Surface-enhanced, multi-dimensional attenuated total reflectance spectroscopy

Abstract

Ultrafast two-dimensional infrared spectroscopy (2D IR) spectroscopy is performed in attenuated total reflectance (ATR) geometry with the Kretschmann configuration in order to measure femtosecond to picosecond dynamics of selfassembled monolayers on gold-coated solid-liquid interfaces. In the monolayers low-absorbing (<200 M-1 cm-1) nitrile functional groups are used as local vibrational probes to monitor vibrational relaxation and spectral diffusion in dependence of different environments of the nitrile group. By comparing spectral diffusion dynamics of the vibrational probe in bulk solution and in the monolayer we find that the dynamics are slowed down by more than a factor of 20 upon immobilization of the sample. Moreover, spectral diffusion dynamics are affected by the local environment within the monolayers as evidenced by 2D ATR IR experiments on mixed monolayers with different aliphatic and aromatic coadsorbates. The results are interpreted in terms of absent excitation energy-transfer as well as solvation dynamics around the nitrile vibrational probe. Our results demonstrate that 2D ATR IR spectroscopy offers the possibility to obtain ultrafast dynamics from sub-monolayer coverages of even low-absorbing vibrational probes such as nitrile functional groups. ABSTRACTUltrafast two-dimensional infrared spectroscopy (2D IR) spectroscopy is performed in attenuated total reflectance (ATR) geometry with the Kretschmann configuration in order to measure femtosecond to picosecond dynamics of selfassembled monolayers on gold-coated solid-liquid interfaces. In the monolayers low-absorbing (<200 M -1 cm -1 ) nitrile functional groups are used as local vibrational probes to monitor vibrational relaxation and spectral diffusion in dependence of different environments of the nitrile group. By comparing spectral diffusion dynamics of the vibrational probe in bulk solution and in the monolayer we find that the dynamics are slowed down by more than a factor of 20 upon immobilization of the sample. Moreover, spectral diffusion dynamics are affected by the local environment within the monolayers as evidenced by 2D ATR IR experiments on mixed monolayers with different aliphatic and aromatic coadsorbates. The results are interpreted in terms of absent excitation energy-transfer as well as solvation dynamics around the nitrile vibrational probe. Our results demonstrate that 2D ATR IR spectroscopy offers the possibility to obtain ultrafast dynamics from sub-monolayer coverages of even low-absorbing vibrational probes such as nitrile functional groups.

Molecule-specific interactions of diatomic adsorbates at metal-liquid interfaces

“…We furthermore investigated the vibrational dynamics of CO in dependence of surface coverage. Due to the fast and strong adsorption of CO on Pt, surface dilution required to first immerse the Pt-coated ATR prisms in a dilute (1 mM, ethanol) solution of benzenethiol for 1 h followed by a subsequent incubation with a 12 C 16 O/ 13 C 18 O containing solution 30 . The adsorption of the benzenethiol on Pt blocks surface adsorption sites and therefore results in a larger average distance between CO molecules.…”

Ultrafast Vibrational Energy Transfer in Catalytic Monolayers at Solid–Liquid Interfaces

“…[24][25][26] Under these circumstances, immobilization of the sample at the interface allows obtaining surface-sensitive signals from solid-liquid interfaces. With this approach, we have recently investigated the ultrafast vibrational dynamics of surface-bound carbon monoxide 17,27 and cyanide 28 as well as self-assembled organic monolayers under various conditions 18,19,29,30 . Figure 1.…”

“…20 Since we however do not observe any direct cross peak, we assume that Eq. 3 overestimates the coupling, which is counter-balanced by the fact that cross-relaxation can proceed to more than one coupling partner on the surface (the model Despite significant efforts reported in literature 30,[47][48][49] , intermolecular couplings of surface-bound molecules have only rarely been observed 38 , and the estimates given above help to understand why that is so. In the present case, we can observe cross peaks with good signal-to-noise ratio, but this is since we have the very strong transition dipole of the symmetric stretch vibration of a metal-carbonyl together with (presumably) a close to optimal packing on the surface.…”

Plasmonic Substrates Do Not Promote Vibrational Energy Transfer at Solid–Liquid Interfaces

“…Specifically, we use 2D ATR IR spectroscopy, which has been introduced recently as a new and very flexible technique for surface vibrational characterization of adsorbates in different environments. [35][36][37] The information content in 2D ATR IR spectra is analogous to that of "classic" 2D IR spectroscopy in transmission geometry 33,34 , but rather exploits evanescent waves at the interface of an ATR element to excite and probe the sample.…”