Top Curr Chem (Z) (2018) 376:24
1 3
we observe a remarkable agreement between the predicted 2DUV spectra of the pyrene
molecule and the experimental results. These results further led to theoretical studies
of the excited-state dynamics in a solvated dinucleoside system, showing that spectroscopic fingerprints of long-lived excited-state minima along the complex photoinduced
decay pathways of DNA/RNA model systems can be simulated at a reasonable computational cost. Our results exemplify the impact of accurate simulation of 2DES spectra
in revealing complex physicochemical properties of fundamental biological systems
and should trigger further theoretical developments as well as new experiments.
Keywords Nonlinear electronic spectroscopy · Theoretical simulations ·
Wavefunction methods · QM/MM computations · DNA/RNA nucleobases ·
Aromatic amino acids
1 Introduction
Two-dimensional (2D) optical spectroscopy based on multipulse laser sequences originated as an extension of the 2D nuclear magnetic resonance (2DNMR) technique [1]
to the optical regime [2]. 2DNMR had an impressive impact in several fields, with
first handover to the infrared (IR) regime (2DIR) now a well-established method often
employed in the characterization of the structure and dynamics of complex molecular systems by directly mapping their vibrational couplings [3]. Mapping of electronic
couplings by 2D electronic spectroscopy (2DES) [4] has become feasible thanks to
advances [5, 6] in ultrafast optical techniques that allow the targeting of electronic
transitions in the visible (Vis) range. 2DES in the Vis range (2DVis) has become
increasingly popular over the last decade, showcasing its great potential by deciphering energy transfer processes in photosynthesis [7–10]. The desirable extension to the
UV domain (2DUV), however, where many fundamental biomolecules display strong
absorption bands, has been slow thus far, impeded by technical difficulties associated
with the use of UV laser pulses [11]. Recent progress [12–18] in attaining interferometric phase stability and sufficient laser bandwidth has enabled access to the first
examples of experimental 2DUV spectra [19–22]. Simulation studies have demonstrated that 2DUV of aromatic residues in the near UV (NUV) and the backbone in
the far UV can effectively probe protein secondary structure [23, 24]. Among the most
recent developments in multidimensional spectroscopy related to 2DES, it is important to highlight the advances in electronic-vibrational spectroscopy [25] and 2D Stark
spectroscopy for characterizing dark charge-transfer states [26], along with the impressive potential of developing techniques in the X-ray regime [27].
The signals recorded in 2DES correlation plots refer to the third-order nonlinear response of the sample, and contain a wealth of information on the excited-state
manifold of the chromophoric units and its photo-induced evolution in time, which
are strongly related due to intra- and inter-chromophoric electronic couplings and
coherence/decoherence effects in chemical and biophysical systems [28].
The electronic transitions involving excited-state absorptions, especially in
2DUV spectra, would encompass high-energy electronic levels whose nature is
64
Reprinted from the journal
1 3
we observe a remarkable agreement between the predicted 2DUV spectra of the pyrene
molecule and the experimental results. These results further led to theoretical studies
of the excited-state dynamics in a solvated dinucleoside system, showing that spectroscopic fingerprints of long-lived excited-state minima along the complex photoinduced
decay pathways of DNA/RNA model systems can be simulated at a reasonable computational cost. Our results exemplify the impact of accurate simulation of 2DES spectra
in revealing complex physicochemical properties of fundamental biological systems
and should trigger further theoretical developments as well as new experiments.
Keywords Nonlinear electronic spectroscopy · Theoretical simulations ·
Wavefunction methods · QM/MM computations · DNA/RNA nucleobases ·
Aromatic amino acids
1 Introduction
Two-dimensional (2D) optical spectroscopy based on multipulse laser sequences originated as an extension of the 2D nuclear magnetic resonance (2DNMR) technique [1]
to the optical regime [2]. 2DNMR had an impressive impact in several fields, with
first handover to the infrared (IR) regime (2DIR) now a well-established method often
employed in the characterization of the structure and dynamics of complex molecular systems by directly mapping their vibrational couplings [3]. Mapping of electronic
couplings by 2D electronic spectroscopy (2DES) [4] has become feasible thanks to
advances [5, 6] in ultrafast optical techniques that allow the targeting of electronic
transitions in the visible (Vis) range. 2DES in the Vis range (2DVis) has become
increasingly popular over the last decade, showcasing its great potential by deciphering energy transfer processes in photosynthesis [7–10]. The desirable extension to the
UV domain (2DUV), however, where many fundamental biomolecules display strong
absorption bands, has been slow thus far, impeded by technical difficulties associated
with the use of UV laser pulses [11]. Recent progress [12–18] in attaining interferometric phase stability and sufficient laser bandwidth has enabled access to the first
examples of experimental 2DUV spectra [19–22]. Simulation studies have demonstrated that 2DUV of aromatic residues in the near UV (NUV) and the backbone in
the far UV can effectively probe protein secondary structure [23, 24]. Among the most
recent developments in multidimensional spectroscopy related to 2DES, it is important to highlight the advances in electronic-vibrational spectroscopy [25] and 2D Stark
spectroscopy for characterizing dark charge-transfer states [26], along with the impressive potential of developing techniques in the X-ray regime [27].
The signals recorded in 2DES correlation plots refer to the third-order nonlinear response of the sample, and contain a wealth of information on the excited-state
manifold of the chromophoric units and its photo-induced evolution in time, which
are strongly related due to intra- and inter-chromophoric electronic couplings and
coherence/decoherence effects in chemical and biophysical systems [28].
The electronic transitions involving excited-state absorptions, especially in
2DUV spectra, would encompass high-energy electronic levels whose nature is
64
Reprinted from the journal