Synthesis and characterization of luminescent organic-inorganic hybrid nanocomposite from polyhedral oligomeric silsesquioxane

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<ul><li><p>Synthesis and characterization of luminescent organic-inorganic</p><p>hybrid nanocomposite from polyhedral oligomeric silsesquioxane</p><p>Yan Feng a, Hong Yao Xu a,b,*, Wang Yan Nie a, Jia Yin Ying a</p><p>a School of Chemistry and Chemical Engineering &amp; Key Laboratory of Environment-friendly Polymer Materials of Anhui Province,</p><p>Anhui University, Hefei 230039, ChinabCollege of Material Science and Engineering &amp; State Key Laboratory of Chemical Fibers and Polymeric Materials Modification,</p><p>Donghua University, Shanghai 201620, China</p><p>Received 31 August 2009</p><p>Abstract</p><p>A novel polyhedral oligomeric silsesquioxane (POSS)-based organic-inorganic hybrid nanocomposite (EF-POSS) was prepared</p><p>by Pt-catalyzed hydrosilylation reaction of octahydridosilsesquioxane (T8H8, POSS) with a luminescent substituted acetylene (2-</p><p>ethynyl-7-(4-(4-methylstyryl)styryl)-9,9-dioctyl-9H-fluorene (EF)) in high yield. The hybrid nanocomposite was soluble in</p><p>common solvents such as CH2Cl2, CHCl3, THF and 1,4-dioxane. Its structure and property were characterized by FTIR,</p><p>NMR, TGA, UV and PL, respectively. The results show that the hybrid nanocomposite with high thermal stability emits stable</p><p>blue light as a result of photo excitation and possesses high photoluminescence quantum efficiency (FFL).</p><p># 2009 Hong Yao Xu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.</p><p>Keywords: POSS; Organic-inorganic hybrid nanocomposite; Photoluminescence; Thermal stability</p><p>Inorganic-organic hybrid polymers have attracted great interest recently because of their better performance in</p><p>thermal stability and oxidative resistance compared to their mother homogeneous polymers [1]. A typical hybrid</p><p>material will contain an organic phase bound covalently with inorganic moieties [2]. Polyhedral oligomeric</p><p>silsesquioxane (POSS) is a class of inorganic compounds that has a well-defined structure with a silica-like core</p><p>(Si8O12) surrounded by eight organic corner groups (functional or inert) [3]. The incorporation of nanosize POSS cores</p><p>into a polymer matrix can result in significant improvements in a variety of physical and mechanical properties.</p><p>In our previous work, the approach to generate functionalized cubic silsesquioxane nanocomposites mainly relied</p><p>on introducing functional group, for example, by hydrosilylation using octahydridosilsesquioxane [4,5] or free radical</p><p>polymerization using octavinylsilsesquioxane [610] nanoplatforms. As reported previously, the introduction of bulky</p><p>POSS could increase the photoluminescence quantum efficiencies and the thermal stability of the conjugated polymers</p><p>[1113]. Therefore, a luminescent substituted acetylene, 2-ethynyl-7-(4-(4-methylstyryl)styryl)-9,9-dioctyl-9H-</p><p>fluorene (EF), has been synthesized in our laboratory [14]. In this paper, we will report the synthesis and</p><p></p><p>Available online at</p><p>Chinese Chemical Letters 21 (2010) 753757</p><p>* Corresponding author at: College of Material Science and Engineering &amp; State Key Laboratory of Chemical Fibers and Polymeric Materials</p><p>Modification, Donghua University, Shanghai 201620, China.</p><p>E-mail address: (H.Y. Xu).</p><p>1001-8417/$ see front matter # 2009 Hong Yao Xu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.doi:10.1016/j.cclet.2009.12.027</p></li><li><p>characterization of POSS-based hybrid nanocomposite with star-type structure by hydrosilylation reaction of T8H8with EF. The photoluminescent and thermal properties of the hybrid nanocomposite were investigated in detail.</p><p>1. Experimental</p><p>Octahydridosilsesquioxane [(HSiO1.5)8, T8H8] was synthesized according to the procedures described in ref. [15].</p><p>2-Ethynyl-7-(4-(4-methylstyryl)styryl)-9,9-dioctyl-9H-fluorene (EF) was prepared in our laboratory. The reaction</p><p>performed using T8H8 with 8 equivalents of EF yielded POSS-based hybrid nanocomposite (EF-POSS) (Scheme 1).</p><p>In a typical reaction, 0.127 g (0.2 mmol) of EF and 10.6 mg (0.025 mmol) of T8H8 in 5 mL dried 1,4-dioxane were</p><p>stirred for 24 h at 60 8C under a nitrogen atmosphere, using the Pt (dcp) as catalyst. The reaction mixture wasprecipitated into hexane to produce a pale yellow powder that was collected by filtration. The powder was then re-</p><p>dissolved in minimal amount of tetrahydrofuran (THF), added dropwise into stirring hexane, and again collected by</p><p>filtration. The finally isolated precipitate was dried in vacuum at 30 8C to get yellow green powder in 60% yield.The resultant product was characterized by FTIR and 1H NMR, 13C NMR, 29Si NMR spectroscopies. The</p><p>thermogravimetric analysis (TGA) was performed in nitrogen flow at a heating rate of 10 8C/min. The UVvis spectrawere recorded on a Hitachi U-4100 spectrometer with a 1 cm quartz cell and photoluminescence (PL) emission spectra</p><p>were recorded using a Shimadzu RF-5301PC fluorometer. PL quantum efficiency (FFL) was determined by a similar</p><p>method described by Crosby and Demas [16] using 9,10-diphenylanthracene [17] as a standard.</p><p>2. Results and discussion</p><p>Fig. 1a shows the FTIR spectra of EF-POSS, EF and T8H8. The pure T8H8 showed three characteristic peaks at 2297</p><p>(SiH stretching), 1120 (SiOSi stretching) and 862 cm1 (SiH bending). The SiH characteristic absorption bandsalmost disappeared in the FTIR spectrum of hybrid nanocomposite after T8H8 reacted with 8-fold EF. However, the</p><p>characteristic SiOSi stretching vibration still existed in the spectrum of EF-POSS. The two characteristic absorption</p><p>bands of EF at 3316 and 2106 cm1, assigning to BBCH and CBBC stretching vibration in the substituted acetylene,disappeared in the hybrid nanocomposite and other EF characteristic absorption bands were still existent in FTIR</p><p>spectrum of resultant hybrid nanocomposite, hinting that the organic molecule EF has been covalently attached to the</p><p>T8H8 core to form the organic-inorganic hybrid nanocomposite (EF-POSS).</p><p>Fig. 1b shows the 1H NMR spectra of EF-POSS, EF and T8H8. Compared with EF and T8H8, all the absorption</p><p>peaks of the hybrid nanocomposite significantly were widened, the peak of BBCH at 3.17 ppm in the pure EF and the</p><p>peak of SiH at 4.25 ppm in the neat T8H8 disappeared in the spectrum of EF-POSS, further proving that</p><p>hydrosilylation reaction of T8H8 and EF has successfully carried out. Simultaneously, the characteristic acetylene</p><p>carbon resonance absorption of the monomer were not found in the 13C NMR spectrum of EF-POSS and all the other</p><p>absorption peaks of carbon atoms in EF-POSS were widened, further substantiating the molecular structure of the</p><p>organic-inorganic hybrid nanocomposite.</p><p>The 29Si NMR spectrum of EF-POSS is also shown in Fig. 1b. For pure T8H8, there was only one resonance peak at</p><p>83.1 ppm. In the spectrum of hybrid nanocomposite, there were three new resonance absorption peaks of CSifrom b-trans and a isomers at 77.2 and 80.2 ppm, and SiOH at 100.5 ppm, which resulted from thehydrolyzation of the part unreacted SiH in air [18]. Based on the ratio of the integral areas of the absorption peaks in</p><p>Y. Feng et al. / Chinese Chemical Letters 21 (2010) 753757754</p><p>Scheme 1. Synthetic route of hybrid nanocomposite.</p></li><li><p>the 29Si NMR spectrum, it could be calculated that the approximate five substituted acetylene molecules were</p><p>incorporated into one POSS core in the hybrid nanocomposite.</p><p>UVvis absorption and PL emission spectra of EF and EF-POSS in the dilute THF solution are shown in Fig. 2. The</p><p>absorption spectrum of EF showed a maximum wavelength at 384 nm, and two shoulder peaks at 368 and 405 nm,</p><p>respectively. The absorption bandwidth was approximately 150 nm. Correspondingly, the PL emission spectrum of EF</p><p>was located in blue light region and displayed vibrational structure with the peak centers at 420 and 445 nm</p><p>accompanied by a shoulder peak at 474 nm. The fluorescence bandwidth was also 150 nm. However, the maximumwavelength and shape of spectra exhibited obvious varieties in the absorption and PL emission spectra of the hybrid</p><p>nanocomposite EF-POSS. The absorption spectrum of EF-POSS showed some broadening to200 nm bandwidth andonly 2 nm red-shift compared to that of the monomer EF. Furthermore, the peak at 420 nm and the shoulder at 474 nm</p><p>in the PL emission spectrum of EF markedly weakened in that of EF-POSS. Only one maximum PL emission peak at</p><p>450 nm remained in the PL emission spectra of EF-POSS and showed a slight red-shift of 5 nm in comparison with that</p><p>of EF. The bandwidth of fluorescence spectrum was also broadened to 180 nm. The disappearance of the vibronicfine structure and the broadening of spectra in the hybrid nanocomposite may be due to some new interaction of p-electronic systems between POSS core and the organic molecule EF, which is covalently attached to the T8H8 core by</p><p>the Pt-catalyzed hydrosilylation reaction. The EF has high PL quantum efficiency (FFL) of 0.65, andFFL of EF-POSS</p><p>is drastically enhanced to 0.77, which may be attributed to the aggregation hindrance of the EF molecules on POSS</p><p>Y. Feng et al. / Chinese Chemical Letters 21 (2010) 753757 755</p><p>Fig. 1. FTIR and 1H NMR spectra of EF-POSS, EF and T8H8. The inset is29Si NMR spectrum of EF-POSS.</p><p>Fig. 2. UVvis absorption and PL emission spectra of EF and EF-POSS in the dilute THF solution.</p></li><li><p>units, in turn, to reduce the degree of dimer formation after excitation [13,19,20]. Therefore, the fluorescent property</p><p>of the hybrid nanocomposite indicates that EF-POSS is likely to be an efficient blue light-emitting hybrid</p><p>nanocomposite.</p><p>As shown in Fig. 3, the thermal degradation temperature Td (5% weight loss) of EF and EF-POSS is 391 and</p><p>408 8C, furthermore, the char yield of EF and EF-POSS at 700 8C is 17.4% and 36.6%, respectively. The Td and charyield of hybrid nanocomposite are obvious elevated in comparison with that of monomer, displaying that the thermal</p><p>stability of the hybrid nanocomposite is enhanced by the incorporation of inorganic POSS core [6,7].</p><p>In conclusion, a novel POSS-based organic-inorganic hybrid nanocomposite was successfully synthesized and its</p><p>photoluminescent property and thermal stability were evaluated. The results indicate that the resultant hybrid</p><p>nanocomposite is not only endowed with stable photoluminescent property and high PL quantum efficiency, but also</p><p>exhibited enhanced thermal stability. This work provides a novel method for designing blue light-emitting hybrid</p><p>nanocomposite with high luminescent quantum efficiency and enhanced thermal stability.</p><p>Acknowledgments</p><p>This research was financially supported by the National Natural Science Fund of China (Nos. 90606011 and</p><p>50472038), Ph.D. Program Foundation of Ministry of Education of China (No. 20070255012), Shanghai Leading</p><p>Academic Discipline Project (No. B603), the Program of Introducing Talents of Discipline to Universities (No. 111-2-</p><p>04) and Open Project of the State Key Laboratory of Crystal Materials (No. KF0809), Youth Scientific Research Fund</p><p>of Anhui University and the Excellent Youth Fund in University of Anhui Province (No. 2008jq1020).</p><p>References</p><p>[1] A. Tsuchida, C. Bolln, F.G. Sernetz, Macromolecules 30 (1997) 2818.</p><p>[2] T.S. Haddad, J.D. Lichtenhan, Macromolecules 29 (1996) 7302.</p><p>[3] P.T. Mather, H.G. Jeon, A. Romo-Uribe, Macromolecules 32 (1999) 1194.</p><p>[4] X. Su, H. Xu, Y. Deng, Mater. Lett. 62 (2008) 3818.</p><p>[5] W.Y. Nie, G. Li, Y. Li, Chin. Chem. Lett. 20 (2009) 738.</p><p>[6] H.Y. Xu, B.H. Yang, J.F. Wang, Macromolecules 38 (2005) 10455.</p><p>[7] H. Xu, B. Yang, J. Wang, J. Polym. Sci. A: Polym. Chem. 45 (2007) 5308.</p><p>[8] B. Yang, H. Xu, J. Wang, J. Appl. Polym. Sci. 106 (2007) 320.</p><p>[9] H. Xu, B. Yang, X. Gao, J. Appl. Polym. Sci. 101 (2006) 3730.</p><p>[10] B. Yang, J. Li, J. Wang, J. Appl. Polym. Sci. 111 (2009) 2963.</p><p>[11] M.Y. Lo, K. Ueno, H. Tanabe, Chem. Rec. 6 (2006) 157.</p><p>[12] H.J. Cho, D.H. Hwang, J.I. Lee, Chem. Mater. 18 (2006) 3780.</p><p>[13] W.J. Lin, W.C. Chen, W.C. Wu, Macromolecules 37 (2004) 2335.</p><p>[14] X. Wang, J. Wu, H. Xu, J. Polym. Sci. A: Polym. Chem. 46 (2008) 2072.</p><p>Y. Feng et al. / Chinese Chemical Letters 21 (2010) 753757756</p><p>Fig. 3. TGA thermograms of EF and EF-POSS.</p></li><li><p>[15] P.A. Agaskar, J. Am. Chem. Soc. 111 (1989) 6858.</p><p>[16] G.A. Crosby, J.N. Demas, J. Phys. Chem. 75 (1971) 991.</p><p>[17] I.B. Berlman, Handbook of Fluorescence Spectra of Aromatic Molecules, Academic Press, New York, 1965.</p><p>[18] I.S. Isayeva, J.P. Kennedy, J. Polym. Sci. A: Polym. Chem. 42 (2004) 4337.</p><p>[19] C.H. Chou, S.L. Hsu, K. Dinakaran, Macromolecules 38 (2005) 745.</p><p>[20] J. Lee, H.J. Cho, N.S. Cho, J. Polym. Sci. A: Polym. Chem. 44 (2006) 2943.</p><p>Y. Feng et al. / Chinese Chemical Letters 21 (2010) 753757 757</p><p>Synthesis and characterization of luminescent organic-inorganic hybrid nanocomposite from polyhedral oligomeric silsesquioxaneExperimentalResults and discussionAcknowledgmentsReferences</p></li></ul>