1 3
Topics in Current Chemistry (2018) 376:28
Finally, the last two contributions deal with two aspects of 2D electronic spectroscopy. The contribution titled “Electronic Couplings in (Bio-) Chemical Processes” by Maiuri and Brazard presents the experimental aspect of 2D electronic
spectroscopy techniques and the role of these techniques to elucidate ground-state
heterogeneity, excitation energy transfer mechanisms, photo-induced coherent oscillations associated with couplings. This experimental approach is extended by the
theoretical contribution “Towards Accurate Simulations of Two-Dimensional Electronic Spectroscopy” by Segarra-Martì et al. It details how 2D spectroscopy can be
used to characterize the ground-state conformational state of small biological relevant molecules by tracking inter-chromophoric electronic couplings.
7 Conclusions and Outlook
Although the development of techniques, tools, and methods of multidimensional
time-resolved spectroscopy have come a long way in the last two decades, researchers have still not managed to establish them as routine spectroscopy tools for chemical analytics. Commercial off-the-shelf setups like those commonly found for transient absorption are currently only available for some 2D infrared and electronic
spectroscopy methods from only a handful of companies, while other multidimensional time-resolved spectroscopy methods still use highly specialized optical setups
and require skilled users to operate them.
Several of the required technologies that allow multidimensional time-resolved
spectroscopy methods to be established as routine spectroscopy tools are already
available and have been demonstrated, as discussed above. Fast and easy data acquisition via spatial light modulators, for example, is in this regard an enabling technology, which has the capacity to generate giant leaps in performance and user-friendliness. Other required technologies are still not completely and routinely available for
a very broad spectral range from the THz to the UV region, like the turn-key generation, manipulation and characterization of ultrashort, spectrally broadband and tunable pulses, and will perhaps still remain in this status for some time to be restricted
to specialized optical labs.
Another point that has prevented the widespread distribution of ultrafast multidimensional spectroscopy in chemistry-related disciplines is strongly connected to
the detailed interpretation of the data. It has become clear from a variety of reports,
that very often there does not exist a single, unambiguous, and “smoking-gun” interpretation of the signals. In contrast, the vast range of possible contributing molecular dynamics, pathways, as well as possible intermolecular interactions introduce
a considerable complexity to the signals and requires sophisticated data treatment,
separation of various contributions by multidimensional fitting, model simulations
with molecular dynamics based on different force fields and parameters, or often
even theory support from high-level and costly quantum chemistry protocols. These
points make clear that an accurate interpretation of the signals generally requires
detailed theoretical knowledge already by the experimentalists themselves, along
with long experience in the different fields of experimental and theoretical ultrafast spectroscopy. As this fact is no technical issue, it will ultimately persist as
15
Reprinted from the journal
Topics in Current Chemistry (2018) 376:28
Finally, the last two contributions deal with two aspects of 2D electronic spectroscopy. The contribution titled “Electronic Couplings in (Bio-) Chemical Processes” by Maiuri and Brazard presents the experimental aspect of 2D electronic
spectroscopy techniques and the role of these techniques to elucidate ground-state
heterogeneity, excitation energy transfer mechanisms, photo-induced coherent oscillations associated with couplings. This experimental approach is extended by the
theoretical contribution “Towards Accurate Simulations of Two-Dimensional Electronic Spectroscopy” by Segarra-Martì et al. It details how 2D spectroscopy can be
used to characterize the ground-state conformational state of small biological relevant molecules by tracking inter-chromophoric electronic couplings.
7 Conclusions and Outlook
Although the development of techniques, tools, and methods of multidimensional
time-resolved spectroscopy have come a long way in the last two decades, researchers have still not managed to establish them as routine spectroscopy tools for chemical analytics. Commercial off-the-shelf setups like those commonly found for transient absorption are currently only available for some 2D infrared and electronic
spectroscopy methods from only a handful of companies, while other multidimensional time-resolved spectroscopy methods still use highly specialized optical setups
and require skilled users to operate them.
Several of the required technologies that allow multidimensional time-resolved
spectroscopy methods to be established as routine spectroscopy tools are already
available and have been demonstrated, as discussed above. Fast and easy data acquisition via spatial light modulators, for example, is in this regard an enabling technology, which has the capacity to generate giant leaps in performance and user-friendliness. Other required technologies are still not completely and routinely available for
a very broad spectral range from the THz to the UV region, like the turn-key generation, manipulation and characterization of ultrashort, spectrally broadband and tunable pulses, and will perhaps still remain in this status for some time to be restricted
to specialized optical labs.
Another point that has prevented the widespread distribution of ultrafast multidimensional spectroscopy in chemistry-related disciplines is strongly connected to
the detailed interpretation of the data. It has become clear from a variety of reports,
that very often there does not exist a single, unambiguous, and “smoking-gun” interpretation of the signals. In contrast, the vast range of possible contributing molecular dynamics, pathways, as well as possible intermolecular interactions introduce
a considerable complexity to the signals and requires sophisticated data treatment,
separation of various contributions by multidimensional fitting, model simulations
with molecular dynamics based on different force fields and parameters, or often
even theory support from high-level and costly quantum chemistry protocols. These
points make clear that an accurate interpretation of the signals generally requires
detailed theoretical knowledge already by the experimentalists themselves, along
with long experience in the different fields of experimental and theoretical ultrafast spectroscopy. As this fact is no technical issue, it will ultimately persist as
15
Reprinted from the journal