title: Relation between bond-length alternation and second electronic hyperpolarizability of conjugated organic molecules.
abstract: The solvent dependence of the second hyperpolarizability, gamma, of a variety of unsaturated organic compounds has been measured by third harmonic generation at 1907 nanometers. It is seen that the measured gamma is a function of solvent polarity. These solvent-dependent hyperpolarizabilities are associated with changes in molecular geometry from a highly bond-length alternated, polyene-like structure for a formyl-substituted compound in non-polar solvents, to a cyanine-like structure, with little bond-length alternation, for a dicyanovinyl-substituted compound in polar solvents. By tuning bond-length alternation, gamma can be optimized in either a positive or negative sense for polymethine dyes of a given conjugation length.
authors.forename: S R
authors.initials: SR
authors.lastname: Marder
authors.forename: C B
authors.initials: CB
authors.lastname: Gorman
authors.forename: B G
authors.initials: BG
authors.lastname: Tiemann
authors.forename: J W
authors.initials: JW
authors.lastname: Perry
authors.forename: G
authors.initials: G
authors.lastname: Bourhill
authors.forename: K
authors.initials: K
authors.lastname: Mansour