Unraveling Confined Dynamics of Guests Trapped in Self-Assembled Pd₆L₄ Nanocages by Ultrafast Mid-IR Polarization-Dependent Spectroscopy

Abstract

Self-assembled coordination cages form host-guest complexes through weak non-covalent interactions. Knowledge of how these weak interactions affect the structure, reactivity, and dynamics of guest molecules is important to further the design principles of current systems and optimize their specific functions. In this manuscript, we apply ultrafast mid-IR polarization dependent pump-probe spectroscopy to probe the effects of two Pd 6 L 4 self-assembled nanocages on the properties and dynamics of fluxional group VIII metal carbonyl guest molecules. We find that the interactions between the Pd 6 L 4 nanocages and guest molecules act to alter the ultrafast dynamics of the guests; restricting rotational diffusional motion and decreasing the vibrational lifetime.

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

“…We apply a modified wobbling-in-a-cone model , to the anisotropy data to quantitatively characterize the degree of spatial restriction and extract the diffusion coefficients. This model was initially developed to interpret the fluorescence depolarization data of molecules embedded in biomembranes , and was later generalized to nuclear magnetic resonance data , and midinfrared anisotropy measurements in various systems. ,, According to this model, the faster component of the anisotropy decay is associated with the restricted orientational motion of the transition dipole moment within a cone-shaped space, and the slower component is associated with the complete reorientation. We note for each of the four samples, the sum of amplitudes ( a 1 + a 2 , Table ) is less than 0.4, the theoretical initial value of the anisotropy decay in an isotropic medium.…”

“…Two-dimensional infrared (2DIR) spectroscopy has proven to be a powerful tool to probe ultrafast equilibrium dynamics of enzymes as well as models of their active sites on femtosecond to picosecond timescales. − ,− Polarization-dependent mid-IR pump–probe spectroscopy has also been widely used to extract the vibrational population and orientational relaxation dynamics of various systems. − In this manuscript, we apply both polarization-dependent mid-IR pump–probe spectroscopy and 2DIR spectroscopy to a series of copper coordination complexes to determine how the structural variation in the secondary coordination sphere impacts the ultrafast dynamics at a small-molecule binding site where a series of trigonal pyramidal Cu I complexes bind O 2 .…”

Cavity-based applications of metallo-supramolecular coordination cages (MSCCs)

“…Recently, Anna and coworkers used ultrafast mid-IR polarization dependent pumpprobe spectroscopy to gain an insight into the effects of encapsulation on the dynamics and properties of group VIII metalcarbonyl complexes. 91 Fujita and co-workers explained the stabilization of cis-bridged isomeric form of di-ruthenium carbonyl complexes within cage I and their carbonyl photosubstitution without metal-metal bond cleavage. 92 Apart from their interesting photochemistry and catalytic properties, the group VIII metal carbonyl complexes exhibit fluxional behavior, where multiple isomers exist in dynamic equilibrium.…”

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

“…Ultrafast infrared spectroscopy has been demonstrated to be a powerful technique to unravel the hydrogen bonding dynamics at a femtosecond time resolution in aqueous solutions. − The specific host–guest interactions of crown ethers with metal cations and other host–guest complexes have been reported in previous studies. − In this letter, the anion recognition dynamics between calix[4]­pyrroles and azide (N 3 – ) anions in the form of their tetrabutylammonium (TBA + ) and Na + salts was investigated in dimethyl sulfoxide (DMSO) solutions. The calix[4]­pyrroles were synthesized following the reported procedure, and the characterization data are given in the Supporting Information (Figures S1–S3).…”