In this study, researchers developed spectroscopic techniques to examine 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.

Multidimensional optical spectroscopies have unravelled a wealth of structural, energetic and dynamical information about molecular, biological and nanomaterial systems. These studies have been able to probe phenomena spanning: quantum coherence in natural light harvesting, exciton dissociation in photovoltaic thin films, bound exciton pair correlations in quantum wells and vibrational dynamics in solid-state materials.

Multidimensional optical spectroscopies now represent some of the premier tools for studying condensed phase dynamics of chemical, biological and nanomaterial systems. Since their first inception, they have rapidly evolved from original infrared and optical domains, spawning three-dimensional counterparts, and can interrogate ultrafast dynamics throughout the entire electromagnetic spectrum. Theoretical calculations by Mukamel predict that future 2D spectroscopies using X-ray pulses could directly probe non-Born–Oppenheimer dynamics involving CIs.

Furthermore, the reduced spot size means samples experience far higher peak powers, which generates larger nonlinear signals which may afford reduced acquisition times. While many forays have been made to perform visible pump–probe microscopy experiments, which with near-field delivery of pulses to samples can attain spatial resolutions below the diffraction limit, to date no experiment has reported spatially resolved 2DES measurements.

If applied to photovoltaic materials, one imagines that spatially resolved 2DES could reveal additional key information about the influence of spatial morphology on energy transfer or charge-separation dynamics. Visible pulses are potentially more damaging to samples than mid-infrared, and can induce photo-bleaching, as already demonstrated for confocal transient absorption measurements. 

The interpretation of oscillatory signals observed in 2DES data for photosynthetic light-harvesting proteins have attracted a lot of controversy. The ongoing debate revolves around whether these signals originate from purely electronic, vibrational or mixed vibronic effects. Recently, theoretical calculations from the Collini and Olaya-Castro groups have shown that fully chiral 2DES experiments could be used to differentiate between purely electronic, vibronic and vibrational coherences.

To date, only experiments using either pump or probe pulses that are elliptically polarized have been demonstrated for 2DES. If experimentally realized, fully chiral 2DES could answer this almost 10-year-old debate.

In conclusion, study determined that a technique would also be incredibly sensitive, as all chiral-specific spectroscopies are, to changes in conformational structure involving chiral centres induced by excited state dynamics.