electronic ground state of a sample (coherent control) [334–339]. The large amount
of vibrational energy that can be deposited in the molecules via vibrational ladderclimbing can be used to overcome energy barriers for isomerization reactions of
chemical bonds, or controlled molecular fragmentation [314, 340]. Combinations of
plasmonic substrates with pulse-shaping techniques in the mid-IR range [341–345]
may further allow the concentration of populations in certain vibrational states
[42, 323]. Based on the drastically enhanced near-fields coherent control may
therefore be applicable to samples other than strongly absorbing metal carbonyl
compounds, thus drastically expanding the applicability of the method.
In the existing initial reports of surface-enhanced 2D IR spectroscopy, fairly
simple samples have been applied such as model molecular monolayers
[179, 181, 243] or nanometer thin polymer films [311]. The currently obtainable
enhancement factors may possibly already now allow ultrafast investigations of
large biological molecules such as proteins [307, 346]. Possible applications for the
increased sensitivity in 2D IR spectroscopy might involve its combinations with
bio-sensing and diagnostics [347–350], or molecular recognition [351–355]. This
would be an important development since 2D IR spectroscopy is intrinsically
sensitive to intermolecular interactions, which form the basis of the mentioned
applications. The developed methods might therefore allow the characterization of
the dynamics of recognition, a characterization of binding strengths, or the
identification of impurities.
In addition to aspects concerning the range of possible samples to be addressed
by ultra-sensitive surface 2D IR spectroscopy, there exists currently a large interest
and technical development in surface-enhanced laser spectroscopy [348, 356–361].
Major developments in this field focus on the substrate properties such as type of
materials, shapes and physical/chemical aspects. The expectation is that possibly
even higher enhancement factors and increased sensitivity of the methods will be
achievable in future studies with purposely engineered plasmonic materials
[358, 362, 363], metamaterials [357, 364], or even graphene as a substrate [356].
The combination of ultrafast spectroscopy methods and optical near-fields is thus
likely to allow unprecedented chemical information from only minimal amounts of
samples.
5.3 Ultrahigh Resolution Spectroscopy: 2D IR Nanoscopy
Conventional optics restrict the achievable spatial resolution for the purpose of
microscopy to at least several micrometers in the mid-IR spectral range [365, 366].
These dimensions are very large compared to the spatial extensions of molecules
and even many nanostructures that exist in blended mixtures of polymers,
mesoporous samples, self-assembled monolayers, heterogeneous catalyst assemblies or other functional materials based on organic electronics. With the currently
available focus diameters, conventional 2D IR spectroscopy or microscopy will,
therefore, yield information from a spatially averaged region in a possibly
nanostructured sample, thus blurring important details on length scales that are
much smaller than the wavelength of IR light. It is widely known that the spatial
resolution can be well extended to dimensions much smaller than the diffraction
Top Curr Chem (Z) (2017) 375:86
123
184
Reprinted from the journal
of vibrational energy that can be deposited in the molecules via vibrational ladderclimbing can be used to overcome energy barriers for isomerization reactions of
chemical bonds, or controlled molecular fragmentation [314, 340]. Combinations of
plasmonic substrates with pulse-shaping techniques in the mid-IR range [341–345]
may further allow the concentration of populations in certain vibrational states
[42, 323]. Based on the drastically enhanced near-fields coherent control may
therefore be applicable to samples other than strongly absorbing metal carbonyl
compounds, thus drastically expanding the applicability of the method.
In the existing initial reports of surface-enhanced 2D IR spectroscopy, fairly
simple samples have been applied such as model molecular monolayers
[179, 181, 243] or nanometer thin polymer films [311]. The currently obtainable
enhancement factors may possibly already now allow ultrafast investigations of
large biological molecules such as proteins [307, 346]. Possible applications for the
increased sensitivity in 2D IR spectroscopy might involve its combinations with
bio-sensing and diagnostics [347–350], or molecular recognition [351–355]. This
would be an important development since 2D IR spectroscopy is intrinsically
sensitive to intermolecular interactions, which form the basis of the mentioned
applications. The developed methods might therefore allow the characterization of
the dynamics of recognition, a characterization of binding strengths, or the
identification of impurities.
In addition to aspects concerning the range of possible samples to be addressed
by ultra-sensitive surface 2D IR spectroscopy, there exists currently a large interest
and technical development in surface-enhanced laser spectroscopy [348, 356–361].
Major developments in this field focus on the substrate properties such as type of
materials, shapes and physical/chemical aspects. The expectation is that possibly
even higher enhancement factors and increased sensitivity of the methods will be
achievable in future studies with purposely engineered plasmonic materials
[358, 362, 363], metamaterials [357, 364], or even graphene as a substrate [356].
The combination of ultrafast spectroscopy methods and optical near-fields is thus
likely to allow unprecedented chemical information from only minimal amounts of
samples.
5.3 Ultrahigh Resolution Spectroscopy: 2D IR Nanoscopy
Conventional optics restrict the achievable spatial resolution for the purpose of
microscopy to at least several micrometers in the mid-IR spectral range [365, 366].
These dimensions are very large compared to the spatial extensions of molecules
and even many nanostructures that exist in blended mixtures of polymers,
mesoporous samples, self-assembled monolayers, heterogeneous catalyst assemblies or other functional materials based on organic electronics. With the currently
available focus diameters, conventional 2D IR spectroscopy or microscopy will,
therefore, yield information from a spatially averaged region in a possibly
nanostructured sample, thus blurring important details on length scales that are
much smaller than the wavelength of IR light. It is widely known that the spatial
resolution can be well extended to dimensions much smaller than the diffraction
Top Curr Chem (Z) (2017) 375:86
123
184
Reprinted from the journal