Synthesis and characterization of luminescent organic-inorganic

hybrid nanocomposite from polyhedral oligomeric silsesquioxane

Yan Feng a, Hong Yao Xu a,b,*, Wang Yan Nie a, Jia Yin Ying a

a School of Chemistry and Chemical Engineering & Key Laboratory of Environment-friendly Polymer Materials of Anhui Province,

Anhui University, Hefei 230039, Chinab College of Material Science and Engineering & State Key Laboratory of Chemical Fibers and Polymeric Materials Modification,

Donghua University, Shanghai 201620, China

Received 31 August 2009

Abstract

A novel polyhedral oligomeric silsesquioxane (POSS)-based organic-inorganic hybrid nanocomposite (EF-POSS) was prepared

by Pt-catalyzed hydrosilylation reaction of octahydridosilsesquioxane (T8H8, POSS) with a luminescent substituted acetylene (2-

ethynyl-7-(4-(4-methylstyryl)styryl)-9,9-dioctyl-9H-fluorene (EF)) in high yield. The hybrid nanocomposite was soluble in

common solvents such as CH2Cl2, CHCl3, THF and 1,4-dioxane. Its structure and property were characterized by FTIR,

NMR, TGA, UV and PL, respectively. The results show that the hybrid nanocomposite with high thermal stability emits stable

blue light as a result of photo excitation and possesses high photoluminescence quantum efficiency (FFL).

# 2009 Hong Yao Xu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Keywords: POSS; Organic-inorganic hybrid nanocomposite; Photoluminescence; Thermal stability

Inorganic-organic hybrid polymers have attracted great interest recently because of their better performance in

thermal stability and oxidative resistance compared to their mother homogeneous polymers [1]. A typical hybrid

material will contain an organic phase bound covalently with inorganic moieties [2]. Polyhedral oligomeric

silsesquioxane (POSS) is a class of inorganic compounds that has a well-defined structure with a silica-like core

(Si8O12) surrounded by eight organic corner groups (functional or inert) [3]. The incorporation of nanosize POSS cores

into a polymer matrix can result in significant improvements in a variety of physical and mechanical properties.

In our previous work, the approach to generate functionalized cubic silsesquioxane nanocomposites mainly relied

on introducing functional group, for example, by hydrosilylation using octahydridosilsesquioxane [4,5] or free radical

polymerization using octavinylsilsesquioxane [6–10] nanoplatforms. As reported previously, the introduction of bulky

POSS could increase the photoluminescence quantum efficiencies and the thermal stability of the conjugated polymers

[11–13]. Therefore, a luminescent substituted acetylene, 2-ethynyl-7-(4-(4-methylstyryl)styryl)-9,9-dioctyl-9H-

fluorene (EF), has been synthesized in our laboratory [14]. In this paper, we will report the synthesis and

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Chinese Chemical Letters 21 (2010) 753–757

* Corresponding author at: College of Material Science and Engineering & State Key Laboratory of Chemical Fibers and Polymeric Materials

Modification, Donghua University, Shanghai 201620, China.

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

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

characterization of POSS-based hybrid nanocomposite with star-type structure by hydrosilylation reaction of T8H8

with EF. The photoluminescent and thermal properties of the hybrid nanocomposite were investigated in detail.

1. Experimental

Octahydridosilsesquioxane [(HSiO1.5)8, T8H8] was synthesized according to the procedures described in ref. [15].

2-Ethynyl-7-(4-(4-methylstyryl)styryl)-9,9-dioctyl-9H-fluorene (EF) was prepared in our laboratory. The reaction

performed using T8H8 with 8 equivalents of EF yielded POSS-based hybrid nanocomposite (EF-POSS) (Scheme 1).

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

stirred for 24 h at 60 8C under a nitrogen atmosphere, using the Pt (dcp) as catalyst. The reaction mixture was

precipitated into hexane to produce a pale yellow powder that was collected by filtration. The powder was then re-

dissolved in minimal amount of tetrahydrofuran (THF), added dropwise into stirring hexane, and again collected by

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

thermogravimetric analysis (TGA) was performed in nitrogen flow at a heating rate of 10 8C/min. The UV–vis spectra

were recorded on a Hitachi U-4100 spectrometer with a 1 cm quartz cell and photoluminescence (PL) emission spectra

were recorded using a Shimadzu RF-5301PC fluorometer. PL quantum efficiency (FFL) was determined by a similar

method described by Crosby and Demas [16] using 9,10-diphenylanthracene [17] as a standard.

2. Results and discussion

Fig. 1a shows the FTIR spectra of EF-POSS, EF and T8H8. The pure T8H8 showed three characteristic peaks at 2297

(Si–H stretching), 1120 (Si–O–Si stretching) and 862 cm�1 (Si–H bending). The Si–H characteristic absorption bands

almost disappeared in the FTIR spectrum of hybrid nanocomposite after T8H8 reacted with 8-fold EF. However, the

characteristic Si–O–Si stretching vibration still existed in the spectrum of EF-POSS. The two characteristic absorption

bands of EF at 3316 and 2106 cm�1, assigning to BBC–H and CBBC stretching vibration in the substituted acetylene,

disappeared in the hybrid nanocomposite and other EF characteristic absorption bands were still existent in FTIR

spectrum of resultant hybrid nanocomposite, hinting that the organic molecule EF has been covalently attached to the

T8H8 core to form the organic-inorganic hybrid nanocomposite (EF-POSS).

Fig. 1b shows the 1H NMR spectra of EF-POSS, EF and T8H8. Compared with EF and T8H8, all the absorption

peaks of the hybrid nanocomposite significantly were widened, the peak of BBC–H at 3.17 ppm in the pure EF and the

peak of Si–H at 4.25 ppm in the neat T8H8 disappeared in the spectrum of EF-POSS, further proving that

hydrosilylation reaction of T8H8 and EF has successfully carried out. Simultaneously, the characteristic acetylene

carbon resonance absorption of the monomer were not found in the 13C NMR spectrum of EF-POSS and all the other

absorption peaks of carbon atoms in EF-POSS were widened, further substantiating the molecular structure of the

organic-inorganic hybrid nanocomposite.

The 29Si NMR spectrum of EF-POSS is also shown in Fig. 1b. For pure T8H8, there was only one resonance peak at

�83.1 ppm. In the spectrum of hybrid nanocomposite, there were three new resonance absorption peaks of C–Si

from b-trans and a isomers at �77.2 and �80.2 ppm, and Si–OH at �100.5 ppm, which resulted from the

hydrolyzation of the part unreacted Si–H in air [18]. Based on the ratio of the integral areas of the absorption peaks in

Y. Feng et al. / Chinese Chemical Letters 21 (2010) 753–757754

Scheme 1. Synthetic route of hybrid nanocomposite.

the 29Si NMR spectrum, it could be calculated that the approximate five substituted acetylene molecules were

incorporated into one POSS core in the hybrid nanocomposite.

UV–vis absorption and PL emission spectra of EF and EF-POSS in the dilute THF solution are shown in Fig. 2. The

absorption spectrum of EF showed a maximum wavelength at 384 nm, and two shoulder peaks at 368 and 405 nm,

respectively. The absorption bandwidth was approximately 150 nm. Correspondingly, the PL emission spectrum of EF

was located in blue light region and displayed vibrational structure with the peak centers at 420 and 445 nm

accompanied by a shoulder peak at 474 nm. The fluorescence bandwidth was also �150 nm. However, the maximum

wavelength and shape of spectra exhibited obvious varieties in the absorption and PL emission spectra of the hybrid

nanocomposite EF-POSS. The absorption spectrum of EF-POSS showed some broadening to�200 nm bandwidth and

only 2 nm red-shift compared to that of the monomer EF. Furthermore, the peak at 420 nm and the shoulder at 474 nm

in the PL emission spectrum of EF markedly weakened in that of EF-POSS. Only one maximum PL emission peak at

450 nm remained in the PL emission spectra of EF-POSS and showed a slight red-shift of 5 nm in comparison with that

of EF. The bandwidth of fluorescence spectrum was also broadened to �180 nm. The disappearance of the vibronic

fine 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

the Pt-catalyzed hydrosilylation reaction. The EF has high PL quantum efficiency (FFL) of 0.65, and FFL of EF-POSS

is drastically enhanced to 0.77, which may be attributed to the aggregation hindrance of the EF molecules on POSS

Y. Feng et al. / Chinese Chemical Letters 21 (2010) 753–757 755

Fig. 1. FTIR and 1H NMR spectra of EF-POSS, EF and T8H8. The inset is 29Si NMR spectrum of EF-POSS.

Fig. 2. UV–vis absorption and PL emission spectra of EF and EF-POSS in the dilute THF solution.

units, in turn, to reduce the degree of dimer formation after excitation [13,19,20]. Therefore, the fluorescent property

of the hybrid nanocomposite indicates that EF-POSS is likely to be an efficient blue light-emitting hybrid

nanocomposite.

As shown in Fig. 3, the thermal degradation temperature Td (5% weight loss) of EF and EF-POSS is 391 and

408 8C, furthermore, the char yield of EF and EF-POSS at 700 8C is 17.4% and 36.6%, respectively. The Td and char

yield of hybrid nanocomposite are obvious elevated in comparison with that of monomer, displaying that the thermal

stability of the hybrid nanocomposite is enhanced by the incorporation of inorganic POSS core [6,7].

In conclusion, a novel POSS-based organic-inorganic hybrid nanocomposite was successfully synthesized and its

photoluminescent property and thermal stability were evaluated. The results indicate that the resultant hybrid

nanocomposite is not only endowed with stable photoluminescent property and high PL quantum efficiency, but also

exhibited enhanced thermal stability. This work provides a novel method for designing blue light-emitting hybrid

nanocomposite with high luminescent quantum efficiency and enhanced thermal stability.

Acknowledgments

This research was financially supported by the National Natural Science Fund of China (Nos. 90606011 and

50472038), Ph.D. Program Foundation of Ministry of Education of China (No. 20070255012), Shanghai Leading

Academic Discipline Project (No. B603), the Program of Introducing Talents of Discipline to Universities (No. 111-2-

04) and Open Project of the State Key Laboratory of Crystal Materials (No. KF0809), Youth Scientific Research Fund

of Anhui University and the Excellent Youth Fund in University of Anhui Province (No. 2008jq1020).

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