title: Continuous symmetry breaking induced by ion pairing effect in heptamethine cyanine dyes: beyond the cyanine limit.
abstract: The association of heptamethine cyanine cation 1(+) with various counterions A (A = Br(-), I(-), PF(6)(-), SbF(6)(-), B(C(6)F(5))(4)(-), TRISPHAT) was realized. The six different ion pairs have been characterized by X-ray diffraction, and their absorption properties were studied in polar (DCM) and apolar (toluene) solvents. A small, hard anion (Br(-)) is able to strongly polarize the polymethine chain, resulting in the stabilization of an asymmetric dipolar-like structure in the crystal and in nondissociating solvents. On the contrary, in more polar solvents or when it is associated with a bulky soft anion (TRISPHAT or B(C(6)F(5))(4)(-)), the same cyanine dye adopts preferentially the ideal polymethine state. The solid-state and solution absorption properties of heptamethine dyes are therefore strongly correlated to the nature of the counterion.
authors.affiliation: University of Lyon, Laboratoire de Chimie, UMR 5182 CNRS - Ecole Normale Superieure de Lyon, 46 allee d'Italie, 69007 Lyon, France.
authors.forename: Pierre-Antoine
authors.initials: PA
authors.lastname: Bouit
authors.forename: Christophe
authors.initials: C
authors.lastname: Aronica
authors.forename: Loïc
authors.initials: L
authors.lastname: Toupet
authors.forename: Boris
authors.initials: B
authors.lastname: Le Guennic
authors.forename: Chantal
authors.initials: C
authors.lastname: Andraud
authors.forename: Olivier
authors.initials: O
authors.lastname: Maury