Recent advances in multidimensional ultrafast spectroscopy

Abstract

Multidimensional ultrafast spectroscopies are one of the premier tools to investigate condensed phase dynamics of biological, chemical and functional nanomaterial systems. As they reach maturity, the variety of frequency domains that can be explored has vastly increased, with experimental techniques capable of correlating excitation and emission frequencies from the terahertz through to the ultraviolet. Some of the most recent innovations also include extreme cross-peak spectroscopies that directly correlate the dynamics of electronic and vibrational states. This review article summarizes the key technological advances that have permitted these recent advances, and the insights gained from new multidimensional spectroscopic probes.

Keywords: multidimensional optical spectroscopy; pulse shaping; two-dimensional electronic–vibrational spectroscopy; ultrafast spectroscopy.

Figure 1.

(a) Isotropic absorptive total 2DIR spectrum of methyl ammonium lead iodide perovskite thin film for waiting time 250 fs. The black line indicates the diagonal of the 2D correlation spectrum. The dashed green lines show fits to the centre line slopes (CLS) for the ground and excited state vibrational features. The pink line is a fit to the nodal line slope (NLS). (b) Time-dependent gradient of the NLS extracted from 2DIR data (open circles) and bi-exponential fit to data (red line).

Figure 2.

Illustrative 2D electronic spectra for a multi-chromophore system, comprised from excitons α, β and γ, for t₂ = (a) 0 ps, and (b) >>0 ps. For simplicity only ground state bleach signals are depicted.

Figure 3.

(a) Pulse sequence for 2D optical spectroscopies, (b) ‘boxcar’ geometry and (c) pump–probe geometry.

Figure 4.

(a) 2DEV pulse sequence, (b) model system containing two electronic states with an associated vibrational manifold. Double-sided Feynman diagrams for the rephasing and non-rephasing 2DEV pathways associated with evolution during t₂ on the (c) excited and (d) ground electronic states.

Figure 5.

Schematic 2DEV spectrum for (a) early waiting times and (b) long waiting times. Overlaid dashed lines depict the two different CLS.

Figure 6.

(a) Schematic non-radiative pathways for β-apo-carotenal in solution. (b–d) 2DEV spectra of C=C antisymmetric stretch feature of bapo in acetonitrile-d₃. Adapted with permission from Oliver & Fleming [128] (Copyright © 2015 American Chemical Society).

Figure 7.

(a) Site basis of system containing five chromophores, labelled A through E, with each chromophore represented by an orb, (b) shaded boxes (1–3) depict the spatial delocalization for each exciton in the same system, (c) crystal structure of LHCII (PDB code 2BHW from Standfuss et al. [149]), where the protein is shown as a blue ribbon, and the skeletal structure of Chl-a, Chl-b and carotenoids are shown in red, green and black, respectively.