fluorene/carbazole alternating copolymers tethered with polyhedral oligomeric silsesquioxanes:...

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Fluorene/Carbazole Alternating Copolymers Tethered with Polyhedral Oligomeric Silsesquioxanes: Synthesis, Characterization, and Electroluminescent Properties

Nana Xie , Jinze Wang , Zhilong Guo , Guangxin Chen , * Qifang Li *

A series of novel fl uorene/carbazole alternating copolymers tethered with polyhedral oligo-meric silsesquioxanes (POSS), which have well-defi ned architectures and similar polymeriza-tion degrees, are synthesized by the Heck coupling reaction to investigate the effects of the number and the position of POSS on the optoelectronic prop-erties. The introduction of POSS results in blue shifts in the photoluminescence (PL) emission spectra (especially for P2 ) and improved thermal spectral stability. Moreover, an appro-priate amount of POSS is benefi cial for enhancing the electro-luminescent properties, and a better performance is obtained when POSS units are tethered to the 9-position of the carba-zole units, rather than fl uorene units. Moreover, POSS facili-tates the balance of electron and hole fl uxes.

1. Introduction

Electroluminescent (EL) polymers have attracted great attention because of their potential applications in full-color plate panel displays. [ 1–3 ] Poly(phenylenevinylene), [ 4 , 5 ] poly(p-phenylene), [ 6 , 7 ] polythiophene, [ 8 , 9 ] polyfl uorene, [ 10–12 ] and polycarbazole [ 13–15 ] have been

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N. Xie, J. Wang, Z. Guo, Prof. G. Chen, Prof. Q. LiState Key Laboratory of Chemical Resource Engineering,and College of Material Science and Engineering,Beijing University of Chemical Technology,Beijing 100029, ChinaE-mail: [email protected]; qfl [email protected] Prof. Q. LiKey Laboratory of Carbon Fiber and Functional Polymers,Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, China

Macromol. Chem. Phys. 2013, 214, 1710−1723© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

widely studied. Among these EL polymers, PFs have been extensively applied due to their good thermal and chemical stability, structural fl exibility by modifying the C-9 position, and high photoluminescence effi ciency. [ 16 ] However, when they are used as EL materials, they tend to form aggregates/excimers or keto defects in the solid state, [ 17 ] resulting in an undesired long-wavelength emis-sion. Several approaches have been explored to address this problem, such as introducing bulky side chains, [ 18 ] interrupting the linear conjugate structures by copoly-merization, [ 19–21 ] and improving the stability of chain ends. [ 22 ]

It is well known that carbazoles are a useful class of hole-transporting materials due to their electron-rich-ness. The incorporation of 3,6-carbazole units into PFs can not only depress the chain aggregation by inter-rupting the π conjugation, but also facilitate the hole transport. [ 19 ]

elibrary.com DOI: 10.1002/macp.201300290

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Fluorene/Carbazole Alternating Copolymers Tethered with Polyhedral Oligomeric Silsesquioxanes: . . .

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MacromolecularChemistry and Physics

Polyhedral oligomeric silsesquioxanes (POSS), a novel class of organic–inorganic hybrid components, which contain a cubic cage made of Si and O atoms and eight R substitution groups, have been widely studied in many fi elds [ 23–30 ] and incorporated into EL materials to construct new luminescent hybrid materials. In pre-vious studies, three methods about incorporating POSS into the conjugated polymers have been reported: cova-lently attaching polymers to a POSS core, [ 31–34 ] synthe-sizing polymers side-chain-tethered by POSS, [ 18 , 35 , 36 ] and attaching POSS to the chain ends of the poly-mers. [ 22 ] These results indicated that POSS could effi -ciently improve the optoelectronic properties of the polymers by reducing the degree of aggregation, and inhibiting the formation of excimers or keto defects. In the methods mentioned above, synthesizing polymers side-chain-tethered by POSS is preferable. Nevertheless, only a limited number of reports have appeared so far regarding polymers side-chain-tethered by POSS and the previous reported copolymers are all random or block copolymers, which may have aggregation caused by dis-ordered POSS particles; no studies have been reported on the effect of POSS on the thermal, photophysical, and EL properties based on alternating copolymers tethered with POSS.

In this paper, we successfully synthesized four novel fl uorene/carbazole alternating copolymers tethered with POSS, which have well-defi ned architectures and similar polymerization degrees. Our main purpose is to investi-gate the effects of the number and the tethered position of POSS on the optoelectronic properties of these copoly-mers. We hope it could provide some guidance for con-structing outstanding EL materials with POSS. Here, the synthesis, characterization, morphologies, thermal prop-erties, photophysics, and electroluminescence of these copolymers were studied in detail.

2. Experimental Section

2.1. Materials

Aminopropylisobutyl POSS (POSS-NH 2 ) was purchased from Hybrid Plastics Company. Carbazoles (95%) were purchased from Alfa Aesar and recrystallized from CH 2 Cl 2 /ethanol (13/10) before use. 2,7-Dibromofl uorene (98%), 1-bromooctane (98%), tributylvinyltin (98%), Pd(OAc) 2 (99%), and P(o-tolyl) 3 (99%) were purchased from Alfa Aesar and used as supplied. 3,6-Dibromo-N-POSS-carbazole (the monomer 11 ) was obtained from Tianfu Zhang. Toluene and benzene were purifi ed by distillation from sodium. Dimethylformamide (DMF) was dried by distillation under reduced pressure over CaH 2 . Tetrahydrofuran (THF) was distilled over sodium. Triethylamine (TEA) was purifi ed by distillation over CaH 2 . All other reagents and solvents were purchased from commercial sources and used without further purifi cation.

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2.2. Preparation of Monomers

2.2.1. (2,7-Dibromo)-9H-fl uorene-9,9-dipropanoic Acid-dibutylester (1)

Synthesis of 1 was conducted according to the literature proce-dure [ 37 ] with some changes. 2,7-Dibromofl uorene (24.75 mmol, 8.02 g) and tetrabutylammonium bromide (2.46 mmol, 0.79 g) were added to 50 mL benzene under a nitrogen atmosphere. 50% NaOH (aq) (98.72 mmol, 8 mL) was added and stirred for 30 min. N-butyl acrylate (98.70 mmol, 12.65 g) was added slowly by addition funnel, and the reaction was stirred for appropriate time under room temperature, decided by thin layer chromatog-raphy (TLC). The reaction was diluted with 160 mL ethyl acetate. This mixture was washed three times with water, once with brine, and the organic layer was dried with MgSO 4 , followed by fi ltering. After removal of the solvent by a rotary evapo-rator, it was purifi ed by column chromatography using CH 2 Cl 2 /petroleum ether (2:1) as eluent and the crude product was sub-sequently recrystallized from hexane to afford 1 as white crystal-line solid (10.77 g, 75%). mp: 63 ° C. 1 H NMR (400 MHz, CDCl 3 , δ ): 7.56–7.46 (m, 6H), 3.90 (t, J = 6.75 Hz, 4H), 2.38 (t, J = 8.06 Hz, 4H), 1.60–1.44 (m, 8H), 1.32–1.23 (m, 4H), 0.88 (t, J = 7.37 Hz, 6H). 13 C NMR (100 MHz, CDCl 3 , δ ): 172.9, 149.5, 139.2, 131.2, 126.5, 122.0, 121.5, 64.4, 54.2, 34.4, 30.5, 28.9, 19.1, 13.7.

2.2.2. (2,7-Dibromo)-9H-fl uorene-9,9-dipropanoic Acid (2)

To a solution of 1 (2.00 g, 3.45 mmol) in 1,4-dioxane (35 mL) was added 21 mL of 0.5 M aqueous KOH solution. The reaction mix-ture was heated to 70 ° C for 24 h. After being cooled to room temperature, the dioxane was removed by rotary evaporation. Aqueous HCl solution was added to the aqueous solution until the pH = 2. The precipitate was collected by fi ltration, washed with copious amounts of water, and dried under vacuum to afford 1.52 g (97%) of white powder. 1 H NMR (400 MHz, DMSO- d 6 , δ ): 11.93 (s, 2H), 7.84 (d, J = 8.13 Hz, 2H), 7.80 (d, J = 1.49 Hz, 2H), 7.58 (dd, J = 8.08, 1.68 Hz, 2H), 2.38–2.30 (m, 4H), 1.38–1.27 (m, 4H). 13 C NMR (100 MHz, DMSO- d 6 , δ ): 173.6, 150.3, 138.8, 130.7, 126.5, 122.2, 121.3, 54.1, 33.3, 28.7.

2.2.3. (2,7-Dibromo)-9H-fl uorene-9,9-dipropanoic Chloride (3)

To a solution of 2 (1.50 g, 3.20 mmol) in dry benzene (35 mL) was added dropwise oxalyl chloride (3.28 mL, 3.85 mmol) at 0 ° C in an ice bath. The mixture was stirred at 0 ° C for 30 min. After that, it was heated to 40 ° C and stirred overnight. Benzene was removed under reduced pressure. A white solid (1.39 g, 86%) was obtained upon recrystallization from hexane/benzene (4:1). 1 H NMR (400 MHz, CDCl 3 , δ ): 7.63–7.55 (m, 4H), 7.48 (s, 2H), 2.48–2.40 (m, 4H), 2.13–2.07 (m, 4H). 13 C NMR (100 MHz, CDCl 3 , δ ): 173.0, 147.7, 139.0, 132.1, 126.2, 122.7, 122.0, 53.1, 41.7, 34.3.

2.2.4. 2,7-Dibromo-9,9-di-POSS Fluorene (4)

POSS-NH 2 (4.93 g, 5.64 mmol) were dissolved in dry THF (40 mL) and then the mixture was cooled to 0 ° C in an ice bath. A solu-tion of 3 (1.39 g, 2.75 mmol) in dry THF (20 mL) was added drop-wise to this mixture over a period of 1 h; the reaction was left

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to proceed at 0 ° C for 0.5 h and then at 45 ° C for an additional 48 h. Reaction progress was monitored by TLC. After removal of the solvent by rotary evaporation, the residue was purifi ed by column chromatography with CH 2 Cl 2 /CH 3 OH (80:1) as eluent and the crude product was subsequently recrystallized from hexane to afford the desired product as a white solid (3.30 g, 55%). 1 H NMR (400 MHz, CDCl 3 , δ ): 7.56–7.46 (m, 6H), 4.95 (t, J = 5.46, 5.46 Hz, 2H), 3.07 (dd, J = 12.96, 6.69 Hz, 4H), 2.44–2.34 (m, 4H), 1.91–1.74 (m, 14H), 1.50–1.34 (m, 8H), 0.98–0.89 (m, 84H), 0.58 (t, J = 6.40, 6.40 Hz, 28H), 0.53–0.46 (m, 4H) (Figure S1, Sup-porting Information). 13 C NMR (100 MHz, CDCl 3 , δ ): 171.6, 150.2, 139.0, 131.1, 126.7, 122.2, 121.2, 54.5, 41.8, 34.9, 30.8, 25.7, 23.9, 22.8, 22.4, 9.4. FTIR (KBr, thin fi lm, cm − 1 ): 2958, 2925, and 2872

(C–H), 1650 (C�O), 1110 (Si–O–Si).

2.2.5. 2,7-Dibromo-9-POSS-9 ′ -acrylic Acid Fluorene (5)

The monomer 5 was similarly prepared following the 4 pro-cedures, by reducing the use level of POSS-NH 2 to 2.53 g (2.89 mmol). The crude product was purifi ed by column chroma-tography with CH 2 Cl 2 /CH 3 OH (50:1) as eluent, and then 1.64 g white solid was obtained. Yield: 45%. 1 H NMR (400 MHz, CDCl 3 , δ ): 7.56–7.46 (m, 6H), 4.97 (t, J = 5.20, 5.20 Hz, 2H), 3.06 (dd, J = 12.84, 6.67 Hz, 2H), 2.44–2.31 (m, 4H), 1.92–1.73 (m, 7H), 1.63–1.54 (m, 2H), 1.50–1.32 (m, 4H), 0.93 (dd, J = 9.00, 6.67 Hz, 42H), 0.57 (t, J = 6.89, 6.89 Hz, 14H), 0.53–0.44 (m, 2H) (Figure S2, Sup-porting Information). 13 C NMR (100 MHz, CDCl 3 , δ ): 177.7, 171.8, 149.7, 139.1, 131.2, 126.6, 122.2, 121.4, 54.3, 41.8, 34.7, 34.4, 30.8, 28.6, 25.7, 23.9, 22.8, 22.4, 9.4. FTIR (KBr, thin fi lm, cm − 1 ): 2958,

2928, and 2869 (C–H), 1718 (C�O of COOH), 1650 (C�O of NH–CO), 1110 (Si–O–Si).

2.2.6. 2,7-Dibromo-9,9-dioctylfl uorene (6)

To the mixture of 2,7-dibromofl uorene (5.00 g, 15.43 mmol) and KOH (10 g, 178.24 mmol) in DMF (50 mL) was added dropwise 1-bromooctane (5.39 mL, 15.43 mol), followed by stirring over-night at room temperature. The solution was poured into water, neutralized with 10% HCl until pH = 7, extracted with CH 2 Cl 2 (three times), and dried with MgSO 4 . After fi ltration and removal of the solvent by a rotary evaporator, the residue was purifi ed by column chromatography using petroleum ether as eluent. The fi nal product was obtained as a white solid (7.54 g, 89.1%). 1 H NMR (400 MHz, CDCl 3 , δ ): 7.51 (d, J = 8.68 Hz, 2H), 7.47–7.42 (m, 4H), 1.94–1.86 (m, 4H), 1.27–0.99 (m, 20H), 0.83 (t, J = 7.10, 7.10 Hz, 6H), 0.58 (dd, J = 9.29, 6.04 Hz, 4H). 13 C NMR (100 MHz, CDCl 3 , δ ): 152.6, 139.1, 130.1, 126.2, 121.5, 121.1, 55.7, 40.1, 31.8, 29.9, 29.2, 23.6, 22.6, 14.1.

2.2.7. 2,7-Divinyl-9,9-dioctylfl uorene (7)

Synthesis of 7 was conducted according to the literature pro-cedures [ 38 ] with some improvements. To a 50 mL one-necked fl ask was added 6 (0.45 g, 0.82 mmol), tributylvinyltin (0.572 g, 1.80 mmol), PdCl 2 (PPh 3 ) 2 (0.058 g, 0.082 mmol), PPh 3 (0.043 g, 0.164 mmol), KF (0.286 g, 4.92 mmol), CuI (0.031 g, 0.164 mmol), a few crystals of 2,6-di- tert -butyl-4-methylphenol as the radical trap, and toluene (8 mL); the system was purged with nitrogen. The mixture was stirred at 100 ° C for 20 h under dark conditions.

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Toluene was removed under reduced pressure and the resultant oil was purifi ed by column chromatography using hexane as eluent to afford the desired product (0.25 g, 69%). 1 H NMR (400 MHz, CDCl 3 , δ ): 7.62 (d, J = 7.80 Hz, 2H), 7.38 (d, J = 7.86 Hz, 2H), 7.35 (s, 2H), 6.80 (dd, J = 17.58, 10.89 Hz, 2H), 5.80 (d, J = 17.53 Hz, 2H), 5.25 (d, J = 10.88 Hz, 2H), 1.98–1.93 (m, 4H), 1.29–1.00 (m, 20H), 0.81 (t, J = 7.18, 7.18 Hz, 6H), 0.63 (d, J = 6.93 Hz, 4H). 13 C NMR (100 MHz, CDCl 3 , δ ): 151.4, 140.7, 137.4, 136.5, 125.2, 120.5, 119.7, 113.0, 54.9, 40.4, 31.8, 30.0, 29.2, 23.7, 22.6, 14.1.

2.2.8. 9-Octylcarbazole (8)

KOH (10.14 g, 180.73 mmol), DMF (20 mL), and 1-bromooctane (5.21 mL, 29.90 mmol) were added into a round-bottom fl ask, and stirred for 1 h at room temperature. Then carbazoles (5.00 g, 29.90 mmol) in DMF (30 mL) was added dropwise into the mix-ture. After being stirred for 12 h, the solution was poured into water, neutralized with 10% HCl until pH = 7, extracted with chloroform (three times), and dried with MgSO 4 . After fi ltration and removal of the solvent by a rotary evaporator, the residue was purifi ed by column chromatography using petroleum ether/ethyl acetate (50:1) as eluent. The fi nal product was obtained as a light yellow oil (7.52 g, 90%). 1 H NMR (400 MHz, CDCl 3 , δ ): 8.08 (d, J = 7.76 Hz, 2H), 7.47–7.41 (m, 2H), 7.37 (d, J = 8.15 Hz, 2H), 7.21–7.17 (m, 2H), 4.24 (t, J = 7.27, 7.27 Hz, 2H), 1.88–1.78 (m, 2H), 1.41–1.16 (m, 10H), 0.85 (t, J = 6.88, 6.88 Hz, 3H). 13 C NMR (100MHz, CDCl 3 , δ ): 140.8, 125.9, 123.2, 120.6, 119.0, 109.0, 43.2, 32.2, 29.7, 29.5, 29.3, 27.6, 23.0, 14.5.

2.2.9. 3,6-Diformyl-9-octylcarbazole (9)

To dry DMF (34.63 mL, 44.74 mmol) and 1,2-dichloroethane (27.70 mL) cooled to 0 ° C, phosphoryl chloride (54.88 g, 35.79 mmol) was added dropwise. To the stirred mixture, heated to 35 ° C, 8 (5.0 g, 17.90 mmol) was added. After stirring for 72 h at 90 ° C, the mixture was poured into 300 mL of water, neutralized with KOH to pH = 7, extracted with chloroform, and dried with MgSO 4 . The solvent was removed under reduced pressure. The residue was purifi ed by column chromatography using petroleum ether/ethyl acetate (5:1) as eluent. The fi nal product was obtained as a light yellow solid (4.80 g, 80%). 1 H NMR (400 MHz, CDCl 3 , δ ): 10.14 (s, 2H), 8.67 (s, 2H), 8.09 (d, J = 8.53 Hz, 2H), 7.55 (d, J = 8.54 Hz, 2H), 4.38 (t, J = 7.28, 7.28 Hz, 2H), 1.96–1.87 (m, 2H), 1.44–1.20 (m, 10H), 0.86 (t, J = 6.56, 6.56 Hz, 3H). 13 C NMR (100 MHz, CDCl 3 , δ ): 191.4, 144.8, 129.7, 127.8, 124.2, 123.2, 109.8, 43.8, 31.7, 29.3, 29.1, 28.9, 27.2, 22.6, 14.0.

2.2.10. 3,6-Divinyl-9-octylcarbazole (10)

Potassium tert -butoxide (t-BuOK, 1.34 g, 11.94 mmol) and dry THF (45 mL) were added to a three-necked round fl ask under a nitrogen atmosphere and stirred for 15 min. Then, methyltri-phenylphosphonium bromide (4.50 g, 12.60 mmol) was added quickly and the system became a bright yellow. After 15 min, the monomer 9 (1.00 g, 2.98 mmol) was added. The system was refl uxed for 6 h. The mixture was poured into 100 mL water, extracted with CH 2 Cl 2 , and dried with MgSO 4 . After removing the solvent, the residue was purifi ed by column chromatography with hexane/CH 2 Cl 2 (15:1) as eluent and the desired product was

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obtained as a white oil (0.72 g, 73%). 1 H NMR (400 MHz, CDCl 3 , δ ): 8.11 (s, 2H), 7.56 (dd, J = 8.47, 1.42 Hz, 2H), 7.31 (d, J = 8.47 Hz, 2H), 6.90 (dd, J = 17.54, 10.87 Hz, 2H), 5.77 (d, J = 17.58 Hz, 2H), 5.19 (d, J = 10.99 Hz, 2H), 4.24 (t, J = 7.21, 7.21 Hz, 2H), 1.87–1.80 (m, 2H), 1.38–1.18 (m, 10H), 0.85 (t, J = 6.92, 6.92 Hz, 3H). 13 C NMR (100 MHz, CDCl 3 , δ ): 140.7, 137.5, 129.0, 124.1, 123.1, 118.4, 111.0, 108.8, 43.2, 31.8, 29.4, 29.2, 29.0, 27.3, 22.6, 14.1.

2.3. Preparation of Copolymers

General procedure of polymerization through the Heck reaction was given as follows. To a 50 mL one-necked fl ask was added the appropriate diene (1 equiv), the appropriate dibromide (1 equiv), Pd(OAc) 2 (0.1 equiv), and P(o-tolyl) 3 (0.5 equiv). The fl ask was evacuated and purged with N 2 . Appropriate anhydrous DMF and TEA were injected by syringe into the mixture. The mixture was heated to 90 ° C and maintained for the appropriate time under a nitrogen atmosphere. The warm reaction mixture was poured into methanol. The yellow precipitate was fi ltered, and further purifi ed by the following procedure. The precipitate was redis-solved in CH 2 Cl 2 and passed through a short Al 2 O 3 column to remove the catalyst residues. The resulting copolymer solution was collected, concentrated, and precipitated into methanol. The yellow solid obtained was dried overnight under vacuum at 50 ° C.

2.3.1. Copolymer P1

Copolymer P1 was prepared in 65% yield from the reaction of 6 with 10 for 3 h. 1 H NMR (400 MHz, CDCl 3 , δ ): 8.33, 7.79–7.26, 4.30, 2.15–1.80, 1.61–0.95, 0.93–0.68 (Figure S3, Supporting Infor-mation). FTIR (KBr, thin fi lm, cm − 1 ): 3021 (C–H), 2925 and 2851 (C–H), 960 ( trans olefi nic bond).

2.3.2. Copolymer P2

Copolymer P2 was prepared in 60% yield from the reaction of 7 with 11 for 2 d. 1 H NMR (400 MHz, CDCl 3 , δ ): 8.36, 7.81–7.28, 5.77–5.64, 5.05–4.82, 3.30–3.10, 2.16–1.95, 1.90–1.74, 1.60–1.01, 1.00–0.85, 0.84–0.75, 0.62–0.51, 0.50–0.40 (Figure S4, Supporting Information). FTIR (KBr, thin fi lm, cm − 1 ): 3027 (C–H), 2958, 2925, and 2866 (C–H), 1110 (Si–O–Si), 960 ( trans olefi nic bond).

2.3.3. Copolymer P3

Copolymer P3 was prepared in 70% yield from the reaction of 4 with 10 for 2 d. 1 H NMR (400 MHz, CDCl 3 , δ ): 8.32, 7.83–7.28, 5.06–4.86, 4.49–4.13, 3.12–3.00, 2.64–2.47, 1.99–1.90, 1.89–1.70, 1.65–1.34, 0.98–0.84, 0.62–0.51, 0.51–0.44 (Figure S5, Supporting Information). FTIR (KBr, thin fi lm, cm − 1 ): 3027 (C–H), 2958, 2925, and 2869 (C–H), 1110 (Si–O–Si), 960 ( trans olefi nic bond).

2.3.4. Copolymer P4

Copolymer P4 was prepared in 50% yield from the reaction of 5 with 10 for 2 d. 1 H NMR (400 MHz, CDCl 3 , δ ): 8.27, 7.82–7.27, 5.07–4.80, 4.50–4.11, 3.21–2.81, 2.72–2.25, 2.16–1.97, 1.90–1.65, 1.51–1.15, 0.90, 0.53 (Figure S6, Supporting Information). FTIR (KBr, thin fi lm, cm − 1 ): 3027 (C–H), 2958, 2925, and 2869 (C–H), 1110 (Si–O–Si), 960 ( trans olefi nic bond).

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2.4. Characterization

1 H NMR and 13 C NMR spectroscopy measurements were carried out on a Bruker AV-400 spectrometer at room temperature using CDCl 3 and DMSO-d 6 as the solvents and tetramethylsilane as the internal standard. Fourier transform IR (FTIR) spectroscopy measurements were performed on a Bruker Tensor-27 Fourier transform infrared spectrometer using the KBr disk method. Relative molecular weight and molecular weight distribution of the copolymers were determined with a Waters 515-2410 gel permeation chromatography (GPC) instrument equipped with a Styragel HT6E-HT5-HT3 chromatographic column, following a guard column and a differential refractive index detector. The sample solution was fi ltered with a 0.45 μ m syringe fi lter prior to injection. The measurements were carried out at 35 ° C, and THF was used as the eluent at a fl ow rate of 1.0 mL · min − 1 . The system was calibrated with polystyrene standards.

Thermogravimetric analysis (TGA) measurements were performed under a nitrogen atmosphere at a heating rate of 10 ° C · min − 1 , using NETZSCH TG 209F3 instrument. The differential scanning calorimetry (DSC) thermograms were obtained under a nitrogen atmosphere at a heating rate of 10 ° C · min − 1 , using NETZSCH DSC 200PC apparatus. Wide-angle X-ray diffraction (WAXD) measurements were carried out on a Bruker D8 Advance X-ray diffractometer, with a step size of 0.02 ° and a scanning rate of 12 ° per minute. High-resolution transmission electron microscopy (HRTEM) images and energy dispersive spectra (EDS) were obtained using a JEM 3010 microscope operating at 300 kV. A drop of 10 mg mL − 1 polymer CH 2 Cl 2 solution was dropped into water, and then the copolymer fi lm formed on the water. Copper grid (200 meshes) without carbon fi lm was used to get the fi lm out. The copper grid coated with the copolymer fi lm was allowed to dry at room temperature. Atomic force microscopy (AFM) images were obtained using a MT7900-EN6 atomic force microscope.

UV–vis absorption and photoluminescence (PL) spectra were recorded on a Shimadzu UV1800 spectrophotometer and an F-7000 FL spectrophotometer, respectively. Cyclic voltammetry (CV) was performed on a PARSTAT2273 electrochemical workstation in CH 2 Cl 2 solutions at a scan rate of 50 mV s − 1 , with a polymer-coated platinum electrode as the working electrode, an Hg/HgCl 2 electrode as the reference electrode, and a platinum wire as the counter electrode. The supporting electrolyte was Bu 4 NPF 6 (0.10 M) and ferrocene was selected as the internal standard. The solution was bubbled with a constant argon fl ow for 10 min before measurements. EL spectra were obtained using a Minolta CS-1000 instrument. The current–voltage ( I – V ) and luminance–voltage ( L – V ) characteristics were determined using a computer-controlled Keithley 236 source-measure unit and a Keithley 2000 multimeter coupled with a Si photomultiplier tube.

2.5. Preparation of Polymer Light-Emitting Diodes (PLEDs)

Glass substrates covered by indium tin oxide (ITO) were pre-cleaned carefully before use. A layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), 35 nm thick, was spin-coated from its aqueous solution on top of the ITO and

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baked at 210 ° C for 10 min under a vacuum. The system was subsequently moved into a glovebox. A 50 nm-thick polymer layer was spin-coated from o-dichlorobenzene solution on the PEDOT:PSS layer and annealed at 120 ° C for 30 min. Afterwards, the system was transferred into an evaporation chamber. A 40-nm thick fi lm of TmPyPB was obtained by evaporation at a rate of 1–2 Å s − 1 using a base pressure below 3 × 10 − 6 Torr. Then a 1 nm LiF and an 85 nm Al layer were sequentially obtained at rates of 1 and 2 Å s − 1 for the LiF and Al, respectively, at base pres-sures of < 1 × 10 − 6 Torr.

3. Results and Discussion

3.1. Synthesis and Characterization

The synthetic procedures used to prepare the mono-mers and polymers are outlined in Scheme 1 and 2 . The synthesis of POSS-substituted fl uorene ( 4 ) began from 2,7-dibromofl uorene with the 9-position functionalized via Michael addition of this bridging carbon with 2 equiv

4

Scheme 1 . Synthetic routes for the monomers.

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of butyl acrylate, and followed by the hydrolyzation of 1 to give diacid 2 in high yield (97%). By acyl chlorination of 2 and then by amidation reaction between 3 and POSS-NH 2 , the monomer 4 was prepared. The monomer 5 was synthesized with the same method as 4 , by reducing the mole fraction of POSS-NH 2 . 2,7-Dibromo-9,9-dioctylfl u-orene ( 6 ) was synthesized by alkylation of 2,7-dibromo-fl uorene. The Stille coupling of 6 with tributylvinyltin yielded the monomer 7 . 3,6-divinyl-9-octylcarbazole ( 10 ) was synthesized starting from carbazoles as follows. First, carbazoles were alkylated with 1-bromooctane in the pres-ence of KOH in DMF to obtain 8 . Then, the 3- and 6-posi-tions of the compound 8 were converted to aldehyde group by the Vilsmeier–Haack reaction, by which the monomer 9 was synthesized. The resulting carbazole diene 10 was obtained by the Wittig reaction between 9 and methyl-triphenylphosphonium bromide with t-BuOK as a base in THF at 65 ° C. Four alternating copolymers were syn-thesized by the Heck coupling reaction of the appropriate diene and dibromide.

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Scheme 2 . Synthetic routes for the copolymers.

The chemical structures of the monomers were veri-fi ed by recording the 1 H NMR, 13 C NMR, and FTIR spectra. Figure 1 depicts the 1 H NMR spectra of POSS-NH 2 , 4 and 5 . The – CH 2 –NH 2 peak of POSS-NH 2 downshifted from 2.68 to 3.07 ppm in 4 and 5 , indicating that POSS-NH 2 had reacted with 3 to form 4 and 5 . In addition, we could observe a new signal characteristic of an amide proton around 5.0 ppm, which also suggested the successful

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Figure 1 . 1 H NMR spectra of: a) POSS-NH 2 , b) 4 , and c) 5 .

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synthesis of 4 and 5 . Figure 2 represents the FTIR spectra of POSS-NH 2 , 4 and 5 . The successful synthesis of 4 and 5 was also confi rmed by FTIR spectra. As shown in Figure 2 , a strong absorption peak around 1110 cm − 1 due to Si–O–Si stretching and a weak absorption around 1650 cm − 1 corresponding to C�O stretching of –NH–CO–, appeared in the FTIR spectra of 4 and 5 , which indicated that POSS-NH 2 had been successfully incorporated into 3 . Moreover,

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Figure 2 . FTIR spectra of: a) POSS-NH 2 , b) 4 , and c) 5 .

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Figure 3 . 1 H NMR spectra of the copolymers.

Table 1. Molecular weights and thermal properties of the copolymers.

Polymer M n a)

[g mol − 1 ] M w a)

[g mol − 1 ]PDI a) DP b) T d c)

[ ° C]

P1 4432 7196 1.62 6 400.3

P2 8560 15 376 1.80 6 378.8

P3 14 417 29 525 2.05 6 389.9

P4 9208 15 699 1.70 6 386.5

a) Determined by GPC in THF using polystyrene standards; b) Number-average degree of polymerization; c) Temperature resulting in 5% weight loss based on initial weight was measured by TGA under N 2 .

the chemical structure of the monomer 5 was further confi rmed by an absorption peak at 1718 cm − 1 due to C�O stretching of –COOH and a broad peak in the range 3000–3700 cm − 1 resulting from –OH stretching in its FTIR spectrum.

The structures of the copolymers were verifi ed by 1 H NMR and FTIR spectra. The 1 H NMR spectra of the copoly-mers are shown in Figure 3 . The appearance of the –CH 2 – signals around 3.1 ppm in the 1 H NMR spectra of the POSS-modifi ed copolymers indicated their successful syn-thesis. Figure 4 depicts the FTIR spectra of the copolymers. They all showed a characteristic peak around 960 cm − 1 due to trans HC�CH stretching, indicating the Heck cou-pling reaction went on well. In Figure 4 , this strong Si–O–Si stretching band near 1100 cm − 1 also confi rmed the presence of POSS, indicating the successful synthesis of the copolymers with POSS as pendant groups.

3.2. Molecular Weights and Thermal Properties

All the copolymers show good solubility in common organic solvents such as chloroform, dichloromethane,

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Figure 4 . FTIR spectra of the copolymers.


THF, and toluene. Their molecular weights and polydis-persity index (PDI) were determined by GPC using THF as eluent against polystyrene standards. The results are summarized in Table 1 and the GPC traces are shown in Figure S7 in the Supporting Information. The number-average molecular weights ( M n ) of these copolymers range from 4432 to 14417 g mol − 1 with a PDI of 1.62–2.05, and the copolymers have similar polymerization degrees that are about six by controlling the polymerization conditions: the amount of the solvent and the polymeri-zation time. The detailed polymerization conditions are summarized in Table S1 in the Supporting Information. It is known that the conjugated length has an important infl uence on the polymer light-emitting diode (PLED) performance. [ 39 ] If the degrees of polymerization (DP) of these copolymers are different, it would be very dif-fi cult to make such a judgment that the better EL per-formance is due to the effect of the existence of POSS in the polymer structure rather than the different conju-gated length. In this case, for investigating the effect of POSS on the device performance, these copolymers were designed to have similar DP to exclude the conjugated length effect.

The thermal properties of these copolymers were inves-tigated by TGA (heating rate of 10 ° C min − 1 ) and DSC (heating rate of 10 ° C min − 1 ). The TGA and DSC curves of the copolymers are shown in Figure S8 and S9 in the Supporting Information. All the copolymers show good thermal stability: the decomposition temperature ( T d ) (5% weight loss) higher than 375 ° C under nitrogen (Table 1 ). The T d of the copolymers is slightly decreased when the POSS units are incorporated into them because of the weakened interchain interaction caused by the high con-tent of bulky POSS. [ 36 ] However, the decomposition tem-peratures of these copolymers are all high enough for semiconducting applications. Additionally, we did not observe obvious glass transition temperature from the DSC curves of these copolymers, which is desirable for good color purity in PLEDs. [ 40 ]



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Figure 5 . WAXD spectra of: a) P1 , b) P2 , c) P3 , d) P4 , and e) POSS-NH 2 .

3.3. Morphology

3.3.1. Wide-Angle X-Ray Diffraction

The X-ray diffraction curves of POSS-NH 2 and four copoly-mers are shown in Figure 5 . P1 is amorphous and only a broad peak at 2 θ = 20 ° with a d spacing of 4.43 Å is observed. As shown in Figure 5 e, POSS-NH 2 shows strong refl ections at 2 θ = 8.0, 8.8, 11.0, 11.8, and 19.9 ° , which correspond to d spacings of 11.0, 10.0, 8.0, 7.49, and 4.44 Å, respec-tively, indicating that POSS-NH 2 has a strong crystallizing ability. The peak at 2 θ = 8.0 ° , with a d spacing of 11.0 Å, refl ects the size of the POSS-NH 2 molecules; the others are attributed to the rhombohedral crystal structure of POSS molecules. [ 41–43 ] However, only a broad peak around 2 θ = 8.3 ° with a d spacing of 10.63 Å and an inconspicuous broad peak at 2 θ = 19.37 ° with a d spacing of 4.58 Å appear in the X-ray patterns of the copolymers tethered with POSS. The small peaks in the WAXD curve of P3 can be attributed to the interaction of the two POSS units that are very close


Figure 6 . a) HRTEM of P3 . b) EDS of P3 .

Macromol. Chem. Phys. © 2013 WILEY-VCH Verlag Gm

to each other. In general, the POSS-modifi ed copolymers are amorphous and the POSS molecules do not form crys-tallization, which is consistent with the DSC results.

3.3.2. High-Resolution Transmission Electron Microscopy

HRTEM measurements have been carried out to study the distribution of POSS in the copolymer matrix. Figure 6 shows the HRTEM image of P3 and its energy dispersive spec-trum (EDS). The HRTEM image of P3 is similar to that of P1 (Figure S10a, Supporting Information) and the small dark dots in the image are caused by contrast. This image reveals that even in high-resolution condition, no POSS aggregates could be observed, and the presence of POSS molecules is confi rmed by the EDS. The HRTEM images of P2 and P4 (Figure S10b,c, Supporting Information) are similar to that of P3 . All these indicate that POSS are well incorporated into the copolymers and homogeneous morphologies are formed, which result from the strict alternative structures, and this is different from previous reports. [ 18 , 35 , 36 ]

3.3.3. Atomic Force Microscopy

AFM analysis was performed to study the topology of the copolymer fi lms. As shown in Figure 7 , the surface roughness of P2 – P4 is larger than that of P1 due to the presence of POSS, indicating the loose molecular packing due to the high content of bulky POSS.

3.4. Photophysical Properties

UV–vis absorption and PL spectra of these copolymers are investigated in both CH 2 Cl 2 solution and thin fi lms, and the data are summarized in Table 2 . Thin fi lms of the copolymers were prepared on quartz plates by spin-coating from their respective CH 2 Cl 2 solution at

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Figure 7 . AFM 3D images of thin fi lms of: a) P1 , b) P2 , c) P3 , and d) P4 .

room temperature. As shown in Figure 8 a, for all the copolymers, the absorption spectra in both CH 2 Cl 2 solu-tions and fi lms show similar patterns with two absorp-tion bands attributed to the n– π ∗ and π – π ∗ transition of the copolymer backbones. For each copolymer, the maximum absorption peak in the fi lm did not have a distinct shift, compared to that in solution. However, both in solutions and fi lms, the maximum absorption peaks of the POSS-modifi ed copolymers had a slight blue-shift compared with P1 . These results indicate that POSS mole cules could suppress the aggregation of the copoly mer backbones.

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Table 2. Photophysical properties of the copolymers in CH 2 Cl 2 solutions and thin fi lms.

Polymer λ max (UV) [nm]

λ max (PL) b) [nm]

Solution Film Φ PL a) Solution Film

P1 409 410 0.78 461 (488) 499

P2 398 400 0.90 441 (468) 482

P3 403 403 0.86 453 (477) 491

P4 404 405 0.89 456 (478) 495

a) PL quantum yield in 10 − 5 M CH 2 Cl 2 solution with respect to qui-nine sulfate in 0.1 N H 2 SO 4 as standard; b) The data in parentheses are the wavelengths of shoulders and subpeaks.


The PL spectra of P1 and P3 in both CH 2 Cl 2 solutions and fi lms are shown in Figure 8 b. The maximum emission peak of P3 shows an 8 nm blue-shift compared with that of P1 , whether in the solution or fi lm. This was because that POSS unit, which was electron-rich moiety, could prevent the aggregation of the copolymer backbones that contained vinylene units. [ 11 ] From Figure 8 c, it could be seen that the main emission peaks of P3 are blue-shifted relative to those of P4 , whether in dilute CH 2 Cl 2 solution or thin fi lm, owing to the reduced energy loss caused by the presence of more POSS. Figure 8 d presents the PL emission spectra of P3 and P2 . The emission peaks of P2 are blue-shifted by Δ λ = 12 nm in dilute CH 2 Cl 2 solution and by Δ λ = 9 nm in thin fi lm in comparison with those of P3 . The possible reasons are as follows: a) the nitrogen atom of the carbazole unit, which is electron rich, sup-plies its unshared electrons to the backbone and makes the backbone electron-rich; b) the POSS unit, which is also electron rich, is connected to the nitrogen atom and enhances its electron-donating capability, so the degree of the electron delocalization in the conjugated backbone is enhanced, which fi nally results in a distinct blue-shift. In addition, the quantum yields of the copolymers with POSS in solutions are higher than that of P1 , which can be attributed to the fact that the effi cient isolation effect of the POSS units inhibits the interchain aggregation/quenching.



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Figure 8 . a) UV–vis absorption spectra of the copolymers in CH 2 Cl 2 solutions and thin fi lms. b–d) PL spectra in CH 2 Cl 2 solutions and thin fi lms of: b) P1 and P3 , c) P3 and P4 , d) P3 and P2 ; S represents in CH 2 Cl 2 solution; F represents as a thin fi lm.

To investigate the thermal spectra stability of the copolymers, their thin fi lms were annealed at 100 ° C for 2 h in air. As shown in Figure 9 a, after annealing,


Figure 9 . PL spectra of: a) P1 , b) P2 , c) P3 , and d) P4 fi lms before and a


the PL emission band of P1 is signifi cantly red-shifted and broadens, compared with that of its fresh fi lm. Nev-ertheless, when bulky POSS are incorporated into the

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Table 3. Electrochemical potentials and energy levels of the copolymers.

Polymer E onset,ox a) [V]

HOMO b) [eV]

LUMO c) [eV]

E g d) [eV]

P1 1.53 − 5.79 − 3.13 2.66

P2 1.54 − 5.75 − 3.07 2.68

P3 1.70 − 5.87 − 3.16 2.71

P4 1.55 − 5.74 − 3.06 2.68

a) Onset oxidation potentials measured by cyclic voltammetry; b) Calculated from the oxidation potentials; c) Calculated from the HOMO energy levels and E g ; d) Energy band gap was estimated from the onset wavelength of the optical absorption of the copoly mer fi lms.

Figure 10 . a) The structure of the PLED. b) The energy level dia-gram of the materials used in the PLED.

copolymers, the PL spectra of the annealed fi lms are almost identical to those of the fresh fi lms (Figure 9 b–d). The results indicated that the thermal spectral stability of the copolymers tethered with POSS was greatly improved, even when the copolymers were exposed in air for a long time; this can be attributed to the outstanding inorganic thermal and oxygen stability of the hybrid POSS. [ 36 ]

3.5. Electrochemical Properties

The electrochemical properties of the copolymers were investigated through CV and the results were listed in Table 3 . The highest occupied molecular orbital (HOMO) energy levels of the copolymers were calcu-lated according to the empirical formula of HOMO = [ − ( E onset,ox − E ox(ferrocene) ) − 4.8] eV, [ 16 , 44 ] where E onset,ox is the onset oxidation potential. The energy bandgap ( E g ) of the copolymers was calculated from the edge of UV–vis absorp-tion spectra and the lowest unoccupied molecular orbital (LUMO) energy levels were obtained according to this equa-tion: LUMO = HOMO + E g . As shown in Table 3 , the HOMO and LUMO energy levels and the band gap energies of P2 – P4 almost coincide with those of P1 . This result indicated that the POSS moieties were not involved in the oxidation of the copolymers and did not affect the redox properties of the copolymers. [ 45 ]

3.6. EL Properties

Double-layer PLED devices with the confi guration ITO/PEDOT:PSS (35 nm)/polymer (50 nm)/TmPyPB (40 nm)/LiF (1 nm)/Al (85 nm) were fabricated to investigate the EL properties of the copolymers. The chemical structure of TmPyPB is shown in Figure S11 in the Supporting Informa-tion. A PLED structure and the energy level diagram of the materials are illustrated in Figure 10 . Figure 11 a displays the normalized EL spectra of the devices. The maximum emission peaks of the copolymers are almost identical, and

20Macromol. Chem. Phys.


a slight blue shift is observed when POSS are introduced. The EL spectrum of P1 shows an additional band between 520 and 600 nm. However, when POSS are incorporated into the copolymers, the long-wavelength emission in the range 520–600 nm is sharply reduced, and a reduced FWHM (full width at half maximum) is obtained. These results suggest that the introduction of bulky POSS into the side chains presumably retards interchain interactions and reduces the degree of exciton migration to defect sites, thereby leading to a purer emission. [ 35 ]

The current density–voltage characteristics of the devices are shown in Figure 11 b. The devices pre-pared from the copolymers tethered with POSS showed slightly higher turn-on voltages in the range of 7.9–8.5 V compared with that prepared from P1 (6.5 V). The cur-rent density decreased with the increase of the POSS con-tent, which resulted from the enhanced light-emitting layer resistivity. Figure 11 c shows the luminance–voltage characteristics of the devices. The introduction of POSS resulted in an improvement in the brightness. However, high POSS content was not favorable for enhancing the

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Figure 11 . a) EL spectra of the devices measured at 15 V. b) Current density–voltage ( J – V ) characteristics of the devices. c) Luminance–voltage ( L – V ) characteristics of the devices. d) Luminous effi ciency-current density characteristics of the devices.

brightness. As shown in Figure 11 d, luminous effi ciency enhanced when POSS were introduced. All these improve-ments in the performance probably result from that POSS units act as chain separators by their steric hindrance and reduce aggregation effects, which is benefi cial to the improvement of exciton recombination by eliminating the excimer formation. [ 46 ] The better EL performance was obtained from the devices prepared from P2 and P4 , especially P2 , compared with those prepared from P1 and P3 . Higher POSS content resulted in lower brightness and higher turn-on voltage, such as the device prepared from P3 . In general, appropriate amount of POSS is benefi cial


Figure 12 . Current density–voltage ( J – V ) characteristics of: a) the ele

Macromol. Chem. Phys.© 2013 WILEY-VCH Verlag Gm

for enhancing the performance of the devices, and the position of the side chain that POSS is tethered to, also has an important infl uence on the EL properties. Improve-ments in recombination in PLEDs may also result from a more balanced transport of holes and electrons in devices by the presence of POSS.

In order to study the effect of POSS on the charge injection and balance, the electron-only (ITO/polymer/TmPyPB/LiF/Al) and the hole-only (ITO/PEDOT:PSS/polymer/Al) devices were fabricated. The current den-sity–voltage characteristics of the electron-only and the hole-only devices are shown in Figure 12 . In Figure 12 a,

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the electron current density improved when POSS were introduced into the copolymers for the electron-only devices fabricated with P2 , P3 , and P4 . This was because the roughness and surface area of the copolymer fi lms increased compared with those of P1 . Interfacial area enhancement of the light-emitting layer and the cathode was favorable for the cathode electron injection. [ 47 ] How-ever, in the electron-only devices, the electron current density of P3 was lower than that of P2 and P4 , which indicated that high POSS content was not favorable for enhancing the electron current density. This was prob-ably resulting from that: a) the surface roughness effect diminished with the large increase of insulating POSS resistivity in the light-emitting layer, which would limit the enhancement of the electron current density; b) excess POSS resulted in the mismatch on the energy level in the electron-only device prepared from P3 compared with the devices of P2 and P4, which was not favorable to the electron transport. As shown in Figure 12 b, the introduc-tion of POSS resulted in a reduced hole-current density for the hole-only devices. Moreover, the hole current density decreased with the increasing POSS content; this could be attributed to that POSS assumed the role of hole-trapper in the light-emitting layer. [ 47 ] In addition, the current density of the hole-only device fabricated with P1 was larger than that of the electron-only device, which indi-cated that the hole was the major carrier in the device. The introduction of POSS benefi ts the balanced trans-port of holes and electrons in devices by increasing the electron current density and reducing the hole current density. Therefore, current effi ciency enhanced with the introduction of POSS.

4. Conclusion

In conclusion, we have successfully synthesized four novel fl uorene/carbazole alternating copolymers with specifi c architectures, in which the number of POSS in side chains and the position of POSS tethered to are different. The POSS molecules are well incorporated into the copolymers and their introduction results in improved photophysical properties. The more POSS groups in side chains, the more effective isolation effect would exist when the position that POSS are tethered to is identical, and the PL spectrum displays more evident blue shift when POSS are tethered to the 9-position of the carbazole unit than that of the fl u-orene unit, because the nitrogen atoms of carbazoles are electron rich. Moreover, the thermal spectral stability of the copolymers in the solid state is effi ciently improved owing to the outstanding inorganic thermal and oxygen stability of hybrid POSS. Besides, POSS could effectively inhibit interchain interaction and facilitate charge bal-ance in devices by increasing the electron current density

Macromol. Chem. Phys. 2© 2013 WILEY-VCH Verlag Gmb

and reducing the hole current density, thereby leading to improved EL performance. The better EL performance was obtained for the devices prepared from P2 and P4 , espe-cially P2 , compared with those prepared from P1 and P3 . In general, appropriate amount of POSS is benefi cial for enhancing the performance of the devices, and the posi-tion of POSS tethered to, also has an important infl uence on the EL properties. All these results show that by control-ling the number and the position of POSS in the side chain, we can construct outstanding EL materials.

Supporting Information

Supporting Information is available from the Wiley Online Library or from the author.

Acknowledgements: We are thankful for fi nancial support from the National Natural Science Foundation of China (No. 20974013), and Polymer Chemistry and Physics, Beijing Municipal Education Commission (BMEC; No. XK100100640).

Received: April 10, 2013 ; Revised: May 9, 2013; Published online: July 5, 2013; DOI: 10.1002/macp.201300290

Keywords: electroluminescence; fl uorene/carbazole copoly-mers; morphology; photophysics; polyhedral oligomeric silsesquioxanes

[ 1 ] G. Gustafsson , Y. Cao , G. M. Treacy , F. Klavetter , N. Colaneri , A. J. Heeger , Nature 1992 , 357 , 477 .

[ 2 ] Z. Peng , S. Tao , X. Zhang , J. Tang , C. S. Lee , S.-T. Lee , J. Phys. Chem. C 2008 , 112 , 2165 .

[ 3 ] M. T. Bernius , M. Inbasekaran , J. O’Brien , W. Wu , Adv. Mater. 2000 , 12 , 1737 .

[ 4 ] J. H. Burroughes , D. D. C. Bradley , A. R. Brown , R. N. Marks , K. Mackay , R. H. Friend , P. L. Burns , A. B. Holmes , Nature 1990 , 347 , 539 .

[ 5 ] Y. Jin , J. Kim , S. Lee , J. Y. Kim , S. H. Park , K. Lee , H. Suh , Macro-molecules 2004 , 37 , 6711 .

[ 6 ] T. I. Wallow , B. M. Novak , J. Am. Chem. Soc. 1991 , 113 , 7411 . [ 7 ] G. Grem , G. Leditzky , B. Ullrich , G. Leising , Adv. Mater. 1992 ,

4 , 36 . [ 8 ] K. Stokes , K. Heuze , R. McCullough , Macromolecules 2003 ,

36 , 7114 . [ 9 ] A. Roviello , A. Buono , A. Carella , G. Roviello , A. Cassinese ,

M. Barra , M. Biasucci , J. Polym. Sci., Part A: Polym. Chem. 2007 , 45 , 1758 .

[ 10 ] R. Abbel , A. P. H. J. Schenning , E. W. Meijer , J. Polym. Sci., Part A: Polym. Chem. 2009 , 47 , 4215 .

[ 11 ] Y. Jin , M. Lee , S. H. Kim , S. Song , Y. Goo , H. Y. Woo , K. Lee , H. Sun , J. Polym. Sci., Part A: Polym. Chem. 2008 , 46 , 4407 .

[ 12 ] J. A. Mikroyannidis , Y.-J. Yu , S.-H. Lee , J.-I. Jin , J. Polym. Sci., Part A: Polym. Chem. 2006 , 44 , 4494 .

[ 13 ] N. Blouin , M. Leclerc , Acc. Chem. Res. 2008 , 41 , 1110 . [ 14 ] N. Naga , N. Tagaya , H. Noda , T. Imai , H. Tomoda , J. Polym.

Sci., Part A: Polym. Chem. 2008 , 46 , 4513 . [ 15 ] Y. Zou , D. Gendron , R. Badrou-Aïch , A. Najari , Y. Tao ,

M. Leclerc , Macromolecules 2009 , 42 , 2891 .

www.MaterialsViews.com013, 214, 1710−1723

H & Co. KGaA, Weinheim


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[ 16 ] Y. Lin , Y. Chen , T. Ye , D. Ma , Y. Li , Eur. Polym. J. 2012 , 48 , 416 .

[ 17 ] I. D. W. Samuel , G. Rumbles , C. J. Collison , S. C. Moratti , A. B. Holmes , Chem. Phys. 1998 , 227 , 75 .

[ 18 ] C.-H. Chou , S.-L. Hsu , K. Dinakaran , M.-Y. Chiu , K.-H. Wei , Macromolecules 2005 , 38 , 745 .

[ 19 ] Y. Li , J. Ding , M. Day , Y. Tao , J. Lu , M. D’iorio , Chem. Mater. 2004 , 16 , 2165 .

[ 20 ] J. A. Mikroyannidis , P. A. Damouras , V. G. Maragos , L.-R. Tsai , Y. Chen , Eur. Polym. J. 2009 , 45 , 284 .

[ 21 ] C. Xia , R. C. Advincula , Macromolecules 2001 , 34 , 5854 . [ 22 ] S. Xiao , M. Nguyen , X. Gong , Y. Cao , H. Wu , D. Moses ,

A. J. Heeger , Adv. Funct. Mater. 2003 , 13 , 25 . [ 23 ] W.-B. Zhang , Y. Li , X. Li , X. Dong , X. Yu , C.-L. Wang ,

C. Wesdemiotis , R. P. Quirk , S. Z. D. Cheng , Macromolecules 2011 , 44 , 2589 .

[ 24 ] K. Zeng , L. Wang , S. Zheng , J. Phys. Chem. B 2009 , 113 , 11831 . [ 25 ] B. X. Fu , A. Lee , T. S. Haddad , Macromolecules 2004 , 37 , 5211 . [ 26 ] X. Ren , B. Sun , C.-C. Tsai , Y. Tu , S. Leng , K. Li , Z. Kang ,

R. M. V. Horn , X. Li , M. Zhu , C. Wesdemiotis , W.-B. Zhang , S. Z. D. Cheng , J. Phys. Chem. B 2010 , 114 , 4802 .

[ 27 ] H. Liu , S. Zheng , K. Nie , Macromolecules 2005 , 38 , 5088 . [ 28 ] Y. Ni , S. Zheng , Chem. Mater. 2004 , 16 , 5141 . [ 29 ] S.-W. Kuo , H.-F. Lee , W.-J. Huang , K.-U. Jeong , F.-C. Chang ,

Macromolecules 2009 , 42 , 1619 . [ 30 ] S. E. Létant , A. Maiti , T. V. Jones , J. L. Herberg , R. S. Maxwell ,

A. P. Saab , J. Phys. Chem. C 2009 , 113 , 19424 . [ 31 ] C.-C. Cheng , C.-H. Chien , Y.-C. Yen , Y.-S. Ye , F.-H. Kob , C.-H. Lin ,

F.-C. Chang , Acta Mater. 2009 , 57 , 1938 . [ 32 ] J. D. Froehlich , R. Young , T. Nakamura , Y. Ohmori , S. Li ,

A. Mochizuki , Chem. Mater. 2007 , 19 , 4991 .

www.MaterialsViews.comMacromol. Chem. Phys.


[ 33 ] Y.-L. Chu , C.-C. Cheng , Y.-P. Chen , Y.-C. Yen , F.-C. Chang , J. Mater. Chem. 2012 , 22 , 9285 .

[ 34 ] W.-J. Lin , W.-C. Chen , W.-C. Wu , Y.-H. Niu , A. K.-Y. Jen , Macro-molecules 2004 , 37 , 2335 .

[ 35 ] C.-H. Chou , S.-L. Hsu , S.-W. Yeh , H.-S. Wang , K.-H. Wei , Macro-molecules 2005 , 38 , 9117 .

[ 36 ] K.-Y. Pu , B. Zhang , Z. Ma , P. Wang , X.-Y. Qi , R.-F. Chen , L.-H. Wang , Q.-L. Fan , W. Hang , Polymer 2006 , 47 , 1970 .

[ 37 ] R. N. Brookins , K. S. Schanze , J. R. Reynolds , Macromolecules 2007 , 40 , 3524 .

[ 38 ] N. Yamamoto , R. Ito , Y. Geerts , K. Nomura , Macromolecules 2009 , 42 , 5104 .

[ 39 ] J. A. Mikroyannidis , K. M. Gibbons , A. P. Kulkarni , S. A. Jenekhe , Macromolecules 2008 , 41 , 663 .

[ 40 ] J. J. Intemann , J. F. Mike , M. Cai , C. A. Barnes , T. Xiao , R. A. Roggers , J. Shinar , R. Shinar , M. Jeffries-EL , J. Polym. Sci., Part A: Polym. Chem. 2013 , 51 , 916 .

[ 41 ] D. Yang , D. Gao , C. Zeng , J. Jiang , M. Xie , React. Funct. Polym. 2011 , 71 , 1096 .

[ 42 ] J. Zhou , Y. Zhao , K. Yu , X. Zhou , X. Xie , New J. Chem. 2011 , 35 , 2781 .

[ 43 ] X.-T. Wang , Y.-K. Yang , Z.-F. Yang , X.-P. Zhou , Y.-G. Liao , C.-C. Lv , F.-C. Chang , X.-L. Xie , J. Therm. Anal. Calorim. 2010 , 102 , 739 .

[ 44 ] Y. Chen , M. E. EI-Khouly , M. Sasaki , Y. Araki , O. Ito , Org. Lett. 2005 , 7 , 1613 .

[ 45 ] J. Lee , H.-J. Cho , B.-J. Jung , N. S. Cho , H.-K. Shim , Macromol-ecules 2004 , 37 , 8523 .

[ 46 ] T. P. Nguyen , C. W. Lee , S. Hassen , H. C. Le , Solid State Sci. 2009 , 11 , 1810 .

[ 47 ] R.-H. Lee , H.-H. Lai , Eur. Polym. J. 2007 , 43 , 715 .

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fluorene/carbazole alternating copolymers tethered with polyhedral oligomeric silsesquioxanes:...

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