared at the higher frequency range, suggesting that the N 3 – anion can interact with the calix[4]­pyrroles through hydrogen bonding interactions.…”

Electrostatic Contributions to the Stability of an End-on Cupric Superoxide

“…720 and 980 nm (SI) are consistent with previous reports of isostructural h 1 cupric superoxide and azide complexes. 7,[35][36][37][38][39] The solid-state structure of 3 34 confirmed that the geometry about copper closely matches the DFT-optimized structure of 2 (SI). Considering the demonstrated importance of H-bonding to cupric superoxide stability, 7,19,40 we evaluated the potential for H-bonding in the secondary coordination spheres of 2 and 3.…”

Resolving the Impact of Hydrogen Bonding on the Phylloquinone Cofactor through Two-Dimensional Infrared Spectroscopy

“…Absorptive 2DIR spectra were obtained in the pump–probe geometry at room temperature, and our experimental setup was described previously . Briefly, a tunable mid-infrared pulse was generated by pumping a two stage optical parametric amplifier (Light Conversion TOPAS C) with 60% of the output of a 800 nm 100 fs 1kHZ Ti:sapphire regenerative amplifier (4W, Coherent Libra).…”

“…Absorptive 2DIR spectra were obtained in the pump−probe geometry 48 at room temperature, and our experimental setup was described previously. 49 Briefly, a tunable mid-infrared pulse was generated by pumping a two stage optical parametric amplifier (Light Conversion TOPAS C) with 60% of the output of a 800 nm 100 fs 1kHZ Ti:sapphire regenerative amplifier (4W, Coherent Libra). The resulting signal and idler were difference frequency mixed in a commercial DFG (Light Conversion) to generate a mid-IR pulse centered at 6 μm with a pulse width of ∼130 cm −1 .…”