How do electronic-vibrational and electron-phonon coupling influence excited state dynamics?

An understanding of electronic-vibrational and electron-phonon coupling is essential in order to understand the non-radiative decay pathways of a whole variety of molecular and nanomaterial systems. We have used 2D electronic (2DES) spectroscopy to understand the involvement of vibrational modes in electronic dissipation negatively charged nitrogen-vacancy (NV) centers in diamond can help to specifically address the lower-lying spin-states,[1] and the potential role of phonon-assisted exciton relaxation in single walled carbon nanotubes.[2]

Figure 1. Absolute 2D electronic spectra of NV defect centers at a series of waiting times, T. Panel (f) shows the oscillating behavior in the boxed region of the spectra (containing a vibronic cross peak). The lower part of (f) shows the signal integrated over ω, as a function of T, while the upper part shows the total integrated intensity. [1]

2D electronic-vibrational spectroscopy allows us to directly follow the evolution of electronic and vibrational degrees of freedom simultaneously. [3] This allows us to gain insight into how specific high-frequency nuclear motions drive electronic non-radiative relaxation. It is desirable to have a good description of these excited potential energy co-ordinates as to understand the role of conical intersections in carotenoids, or E22-E11 relaxation in single-walled carbon nanotubes.

Helpful Background Reading:

Vibrational and electronic dynamics of nitrogen–vacancy centres in diamond revealed by two-dimensional ultrafast spectroscopy. VM Huxter, TAA Oliver, D Budker, and GR Fleming, Nat Phys, 9, 744–749 (2013).
Two-dimensional electronic spectroscopy reveals the dynamics of phonon-mediated excitation pathways in semiconducting single-walled carbon nanotubes. MW Graham, TR Calhoun, AA Green, et al., Nano Lett, 12, 813–819 (2012).
Correlating the motion of electrons and nuclei with two-dimensional electronic-vibrational spectroscopy. TAA Oliver, NHC Lewis, and GR Fleming, Proc Natl Acad Sci USA, 111,10061–10066 (2014).

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