title: Quantum Chemical Benchmark Studies of the Electronic Properties of the Green Fluorescent Protein Chromophore. 1. Electronically Excited and Ionized States of the Anionic Chromophore in the Gas Phase.
abstract: We present the results of quantum chemical calculations of the electronic properties of the anionic form of the green fluorescent protein chromophore in the gas phase. The vertical detachment energy of the chromophore is found to be 2.4-2.5 eV, which is below the strongly absorbing ππ* state at 2.6 eV. The vertical excitation of the lowest triplet state is around 1.9 eV, which is below the photodetachment continuum. Thus, the lowest bright singlet state is a resonance state embedded in the photodetachment continuum, whereas the lowest triplet state is a regular bound state. Based on our estimation of the vertical detachment energy, we attribute a minor feature in the action spectrum as due to the photodetachment transition. The benchmark results for the bright ππ* state demonstrated that the scaled opposite-spin method yields vertical excitation within 0.1 eV (20 nm) from the experimental maximum at 2.59 eV (479 nm). We also report estimations of the vertical excitation energy obtained with the equation-of-motion coupled cluster with the singles and doubles method, a multireference perturbation theory corrected approach MRMP2 as well as the time-dependent density functional theory with range-separated functionals. Expanding the basis set with diffuse functions lowers the ππ* vertical excitation energy by 0.1 eV at the same time revealing a continuum of "ionized" states, which embeds the bright ππ* transition.
authors.affiliation: Department of Chemistry, University of Southern California, Los Angeles, California 90089, Department of Chemistry, M.V. Lomonosov Moscow State University, Moscow 119991, Russia, and Institute of Biochemical Physics, Russian Academy of Sciences, Moscow 119334, Russia.
authors.forename: Evgeny
authors.initials: E
authors.lastname: Epifanovsky
authors.affiliation: Department of Chemistry, University of Southern California, Los Angeles, California 90089, Department of Chemistry, M.V. Lomonosov Moscow State University, Moscow 119991, Russia, and Institute of Biochemical Physics, Russian Academy of Sciences, Moscow 119334, Russia.
authors.forename: Igor
authors.initials: I
authors.lastname: Polyakov
authors.affiliation: Department of Chemistry, University of Southern California, Los Angeles, California 90089, Department of Chemistry, M.V. Lomonosov Moscow State University, Moscow 119991, Russia, and Institute of Biochemical Physics, Russian Academy of Sciences, Moscow 119334, Russia.
authors.forename: Bella
authors.initials: B
authors.lastname: Grigorenko
authors.affiliation: Department of Chemistry, University of Southern California, Los Angeles, California 90089, Department of Chemistry, M.V. Lomonosov Moscow State University, Moscow 119991, Russia, and Institute of Biochemical Physics, Russian Academy of Sciences, Moscow 119334, Russia.
authors.forename: Alexander
authors.initials: A
authors.lastname: Nemukhin
authors.affiliation: Department of Chemistry, University of Southern California, Los Angeles, California 90089, Department of Chemistry, M.V. Lomonosov Moscow State University, Moscow 119991, Russia, and Institute of Biochemical Physics, Russian Academy of Sciences, Moscow 119334, Russia.
authors.forename: Anna I
authors.initials: AI
authors.lastname: Krylov