bath in both |gi and |ei. The sensitivity of the dynamics also to excited state
correlation dynamics originates from the involvement of the initial electronic
excitation in the 2D EV spectra. Assuming absent inhomogeneous broadening of the
sample a close analysis of the 2D EV spectra revealed that the coupling of the C=C
stretch mode is about 50% stronger in the excited state than in the ground state.
Such information is not easily available by other methods such as 2D IR or 2D ES
and 2D EV may, therefore, provide an advantageous and straight forward way of
measuring solvent-solute interactions in excited electronic states, as well as in
ground electronic states of more general systems as well.
Also, 2D EV spectroscopy should be viewed as a very young method, the
potential of which still needs to be evaluated. However, applications have already
been realized, which aim at addressing physical and chemical questions in large bioorganic molecules. Fleming et al. have investigated 2D EV signals of chlorophyll a
and b to distinguish different solvation states of the sample [281]. They found
differently coordinated magnesium ions that manifest themselves as distinct spectral
features in the 2D EV spectra. Additionally, the electronic excitation transfer
through light-harvesting complex II (LHC II) could recently be measured with 2D
EV spectroscopy for the first time precisely [284]. Using the distinct vibrational
bands of chlorophyll a and b, the energy transfer could be observed with high
chemical selectivity. A detailed analysis of the signals even made it possible to
reveal the underlying relaxation pathways. These results may in future help to
evaluate the quality of theoretical predictions for energy transfer pathways for such
complex light-harvesting systems. Also, carbonyl carotenoids have been investigated with the help of 2D EV spectroscopy [286]. Lineshape analyses were used to
make a precise assignment of the observable excited state vibrational signatures and
excluded excited state isomerization reactions in these molecules. Furthermore, the
authors were able to identify correlated electronic and vibrational lineshapes on
timescales longer than the lifetime of a particular excited state in the sample. The
observations were used to argue that the relaxation between different excited states
is impulsive and involves a conical interaction. Similar results have been obtained
by help of other 2D vibrational methods on closely related samples [287]. The so far
presented experiments have thus set the stage for more extensive applications of 2D
EV on larger samples as large as pigment-protein complexes.
5 Prospects for 2D IR Spectroscopy
As discussed above, there exists a large range of possible applications for 2D IR
spectroscopy to study ultrafast dynamics, chemical reactions, or intermolecular
interactions from samples in different environments. However, the general
applicability of IR spectroscopy as an analytical tool in chemistry, biology and
life sciences is much broacher and spans examples from industrial processes to
ultra-sensitive analytics. In the upcoming section a few examples are given, for
which 2D IR spectroscopy can be expected to yield a profound impact in the course
of the coming years of experimental developments and applications.
Top Curr Chem (Z) (2017) 375:86
123
179
Reprinted from the journal
correlation dynamics originates from the involvement of the initial electronic
excitation in the 2D EV spectra. Assuming absent inhomogeneous broadening of the
sample a close analysis of the 2D EV spectra revealed that the coupling of the C=C
stretch mode is about 50% stronger in the excited state than in the ground state.
Such information is not easily available by other methods such as 2D IR or 2D ES
and 2D EV may, therefore, provide an advantageous and straight forward way of
measuring solvent-solute interactions in excited electronic states, as well as in
ground electronic states of more general systems as well.
Also, 2D EV spectroscopy should be viewed as a very young method, the
potential of which still needs to be evaluated. However, applications have already
been realized, which aim at addressing physical and chemical questions in large bioorganic molecules. Fleming et al. have investigated 2D EV signals of chlorophyll a
and b to distinguish different solvation states of the sample [281]. They found
differently coordinated magnesium ions that manifest themselves as distinct spectral
features in the 2D EV spectra. Additionally, the electronic excitation transfer
through light-harvesting complex II (LHC II) could recently be measured with 2D
EV spectroscopy for the first time precisely [284]. Using the distinct vibrational
bands of chlorophyll a and b, the energy transfer could be observed with high
chemical selectivity. A detailed analysis of the signals even made it possible to
reveal the underlying relaxation pathways. These results may in future help to
evaluate the quality of theoretical predictions for energy transfer pathways for such
complex light-harvesting systems. Also, carbonyl carotenoids have been investigated with the help of 2D EV spectroscopy [286]. Lineshape analyses were used to
make a precise assignment of the observable excited state vibrational signatures and
excluded excited state isomerization reactions in these molecules. Furthermore, the
authors were able to identify correlated electronic and vibrational lineshapes on
timescales longer than the lifetime of a particular excited state in the sample. The
observations were used to argue that the relaxation between different excited states
is impulsive and involves a conical interaction. Similar results have been obtained
by help of other 2D vibrational methods on closely related samples [287]. The so far
presented experiments have thus set the stage for more extensive applications of 2D
EV on larger samples as large as pigment-protein complexes.
5 Prospects for 2D IR Spectroscopy
As discussed above, there exists a large range of possible applications for 2D IR
spectroscopy to study ultrafast dynamics, chemical reactions, or intermolecular
interactions from samples in different environments. However, the general
applicability of IR spectroscopy as an analytical tool in chemistry, biology and
life sciences is much broacher and spans examples from industrial processes to
ultra-sensitive analytics. In the upcoming section a few examples are given, for
which 2D IR spectroscopy can be expected to yield a profound impact in the course
of the coming years of experimental developments and applications.
Top Curr Chem (Z) (2017) 375:86
123
179
Reprinted from the journal