evoking a T-jump. This T-jump it thought to subsequently randomize the orientation
of the electrolyte molecules near the electrode, thereby establishing a nonequilibrium potential difference to which molecules at the electrode-electrolyte
interfaces can respond by re-orientation, or re-structuration of their coordinationsphere and solvation shell [391]. V-jump spectroscopy has already been applied to
study frequency shifts of adsorbate molecules at Pt electrodes [391, 392]. It was
demonstrated that the time-resolution can be in the range of tens to hundreds of
picoseconds. However, the magnitude of the demonstrated jumps is rather low
(\ 200 mV) [391, 392] and optimizations might be needed to study charge-transfer
phenomena. V-jump 2D IR spectroscopy would nevertheless still be extremely
useful for studying different orientational dynamics of molecules near electrodes.
Such dynamics are particularly relevant in the fields of heterogeneous catalysis, but
applications can also be envisioned regarding liquid-crystal displays, batteries and
organic electronics.
6 Concluding Remarks
2D IR spectroscopy in all its variants has seen a considerable broadening of possible
applications over the last approximately 20 years. In this overview, it was attempted
to present some of the highlights from recently presented examples that bear the
potential to bring 2D IR spectroscopy to the next level of applications. Currently, a
vast range of experiments is possible to be conducted, covering aspects from
equilibrated, as well as non-equilibrated ground state sample systems to rapidly
evolving systems such as molecules in excited electronic states and samples
subjected to other external perturbations such as temperature jumps. Starting from
the ‘‘classical’’ applications of 2D IR spectroscopy on bulk samples, for which the
elucidation of spectral diffusion, energy transfer, chemical exchange and vibrational
couplings in molecules can be considered as almost routine, many additional ways
have been found in recent years to obtain that type of information from molecules in
a range of different other environments. This includes molecules under three- and
two-dimensional confinement, partially even reaching a demonstrated sensitivity
that allows measuring sub-monolayer surfaces coverages from molecules with only
weakly absorbing IR-labels. Moreover, recent developments also achieved the
combination of ultrafast vibrational spectroscopy with microscopy and electrochemistry, the controlled realization of higher-order pulse sequences for 3D IR
spectroscopy, the application of ultra-broadband IR light sources to cover a
maximum spectral range of IR-active vibrations, or the application of plasmonic
substrates for surface-enhanced 2D IR spectroscopy. All these methods will allow in
future applications the resolution of molecular dynamics and interactions under a
variety of chemical and physical conditions with unprecedented accuracy and
sensitivity.
In addition to the already established developments, different extensions of 2D
IR spectroscopy have been devised or at least proposed, all of which will make the
application of the method even broader. The combination of 2D IR spectroscopy
with microfluidics has recently been realized. This method will allow tackling a
Top Curr Chem (Z) (2017) 375:86
123
187
Reprinted from the journal
of the electrolyte molecules near the electrode, thereby establishing a nonequilibrium potential difference to which molecules at the electrode-electrolyte
interfaces can respond by re-orientation, or re-structuration of their coordinationsphere and solvation shell [391]. V-jump spectroscopy has already been applied to
study frequency shifts of adsorbate molecules at Pt electrodes [391, 392]. It was
demonstrated that the time-resolution can be in the range of tens to hundreds of
picoseconds. However, the magnitude of the demonstrated jumps is rather low
(\ 200 mV) [391, 392] and optimizations might be needed to study charge-transfer
phenomena. V-jump 2D IR spectroscopy would nevertheless still be extremely
useful for studying different orientational dynamics of molecules near electrodes.
Such dynamics are particularly relevant in the fields of heterogeneous catalysis, but
applications can also be envisioned regarding liquid-crystal displays, batteries and
organic electronics.
6 Concluding Remarks
2D IR spectroscopy in all its variants has seen a considerable broadening of possible
applications over the last approximately 20 years. In this overview, it was attempted
to present some of the highlights from recently presented examples that bear the
potential to bring 2D IR spectroscopy to the next level of applications. Currently, a
vast range of experiments is possible to be conducted, covering aspects from
equilibrated, as well as non-equilibrated ground state sample systems to rapidly
evolving systems such as molecules in excited electronic states and samples
subjected to other external perturbations such as temperature jumps. Starting from
the ‘‘classical’’ applications of 2D IR spectroscopy on bulk samples, for which the
elucidation of spectral diffusion, energy transfer, chemical exchange and vibrational
couplings in molecules can be considered as almost routine, many additional ways
have been found in recent years to obtain that type of information from molecules in
a range of different other environments. This includes molecules under three- and
two-dimensional confinement, partially even reaching a demonstrated sensitivity
that allows measuring sub-monolayer surfaces coverages from molecules with only
weakly absorbing IR-labels. Moreover, recent developments also achieved the
combination of ultrafast vibrational spectroscopy with microscopy and electrochemistry, the controlled realization of higher-order pulse sequences for 3D IR
spectroscopy, the application of ultra-broadband IR light sources to cover a
maximum spectral range of IR-active vibrations, or the application of plasmonic
substrates for surface-enhanced 2D IR spectroscopy. All these methods will allow in
future applications the resolution of molecular dynamics and interactions under a
variety of chemical and physical conditions with unprecedented accuracy and
sensitivity.
In addition to the already established developments, different extensions of 2D
IR spectroscopy have been devised or at least proposed, all of which will make the
application of the method even broader. The combination of 2D IR spectroscopy
with microfluidics has recently been realized. This method will allow tackling a
Top Curr Chem (Z) (2017) 375:86
123
187
Reprinted from the journal