title: Investigation of chromophore-chromophore interaction by electro-optic measurements, linear dichroism, x-ray scattering, and density-functional calculations.
abstract: Free-beam interferometry and angle-resolved absorption spectra are used to investigate the linear electro-optic coefficients and the linear dichroism in photoaddressable bis-azo copolymer thin films. From the first- and second order parameters deduced, the chromophore orientation distribution is calculated and displayed for several poling temperatures and chromophore concentrations. The influence of dipole-dipole interaction on the overall polymer dynamics is discussed. The first order parameter, and therefore the Pockels effect, peaks for a poling temperature of around 10 degrees C above the glass transition. The decrease of the Pockels effect above this temperature region is triggered by a head-to-tail chromophore orientation, i.e., a transition to a microcrystalline phase, increasing the second order parameter. Comparison of the experimentally observed absorption spectra and those obtained by density-functional calculations support the picture of differently aligned bis-azo dye molecules in a trans,trans configuration. Complementary wide-angle x-ray scattering is recorded to confirm the various kinds of ordering in samples poled at different temperatures.
authors.affiliation: Optics and Plasma Research Department, Risø National Laboratory, 4000 Roskilde, Denmark. dirk.apitz@risoe.dk
authors.forename: D
authors.initials: D
authors.lastname: Apitz
authors.forename: R P
authors.initials: RP
authors.lastname: Bertram
authors.forename: N
authors.initials: N
authors.lastname: Benter
authors.forename: W
authors.initials: W
authors.lastname: Hieringer
authors.forename: J W
authors.initials: JW
authors.lastname: Andreasen
authors.forename: M M
authors.initials: MM
authors.lastname: Nielsen
authors.forename: P M
authors.initials: PM
authors.lastname: Johansen
authors.forename: K
authors.initials: K
authors.lastname: Buse
mesh_terms: D000465:Algorithms; D001391:Azo Compounds / Q000032:analysis / Q000737:chemistry*; D002942:Circular Dichroism; D003198:Computer Simulation; D004563:Electrochemistry; D005456:Fluorescent Dyes / Q000032:analysis / Q000737:chemistry*; D007368:Interferometry; D008422:Materials Testing; D008567:Membranes, Artificial; D008956:Models, Chemical; D014961:X-Ray Diffraction
chemical_list: D001391:Azo Compounds; D005456:Fluorescent Dyes; D008567:Membranes, Artificial