| This thesis research focuses on the fabrication of novel multilayer thin films with unique optical properties employing molecular level self-assembly. Two different classes of polymers, azo and fluorescent polymers, have been synthesized and used for fabrication of optical devices, specifically thin film nonlinear optical devices and optical chemical sensors by electrostatic layer-by-layer self-assembly.; For thin film nonlinear optical devices, a poly(acrylic acid) based precursor anilino-functional polymer was first synthesized and used as a polyanion. This polymer was assembled into mono and multilayer thin films by electrostatic layer-by-layer self-assembly technique in conjunction with a polycation. The aniline group in the assembled polymer layer was subsequently converted to an azobenzene chromophore by post azo coupling reaction with appropriate diazonium salts. This method provides easy control of film thickness and well ordered chromophore structure in the multilayer. Second harmonic generation was observed in all multilayer films indicating acentric organization of the chromophores synthesized in the multilayered films. The second harmonic intensity and film thickness are dependent on the assembly conditions (pH etc.) of the polyions. The post functionalized azopolymer layers were further modulated by light driven mass transport.; Thin film optical sensors for pH, metal ions (ferric and mercury) and 2,4-dinitro toluene detection were developed. To fabricate the pH sensor, a fluorescent molecule, 1-hydroxypyren-3,6,8-trisulfonate, was assembled with a polycation by electrostatic layer-by-layer self-assembly technique. The fluorescent indicator molecule exhibits distinct and well-defined emission peaks for protonated and deprotonated forms. The relative peak positions and intensity of fluorescence of the protonated and deprotonated forms change in response to pH variations. For metal ions (ferric and mercury) and 2,4-dinitro toluene sensing, the indicator molecules were covalently incorporated into poly(acrylic acid) and subsequently assembled with a polycation employing electrostatic layer-by-layer self-assembly. The sensor is based on the fluorescence quenching of indicator molecules by electron transfer from indicator to electron-deficient analytes such as ferric ions, mercury and 2,4-dinitro toluene. Fluorescence intensities decreased with increasing concentration of analytes. Quenching behavior follows Stern-Volmer bimolecular quenching kinetics. Linear increase in absorbance, film thickness and emission intensity was observed as a function of number of bilayers deposited in all these films. |
