1 3
Top Curr Chem (Z) (2018) 376:24
peaks (with the opposite sign relative to diagonal peaks) due to excited-state
absorptions (ESAs) to the high-lying states. For t 2 > 0, the s dynamics shape the
2DES spectra, with SE and ESA peaks exhibiting at short waiting times, fluctuations along Ω probe , an indirect probe of the coherent vibrational dynamics along
the photoactive state, and at longer waiting times, Stoke shifts associated with
internal energy redistribution and dissipation in the environment, as well as intensity decay, a function of the finite excited-state lifetimes. For additional details on
2DES experimental techniques and map features, we recommend the review by
Maiuri and Brazard in this series [33].
2.1 2DES in the Ultraviolet: A New Light in Photobiology
The emergence of novel UV pulse technologies [14] has enabled the use of pump
and/or probe laser pulses in the UV window. These efforts may have a particular
impact in monitoring biologically relevant processes [34]. Indeed, cyclic aromatic
groups are often the UV-active chromophores that play a major role in photoinduced
events in biological systems [35]. UV light, in fact, is absorbed by an incredibly
large portion of biomolecules, ranging from proteins to nucleic acids. As shown in
Fig. 2, adsorption by both protein and nucleic acid backbones occurs exclusively at
high energies, i.e. above ca. 5 eV (i.e. at wavelengths below ca. 250 nm). Aromatic
rings in proteins and DNA/RNA, including tryptophan (Trp), phenylalanine (Phe),
tyrosine (Tyr) and histidine (His) amino acid side chains and adenine (Ade), guanine (Gua), cytosine (Cyt), thymine (Thy) and uracil (Ura) nucleobases, feature their
most intense absorptions in the same spectral window as their backbones. However, all these aromatic units (except histidine) have distinctive absorption bands
associated with π → π* transitions at lower energies (i.e. around 4.4–5.0 eV, ca.
250–280 nm), thus providing a UV range where their excitations are clearly separated from those of the backbone. Notably, when considering even lower transition
energies in the NUV range around 300–400 nm (i.e. 3.1–4.1 eV), quite important
UV-active biomolecules are found, including essential cofactors such as plastoquinones, flavins and reduced nicotinamide adenine dinucleotide (NADH), to name a
few. This evidence suggests that the low-energy UV window represents a promising
option for monitoring many photoinduced biological phenomena involving aromatic
units in proteins or DNA/RNA and eventually coenzymes.
Thus, since 2DES experiments may provide unique information on electronic coupling and related electron/energy transfer processes (see Sect. 1.1), applications of this
nonlinear spectroscopic technique in the UV range could shed new light on a vast number of biological processes, from various enzymatic redox catalysis to photosynthesis,
and could be used either to obtain structural information (in the GS) or to track photoinduced excited-state events. Notably, given its high spectral and temporal resolution,
2DUV spectroscopy can be used to disentangle complex decay processes such as in
DNA/RNA polynucleotides, where multiple chromophores exhibit various competitive
deactivation pathways, with timescales from sub-100 fs to nanoseconds. In this context,
developing computational protocols for accurate simulation of 2DUV spectroscopy is
67
Reprinted from the journal
Top Curr Chem (Z) (2018) 376:24
peaks (with the opposite sign relative to diagonal peaks) due to excited-state
absorptions (ESAs) to the high-lying states. For t 2 > 0, the s dynamics shape the
2DES spectra, with SE and ESA peaks exhibiting at short waiting times, fluctuations along Ω probe , an indirect probe of the coherent vibrational dynamics along
the photoactive state, and at longer waiting times, Stoke shifts associated with
internal energy redistribution and dissipation in the environment, as well as intensity decay, a function of the finite excited-state lifetimes. For additional details on
2DES experimental techniques and map features, we recommend the review by
Maiuri and Brazard in this series [33].
2.1 2DES in the Ultraviolet: A New Light in Photobiology
The emergence of novel UV pulse technologies [14] has enabled the use of pump
and/or probe laser pulses in the UV window. These efforts may have a particular
impact in monitoring biologically relevant processes [34]. Indeed, cyclic aromatic
groups are often the UV-active chromophores that play a major role in photoinduced
events in biological systems [35]. UV light, in fact, is absorbed by an incredibly
large portion of biomolecules, ranging from proteins to nucleic acids. As shown in
Fig. 2, adsorption by both protein and nucleic acid backbones occurs exclusively at
high energies, i.e. above ca. 5 eV (i.e. at wavelengths below ca. 250 nm). Aromatic
rings in proteins and DNA/RNA, including tryptophan (Trp), phenylalanine (Phe),
tyrosine (Tyr) and histidine (His) amino acid side chains and adenine (Ade), guanine (Gua), cytosine (Cyt), thymine (Thy) and uracil (Ura) nucleobases, feature their
most intense absorptions in the same spectral window as their backbones. However, all these aromatic units (except histidine) have distinctive absorption bands
associated with π → π* transitions at lower energies (i.e. around 4.4–5.0 eV, ca.
250–280 nm), thus providing a UV range where their excitations are clearly separated from those of the backbone. Notably, when considering even lower transition
energies in the NUV range around 300–400 nm (i.e. 3.1–4.1 eV), quite important
UV-active biomolecules are found, including essential cofactors such as plastoquinones, flavins and reduced nicotinamide adenine dinucleotide (NADH), to name a
few. This evidence suggests that the low-energy UV window represents a promising
option for monitoring many photoinduced biological phenomena involving aromatic
units in proteins or DNA/RNA and eventually coenzymes.
Thus, since 2DES experiments may provide unique information on electronic coupling and related electron/energy transfer processes (see Sect. 1.1), applications of this
nonlinear spectroscopic technique in the UV range could shed new light on a vast number of biological processes, from various enzymatic redox catalysis to photosynthesis,
and could be used either to obtain structural information (in the GS) or to track photoinduced excited-state events. Notably, given its high spectral and temporal resolution,
2DUV spectroscopy can be used to disentangle complex decay processes such as in
DNA/RNA polynucleotides, where multiple chromophores exhibit various competitive
deactivation pathways, with timescales from sub-100 fs to nanoseconds. In this context,
developing computational protocols for accurate simulation of 2DUV spectroscopy is
67
Reprinted from the journal