title: Oxazines: A New Class of Second-Order Nonlinear Optical Switches.
abstract: A combined experimental-theoretical investigation has revealed that oxazine-based compounds are multiaddressable, multistate, and multifunctional molecular switches exhibiting contrasts of both linear and second-order nonlinear optical properties. The switching properties are particularly large when the substituent is a donor group. In this study, the cleavage of the C-O bond at the junction of the indole and oxazine cycles (of the closed a forms) is acido-triggered, leading to an open form (b(+)) characterized by larger first hyperpolarizabilities (βHRS) and smaller excitation energies than in the closed form. These results are confirmed and interpreted utilizing ab initio calculations that have been carried out on a broad set of compounds to unravel the role of the substituent. With respect to acceptor groups, oxazines bearing donor groups are characterized not only by larger βHRS and βHRS contrast ratios but also by smaller excitation energies, larger opening-induced charge transfer, and reduction of the bond length alternation, as well as smaller Gibbs energies of the opening reaction. Compared to protonated open forms (b(+)), calculations on the zwitterionic open forms (b) have pointed out similarities in the long-wavelength UV/vis absorption spectra, whereas their βHRS values might differ strongly as a function of the substituent. Indeed, the open forms present two NLOphores, the indoleninium-substituent entity and the nitrophenol (present in the protonated open form, b(+)) or nitrophenolate (present in the zwitterionic open form, b) moiety. Then, nitrophenolate displays a larger first hyperpolarizability than nitrophenol and the β tensor of the two entities might reinforce or cancel each other.
authors.affiliation: University of Namur , Laboratoire de Chimie Théorique, Unité de Chimie Physique Théorique et Structurale, rue de Bruxelles, 61, B-5000 Namur, Belgium.
authors.forename: Pierre
authors.initials: P
authors.lastname: Beaujean
authors.affiliation: Université de Bordeaux , Institut des Sciences Moléculaires (ISM), UMR 5255 CNRS, Cours de la Libération 351, F-33405 Talence Cedex, France.
authors.forename: Flavie
authors.initials: F
authors.lastname: Bondu
authors.affiliation: University of Namur , Laboratoire de Chimie Théorique, Unité de Chimie Physique Théorique et Structurale, rue de Bruxelles, 61, B-5000 Namur, Belgium.
authors.forename: Aurélie
authors.initials: A
authors.lastname: Plaquet
authors.affiliation: Laboratory for Molecular Photonics, Department of Chemistry, University of Miami , 1301 Memorial Drive, Coral Gables, Florida 33146-0431, United States.
authors.forename: Jaume
authors.initials: J
authors.lastname: Garcia-Amorós
authors.affiliation: Laboratory for Molecular Photonics, Department of Chemistry, University of Miami , 1301 Memorial Drive, Coral Gables, Florida 33146-0431, United States.
authors.forename: Janet
authors.initials: J
authors.lastname: Cusido
authors.affiliation: Laboratory for Molecular Photonics, Department of Chemistry, University of Miami , 1301 Memorial Drive, Coral Gables, Florida 33146-0431, United States.
authors.forename: Françisco M
authors.initials: FM
authors.lastname: Raymo
authors.affiliation: Université de Bordeaux , Institut des Sciences Moléculaires (ISM), UMR 5255 CNRS, Cours de la Libération 351, F-33405 Talence Cedex, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Castet
authors.affiliation: Université de Bordeaux , Institut des Sciences Moléculaires (ISM), UMR 5255 CNRS, Cours de la Libération 351, F-33405 Talence Cedex, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Rodriguez
authors.affiliation: University of Namur , Laboratoire de Chimie Théorique, Unité de Chimie Physique Théorique et Structurale, rue de Bruxelles, 61, B-5000 Namur, Belgium.
authors.forename: Benoît
authors.initials: B
authors.lastname: Champagne