title: Efficient, thermally stable, second order nonlinear optical response in organic hybrid covalent/ionic self-assembled films.
abstract: A covalent/electrostatic layer-by-layer self-assembly method was used to achieve polar ordering of a water soluble, reactive dye in the fabrication of nonlinear optical (NLO) films. We observed a quadratic relationship between the second harmonic intensity I2(omega) and bilayer number for all films made with Procion Brown MX-GRN, demonstrating that the polar ordering of the chromophores is consistent in each successive bilayer. As the ionic strength of the dye deposition solution was increased to 0.5 M NaCl, the of the films increased by approximately 250% to 50 x 10(-9) esu, with a corresponding average chromophore tilt angle of 38 degrees . This was attributed to increased shielding of the dye charges which led to higher chromophore density in the bilayers. The electrooptic coefficient for films of 50 bilayers fabricated at 0.5 M NaCl was 14 +/- 2 pm/V. Importantly, these films exhibited excellent thermal stability, with only a 10% decrease in (I2(omega))(1/2) after 36 h at 85 degrees C and then 24 h at 150 degrees C. Furthermore, the (I2(omega))(1/2) recovered completely upon cooling to room temperature. These results with a commodity textile dye point to the potential value of this class of reactive chromophores and this self-assembly method for fabrication of electrooptic materials at ambient conditions from aqueous solutions.
authors.affiliation: Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA.
authors.forename: James R
authors.initials: JR
authors.lastname: Heflin
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Guzy
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Neyman
authors.forename: Kylie J
authors.initials: KJ
authors.lastname: Gaskins
authors.forename: Charles
authors.initials: C
authors.lastname: Brands
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Wang
authors.forename: Harry W
authors.initials: HW
authors.lastname: Gibson
authors.forename: Richey M
authors.initials: RM
authors.lastname: Davis
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Van Cott