title: Locally-excited (LE) versus charge-transfer (CT) excited state competition in a series of para-substituted neutral green fluorescent protein (GFP) chromophore models.
abstract: In this paper, I provide a characterization of the low-energy electronic structure of a series of para-substituted neutral green fluorescent protein (GFP) chromophore models using a theoretical approach that blends linear free energy relationships (LFERs) with state-averaged complete-active-space self-consistent field (SA-CASSCF) theory. The substituents are chosen to sample the Hammett σ(p) scale from R = F to NH2, and a model of the neutral GFP chromophore structure (R = OH) is included. I analyze the electronic structure for different members of the series in a common complete-active-space valence-bond (CASVB) representation, exploiting an isolobal analogy between active-space orbitals for different members of the series. I find that the electronic structure of the lowest adiabatic excited state is a strong mixture of weakly coupled states with charge-transfer (CT) or locally excited (LE) character and that the dominant character changes as the series is traversed. Chromophores with strongly electron-donating substituents have a CT-like excited state such as expected for a push-pull polyene or asymmetric cyanine. Chromophores with weakly electron-donating (or electron-withdrawing) substituents have an LE-like excited state with an ionic biradicaloid structure localized to the ground-state bridge π bond.
authors.affiliation: School of Mathematics and Physics, The University of Queensland , Brisbane, QLD 4072, Australia.
authors.forename: Seth
authors.initials: S
authors.lastname: Olsen
mesh_terms: D004579:Electron Transport; D049452:Green Fluorescent Proteins / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D013816:Thermodynamics
chemical_list: D049452:Green Fluorescent Proteins