Non-Linear Organic Dyes In Polyceram Hosts
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NON-LINEAR ORGANIC DYES IN POLYCERAM HOSTS J.M. Boulton, J.
Thompson, H.H. Fox, I. Gorodisher, G. Teowee, P.D. Calvert and D.R. Uhlmann Department of Materials Science and Engineering, University of Arizona, Tucson, AZ 85721.
ABSTRACT Non-linear organic dyes, such as 2-methyl-4-nitroaniline (MNA) and p-nitroaniline (pNA), have been incorporated in Polyceram monoliths and thick films prepared by the hydrolysis and co-condensation of tetraethoxysilane and trimethoxysilylpropyl substituted polyethyleneimine. Strong second harmonic generation was observed. 1.
INTRODUCTION
Sol-gel derived materials offer exciting potential as hosts for dye molecules [1,2]. For example, films containing laser dyes have been extensively studied [3-8], as well as materials incorporating dyes capable of hole burning [e.g., 9-11]. Organically modified silica gels containing spiropyranes show long-acting photochromic behavior [12]. Gels based on EtSi(OEt) 3 exhibit normal photochromic behavior (colorless to color), while Polycerams based on Si(OMe) 4 and poly(dimethylsiloxane) give reversed photochromism due to differences in cage properties. Sol-gel derived materials have been investigated as hosts for non-linear organics. For example, composites of silica and poly(p-phenylenevinylene) gave promising third order waveguiding films [13]. Organic dyes, such as 2-methyl-4-nitroaniline (MNA) have high values of second harmonic generation, but a necessary criterion for second order generation is that the molecular environment must be non-centrosymmetric. There has been some investigation into the effect of enclosing MNA in a gel network, with either a host material of silica gel [14,15] or a silica gel-PMMA composite [15, 16]. The silica gel host was inadequate, since the acidic surface allowed for the oxidative decomposition of the MNA, changing from yellow to brown [15]. PMMA incorporation provided a method for sealing and coating the pores to protect the dye. The changed porosity reduced scattering effects as well. The electro-optical DC Kerr effect of the composite has been studied [16]. The present authors have been investigating the properties of organically modified oxides (Polycerams) (17,18]. These unique, hybrid materials offer many advantages over conventional alkoxide-derived gels. Advantages include the ability to tailor the chemical and physical properties and the ability to form thick films and monoliths relatively easily. The present paper reports the results of incorporating nitroanilines in these materials.
Mat. Res. Soc. Symp. Proc. Vol. 180. 01990 Materials Research Society
988
2.
EXPERIMENTAL
2.1
Preparation of Materials
Tetraethoxysilane (TEOS) and trimethoxysilylpropyl substituted polyethyleneimine (MPEI), (50 wgt. pct. in isopropanol m.w. 1500-2000) were purchased from Petrarch (Bristol, PA). MNA and pNA were obtained from Aldrich Chemical Co. (Milwaukee, WI). All other reagents were reagent grade. Sample preparation consisted of refluxing TEOS and H20 (acidified to 0.15M HCl) in iso-propanol (IPA) at a H20:TEOS
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