title: Synthetic, Optical and Theoretical Study of Alternating Ethylenedioxythiophene-Pyridine Oligomers: Evolution from Planar Conjugated to Helicoidal Structure towards a Chiral Configuration.
abstract: A series of alternating 3,4-ethylenedioxythiophene-alkynylpyridine oligomers (DA)nwith increased solubility are synthesized and their photophysical properties and nonlinear optical properties are investigated. Their quadratic polarizabilities are determined from hyper-Rayleigh scattering experiments to obtain information on their conformations in solution. These chromophores, based on the alternation of electron-rich (D) and electron-deficient (A) moieties, exhibit optical properties that arise from the combination of dipolar and helicoidal features in the (DA)nhomologue series where n=1-4. The transition from dipolar conjugated planar structures (n=1, 2) to helicoidal structures (n=3, 4) is clearly evidenced by results from symmetry-sensitive second-order nonlinear optical experiments. This suggests an approach towards highly efficient chiral chromophores for second-order nonlinear optics. Interestingly, this structural evolution also has significant impact on the photophysical properties: both absorption and fluorescence emission show bathochromic and hyperchromic shifts with increasing number of repeating units in the dipolar planar derivatives (n=1-2) but show saturation effects in the helicoidal structures (n=2-4). In addition, the helicoidal structures show sizeable two-photon absorption at 700-750 nm (40-100 GM) for compounds lacking either electron-donating or electron-withdrawing substituents.
authors.affiliation: Chimie et Photonique Moléculaires, UMR 6510 CNRS, Université de Rennes 1, 35042, Rennes, France.|Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS, Université de Rennes 1, 35042, Rennes, France.
authors.forename: Floris
authors.initials: F
authors.lastname: Chevallier
authors.affiliation: Chimie et Photonique Moléculaires, UMR 6510 CNRS, Université de Rennes 1, 35042, Rennes, France.
authors.forename: Marina
authors.initials: M
authors.lastname: Charlot
authors.affiliation: Chimie et Photonique Moléculaires, UMR 6510 CNRS, Université de Rennes 1, 35042, Rennes, France.|Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS, Université de Rennes 1, 35042, Rennes, France.
authors.forename: Florence
authors.initials: F
authors.lastname: Mongin
authors.affiliation: Laboratoire de Chimie Théorique, Université de Namur, 5000, Namur, Belgium.
authors.forename: Benoît
authors.initials: B
authors.lastname: Champagne
authors.affiliation: Department of Chemistry, University of Leuven, 3001, Leuven, Belgium.
authors.forename: Edith
authors.initials: E
authors.lastname: Franz
authors.affiliation: Department of Chemistry, University of Leuven, 3001, Leuven, Belgium.
authors.forename: Koen
authors.initials: K
authors.lastname: Clays
authors.affiliation: Chimie et Photonique Moléculaires, UMR 6510 CNRS, Université de Rennes 1, 35042, Rennes, France.|Université de Bordeaux, Institut des Sciences Moléculaires, UMR 5255 CNRS, 33405, Talence, France.
authors.forename: Mireille
authors.initials: M
authors.lastname: Blanchard-Desce
keywords: fluorescence; helicoidal structures; hyper-Rayleigh scattering; nonlinear optics; two-photon absorption