title: ATOP dyes. optimization of a multifunctional merocyanine chromophore for high refractive index modulation in photorefractive materials.
abstract: This paper reports synthesis, characterization and structural optimization of amino-thienyl-dioxocyano-pyridine (ATOP) chromophores toward a multifunctional amorphous material with unprecedented photorefractive performance. The structural (dynamic NMR, XRD) and electronic (UV/vis, electrooptical absorption, Kerr effect measurements) characterization of the ATOP chromophore revealed a cyanine-type pi-conjugated system with an intense and narrow absorption band (epsilon(max) = 140 000 L mol(-)(1) cm(-)(1)), high polarizability anisotropy (deltaalpha(0) = 55 x 10(-)(40) C V(-)(1) m(2)), and a large dipole moment (13 D). This combination of molecular electronic properties is a prerequisite for strong electrooptical response in photorefractive materials with low glass-transition temperature (T(g)). Other important materials-related properties such as compatibility with the photoconducting poly(N-vinylcarbazole) (PVK) host matrix, low melting point, low T(g), and film-forming capabilities were optimized by variation of four different alkyl substituents attached to the ATOP core. A morphologically stable PVK-based composite containing 40 wt % of ATOP-3 showed an excellent photorefractive response characterized by a refractive index modulation of Deltan approximately 0.007 and a gain coefficient of Gamma approximately 180 cm(-)(1) at a moderate electrical field strength of E = 35 V microm(-)(1). Even larger effects were observed with thin amorphous films consisting of the pure glass-forming dye ATOP-4 (T(g) = 16 degrees C) and 1 wt % of the photosensitizer 2,4,7-trinitro-9-fluorenylidene-malononitrile (TNFM). This material showed complete internal diffraction at a field strength of only E = 10 V microm(-)(1) and Deltan reached 0.01 at only E = 22 V microm(-)(1) without addition of any specific photoconductor.
authors.affiliation: Department of Organic Chemistry II, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Würthner
authors.forename: S
authors.initials: S
authors.lastname: Yao
authors.forename: J
authors.initials: J
authors.lastname: Schilling
authors.forename: R
authors.initials: R
authors.lastname: Wortmann
authors.forename: M
authors.initials: M
authors.lastname: Redi-Abshiro
authors.forename: E
authors.initials: E
authors.lastname: Mecher
authors.forename: F
authors.initials: F
authors.lastname: Gallego-Gomez
authors.forename: K
authors.initials: K
authors.lastname: Meerholz