PREPARATION OF HYBRID ORGANIC-INORGANIC POLYMERS DOPED WITH LUMINESCENT MOLECULES AND THEIR CHARACTERIZATIONS

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1 PREPARATION OF HYBRID ORGANIC-INORGANIC POLYMERS DOPED WITH LUMINESCENT MOLECULES AND THEIR CHARACTERIZATIONS Pina Pitriana 1, Fitri Fitrilawati 1, Pardi Sampe Tola 2, Rany Miranti 2, Rahmat Hidayat2 1 Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran 2 Physics of Magnetic and Photonic Research Group Division, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung Abstract. We have synthesized hybrid organic-inorganic polymer prepared from an organically modified siloxane monomer using sol-gel technique. Europium (III) complexes and organic dye lasers that exhibit strong luminescence properties were incorporated as doped materials. The effect of some synthesis condition parameters on the gel yield efficiency and the characterization results, using FT-IR, UV-Vis absorption and luminescence spectroscopy, will be presented. The hybrid polymer doped with Eu(DBM) 3 complexes prepared in this work shows better optical transmittance compared to the hybrid polymer mixed with commercially available Eu(DBM)3-phen, which is attributed to the reduction of complex segregation in the polymers. Keywords: organic-inorganic hybrid polymers, lanthanide complexes, organic dye doped polymers, luminescence. 1 Introduction Polymers or plastics are materials that we can find easily in our daily life in various applications for replacing glass, metal and wood materials. Polymers, such as acrylic and styrene based polymers are typical example of most commonly used polymers. However, such kinds of polymers are still having some weakness on their mechanic and thermal stability. In particular, their glass transition temperature (Tg) and decomposition temperature (Td) are relatively low. In order to overcome those limitations, there are many efforts to develop new polymers that have good functionality and mechanic and thermal stability. [1] The polymers that called as hybrid polymers are rapidly emerging recently. The polymers contain organic and inorganic backbones such that they have similar properties like inorganic glasses or ceramics but can be functionalized and processed like organic carbon based polymers. [2,3] For some applications, these hybrid polymers are often used as host matrix for functional organic materials such as dyes laser [4], metal complexes [5], and rare earth ions [6]. These doped hybrid polymers can be used for waveguide [5], laser source [4,7]. Hybrid polymers doped with rare earth ions, such as Erbium (Er 3+ ), Neodymium (Nd 3+ ) and Europium (Eu 3+ ), exhibit luminescence properties which are suitable for laser source and optical amplifier in optical communications [4]. Another lanthanide ion like Gd 3+ has quantum efficiency close to 1, but its luminescence occurs at ultra-violet area so that it is not interesting for polymer fiber laser. 2 Experiment The preparation of hybrid polymers involves two steps of polymerizations, that is, the polymerization of inorganic chains by sol-gel process and the polymerization of organic chains by thermal- or photo-polymerization. The sol-gel process consists of hydrolysis and condensation processes, which give the reaction product in the form of gel. We called it as precursor gel hereafter. This precursor gel was made from a solution with composition of monomer (3-(trimethoxysilyl)propyl methacrylate), ethanol, water and acid catalyst. Generally, although sol-gel process does not involve complicated reactions, controlling the process rate is rather difficult. In order to find the composition and process condition that will give the optimum yield of gel product per monomer mass, the sol-gel synthesis was carried out for various monomer:h2o weight ratio. During the preparation of these gel precursors, organic laser dye, such as Eu(DBM)3, Eu(DBM)3-phen, Rhodamin 6G perchlorate (R6G), or [2-[2-[4- (dimethylamino)-phenyl]ethenyl]-6-methyl-4h-pyran-4-ylidene]-propanedinitrile (DCM) was added in the solution. For preparing thin films of these hybrid polymers, the precursor gel was drop-casted or spincasted on a substrate and then photo-polymerized by using a UV lamp for several minutes. Preand post-bake were done at o C for more than one hour in an oven. These thin films are then characterized by using a FT-IR spectrometer, UV-Vis spectrometer and photoluminescence spectrometer utilizing a CCD spectrometer. 468

2 Figure 1. (a) The curve of sol-gel process yield versus the weight ratio of monomer:h 2O. (b) The dependence of sol-gel process yield on the process duration for the monomer:h2o weight ratio of 1:16. 3 Results and Discussion Figure 1(a) shows the yield of sol-gel process for various monomer:h2o weight ratio, that is 1:4, 1:8, 1:12, 1:16, and 1:20 1:16. The yield was calculated from the weight of obtained precursor divided by the weight of monomer used in the process. The figure shows that the yield is almost independent of the monomer:h2o weight ratio. The yield is approximately 85%. On the other hand, Figure 1(b) shows that the yield of the sol-gel process using solution with the monomer:h2o weight ratio of 1:16. The data shows that the yield is strongly dependent on the duration of sol-gel process and there is a minimum or critical time required for changing from sol to gel. We tried to fit the data with exponential function in the form of where t is the sol-gel process duration, tc is the critical time for gel formation and ymax is the estimated maximum yield that can be obtained at infinite time of process duration. From the curve fitting, for this particular process condition, we obtained that critical time is about 500 minutes and the gel formation rate (k) is about 3.2 mg/min. The yield saturates after 1500 minutes showing that the monomers have been significantly depleted. Because the reaction rate is commonly dependent on the square of monomer concentration, the gel formation rate therefore significantly decreases at time larger than 1500 minutes. FT-IR spectra in Figure 2 show that the product of sol-gel process has -Si-O-Si- inorganic chain as indicated by the reduction infrared absorption band at about 1150 cm -1 in comparison to that observed in the FT-IR spectrum of the monomer. Thin films of hybrid polymers have been successfully prepared by photo-polymerization technique using radical photo-initiator under UV light radiation. After photo-polymerization, the reduction of C=C absorption band at about 1600 cm -1 was clearly observed. This indicates the conversion C=C bond to C-C bond which is the result from the polymerization of methacrylate (organic) group. The precursor gels that were obtained in this work show high optical transparency at the visible region. The absorption spectra in Figure 3 show that hybrid polymer doped with Eu(DBM)3, without the presence of phenanthroline ligand, have much better optical transparency than the one doped with Eu(DBM)3-phen. It can be clearly seen that the absorption spectra of hybrid polymer doped with Eu(DBM)3-phen have long absorption tail extending to long wavelength region. These results indicates that doping with Eu(DBM)3 leads to better solubility of the complex resulting in much less complex segregation in comparison to the case of doping with Eu(DBM)3-phen. The photoluminescence characteristics of this Eu(DBM)3 doped hybrid polymer, however, is almost similar that of the Eu(DBM)3-phen doped polymer, as indicated in Figure 4. This polymer also shows intense photoluminescence. Other polymer hybrids that are doped with R6G and DCM also show intense photoluminescence with similar spectra as observed when the dyes are dissolved in ethanol. (1) 469

3 4 Conclusion In this work, we have successfully prepared the precursor gel of hybrid polymers containing luminescent or organic laser dyes such as Europium complexes, R6G and DCM. The segregation of dyes was not observed Europium complexes without the presence of phenanthroline ligand leading to high optical transparency. Intense photoluminescence were observed all cases of doping, which indicates that the polymerization process (including the solgel process) and the polymer structure do not disrupt the dyes. Figure 2. FT-IR spectra of precursor gel of hybrid polymer and hybrid polymer obtained after photopolymerization. Figure 3. Absorption spectra of hybrid polymer doped with 3% and 5% Eu(DBM)3. Inset: 3% dan 5% Eu(DBM)3-phen. 470

4 Figure 4. Photoluminescence spectrum of hybrid polymer doped with Eu(DBM)3. Acknowledgement Figure 5. Photoluminescence spectrum of hybrid polymer doped with R6G. We would like to thank for the supports from Hibah Bersaing Project, no. 013/SP2H/PP/DP2M/III/2008 and JSPS/DGHE Joint Research Project References [1] Haas, Karl-Heinz. (2003). Hybrid Inorganic/Organic Polymers with Nanoscale Building Blocks: Precursors, Processing, Properties and Applications. ISC Fraunhofer Institut für Silikatforschung, Würzburg, Germany. [2] Soo Bae, Byeong. Sol-Gel Nano material and Prosses, Dept of Material Sceince and Engineering. [3] Kickelbick, Guido. Hybrid Materials. (2007).Wiley-VCH Verlag GmbH & Co. KgaA [4] Lebeau, Benedicte & Sanchez, Clement. (1999). Sol-Gel Derived Hybrid Inorganic-Organic Nanocomposites for Optics. Solid State & Material Science, 4: [5] Wang, Bing & Wilkes, Garth L. (1992). High Refractive-Index Ceramic/Polymer Hybrid Material

5 [6] Condoncillo, E et al. (1998). Room Tempherature Synthesis of Hybrid Oranic-Inorganic Nanocomposites Containing Eu2 +. Journal Material Chemistry. 8(3), [7] Obi, Samuel. (2006). Replicated Optical Microstructures in Hybrid Polymers: Process Technology and Applications. Doctor of Science Dissertation. Institute of Microtechnology University of Neuchâtel Rue Jaquet-Droz,Neuchâtel Switzerland. [8] Arsyad, Waode Sukmawati. (2007). Preparasi dan Spektroskopi Optik Polimer Hibrid Organik-Inorganik dengan Kandungan Europium (III) Kompleks untuk Aplikasi Komponen Optik. Thesis. ITB. PINA PITRIANA, FITRI FITRILAWATI Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, Jl. Raya Jatinangor Km.21, Sumedang 45363, West Java qolbunsalim_pina@yahoo.co.uk PARDI SAMPE TOLA, RANY MIRANTI, RAHMAT HIDAYAT Physics of Magnetic and Photonic Research Group Division, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung Jl. Ganesha 10, Bandung 40132, Jawa Barat 472