Fig. 17b and c. An additional important feature of nonlinear spectroscopy in
combination with microscopy is the dependence of the signals strength on the fourth
power of the transition dipole moment (Sect. 2) [10]. This enhances the contrast in
the images over comparable data from FT IR microscopes due to the squaredependence of the stationary signal in the latter case [59, 60]. Although up to now
no temporal resolution has been demonstrated in combination with imaging, such
experiments will be very useful in biological applications, tissue analysis, or for
studying chemical exchange and energy transfer in heterogeneous systems, as well
as combinations with transient 2D IR spectroscopy methods (see Sect. 4.4).
4.3 3D IR Spectroscopy
2D IR spectroscopy has been incredibly valuable in characterizing inter- and
intramolecular dynamics of high-frequency vibrational modes from molecules in
liquids and in different other environments. However, there exist a couple of
important aspects and situations, which cannot easily be probed via third-order
nonlinear spectroscopy. These cases thus require higher-order methods, such as socalled 3D IR spectroscopy and transient 2D IR spectroscopy, and these are
considered in this and the upcoming section.
We start with considering the 3D IR technique as an extension of 2D IR
spectroscopy. Although any type of time-resolved spectroscopy that involves
multiple combinations of temporal and frequency axes ([ 2) can be considered as at
least ‘‘three-dimensional’’ [185], it is important to classify what exactly is meant by
3D IR spectroscopy in the context discussed here. Conventional 3D IR spectroscopy
is thought of as being limited to only those cases where the sample evolves in
coherent states during at least three time-variables (t 1/3/5 ) that are distributed
between five excitation and detection fields in combination with a local oscillator
field (Fig. 18a) [232]. Time-variables t 2/4 are then responsible for the dynamics of
for instance population and inter-state coherence relaxation of the sample. In
contrast to other methods, which can in principle be used to report partly similar
information (e.g. 2D Raman spectroscopy [233–236]), 3D IR involves only fully
resonant interactions in the electronic ground state potential of the sample molecule.
Just as 2D IR spectroscopy has been introduced as a pump-probe experiment with
frequency-resolved pump and probe pulses, 3D IR spectroscopy has been proposed
as a ‘‘hole-burning experiment with 2D IR detection’’, for which pump-frequency
dependent lineshape dynamics such as spectral diffusion or chemical exchange,
energy transfer and couplings can be investigated [232, 237]. Considering the five
contributing excitation and detection fields, a much larger set of energy level
diagrams as for 2D IR spectroscopy can be expected to take part in the signal
generation process [10, 62]. Figure 18b–d gives only a few examples, which are
relevant in a three-level system that is generally considered for ground state bleach
and excited state absorption pathways. Figure 18b shows a contribution that is an
extension of the ground state bleach signal from third-order 2D IR spectroscopy and
an analogous diagram can be drawn for stimulated emission (not shown explicitly)
[238, 239]. In contrast, Fig. 18c and d shows contributions that involve also excited
state absorption transitions (1–2) and measure dynamics of higher-lying vibrational
Top Curr Chem (Z) (2017) 375:86
123
159
Reprinted from the journal
combination with microscopy is the dependence of the signals strength on the fourth
power of the transition dipole moment (Sect. 2) [10]. This enhances the contrast in
the images over comparable data from FT IR microscopes due to the squaredependence of the stationary signal in the latter case [59, 60]. Although up to now
no temporal resolution has been demonstrated in combination with imaging, such
experiments will be very useful in biological applications, tissue analysis, or for
studying chemical exchange and energy transfer in heterogeneous systems, as well
as combinations with transient 2D IR spectroscopy methods (see Sect. 4.4).
4.3 3D IR Spectroscopy
2D IR spectroscopy has been incredibly valuable in characterizing inter- and
intramolecular dynamics of high-frequency vibrational modes from molecules in
liquids and in different other environments. However, there exist a couple of
important aspects and situations, which cannot easily be probed via third-order
nonlinear spectroscopy. These cases thus require higher-order methods, such as socalled 3D IR spectroscopy and transient 2D IR spectroscopy, and these are
considered in this and the upcoming section.
We start with considering the 3D IR technique as an extension of 2D IR
spectroscopy. Although any type of time-resolved spectroscopy that involves
multiple combinations of temporal and frequency axes ([ 2) can be considered as at
least ‘‘three-dimensional’’ [185], it is important to classify what exactly is meant by
3D IR spectroscopy in the context discussed here. Conventional 3D IR spectroscopy
is thought of as being limited to only those cases where the sample evolves in
coherent states during at least three time-variables (t 1/3/5 ) that are distributed
between five excitation and detection fields in combination with a local oscillator
field (Fig. 18a) [232]. Time-variables t 2/4 are then responsible for the dynamics of
for instance population and inter-state coherence relaxation of the sample. In
contrast to other methods, which can in principle be used to report partly similar
information (e.g. 2D Raman spectroscopy [233–236]), 3D IR involves only fully
resonant interactions in the electronic ground state potential of the sample molecule.
Just as 2D IR spectroscopy has been introduced as a pump-probe experiment with
frequency-resolved pump and probe pulses, 3D IR spectroscopy has been proposed
as a ‘‘hole-burning experiment with 2D IR detection’’, for which pump-frequency
dependent lineshape dynamics such as spectral diffusion or chemical exchange,
energy transfer and couplings can be investigated [232, 237]. Considering the five
contributing excitation and detection fields, a much larger set of energy level
diagrams as for 2D IR spectroscopy can be expected to take part in the signal
generation process [10, 62]. Figure 18b–d gives only a few examples, which are
relevant in a three-level system that is generally considered for ground state bleach
and excited state absorption pathways. Figure 18b shows a contribution that is an
extension of the ground state bleach signal from third-order 2D IR spectroscopy and
an analogous diagram can be drawn for stimulated emission (not shown explicitly)
[238, 239]. In contrast, Fig. 18c and d shows contributions that involve also excited
state absorption transitions (1–2) and measure dynamics of higher-lying vibrational
Top Curr Chem (Z) (2017) 375:86
123
159
Reprinted from the journal