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