The functioning of light-sensitive proteins is closely connected to the ways, by which the protein environment tunes the intrinsic photoresponse of their chromophores and guides their excited state evolution. Recently, we have disclosed a striking fundamental interplay between electronic and nuclear dynamics in competing excited-state decay channels of the anionic Green Fluorescent Protein (GFP) chromophore . A non-adiabatic nature of the excited-state dynamics unexpectedly results in co-existing mutual energy-borrowing mechanisms between nuclei and electrons. By combining a novel time-domain approach to action spectroscopy and a highly correlated multi-reference electronic structure theory, we show that the energy exchange is remarkably fast and, importantly, mode-specific. The de-excitation includes vibrationally assisted electron emission out of the first excited state and internal conversion back to the hot ground state, where the latter is shown to proceed through the two distinct types of conical intersections [1,2]. The mode-specificity paves the way to a control of the branching ratio in the GFP chromophore and, ultimately, of electron transfer in the GFP photochemistry, given the striking similarity of the spectral shapes and the early-time excited-state dynamics in the gas phase and in the protein environment. In the case of the neutral GFP chromophore, the photo-induced non-adiabatic dynamics results in the existence of hidden proton transfer pathways in the Blue Fluorescent Protein mKalama1 . The complete photocycle of this protein has been disclosed based on the joint theoretical and experimental time-resolved spectral studies, revealing a proton transfer coupled to photo-induced isomerization as well as a radical formation induced by multi-photon ionization. Finally, we have identified higher electronically excited states of the isolated GFP chromophore anion in the UV region down to 210 nm . By forming a dense manifold well separated from the photochemically active first excited state, these molecular resonances are found to serve as a doorway for very efficient electron detachment in the gas phase. Being resonant with the quasi-continuum of a solvated electron, this electronic band in the protein might play a major role in the GFP photophysics, where resonant GFP photoionization triggers the protein photoconversion with UV and multi-photon visible light.
References:  A.V. Bochenkova, L.H. Andersen. Faraday Discuss., 163, 297 (2013)  Y. Toker, D.B. Rahbek, B. Klaerke, A.V. Bochenkova, L.H. Andersen. Phys. Rev. Lett., 109, 128101 (2012)  R.B. Vegh, D.A. Bloch, A.S. Bommarius, M. Verkhovsky, S. Pletnev, H. Iwai, A.V. Bochenkova, K.M. Solntsev. J. Am. Chem. Soc., to be submitted (2014)  A.V. Bochenkova, B. Klaerke, D.B. Rahbek, J. Rajput, Y. Toker, L.H. Andersen. Phys. Rev. Lett., submitted (2014)
Host: Kyril Solntsev
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