Novel Polymer Dyes for Nonlinear Optical Applications Using Ionic Self-Assembled Monolayer Technology

Abstract

Fabrication of organic thin films by spontaneous molecular assembly is a powerful tool for creating carefully controlled supramolecular structures for nonlinear optical (NLO) applications. Recently, Decher and co-workers extended the work of Iler et al. to a new method of depositing thin films by layer-by-layer adsorption of linear polyions. [1,2] This ionic self-assembled monolayer (ISAM) technique provides significant advantages over other thin-film fabrication methods, including long-term stability, ease of fabrication, and greater film thickness. We have fabricated NLO films hundreds of bilayers thick with consistent, reproducible film growth with each bilayer. The observation of NLO behavior in polymer/organic dye ISAM thin films using commercially available dye molecules, specifically Poly S-119 (from Sigma), has already been reported. [3,4] The polar ordering of molecules that occurs due to the inherent nature of the ISAM process suggests that a number of similar NLO thin films may be synthesized using both other standard chromophore dyes and molecules specifically designed to yield an enhanced macro-scale net dipole moment. Consequently, we have designed and synthesized several new NLO polymers, including poly(methacrylic acids) and polyesters ( Fig. 1), and fabricated non-centrosymmetric thin films using the ISAM process. In this paper, we present results that demonstrate the second-order NLO behavior of these polydye materials. Multilayer thin films of designed and synthesized polydye 1, polydye 2, and polydye 4 were self-assembled on glass substrates with polydiallyldimethylammonium chloride (PDDA) as the passive polycation layer. Uniform polydye films with up to 88 bilayers have already been fabricated, with an average bilayer thickness of the order of 2 nm, based on ellipsometry data. We have previously described in detail the process of synthesis of more than 1000 ISAM layers with good surface morphology, [5±7] resulting in films micrometers thick. UV-vis spectroscopy was used to identify the absorption and transmission characteristics of the NLO thin films as well as to quantify the growth of the multilayer structures. For example, optical absorbance spectra measured during the growth of two PDDA/polydye films on modified glass substrates are shown in Figures 2 and 3. The absorbance peaks of polydye 2 and polydye 4 are located at 435 and 365 nm, respectively, and exhibit a linear increase with the addition of each bilayer. This demonstrates that each bilayer contributes an equal amount of material to the thinfilm growth. In addition, the maximum differences between data collected at different locations across each film are at most a few percent, indicating excellent uniformity of the films. The ISAM method therefore produces thin films that are homogeneous through the film thickness as well as across the width and length of the film.Thin-film emission characteristics have important implications for optical and optoelectronic devices. As examples, the fluorescence spectra of polydye 2 and polydye 4...

Dielectric function of two-phase colloid–polymer nanocomposite

“…We fabricated samples of several hundred DLs and multilayer systems of more than 1000 layers were reported. 21 Fabrication of gold nano-rods and -spheres Nano-spheres. Spherical gold nano-spheres (GNS), useful for LbL, can be produced by the wet-chemical reduction of hydrogen tetrachloroaurate (HAuCl 4 Á3H 2 O) with trisodium citrate.…”

“…10,11 These localized surface plasmons (LSPs) have been subject to extended theoretical modelling [10][11][12][13][14][15] and experimental investigations. 10,11,[16][17][18][19][20][21][22] Studies have e.g. investigated the influence of surface modifications, 22 and of the embedding media 10,23 on the LSP properties.…”

Side-by-Side Directed Multilayer Patterning Using Surface Templates

“…Researchers have investigated conducting [5±8] or luminescent films, [9±13] nonlinear optical dyes, [14,15] or electrochemical mediators [16±18] formed with this technique. Many of the proposed applications for layer-by-layer thin films, such as electro-optical devices, sensors, or plastic circuitry, require the ability to pattern the films to form micrometer-scale features.…”

Fabrication of highly ordered multilayer thin films and its applications

“…Most of these applications require the preparation of stable and well-organized films with fast fabrication processes. Since the ionic layer-by-layer self-assembly (SA) technique was introduced for the fabrication of polyelectrolyte multilayer, this self-assembling technique has been extended to conducting polymer composites, nonlinear optical dyes, and the assembly of nanoparticles or biomolecular systems [Decher, 1997;Lenahan et al, 1998;Kotov et al, 1995;Lvov et al, 1995]. This layer-bylayer SA method is principally based on self-diffusion rearrangement, and thus various experimental factors should be taken into account in order to increase the surface coverage of a polymer layer adsorbing onto a substrate: the adsorption time, the pH control, the concentration of polyelectrolyte and the amount of added ionic salt.…”