Controllable preparation and properties of active functional hybrid materials with different chromophores

Abstract

A convenient and efficient strategy for preparing active functional hybrid materials was proposed based on an investigation of the controllable preparation of a series of anthracene-containing organic–inorganic functional hybrid materials with active ethylene groups. These functional hybrid materials with different active vinyls were controllably prepared through a Heck reaction with octavinyl-polyhedral oligomeric silsesquioxane (OV-POSS) as the raw material by adjusting the feed ratio. Their structures and properties were characterized and evaluated by various measurements. The influence of molecular structure on the optical properties of the resulting hybrids was investigated in detail. It was found that the incorporation of nano-sized inorganic polyhedral oligomeric silsesquioxane (POSS) can efficiently prevent aggregation of hybrid molecules owing to the prohibition of π–π stacking between chromophore groups, which was also confirmed by theoretical simulation. Simultaneously, thermogravimetric analysis (TGA) results also show that the inorganic POSS causes the good thermal stabilities of the hybrids.

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Introduction

Organic–inorganic molecular hybrid nanocomposites are of great interest because they offer the potential to realize remarkable and complementary properties which cannot be obtained from a single material.^1–3 Polyhedral oligomeric silsesquioxane (POSS) is a class of inorganic compounds with nano-scale dimensions (0.5–3 nm) and well-defined cubeoctameric structures with a silica-like core (Si₈O₁₂) surrounded by eight organic corner groups (functional or inert). This makes POSS molecules excellent platforms and blocks for nanotechnology applications and architecture of novel organic–inorganic hybrid nanocomposites.^4–6 More importantly, POSS molecules offer a unique opportunity for preparing organic–inorganic molecular hybrids with the inorganic structural units covalently incorporated and truly molecularly dispersed into resultant hybrids, which effectively overcomes the aggregation effect that occurs in common hybrid composites based on physical mixtures.^7–11 Thus, the POSS molecules with unique structures provide many possibilities and opportunities to tailor the properties of materials.^12,13 Many POSS-based hybrid nanocomposites with different architectures have been prepared such as linear or pendant type hybrids,^14–17 star type hybrids^18,19 and network type hybrids,^20–22 and their thermal properties and thermally enhanced mechanisms^23,24 were investigated. Various functional POSS-based materials have been designed and reported. However, these works were mainly focused on the design of single functional materials. With the development of technology and society, the requirement of multifunctional materials was proposed step by step.

In previous publications, the reaction between the functional molecules and POSS was the typical path to produce hybrid materials.^25–27 The hydrosilylation reaction is one of the widely used ways to modify POSS molecules, but the structure is hard to control when the feed ratio is greater than 1 : 4.²⁸ Click chemistry reactions are also a widely used method to prepare functional hybrid materials.^29–31 It is well known that OV-POSS is a commonly used material to prepare functional hybrid materials but the structure is difficult to control.³² The controllable preparation of OV-POSS hybrid materials is always a tough issue in this field. The key to solving the problem lies in the controllable preparation of functional hybrid materials with active groups.

In this paper, a convenient and efficient strategy for preparing active functional hybrid materials (Ft-OV-POSS) was investigated by a molecular design based on the study of the controllable preparation of a series of anthracene-containing organic–inorganic functional hybrid materials with active ethylene groups. These active functional hybrid materials will provide an important foundation for the preparation of multifunctional hybrids materials in the future.

Results and discussion

Preparation of the hybrid materials

In this work, anthracene was selected as a luminescent and optical identification group, and ethylene groups were selected as the active groups. The active functional hybrid materials were designed and prepared using OV-POSS as a raw material to react with 9-bomoanthracene (9-BA) by a typical Heck reaction.

The resulting hybrid materials with different numbers of active groups and functional groups were obtained by changing the feed ratio, using Pd(Ac)₂ and PPh₃ as the catalyst system and Et₃N as an acid-binding agent. During the reaction, triethylamine hydrobromide precipitates were produced. The reaction degree can be conveniently observed and estimated based on the amount of salt. All the products have good solubility in common solvents, such as THF, DCM, chloroform, toluene and ethyl acetate. When the solutions were spin-coated on a glass sheet, a uniform film was formed (observed via microscopic examination), which shows the good film-forming ability of the resultant materials. Simultaneously, it was found that the yield of H1 is relatively low when the feed ratio of 9-BA to OV-POSS is 1 : 1 (molar ratio). The probable reason may be that it is hard to form the complex of palladium and 9-BA when the concentration of 9-BA is low. However, when the feed ratio was increased to 2 : 1 and 10 : 1 for H2 and H3 respectively, they were obtained in moderate yields.

Characterization and discussion

FTIR analysis. Fig. 1(a) shows the FTIR spectra of OV-POSS, 9-BA and the hybrid materials. Obviously, the existence of the peaks at 1118 cm⁻¹ (Si–O–Si stretching) in all the hybrid materials’ spectra indicates the presence of a POSS core. On the other hand, the peaks representing the anthryl groups at 3075, 3048 (Ar–H stretching), 1622, 1440 (Ar stretching) and 727 cm⁻¹ (C–H bending) can also be seen in the spectra of the hybrid materials, which prove the incorporation of the anthryl groups into the resulting hybrids. Furthermore, the peaks at 3065, 3027, 2987 and 2961 cm⁻¹ gradually fade out with increased feed ratio and the peaks at 3075 and 3048 cm⁻¹ displayed a more clear pattern in the magnification of the IR spectra between 2900 and 3200 cm⁻¹ (Fig. 1(b)), clearly revealing the growth of the average substituted number from H1 to H3.

Fig. 1 The FTIR spectra of OV-POSS, 9-BA, H1, H2 and H3 (a) and the magnified spectra between 2900 and 3200 cm⁻¹ (b).

¹H-NMR analysis. ¹H-NMR tests were carried out and the results were shown in Fig. 2(a). The peaks around 6.0 ppm in the ¹H-NMR spectra represent the hydrogen atoms on unreacted ethenyls (H a–b, 3(8 − x)) and the hydrogen atoms on reacted ethenyls which are near to the POSS (H c, x). The peaks above 6.5 ppm represent all the hydrogen atoms on the anthryls and the hydrogen atoms on reacted ethenyls which are near to the anthryls (H d–m, 10x) in Fig. 2(b). On the other hand, the ratio of the area above 6.5 ppm to the area around 6.0 ppm, which can be obtained by integrating the area of the peak in the ¹H-NMR spectra, is recorded as r. As the ratio (r) and the expression of the hydrogen atoms were all obtained, the average substituted number (x) of the hybrid materials can be calculated approximately by eqn (1):

10x/(3(8 − x) + x) = r (1)

Fig. 2 ¹H-NMR spectra of OV-POSS, H1, H2 and H3 (a) in CDCl₃ and the location of hydrogen atoms in the hybrid molecule (b).

The calculated results from the ¹H-NMR spectra reveal that the average functional group numbers (x) of H1 and H2 are 1.3 and 2.7 respectively. However, as no obvious peak existed in the spectrum of H3 around 6.0 ppm, it can be said that almost all the ethenyls had reacted in H3. Moreover, the anthryl peaks in the spectra of H2 and H3 show a slight shift to a high-field region. This may attributed to the T-shape interaction which is caused by the shielding effect of the electron cloud of aromatic rings to the hydrogen atoms when the distances between them are close enough.³³

HMQC 2D-NMR analysis. To further confirm the conclusion above, we obtained the 2D-NMR HMQC spectra of H1, H2 and H3 which are shown in Fig. 3, and the data were summarized in Table 1. The spectra of H1 and H2 have obvious peaks related to the unreacted ethenyls (δ_H 6.0, δ_C 136.8, 137.4), but these peaks did not appear in the spectrum for H3, which further supports that almost all the ethenyls had reacted in H3. This is consistent with the results of the ¹H-NMR spectra. Furthermore, the peaks around δ_H 5.9–6.5 ppm, δ_C 129.0 ppm shifted to a low-field region from H1 to H3, which revealed the disappearance of unreacted ethenyls. This shift also coincides with the ¹H-NMR results and explains why the peak around 6.0 ppm for H2 has a slight shift to a low-field in the ¹H-NMR spectra.

Fig. 3 ¹H–¹³C 2D-NMR HMQC spectra of H1 (a), H2 (b), and H3 (c) in CDCl₃.

Table 1 ¹H–¹³C 2D-NMR HMQC data for H1, H2 and H3

Position^a	Sample
	H1		H2		H3
	δH	δC	δH	δC	δH	δC
a The position is displayed in Fig. 2(b).
a,b,c	6.0	136.8	6.0	137.4	—	—
d	5.9	128.8	6.0	128.4	5.9	129.0
	—	—	—	—	6.4	129.3
Anthryl	8.2	126.0	8.2	125.5	8.4	125.2
	7.9	128.6	7.8	128.7	7.9	128.5
	—	—	—	—	8.3	127.3
	7.4	125.3	7.2	125.3	7.3	128.1
	—	—	7.2	125.4	7.1	125.2

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Particle size analysis. In fact, it is difficult to show the real molecular structure using the particle size distribution measurement owing to the laser scattering error of asymmetric molecules and the strong optical absorption of asymmetric hybrid molecules. However, the average particle size can also indirectly reflect the structure of the resulting hybrid molecules. Thus, particle size tests were carried out. The results are shown in Fig. 4. From Fig. 4, it can be easily seen that the average diameter of H1 is the smallest and H3 is the largest. Undoubtedly, a bigger size means more anthryls in one molecule.

Fig. 4 Particle size distribution of H1, H2, and H3 in toluene with a concentration of 1 g L⁻¹.

UV-vis spectra analysis. Fig. 5 shows the UV-vis spectra of the hybrid materials H1, H2, and H3. It can be seen that the absorption intensity of the peak at 372 nm, corresponding to the anthryl groups merit increases with the feed ratio. This demonstrates that the higher feed ratio leads to the incorporation of more anthryls into the hybrid molecules. The peak at 372 nm in the hybrids with more anthryl groups displays a slight red shift of ca. 1–2 nm, which may attributed to the interaction between the function groups. However, the normalized curves (upper right inserted plate) shows little difference in the pattern, revealing that they have almost the same molecular structure, further supporting that the OV-POSS may mainly show a single-substituted structure.

Fig. 5 The UV-vis spectra of H1, H2 and H3 in toluene (1 × 10⁻² g L⁻¹). Inset: the normalized spectra.

The theoretical amount of chromophores (N/mol) in a certain mass of hybrid materials can be calculated through the average reacted ethenyl number of the hybrid materials (x, the average substituted number was calculated from the ¹H-NMR results) by eqn (2) and (3).

M = 633 + 177x (2)

N = x × m/M (3)

Eqn (2) was used to calculate the average molecular weight, where 633 and 177 are the molecular weights of OV-POSS and the anthryl group, respectively. (633 + 177x) is the average molecular weight (M/g mol⁻¹) of the different hybrid materials when x = 1.3, 2.7 and 8.0. When the average molecular weights of the hybrid materials were obtained, the amount of molecules in a certain mass (n) could be calculated as m/M in eqn (3), where m (10 mg) was the mass of the hybrid materials. In order to compare with the results of the UV-vis spectra, the theoretical chromophore amount (N) should be calculated by multiplying the amount of molecules (n) by x, which is shown in eqn (3). As shown in Table 2, the theoretical ratio of the amount of chromophores (N) in a certain mass of H1, H2 and H3 was 100 : 164 : 264, which was calculated from the ¹H-NMR results.

Table 2 The chromophore ratio results calculated from the ¹H-NMR and UV-vis spectra

Sample	Feed ratio	Reacted ethenyls (r)^a	Theoretical chromophores in certain mass^b (mol)	Ratio^c	UV-vis absorption	Ratio^d
a Calculated from the ^1H-NMR and 2D-NMR.b Use equation m/M × x to calculate, m = 10 mg, M = 633 + 177x, m is the mass of the hybrid materials, x is the calculated average substituted number of H1, H2 and H3; M is the average molecular weight of the hybrid materials.c Take the theoretical chromophores in a certain mass of H1 as 100%.d Take the UV-vis absorption of H1 at 373 nm as 100%.
H1	1 : 1	1.3	1.48 × 10^−5	100	0.181	100
H2	2 : 1	2.7	2.43 × 10^−5	164	0.305	168
H3	10 : 1	8.0	3.92 × 10^−5	264	0.467	258

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According to the Lambert–Beer Law, the absorption (Abs) of the UV-vis spectrum is positively proportional to the amount of chromophores. Therefore the UV-vis absorption intensity of the hybrid materials can reflect the ratio of the amount of chromophores in the solution. For comparison, the solutions with same mass concentration were prepared for the measurement of the UV-vis spectra. In these solutions, the absorption intensity of H1 was taken as 100%, and that of H2 and H3 were 168% and 258% respectively, which hints the ratio of UV-vis absorption of H1, H2 and H3 to be 100 : 168 : 258. The similarity of two ratios reveals the consistency of the structures of the hybrid materials. In addition, the linear region of the instrument is 0.1–2.8 which promises a precise result.

PL spectra analysis. In order to understand the interaction between the functional groups in a single molecule, solution PL spectra were performed and the results are displayed in Fig. 6. The emitting peaks of 9-BA, H1, H2 and H3 are located at 422 nm, 451 nm, 458 nm and 461 nm respectively. 9-BA shows more precise peaks and the resulting hybrids with more anthryls show an obvious red shift owing to the incorporation of ethylenes, J-aggregation and the T-shape interaction of anthryls in the hybrid molecules. In addition, the intensity of the PL spectra of the hybrids was in the order of H2 > H3 > H1 > 9-BA at same mass concentration. Apparently, the H3 solution has the highest chromophore concentration but its PL intensity is lower than that of H2. On the other side, the PL intensity of H2 is 141% of H1’s, which does not correspond to the UV-vis spectra result of 100 : 164.

Fig. 6 The PL spectra of 9-BA, H1, H2, and H3 in toluene. Excitation wavelength: 373 nm, (2 × 10⁻² g L⁻¹).

It can be supposed from the intensity between H2 and H1 that these functional groups prefer to be substituted on a position with less steric hindrance when there are less anthryls in the molecule but the interaction between the anthryl groups in H2 is still inevitable. However, when there are more anthryls, the aggregation and interaction are much stronger, and J-aggregation and T-shape interaction not only lead to a red shift, but also lead to the decrease of the fluorescence intensity.^33,34

The mixture solvent (toluene as a good solvent and methanol as a poor solvent) was used to explore the relationship between the molecular structure and the aggregation effect of hybrid molecules. The results are shown in Fig. 7. With the increasing percentage of methanol, 9-BA showed a blue shift but the hybrid materials showed a red shift. This phenomenon revealed that the incorporation of POSS had changed the π–π stacking H-aggregation of the organic group into J-aggregation and dipole–dipole interaction. Moreover, the red shift of H1, H2 and H3 were 12 nm, 18 nm and 25 nm respectively. Obviously, if there are more anthryls in the molecules, the stronger interaction between the chromophores will lead to a larger red shift. H3 showed the largest red shift, which hinted that it had the largest substituted number. This corresponds with the results from the FTIR and ¹H-NMR spectra.

Fig. 7 The PL spectra of 9-BA (a), H1 (b), H2 (c), and H3 (d) with different percentages of poor solvent. (Excitation wavelength: 373 nm; 2 × 10⁻² g L⁻¹; 0, 20, 40, 60, 80, 98 vol% of methanol in toluene – from top to bottom.)

Owing to the good film-forming ability of these hybrids, to further study the aggregation behaviors of the hybrid materials, solid state PL spectra were obtained and the results are shown in Fig. 8. It can be noticed that the PL spectra of H1, H2 and H3 in solid state have a further red shift from 451 to 468 nm for H1 with Δλ = 17 nm, from 458 to 505 nm for H2 with Δλ = 47 nm, and from 461 to 512 nm with Δλ = 51 nm. Interestingly, 9-BA showed a red shift from 422 to 464 nm with Δλ = 42 nm. The results reveal that H1 has the lowest aggregation effect but H2 and H3 still aggregate strongly, which is in agreement to the results above and our previous work,^22,26,34,35 and also proves the prediction that more anthryls promote the interaction between the chromophores.

Fig. 8 Normalized PL spectra of 9-BA (a), H1 (b), H2 (c), and H3 (d) in solution (excitation wavelength: 373 nm; 2 × 10⁻² g L⁻¹) and solid state film (excitation wavelength: 373 nm; opaque film).

Thermal stability. Fig. 9 shows the thermal properties of these hybrids. In Fig. 9, we can see that 9-BA had completely decomposed at 246 °C, but the thermal decomposition temperatures (T_d, 5 wt% loss) of H1, H2 and H3 were 468 °C, 480 °C, and 407 °C, respectively, which hints that the resulting hybrids show very high thermal stability. This may mainly attributed to the thermal hindrance of the inorganic POSS core that possesses high thermal properties.^{7,25,28,36,37} Even at 900 °C, the total weight losses are only 12.5%, 12.4% and 32.5% for H1, H2 and H3, respectively, which accounts for only 24.1%, 19.8% and 40% of the theoretical value.

Fig. 9 TGA curves of 9-BA, H1, H2, and H3 from r.t. to 900 °C in a N₂ ramp of 10 mL min⁻¹.

Theoretical simulation. In order to understand the interaction behaviors of the anthryls in the hybrid materials, theoretical simulations were carried out. The structures of the hybrids were optimized with the DFT B3LYP/6-31G(d) method on Gaussian09 software. Six kinds of molecular models were chosen for the optimization. Fig. 10 shows the molecular models: M2 has two anthryls on body diagonal positions; M3 and M4 have three and four anthryls respectively at face diagonal positions to each other; M5 has one more anthryl than M4; M8 has 8 anthryls on every ethenyl and M2o has two anthryls on neighbouring positions. The corresponding band gap (E_g) and distance of the different groups in the hybrid molecules to different substituted hybrids are summarized in Table 3. (The shortest distances between the anthryls in a single molecule are defined as the nearest distance between two carbon atoms on different anthryls.)

Fig. 10 Models for theoretical simulation with different substituted position.

According to the simulation results in Table 3, E_g and the intramolecular distance between anthryls decreased with the increase in substituted number. Apparently, a lower E_g means low energy which is consistent with the red shift of the PL spectra. The shorter intramolecular distance between the anthryls hints that a higher intramolecular interaction, which corresponds with the red shift in the solution PL spectra. In order to illustrate the influence of the substituted position on the intramolecular group interaction, a two ortho-position substituted model (M2o) was also chosen in the simulation. The results reveal that the shortest distance between two carbon atoms in two anthryls is at ca. 4.180 nm when two functional groups are located at this position. Based on previous reports, a strong interaction will occur.^22,38 In addition, in M8, the arrangement of anthryls benefit J-aggregation and T-shape interaction (Fig. 11), which is consistent with the red shift of the PL spectra from H1 to H3.

Table 3 Substituted position and the theoretical simulation results of band gap (E_g) and shortest distance between anthryls in a single molecule

No.	Substituted position	Band gap Eg (eV)	Shortest distance between anthryls in a single molecule (Å)
M2	1,7	3.404	13.620
M3	1,3,6	3.373	8.537
M4	1,3,6,8	3.345	7.685
M5	1,2,3,6,8	3.361	4.181
M8	All	3.233	3.850
M2o	1,2	3.268	4.180

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Fig. 11 Optimization results of the M2, M3, M4, M5, M8 and M2o models and their smallest distance between anthryls (shortest distances of two carbon atoms in different anthryls).

Finally, the aggregation behaviour of the dimers of the hybrid materials with one functional group was optimized and the results were shown in Fig. 12. Fig. 12(a) displays the optimized result starting from a face to face position. The shortest distance between two anthryls was 5.213 Å and the dihedral angle was 55°, which illustrated that the interaction between the anthryls was very weak^33,39 and resulted in the minimal red shift of H1’s PL spectra between a solution and a solid state. On the other hand, the optimized result of the dimer starting from a head to head position showed a smaller shortest distance (4.056 Å) and a dihedral angle of 52°, which implies that the interaction between the anthryls was stronger. In Fig. 12(b), it can be observed that the anthryls overlapped slightly and took an untypical J-aggregation. Besides, the shortest distance of a proton on one anthryl to the surface of the other anthryl is 3.146 Å, providing evidence of the existence of T-shape interaction.³³ In summary, the hybrids with fewer anthryls showed almost no intramolecular interaction and less aggregation in a condensed state, but the hybrids with more anthryls displayed both intramolecular interaction and inter-molecular interaction, which leads to a greater red shift and the decrease of the PL intensity.

Fig. 12 Optimization results of dimers starting from face to face (a) and head to head (b) positions.

Experimental

Synthetic procedures

The hybrids were prepared by typical Heck reaction. The reactions were carried out in a nitrogen atmosphere with a vacuum-line system. H1 was taken as an example: 2.532 g (4 mmol) OV-POSS, 1.028 g (4 mmol) 9-bromoanthracene, 0.045 g (0.2 mmol, 5 mol% of 9-bromoanthracene) Pd(Ac)₂ and 0.210 g (0.8 mmol, 20 mol% of 9-bromoanthracene) PPh₃ were added to a 200 mL Schlenk flask, the flask was vacuumized and filled with nirtogen for three times to maintain an inert atmosphere. 30 mL toluene and 10 mL Et₃N were then added and stirred for 12 h at room temperature, then heated to 80 °C to react for 48 h, and a brown solution and white precipitate were observed. The solution was cooled down to room temperature and then filtered through 1 cm Celite. The solution was rotary evaporated. The product was obtained and purified by column chromatography with CH₂Cl₂/petroleum ether as the eluting agent.

H1. A brown transparent solid was obtained in 23.6% yield. FTIR (KBr), ν (cm⁻¹): 3061, 3024, 2985, 2957 (Si–CH=CH₂), 1623, 1442 (Ar), 1602 (Si–CH=CH₂), 1123 (Si–O–Si), 722 (Ar–H). 2D-NMR HMQC: ¹H-NMR (400 MHz, CDCl₃), δ, (ppm): 6.01 (br, Si–CH=CH₂), 7.40, 7.92, 8.24 (br, Ar–H); ¹³C-NMR (100.13 MHz, CDCl₃), δ, (ppm): 125.15, 128.94 (Ar–H, Si–CH=CH–Ar), 136.92 (Si–CH=CH₂). ²⁹Si-NMR (79.49 MHz), δ, (ppm): −80.17, −79.52 (Si–CH=CH₂), −78.93 (Si–CH=CH–Ar). The preparation processes of H2 and H3 were similar to H1 with feed ratios of 2 : 1 and 10 : 1, respectively.

H2. A brown transparent solid was obtained in57.5%yield. FTIR (KBr), ν (cm⁻¹): 3059, 3023, 2984, 2958 (Si–CH=CH₂), 3048 (Ar–H), 1623, 1442 (Ar), 1602 (Si–CH=CH₂), 1123 (Si–O–Si), 732 (Ar–H). 2D-NMR HMQC: ¹H-NMR (400 MHz, CDCl₃), δ, (ppm): 6.08 (br, Si–CH=CH₂), 7.23, 7.79, 8.18 (br, Ar–H); ¹³C-NMR (100.13 MHz, CDCl₃), δ, (ppm): 125.46, 128.47 (Ar–H, Si–CH=CH–Ar), 137.14 (Si–CH=CH₂). ²⁹Si-NMR (79.49 MHz), δ, (ppm): −79.59 (Si–CH=CH₂), −78.86 (Si–CH=CH–Ar).

H3. A brown transparent solid was obtained in 68.3% yield. FTIR (KBr), ν (cm⁻¹): 3061, 3027, 3048 (Si–CH=CH₂, Ar–H), 1623, 1442 (Ar), 1602 (Si–CH=CH₂), 1123 (Si–O–Si), 732 (Ar–H). 2D-NMR HMQC: ¹H-NMR (400 MHz, CDCl₃), δ, (ppm): 6.50 (br, Si–CH=CH–Ar), 7.23, 7.79, 8.18 (br, Ar–H); ¹³C-NMR (100.13 MHz, CDCl₃), δ, (ppm): 125.15, 128.55 (Ar–H, Si–CH=CH–Ar). ²⁹Si-NMR (79.49 MHz), δ, (ppm): 79.13 (Si–CH=CH–Ar).

Materials and methods

Octavinylsilsequioxane was purchased from Amwest Technology Company, palladium acetate and triphenylphosphine were purchased from Sinopharm Chemical Reagent Co., Ltd, and 9-bromoanthracene was purchased from Shanghai Jiachen Chemical Co., Ltd. All solvents were AR commercial products, but toluene and triethylamine were purified before used.

The FTIR spectra were measured with a Nicolet NEXUS 8700 FTIR spectrophotometer using KBr powder at room temperature. ¹H-NMR and 2D-NMR HMQC spectra were recorded on a Bruker AVANCE/DMX 300 spectrometer. ²⁹Si NMR spectra were recorded on a Bruker DMX-400 spectrometer. UV-vis spectra were recorded on a Lambda 35 UV/Vis spectrometer (Perkin Elmer Precisely) using a 1 cm square quartz cell in toluene with a concentration of 10⁻² g L⁻¹. The PL spectra in solvent were recorded on a LS55 fluorescence spectrometer (Perkin Elmer Precisely) using a 1 cm square quartz cell with an excitation wavelength of 373 nm in toluene and the mixture solvent of toluene/methanol had a concentration of 2 × 10⁻² g L⁻¹. Solid PL spectra were recorded on the same instrument with an opaque film on a 1 mm quartz cell. Thermogravimetric analysis (TGA) was carried out using a NETZSCH TG 209 F1 instrument with a heating rate of 10 °C min⁻¹ from r.t. to 900 °C under a continuous nitrogen purge. Particle size tests were carried out using a Nano ZS Particle Size & Zeta Potential Analyzer (Malvern) in toluene with a concentration of 1 g L⁻¹.

Conclusions

In conclusion, hybrids with different active functional groups can be synthesized controllably by changing the feed ratio easily, which provides an important platform for the preparation of multifunctional hybrid materials in the future. The incorporation of POSS into hybrids can effectively prohibit the optical aggregation between optical chromophores. Simultaneously, it was found that these resultant hybrids possess very well thermal stability.

Acknowledgements

This work is financially supported by the National Natural Science Fund of China (Grant nos 21271040, 21171034 and 51073031), Shanghai Youth Natural Science Foundation (12ZR1440100), “Chen Guang” project supported by Shanghai Municipal Education Commission, Shanghai Education Development Foundation (12CG37) and the Fundamental Research Funds for the Central Universities (12D10603).

Notes and references

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