title: Control of the orientational order and nonlinear optical response of the "push-pull" chromophore RuPZn via specific incorporation into densely packed monolayer ensembles of an amphiphilic 4-helix bundle peptide: second harmonic generation at high chromophore densities.
abstract: The macroscopic nonlinear optical response of the "push-pull" chromophore RuPZn incorporated into a single monolayer of the amphiphilic 4-helix bundle peptide (AP0) covalently attached to a solid substrate at high in-plane density has been measured. The second-order susceptibility, chi(zzz), was found to be in the range of approximately 15 x 10(-9) esu, consistent with a coherent sum of the nonlinear contributions from the individual chromophores (beta) as previously measured in isotropic solution through hyper-Rayleigh scattering as well as estimated from theoretical calculations. The microscopic hyperpolarizability of the RuPZn chromophore is preserved upon incorporation into the peptide monolayer, suggesting that the chromophore-chromophore interactions in the densely packed ensemble do not substantially affect the first-order molecular hyperpolarizability. The polarization angle dependence of the second harmonic signal reveals that the chromophore is vectorially oriented in the two-dimensional ensemble. Analysis of the order parameter together with information obtained from grazing incidence X-ray diffraction help in determining the chromophore orientation within the AP0-RuPZn monolayer. Taking into account an average pitch angle of approximately 20 degrees characterizing the coiled-coil structure of the peptide bundle, the width of the bundle's tilt angle distribution should be sigma < or = 20 degrees, resulting in a mean value of the tilt angle 23 degrees < or = theta(0) < or = 37 degrees.
authors.affiliation: Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA. gonella@temple.edu
authors.forename: Grazia
authors.initials: G
authors.lastname: Gonella
authors.forename: Hai-Lung
authors.initials: HL
authors.lastname: Dai
authors.forename: H Christopher
authors.initials: HC
authors.lastname: Fry
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Therien
authors.forename: Venkata
authors.initials: V
authors.lastname: Krishnan
authors.forename: Andrey
authors.initials: A
authors.lastname: Tronin
authors.forename: J Kent
authors.initials: JK
authors.lastname: Blasie
mesh_terms: D016018:Least-Squares Analysis; D017975:Ruthenium Compounds / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D017975:Ruthenium Compounds