Electronic–vibrational coupling probed by 4D Raman–electronic spectroscopy

Abstract

Electronic-vibrational coupling is the driving force behind many fundamental photochemical processes, ranging from phonon-assisted carrier cooling in semiconductors to photoisomerization in proteins and molecular chromophores. Correlations between electronic and vibrational transitions are sensitive reporters of the structural dynamics underlying these processes, yet they have proved challenging to study. Gradient assisted multidimensional electronic–Raman spectroscopy (GAMERS) is a powerful new technique for correlating such interactions across two electronic and two Raman (vibrational) dimensions, enabling functional group-level specificity. Its ability to resolve coherence pathway-specific signatures in a cyanine dye is demonstrated. Additionally, we show that GAMERS enables two structurally similar chromophores with nearly identical electronic spectra to be distinguished based on differences in their 2D electronic–2D Raman spectra. Finally, GAMERS is applied to colloidal CdSe quantum dots, exposing the coupling of excitons to both optical and acoustic phonons.