Supramolecular Approaches to Second-Order Nonlinear Optical Materials. Self-Assembly and Microstructural Characterization of Intrinsically Acentric [(Aminophenyl)azo]pyridinium Superlattices

Abstract

This paper describes the synthesis and characterization of self-assembled second-order nonlinear optical multilayer materials containing the high-hyperpolarizability [(aminophenyl)azo]pyridinium chromophore. The chromophoric multilayers are assembled on clean glass or single-crystal silicon substrates via the following iterative reaction sequence: (1) treatment with 4-ClCH2C6H4SiCl3, 3-BrC3H6SiCl3, or 3-IC3H6SiCl3 to afford a self-assembled coupling layer; (2) quaternization of 4-[[4-[N,N-bis(hydroxylethyl)amino]phenyl]azo]pyridine in a “topotactic” fashion to generate an [(aminophenyl)azo]pyridinium chromophore layer; (3) cross-linking with octachlorotrisiloxane to afford a capping layer (which also regenerates surface hydroxyl groups for subsequent layer deposition). The new chromophore precursor 4-[[4-[N,N-bis(hydroxylethyl)-amino]phenyl]azo]pyridine was synthesized by diazotization of 4-aminopyridine followed by coupling with N-phenyldiethanolamine and has been characterized by elemental analysis, mass spectrometry, and infrared, UV−vis, and NMR spectroscopies. The chromophoric multilayers have been characterized by X-ray photoelectron and transmission optical spectroscopies, spectroscopic ellipsometry, X-ray reflectivity, advancing contact angle measurements, and polarized second harmonic generation (SHG). The excellent structural regularity of the chromophoric multilayers is indicated by the linear dependence of the [(aminophenyl)azo]pyridinium chromophore longitudinal HOMO → LUMO charge-transfer excitation absorbance at 572 nm and the ellipsometry- and X-ray reflectivity-derived multilayer thicknesses on the number of assembled trilayers, while the uniform polar order of the stacked chromophoric multilayers is evidenced by the quadratic dependence of the second harmonic generation intensities on the number of trilayers. The [(aminophenyl)azo]pyridinium multilayers are photochemically stable, have very high structural regularities, and exhibit a second-order nonlinear optical susceptibility (χ(2)) of ∼3.6 × 10-7 esu (∼150 pm/V) at a fundamental wavelength of 1064 nm. Finally, atomic force microscopy reveals that the surfaces of the self-assembled multilayers are very smooth (root mean square roughness = 12 Å for a 10 trilayer sample), undoubtedly reflecting the high three-dimensional structural regularities of the individual layers.

Biomimetic Micropatterning of Titanium Dioxide Thin Films for Gate Dielectrics

“…The UV-irradiated regions become hydrophilic due to Si-OH group formation, while the nonirradiated region remained unchanged, i.e. it was composed of hydrophobic octadecyl groups, which gave rise to patterned OTS-SAM [9][10][11][12].…”

Molecular orientation-photoconductivity relationship study of phthalocyanine polymer-oriented thin films

“…Therefore, with the emergence of the supramolecular thin films, one of the interesting things is how to fabricate PPc ultrathin films. So far, several techniques have been used to obtain the ultrathin layers: 13 (a) the poling of initially nonpolar polymer films, 14,15 (b) the Langmuir-Blodgett (LB) assembly of polar monolayers, 16,17 and (c) the defined growth of films of polar polymers by self-assembly 18,19 or grafting. 20,21 Phthalocyanine polymer ultrathin films with unique and ordered molecular structures had been fabricated through the LB technique 22 and self-assembly.…”

Synthesis of 5-nitropyridin-2-ylazo push-pull derivatives

“…Incorporation of π-deficient pyridine conserves the photoactivity of azobenzene and additionally provides the capability of self-assembly through H-bonding or metal coordination [3]. Although a number of investigations have been reported in the literature on pyridin-4-ylazo dyes [3][4][5][6], only a few pyridin-2-ylazo dyes have been synthesized [7,8], and to our knowledge no reports exist on 5-nitropyridin-2-yl-azo pushpull chromophore.The aim of the present study was to synthesize 5-nitropyridin-2-ylazobenzene derivatives 1a-c bearing in the electron-releasing part of the molecule a diethanolamino group [N(CH 2 CH 2 OH) 2 ] and an octyloxy group that efficiently, as our previous research shows [9], improve solubility and are expected to avoid the formation of undesirable centrosymmetric structures in the solid state. N N N N CH 2 CH 2 OH CH 2 CH 2 OH O 2 N R 1a-c a R = H, b R = OMe, c R = OC 8 H 17…”

“…Incorporation of π-deficient pyridine conserves the photoactivity of azobenzene and additionally provides the capability of self-assembly through H-bonding or metal coordination [3]. Although a number of investigations have been reported in the literature on pyridin-4-ylazo dyes [3][4][5][6], only a few pyridin-2-ylazo dyes have been synthesized [7,8], and to our knowledge no reports exist on 5-nitropyridin-2-yl-azo pushpull chromophore.…”

“…under conditions used for obtaining 2-nitrosopyridine in 44% yield [13], did not proceed. After the temperature was allowed to rise to 20°C, oxidation proceeded, and a yellow crude product 3 was obtained, that, unfortunately, was unstable in the solution and unlike 2-nitrosopyridine did not react with N-acetylphenylene-1,4-diamine (6) in the presence of AcOH. When oxidation of compound 4 was conducted in methanol, 2,5-dinitropyridine (5) was obtained in 78% yield.…”