sources from the THz to the UV/VIS range (Fig. 1). Such an approach allows 2D IR
to be performed in a transient manner on non-equilibrium dynamics, which
significantly increases the temporal range of applicability by an initial light-induced
perturbation. Using such light-triggered changes in the sample conditions in
conjunction with synchronized laser systems thus bridges the gap between the
quasi-static and the ultrafast 2D IR experiments and allows measurements on
timescales over many orders of magnitude from femtoseconds to milliseconds and
beyond.
Taking everything together, it is thus not astonishing that 2D IR has been
developed to a point where it is considered as an advantageous method for
molecular structural characterization, and many examples exist in the literature,
where for instance secondary structure of proteins under fully solvated conditions
has been determined [1, 24, 30].
1.4 Scope of this Chapter
Numerous overviews about 2D IR spectroscopy have been presented over the last
approximately 18 years, each focusing either on selected aspects of the method,
providing a brief overview, or giving a detailed theoretical description of the
signals, as well as on technical aspects [10, 15, 17, 18, 30, 32–53]. In particular,
detailed theoretical descriptions of time-resolved spectroscopy in general, and
multi-dimensional optical spectroscopy in particular, are available elsewhere
[1, 10, 18, 48, 54, 55]. This chapter attempts to (i) give the non-specialist reader
a balanced summary of what is currently possible with 2D IR spectroscopy, (ii)
indicate areas where shortcomings impose significant challenges for the technique
to be applied and (iii) outline future research directions, which make the
applicability of 2D IR spectroscopy even broader. The text uses some examples
of ‘‘classic’’ 2D IR spectroscopy for ultrafast molecular structure determination, and
in large parts additionally presents most recently reported highlights, where the
method has been applied for addressing certain scientific questions, and to obtain
molecular information that is difficult or even impossible to retrieve otherwise.
Recent developments aim at making 2D IR spectroscopy available for analysis of
molecules at surfaces, applications to samples in confined environments, combinations with microscopy, as well as different types of combinations of vibrational
and electronic spectroscopy for the elucidation of non-equilibrium dynamics. From
the status of routinely performable experiments, a full series of groundbreaking
investigations can be envisioned, which will allow chemists, physicists and material
scientists to obtain unprecedented insight into molecular structure from different
perspectives. Some of these examples are indicated in the outlook of this chapter.
2 Essential Elements of 2D IR Spectroscopy
2D IR is a pump probe type of nonlinear spectroscopy, for which both the pump as
well as the probe pulse are spectrally resolved to generate frequency-frequency
correlation plots (Fig. 1) [16]. The signals are generated from a set of different
Top Curr Chem (Z) (2017) 375:86
123
119
Reprinted from the journal
to be performed in a transient manner on non-equilibrium dynamics, which
significantly increases the temporal range of applicability by an initial light-induced
perturbation. Using such light-triggered changes in the sample conditions in
conjunction with synchronized laser systems thus bridges the gap between the
quasi-static and the ultrafast 2D IR experiments and allows measurements on
timescales over many orders of magnitude from femtoseconds to milliseconds and
beyond.
Taking everything together, it is thus not astonishing that 2D IR has been
developed to a point where it is considered as an advantageous method for
molecular structural characterization, and many examples exist in the literature,
where for instance secondary structure of proteins under fully solvated conditions
has been determined [1, 24, 30].
1.4 Scope of this Chapter
Numerous overviews about 2D IR spectroscopy have been presented over the last
approximately 18 years, each focusing either on selected aspects of the method,
providing a brief overview, or giving a detailed theoretical description of the
signals, as well as on technical aspects [10, 15, 17, 18, 30, 32–53]. In particular,
detailed theoretical descriptions of time-resolved spectroscopy in general, and
multi-dimensional optical spectroscopy in particular, are available elsewhere
[1, 10, 18, 48, 54, 55]. This chapter attempts to (i) give the non-specialist reader
a balanced summary of what is currently possible with 2D IR spectroscopy, (ii)
indicate areas where shortcomings impose significant challenges for the technique
to be applied and (iii) outline future research directions, which make the
applicability of 2D IR spectroscopy even broader. The text uses some examples
of ‘‘classic’’ 2D IR spectroscopy for ultrafast molecular structure determination, and
in large parts additionally presents most recently reported highlights, where the
method has been applied for addressing certain scientific questions, and to obtain
molecular information that is difficult or even impossible to retrieve otherwise.
Recent developments aim at making 2D IR spectroscopy available for analysis of
molecules at surfaces, applications to samples in confined environments, combinations with microscopy, as well as different types of combinations of vibrational
and electronic spectroscopy for the elucidation of non-equilibrium dynamics. From
the status of routinely performable experiments, a full series of groundbreaking
investigations can be envisioned, which will allow chemists, physicists and material
scientists to obtain unprecedented insight into molecular structure from different
perspectives. Some of these examples are indicated in the outlook of this chapter.
2 Essential Elements of 2D IR Spectroscopy
2D IR is a pump probe type of nonlinear spectroscopy, for which both the pump as
well as the probe pulse are spectrally resolved to generate frequency-frequency
correlation plots (Fig. 1) [16]. The signals are generated from a set of different
Top Curr Chem (Z) (2017) 375:86
123
119
Reprinted from the journal