contributions remain. Additional temperature dependent measurements of the spectral
diffusion dynamics indicated that the structural fluctuations accelerate at elevated
temperatures and that portions of the lineshape become even motionally narrowed.
Finally, permanent structural rearrangements in the crystals by annealing was
demonstrated to be absent in basanite since repeated cycles of temperature-dependent
experiments yielded identical spectral diffusion for the different temperatures. These
experiments thus overall demonstrated that water molecules in such mineral structures
are not static, but sensitively respond to the three-dimensional arrangement of the
crystal constituents. The observed dynamic contributions may have a considerable
influence on the stability of three-dimensional structures also in other natural crystals.
Establishing a systematic understanding of the origin of structural fluctuations in
different naturally abundant minerals might furthermore allow establishing a firm
view of the thermodynamic as well as kinetic properties of these materials.
In a similar manner, 2D IR has already been used to study molecular dynamics in
other systems under three-dimensional confinement. Also, Fayer’s group investigated structural fluctuations of molecules in synthetic metal-organic frameworks
(MOFs) [215]. Of particular interest in these experiments were the structural
flexibility of the MOF itself, which is invoked as a key property for the several
aspects of functionality [217]. Attaching metal-carbonyl local probes to the
structural backbone of the MOF, it could be shown that structural fluctuations of the
framework are complex, bi-exponential and occur to large extents on timescales
longer than 0.5 ns, what is considerable slower as dynamics in isotropic
environments and even at surfaces and interfaces (Sect. 3.2.1) [15]. Importantly,
contrasting with an intuitive expectation, the dynamics become even slower
([ 2 ns) when the pores of the MOF are filled with solvent molecules. This was
attributed to significantly restricted dynamics of the solvent molecules in the pores,
as well as severe restrictions of the MOF to undergo structural deformations.
It is, however, important to note that structural fluctuations of molecules under
three-dimensional confinement do not always occur on the timescale of multiple
tens of picoseconds or longer. Organic cations in 3D lead-iodide perovskite crystals
are a good example of relatively fast molecular motions on timescales of a few
hundreds of femtoseconds to picoseconds, while slower dynamics are only of very
minor importance [212]. These structural fluctuations have been identified as
‘‘wobbling-in-a-cone’’, as well as jump-like reorientation of the organic molecules
in this type of material. It may be expected that such ultrafast orientational
dynamics can be of hallmark importance for the dielectric response of the sample
and, therefore, for opto-electronic properties of these novel materials.
4 Extensions of 2D IR Spectroscopy
Recent extensions of 2D IR spectroscopy involve detailed applications, as well as
technological advancements in the field of spectro-electrochemistry, microscopy,
the combination with electronic spectroscopy and efforts to merge electronic and
vibrational spectroscopy. In the following sections, highlights from these recent
Top Curr Chem (Z) (2017) 375:86
123
154
Reprinted from the journal
diffusion dynamics indicated that the structural fluctuations accelerate at elevated
temperatures and that portions of the lineshape become even motionally narrowed.
Finally, permanent structural rearrangements in the crystals by annealing was
demonstrated to be absent in basanite since repeated cycles of temperature-dependent
experiments yielded identical spectral diffusion for the different temperatures. These
experiments thus overall demonstrated that water molecules in such mineral structures
are not static, but sensitively respond to the three-dimensional arrangement of the
crystal constituents. The observed dynamic contributions may have a considerable
influence on the stability of three-dimensional structures also in other natural crystals.
Establishing a systematic understanding of the origin of structural fluctuations in
different naturally abundant minerals might furthermore allow establishing a firm
view of the thermodynamic as well as kinetic properties of these materials.
In a similar manner, 2D IR has already been used to study molecular dynamics in
other systems under three-dimensional confinement. Also, Fayer’s group investigated structural fluctuations of molecules in synthetic metal-organic frameworks
(MOFs) [215]. Of particular interest in these experiments were the structural
flexibility of the MOF itself, which is invoked as a key property for the several
aspects of functionality [217]. Attaching metal-carbonyl local probes to the
structural backbone of the MOF, it could be shown that structural fluctuations of the
framework are complex, bi-exponential and occur to large extents on timescales
longer than 0.5 ns, what is considerable slower as dynamics in isotropic
environments and even at surfaces and interfaces (Sect. 3.2.1) [15]. Importantly,
contrasting with an intuitive expectation, the dynamics become even slower
([ 2 ns) when the pores of the MOF are filled with solvent molecules. This was
attributed to significantly restricted dynamics of the solvent molecules in the pores,
as well as severe restrictions of the MOF to undergo structural deformations.
It is, however, important to note that structural fluctuations of molecules under
three-dimensional confinement do not always occur on the timescale of multiple
tens of picoseconds or longer. Organic cations in 3D lead-iodide perovskite crystals
are a good example of relatively fast molecular motions on timescales of a few
hundreds of femtoseconds to picoseconds, while slower dynamics are only of very
minor importance [212]. These structural fluctuations have been identified as
‘‘wobbling-in-a-cone’’, as well as jump-like reorientation of the organic molecules
in this type of material. It may be expected that such ultrafast orientational
dynamics can be of hallmark importance for the dielectric response of the sample
and, therefore, for opto-electronic properties of these novel materials.
4 Extensions of 2D IR Spectroscopy
Recent extensions of 2D IR spectroscopy involve detailed applications, as well as
technological advancements in the field of spectro-electrochemistry, microscopy,
the combination with electronic spectroscopy and efforts to merge electronic and
vibrational spectroscopy. In the following sections, highlights from these recent
Top Curr Chem (Z) (2017) 375:86
123
154
Reprinted from the journal