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Top Curr Chem (Z) (2018) 376:10
[85–87] or photocurrent [65, 88] detection schemes. 2DES technique has been also
implemented in the ultraviolet spectral range [89] or adding external perturbations
such as an electric field (2DES Stark [90]). Moreover, some attempts have been
made to study the coherent effects observed in 2DES experiment using incoherent
light as excitation source [91–94].
7.1 2DES‑UV
2DES was successfully implemented in the deep-UV region in the collinear [95] and
non-collinear [89] geometry. Those developments were not possible until recently,
because the control of the dispersion of UV pulses and the stability of their phase
(stability of 2–3 nm) are more challenging in UV.
Various biological samples absorbed in UV, especially DNA or proteins. For
instance, it is well known that the photodeactivation of DNA nucleobases is faster
than the one of DNA polynucleotides [96, 97]. However, the nature of this fast photodeactivation remains controversial: the most accepted explanation is an ultrafast
deactivation through a conical intersection between the excited state and ground
state potential energy surfaces [98]. 2DES-UV experiments clearly show that the
deactivation pathway is universal for all the nucleobases and is a two-step mechanism: the initial bright state ππ* is depopulated to a dark state nπ* and then to the
ground state through two conical intersections [89].
Biological applications will benefit from this new development. Indeed, all the
advantages of 2DES can be retrieved in UV region: heterogeneity, excitation energy
transfer, coherent oscillation, and photoreactivity.
7.2 Incoherent 2DES
The large majority of 2DES experiments involved the use of coherent femtosecond
pulses. Recently, some attempts have been made to perform 2DES using quasi-incoherent light—I
(4)
2DES, where I
(4)
refers to four incoherent excitation fields. Incoherent excitation light combined with time-domain interferometry can produce a
strong four-wave mixing signal in the phase-matched direction and this signal can be
resolved in phase and amplitude using a local oscillator field. The light used in this
series of experiments is referred to as noisy light, and can be continuous light, but
often is constituted by pulses on the order of hundreds of nanoseconds, still “continuous” with respect to the femto-to-picosecond dynamics. Moreover, the coherent
oscillations can be measured and then Fourier transformed to produce 2DES maps.
The 2DES maps measured with this technique have similar information as conventional 2DES maps [91–94].
7.3 2DES Stark
Recently, a new method combining 2DES and Stark spectroscopy has been proposed and implemented successfully [90]. This method has the main advantages of
distinguishing kinetic processes as energy and charge transfer, which is difficult in
55
Reprinted from the journal
Top Curr Chem (Z) (2018) 376:10
[85–87] or photocurrent [65, 88] detection schemes. 2DES technique has been also
implemented in the ultraviolet spectral range [89] or adding external perturbations
such as an electric field (2DES Stark [90]). Moreover, some attempts have been
made to study the coherent effects observed in 2DES experiment using incoherent
light as excitation source [91–94].
7.1 2DES‑UV
2DES was successfully implemented in the deep-UV region in the collinear [95] and
non-collinear [89] geometry. Those developments were not possible until recently,
because the control of the dispersion of UV pulses and the stability of their phase
(stability of 2–3 nm) are more challenging in UV.
Various biological samples absorbed in UV, especially DNA or proteins. For
instance, it is well known that the photodeactivation of DNA nucleobases is faster
than the one of DNA polynucleotides [96, 97]. However, the nature of this fast photodeactivation remains controversial: the most accepted explanation is an ultrafast
deactivation through a conical intersection between the excited state and ground
state potential energy surfaces [98]. 2DES-UV experiments clearly show that the
deactivation pathway is universal for all the nucleobases and is a two-step mechanism: the initial bright state ππ* is depopulated to a dark state nπ* and then to the
ground state through two conical intersections [89].
Biological applications will benefit from this new development. Indeed, all the
advantages of 2DES can be retrieved in UV region: heterogeneity, excitation energy
transfer, coherent oscillation, and photoreactivity.
7.2 Incoherent 2DES
The large majority of 2DES experiments involved the use of coherent femtosecond
pulses. Recently, some attempts have been made to perform 2DES using quasi-incoherent light—I
(4)
2DES, where I
(4)
refers to four incoherent excitation fields. Incoherent excitation light combined with time-domain interferometry can produce a
strong four-wave mixing signal in the phase-matched direction and this signal can be
resolved in phase and amplitude using a local oscillator field. The light used in this
series of experiments is referred to as noisy light, and can be continuous light, but
often is constituted by pulses on the order of hundreds of nanoseconds, still “continuous” with respect to the femto-to-picosecond dynamics. Moreover, the coherent
oscillations can be measured and then Fourier transformed to produce 2DES maps.
The 2DES maps measured with this technique have similar information as conventional 2DES maps [91–94].
7.3 2DES Stark
Recently, a new method combining 2DES and Stark spectroscopy has been proposed and implemented successfully [90]. This method has the main advantages of
distinguishing kinetic processes as energy and charge transfer, which is difficult in
55
Reprinted from the journal