Solvent-Mediated Vibrational Energy Relaxation from Vaska’s Complex Adducts in Binary Solvent Mixtures

Abstract

A vibrational pump-probe and FTIR study was performed on two different adducts of Vaska's complex in two different sets of binary solvent mixtures. The carbonyl vibrational mode in the oxygen adduct exhibits solvatochromic shifts of ~10 cm(-1) in either benzyl alcohol or chloroform relative to benzene-d6, whereas this vibration is nearly unchanged for the iodine adduct for the same three solvents. The width and center frequency of the carbonyl stretch for each adduct are compared to its vibrational lifetime in binary mixtures of benzene-d6 with either benzyl alcohol or chloroform. In neat solvents, the trends in line width, frequency, and vibrational lifetime are consistent for the two adducts, but complex relationships emerge when the trends in each property are compared as a function of mixed solvent composition. ν(CO) is more sensitive to the solvation environment around the trans ligand, whereas the line width and lifetime depend on the environment around the CO group itself. The carbonyl frequency and width vary nonlinearly across the two binary solvent series, indicating preferential solvation. In contrast, the vibrational lifetime changes linearly with solvent composition and is correlated with the mole fraction of chloroform but anticorrelated with the mole fraction of benzyl alcohol. The results are explained by differences in the densities of solvent modes that affect intermolecular relaxation of the carbonyl mode.

Enhanced vibrational solvatochromism and spectral diffusion by electron rich substituents on small molecule silanes

“…All of the 2D-IR spectra were analyzed using the centerline slope (CLS) method and then iteratively fit with the linear line shape to obtain the frequency-frequency correlation function (FFCF) as a homogeneous term plus a sum of exponentials: 48,49 IR pumpprobe spectroscopy was carried out with the pump and probe beams polarized at the magic angle to remove contributions from orientational relaxation, 50 as described previously. 51 The data were fit from 1 to 75 ps to determine the population relaxation times (lifetime, T 1 ) for the v = 0-1 and 1-2 transitions. The vibrational relaxation times for these two transitions were consistently the same within errors, and the 0-1 values were used in data analyses.…”

2D-IR Spectroscopy of Porous Silica Nanoparticles: Measuring the Distance Sensitivity of Spectral Diffusion

“…IR pump probe spectroscopy was performed using the same laser system as the 2D-IR measurements above. 13 Approximately 0.3% of the full IR laser power was split from the parent beam with the uncoated surface of a ZnSe window followed by a reflection from the uncoated face of a 3° CaF 2 wedge. This beam was used as the probe beam while the remaining stronger beam was used as the pump.…”

Measuring Dopant-Modulated Vibrational Energy Transfer over the Surface of Silicon Nanoparticles by 2D-IR Spectroscopy

“…In these spectra, the excitation axis (ω 1 ) was achieved by scanning a time delay between pulses 1 and 2, τ, in increments of 5 fs and subsequent Fourier transformation. The emission axis (ω 3 ) was obtained by optical Fourier transform of the heterodyne detected vibrational echo signal. , All eight frames in Figure have a region in the top left corner that has been magnified by a factor of 5 to make the features more apparent. At a relatively short waiting time of T w = 1 ps, the off-diagonal region connecting the mono and polyhydride stretches has a small amplitude for the intrinsic SiNP sample but is nearly featureless for the doped samples.…”

“…The 2D-IR instrument has been described previously. , Mid-IR pulses (3 μJ/pulse, 1 kHz repetition rate, 90 fs duration fwhm, ≈200 cm –1 bandwidth fwhm) were tuned to the silicon hydride stretching region (∼2100 cm –1 ), divided into three ∼1 μJ p-polarized pulses, and focused on the sample in a BOXCARS geometry . The generated vibrational echo signal was coaligned with a local oscillator reference pulse (0.3–0.5 nJ per pulse), spectrally resolved in a 0.32 m monochromator with a 75 line/mm grating, and detected with a liquid N 2 cooled 64-element mercury cadmium telluride (MCT) linear array detector (Infrared Associates, Inc.).…”