Stephen B. Roscoe

Self-assembled chromophoric thin film NLO materials. Effect of coupling agent surface functionalization and ion exchange processes on second harmonic generation characteristics

Abstract A systematic study of the reaction of 1-chloromethyl-4-(2-trichlorosilylethyl)-benzene (coupling agent) with the surface SiOH groups of glass for times from 15 min to 48 h, followed by stilbazole chromophore precursor deposition/quaternization, is reported. Second harmonic generation characteristics of these thin film materials indicate that a 15 min coupling agent reaction attains approximately 65% of full surface coverage (based on χ zzz (2) ) of benzylic chloride moieties, but that 24 h is the optimal time for maximum coverage. The surface-anchored chromophoric chloride salts in such materials undergo facile ion exchange with iodide, p -aminobenzenesulphonate, and ethyl orange, leading to enhancements in χ zzz (2) of up to 50%.

The Effect of Chromophore Architecture and Deposition Conditions on the Optical and Microstructural Characteristics of Self-Assembled Chromophoric Thin Film NLO Materials

Abstract Construction on inorganic oxide substrates of covalently self-assembled second-order nonlinear optical (NLO) materials containing a variety of acentrically organized high-β chromophores is investigated as a function of film deposition conditions. Structurally different chromophores exhibit varying packing arrangements on the surface. Changing the medium for the chromophorc deposition reaction on functionalized surfaces from a polar solvent to a nonpolar solvent and raising the temperature increases the chromophore number density on the surface and yields improved NLO response. These robust thin film materials show very high second harmonic generation (SHG) efficiencies with X (2) zzz for ∼ 25 A thick monolayers of up to 7 × 10−7 esu at 1064 nm.

Descriptive Chemistry Of Self-Assembled Multilayer Second-Order NLO Materials. Chemical, Microstructural and Performance Interrelationships

The construction of covalently self-assembled second-order nonlinear optical (NLO) Materials containing stilbazole or alkynyl-type high-β chromophores acentrically organized on inorganic oxide substrates is discussed. These structurally different chromophores exhibit differing packing densities on the surface when introduced under the same reaction conditions. In the stilbazolium chromophores, ion-exchange of the chloride counter-anion with very large anionie organic dyes results in appreciably enhanced second harmonic generation (SHG) efficiency. The frequency-dependent SHG response for self-assembled Monolayers derived from the alkynyl-type chromophore was also investigated. The linear absorption spectra exhibit two maxima in the visible region which are assigned to electronically isolated chromophores (480 nm) and aggregated species (540 nm). The dispersion of the second-order NLO coefficient reveals that both microstructures are NLO-active. The origin of the SHG response from both assemblies is discussed.