Excited State Electronic Landscape of mPlum Revealed by Two-Dimensional Double Quantum Coherence Spectroscopy Patrick E. Konold Ralph Jimenez 10.1021/jp5119772.s001 https://acs.figshare.com/articles/journal_contribution/Excited_State_Electronic_Landscape_of_mPlum_Revealed_by_Two_Dimensional_Double_Quantum_Coherence_Spectroscopy/2192257 Red fluorescent proteins (RFPs) are widely used probes for monitoring subcellular processes with extremely high spatial and temporal precision. In this work, we employed spectrally resolved transient absorption (SRTA) and two-dimensional double quantum coherence (2D2Q) spectroscopy to investigate the excited state electronic structure of mPlum, a well-known RFP. The SRTA spectra reveal the presence of excited state absorption features at both the low- and high-energy sides of the dominant ground state bleach contribution. The 2D2Q spectra measured at several excitation wavelengths reveal a peak pattern consistent with the presence of more than three electronic states (i.e., ground, excited, and doubly excited). Numerical modeling of this response suggests that the features are consistent with a 1–1–2 electronic structure. The two closely spaced (∼1500 cm<sup>–1</sup>) levels in the double quantum manifold appear at opposite anharmonicities relative to twice the energy of the lowest energy transition. These observations explain the excited state absorption contributions observed in spectrally resolved transient grating and transient absorption measurements and demonstrate the utility of multidimensional spectroscopy in unraveling congested spectra relative to conventional one-dimensional methods. 2015-02-26 00:00:00 presence energy transition ground state bleach contribution monitoring subcellular processes 2 D 2Q spectra peak pattern SRTA spectra excitation wavelengths quantum manifold RFP absorption measurements Excited State Electronic Landscape mPlum Revealed state absorption contributions Numerical modeling state absorption features spectroscopy