Materials Letters 62 (2008) 3818–3820

Contents lists available at ScienceDirect

Materials Letters

j ourna l homepage: www.e lsev ie r.com/ locate /mat le t

Preparation and optical limiting properties of a POSS-containing organic–inorganichybrid nanocomposite

Xinyan Su a, Hongyao Xu a,b,⁎, Yan Deng c, Jirong Li a, Wei Zhang a, Pei Wang c

a School of Chemistry and Chemical Engineering, Anhui University, Hefei 230039, Chinab College of Material Science and Engineering & State Key Laboratory of Chemical Fibers and Polymeric Materials, Donghua University, Shanghai 201620, Chinac Department of Physics, University of Science and Technology of China, Hefei 230026, China

⁎ Corresponding author. College of Material ScienceLaboratory of Chemical Fibers and Polymeric Materials,201620, China. Tel.: +86 21 67792874.

E-mail address: hongyaoxu@163.com (H. Xu).

0167-577X/$ – see front matter © 2008 Elsevier B.V. Aldoi:10.1016/j.matlet.2008.04.074

A B S T R A C T

A R T I C L E I N F O

Article history:

A novel POSS-containing org Received 9 January 2008Accepted 28 April 2008Available online 5 May 2008

Keywords:NanocompositePOSSOrganic–inorganic hybridOptical limiting

anic–inorganic hybrid nanocomposite (P) was prepared by the Pt-catalyzed hydro-silylation reaction of octahydridosilsesquioxane (T8H) with substituted acetylene, CH≡CCH2O–C6H4–COO–C6H4-p-NfN–C6H4-p-OCH3 (M). The hybrid nanocomposite was soluble in common solvents such as CHCl3, THF, tolueneand C2H4Cl2. Its structure was characterized by FT-IR, 1H NMR, and 29Si NMR, respectively. Optical limitingpropertywas evaluated by a Q-switchedNd:YAG laser systemwith awavelength of 532 nm, 4 ns pulsewidth anda repetition of 1 Hz. The result shows that the POSS-based organic–inorganic hybrid nanocomposite exhibitsnovel optical limiting property, well photo and high thermal stability (Td, temperature for 5%weight loss, as highas 319 °C). The optical limiting property increases with the increase of solution concentration.

© 2008 Elsevier B.V. All rights reserved.

1. Introduction

With the rapid development of laser technology, there is a strongdemand for optical limiting (OL) materials to protect human eyes andoptical sensors from intense laser beams. Many materials such asfullerenes (C60) [1], phthalocyanines [2], porphyrins [3], organome-tallic compounds [4], and polyacetylenes and their nanocomposites[5–8] have been investigated. Recently, polyhedral oligomeric silses-quioxane (POSS)-based hybrid materials have received considerableinterest among the academic community and industries due to itsunique structure of POSS. POSS is a type of nanoscale molecule thathas a well-defined structure with a cube-like inorganic core (Si8O12)surrounded by eight organic corner groups (reactive or inert) [9]. Thenumber and type of the functional corner groups on POSS cages can bereadily varied, which makes POSS molecules to be excellent nanodi-mensional build blocks for preparing various organic–inorganic hy-brid nanocomposites [10–13]. Our group has recently reported a seriesof POSS-containing hybrid materials, which exhibit superior thermalproperties and good solubility [14–19]. Hence, POSS is incorporatedinto organic NLO chromophores to produce POSS-based organic–in-organic hybrid functional material (Scheme 1) and expected to endowthe hybrid materials with novel optical properties and enhancedthermal stability.

and Engineering & State KeyDonghua University, Shanghai

l rights reserved.

2. Experimental

Octahydridosilsesquioxane [(HSiO1.5)8, T8H] was synthesized accor-ding to the procedures described in ref [20]. 4-((4-Methoxyphenyl)diazenyl)phenyl 4-(prop-2-ynyloxy)benzoate (M) was made in ourlaboratory [21].

FTIR spectra were measured with a Nicolet NEXUS 870 FTIR spec-trophotometer. 1H NMR and 29Si NMR spectra were recorded on aBruker DMX-400 spectrometer using chloroform-d (CDCl3). TGA wasundertaken on a TA Instruments TGA 2050 thermogravimetric analy-zer with a heating rate of 20 °C/min in the nitrogen atmosphere. Theinvestigation of the optical limiting properties of the samples wascarried out by a Q-switched Nd:YAG laser system with an outputwavelength of 532 nmwith a 4 ns pulsewidth and a repetition of 1 Hz.The experimental arrangement is similar with that in the literature[21]. The samples were housed in quartz cells with a path of 2 mm.

Thehydrosilylation reaction for preparinghybrid nanocompositewascarried out under nitrogen using a vacuum-line system. 5 mL C2H4Cl2,21.2 mg (0.05 mmol) T8H, 1.0 mg Pt(dcp) and 0.154 g (0.4 mmol) chro-mophoreMwere added into abaked20mL Schlenk tubewith a side arm.The mixture was stirred at 80 °C for 10 h. After cooling to the roomtemperature, the mixture was then poured into 200 mL hexane undervigorously agitation to dissolve the unreacted parts and precipitate theresultant compound. The precipitate was centrifuged and redissolved inTHF. Then the THF solution was added dropwise into 200 mL hexane toprecipitate the compound. The dissolution-precipitation process wasrepeated three times, and the finally isolated precipitate was dried invacuum at 30 °C to get yellow powder. Yield: 51.3%. Mn=3610, PDI, 1.02(GPC, polystyrene). FT-IR (KBr, cm−1): 3071 (fC–H), 2929, 2838 (CH3),

Scheme 1. Synthetic route of organic–inorganic hybrid nanocomposite.

Fig. 2. Optical responses to 4 ns, 532 nm laser light of nanocomposite (P) in THF withdifferent linear transmittances.

3819X. Su et al. / Materials Letters 62 (2008) 3818–3820

2264 (Si–H), 1734 (CfO), 1603 (CfC), 1254 (C–O–C), 1107 (Si–O–Si), 841(p-Ar). 1H NMR (CDCl3, 400 MHz, ppm), δ 8.07, 7.87 (br, Ar–H), 6.90(br, Ar–H), 6.11 (br, CHfCHSi β-trans), 5.97 (br, CHfCHSi β-trans andCH2fC–Si α), 4.70 (br, OCH2,), 4.26(s, Si–H), 3.88 (br, OCH3). 29Si NMR(CDCl3, 79.5 MHz, ppm) δ −80.01 (Si–C β-trans), −81.62 (Si–C α), −83.51(Si–H).

3. Results and discussion

The POSS-based hybrid nanocomposite (P) containing azobezene chromophorewas synthesized by hydrosilylation reaction. The IR spectrum of hybrid nanocompositeshows strong characteristic absorption of Si–O–Si at 1107 cm−1, along with CfOvibration absorption band at 1734 cm−1. Simultaneously, the characteristic ≡C–H andC≡C stretching vibration of chromophore (M) completely disappear when chromo-phore is incorporated into POSS, indicating the hydrosilylation reaction is effectivelyactualized. Fig. 1 displays the 1H NMR spectra of chromophore (M) and hybrid nano-composite (P). The absorption of the acetylene proton in the 1H NMR spectrum ofchromophore (M) appears at δ 2.58 ppm as a singlet peak, which, however, completelydisappears in the 1H NMR spectrum of hybrid (P). On the contrary, nanocomposite(P) exhibits broad characteristic absorption peaks at δ 6.11, 5.97 ppm corresponding tothe olefin protons, further supporting that C≡C have completely changed into CfCgroup and the chromophores are covalently attached to the POSS core. Simultaneously,the 29Si NMR spectrum (the inset of Fig. 1) of nanocomposite shows new peaks of Si–Cfrom β-trans and α isomers at -80.01 and −81.62 ppm, further supported the objectivehybrid was synthesized successfully by hydrosilylation reaction. Based on the ratio ofthe integrated areas of the absorption peaks in the 29Si NMR spectrum [19], it can becalculated that the approximate several chromophores were incorporated into onePOSS molecule in the nanocomposite.

Fig. 2 shows optical responses of nanocomposite in THF with different lineartransmittances. At very low incident fluence, the output fluence of nanocompositesolution increases linearly with the incident fluence obeying the Beer–Lambert law.However, at high incident fluence, a nonlinear relationship between the output andinput fluence is observed. With a further increase in the incident fluence, the trans-mitted fluence of P solution reaches a plateau, showing significant optical limitingproperty. From Fig. 2, it is also found that the limiting effect is affected by concentration

Fig. 1. 1H NMR spectra of chromophore (M) and nanocomposite (P) in CDCl3. The inset is29Si NMR spectrum of nanocomposite (P).

and the limiting threshold decreases from 0.77 to 0.41 J/cm2 when solution con-centration increases from 0.49 mg/mL(T=85%) to 1.07 mg/mL (T=54%), which may beowing to higher concentration solution having more molecules per unit volume toabsorb the energy of the harsh laser more efficiently [21]. The optical limiting pro-perties of the nanocomposite may mainly originate from RSA [22]. Simultaneously, wemeasured the optical limiting properties of monomer at the two transmittance (T=85%,T=54%) and UV–vis absorption spectrum of the nanocomposite before and after thelaser irradiation, respectively, and found that the OL property of the nanocomposite atthe same transmittance (T=85%, T=54%, respectively) does not show significantlydifference compared with that of M, and the pattern and intensity of UV–vis absorptionspectrum have almost no change, indicating that incorporation the silsesquioxane core

Fig. 3. TGA thermograms of azobezene chromophore (M) and nanocomposite (P) at aramp rate of 20 °C/min in nitrogen flow.

3820 X. Su et al. / Materials Letters 62 (2008) 3818–3820

onto the NLO chromophore has no effect on the optical limiting property of thechromophore and the hybrid nanocomposite also possesses good photostability.

As shown in Fig. 3, the thermal degradation temperature Td (5% weight loss) ofchromophore (M) and nanocomposite (P) are 272 °C and 319 °C, respectively. The Td ofnanocomposite is obvious elevated in comparison with that of chromophore, displayingthat the thermal stability of the hybrid nanocomposite is greatly enhanced by the in-corporation of inorganic POSS core [14,19,23].

4. Conclusion

In conclusion, an organic–inorganic hybrid nanocomposite was suc-cessfully synthesized and characterized. Its optical limitingpropertyandthermal stability were evaluated. The results indicate that the hybridnanocomposite yieldedby incorporation of chromophore into POSS coreis not only endowed with novel optical limiting property, but also exhi-bited well photo and thermal stability. This work provides a novelmethod for design of practical optical limiting materials.

Acknowledgement

This research was financially supported by the National NaturalScience Fund of China (Grant Nos. 90606011 and 50472038), Pro-gram for New Century Excellent Talents in University (NCET-04-0588) and Ph.D. Program Foundation of Ministry of Education ofChina (No. 20070255012).

References

[1] Tutt LW, Kost A. Nature 1992;356:225.[2] Chen Y, O'Flaherty S, Fujitsuka M, Hanack M, Subramanian LR, Ito O, et al. Chem

Mater 2002;14:5163.[3] McEwan K, Lewis K, Yang G-Y, Chng L-L, Lee Y-W, Lau W-P, et al. Adv Funct Mater

2003;13:863.[4] Pittman M, Plaza P, Martin MM, Meyer YH. Opt Commun 1998;158:201.[5] Lam JWY, Tang BZ. Acc Chem Res 2005;38:745.[6] Li Z, Dong Y, HausslerM, Lam JWY, Dong Y,Wu L, et al. J Phys Chem B 2006;110:2302.[7] Tang BZ, Xu H, Lam JWY, Lee PPS, Xu K, Sun Q, et al. Chem Mater 2000;12:1446.[8] Tang BZ, Xu H. Macromolecules 1999;32:2569.[9] Baney RH, Itoh M, Sakakibara A, Suzuki T. Chem Rev 1995;95:1409.[10] Liu L, Hu Y, Song L, Chen H, Nazare S, Hull TR. Mater Lett 2007;61:1077.[11] Chena Y, Kang E-T. Mater Lett 2004;58:3716.[12] Cho HJ, Hwang DH, Lee JI, Jung YK, Park JH, Lee J, et al. Chem Mater 2006;18:3780.[13] Lin WJ, Chen WC, Wu WC, Niu YH, Jen AKY. Macromolecules 2004;37:2335.[14] Xu H, Yang B, Wang J, Guang S, Li C. J Polym Sci, Part A: Polym Chem 2007;45:5308.[15] Yang B, Xu H, Wang J, Gang S, Li C. J Appl Polym Sci 2007;106:320.[16] Xu H, Yang B, Gao X, Li C, Guang S. J Appl Polym Sci 2006;101:3730.[17] Xu H, Kuo S-W, Lee J-S, Chang F-C. Polymer 2002;43:5117.[18] Huang C-F, Kuo S-W, Lin H-C, Chen J-K, Chen Y-K, Xu H, et al. Polymer

2004;45:5913.[19] Xu H, Yang B, Wang J, Guang S, Li C. Macromolecules 2005;38:10455.[20] Agaskar PA. J Am Chem Soc 1989;111:6858.[21] Yin S, Xu H, Su X, Li G, Song Y, Lam JWY, et al. J Polym Sci, Part A: Polym Chem

2006;44:2346.[22] Sun WF, Bader MM, Carvalho T. Opt Commun 2003;215:185.[23] Haddad TS, Lichtenhan JD. Macromolecules 1996;29:7302.