Synthesis of polyhedral oligomeric silsesquioxane-functionalized polyfluorenes: Hybrid organic–inorganic π-conjugated polymers

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<ul><li><p>Synthetic Metals 156 (2006) 590596</p><p>Synthesis of polyhedral oligomeric silsesp nic</p><p>Jo o-Ha Center olecul</p><p>blic oechnoary 20006</p><p>Abstract</p><p>Polyfluor ere sization. The entsstability. Th paresuppressed i his eshowed a de hesebrightness o 2006 Else</p><p>Keywords: Polyhedral oligomeric silsesquioxane (POSS); Yamamoto coupling; Electroluminescence</p><p>1. Introduction</p><p>Since thapplicationmaterials fdiodes (PLacademiapropertiesand simplefabricatedStable, bluchallenge iprimary cogated polyfor this appties, both phnescent (ELat the fluormon organ</p><p> CorresponE-mail ad</p><p>compared to other conjugated polymers) [3]. However, PLEDs</p><p>0379-6779/$doi:10.1016/je discovery by the Cambridge group of the potentials of -conjugated polymers as active light-emittingor flat panel displays [1], polymeric light-emittingEDs) have attracted a great deal of attention fromand industry. These materials offer advantageoussuch as good processibility, low operating voltages,color tunability compared to organic LEDs (OLEDs)with low molecular weight organic materials [2,3].e-emitting conjugated polymers are the most recentn creating PLED-based materials to emit all threelors (RGB: red, green, blue), and among the conju-mers, polyfluorenes (PFs) are promising candidateslication [4,5]. PFs have many advantageous proper-ysical (high photoluminescent (PL) and electrolumi-) efficiencies) and chemical (facile functionalizationene C-9 position provides good solubility in com-ic solvents like chloroform, toluene, and p-xylene</p><p>ding author. Tel.: +82 42 869 2827; fax: +82 42 869 2810.dress: hkshim@kaist.ac.kr (H.-K. Shim).</p><p>fabricated with PF derivatives show an emission band tailing tolonger (green) wavelengths and deterioration in both color purityand stability [6,7]. The suggested reasons for the tailing emis-sions in their EL spectrum include (1) aggregation and excimerformation [5,8] and/or (2) thermal oxidation and intermolecularcrosslinking between PF chains [9]. Many types of PF deriva-tives, such as spiro-functionalized PFs [7], PFs encapsulatedwith dendrimer moieties [8], networked PFs [5c] asymmetric9,9-substituted PFs [6d], end-capped PFs with bulky unreactivemoieties [6c], cyclodextrin-threaded PFs [10], and PFs copoly-merized with perylene dyes [11], have been demonstrated to beeffective towards suppressing excimer formation and aggrega-tion and/or thermal oxidation and intermolecular crosslinkingbetween PF chains. However, obtaining conjugated polymersthat exhibit pure blue emission remains a goal [7,8,12]. POSS-functionalized polymers are organicinorganic hybrid materialsthat have received considerable recent attention as modifiers fornanoparticles [13,14]. The POSS unit is a cube-shaped molecule,in which an inorganic core is surrounded by eight organic groups[13,14]. The POSS moieties in linear polymeric POSS sys-tems contain seven organic solubilizing groups (cyclohexyl orcyclopentyl) and one functional group on the inorganic core.</p><p> see front matter 2006 Elsevier B.V. All rights reserved..synthmet.2006.02.011olyfluorenes: Hybrid organicinorganghee Lee a, Hoon-Je Cho a, Nam Sung Cho a, Dfor Advanced Functional Polymers, Department of Chemistry and School of M</p><p>Technology, Dae-jon 305-701, Repub Department of Applied Chemistry, Kumoh National Institute of T</p><p>Received 9 March 2005; received in revised form 16 FebruAvailable online 2 May 2</p><p>enes with appended polyhedral oligomeric silsesquioxanes (POSSs) wresulting copolymers exhibit good solubility in common organic solv</p><p>e PL quantum yields of the copolymers were drastically enhanced comntermolecular aggregation and/or thermal oxidation and crosslinking. Tep blue emission in electroluminescent devices. LED devices with tf 260460 cd/m2.vier B.V. All rights reserved.quioxane-functionalized-conjugated polymers</p><p>oon Hwang b, Hong-Ku Shim a,ar Science (BK21), Korea Advanced Institute of Science andf Korealogy, Kumi 730-701, Republic of Korea06; accepted 20 February 2006</p><p>uccessfully synthesized through Ni(0)-mediated polymer-such as chloroform, chlorobenzene, etc. and good thermald to PDHF because the POSS-functionalized PFs stronglyffective dilution effect and the higher stability of the POSSpolymers showed low turn-on voltage of near 4.0 V and</p></li><li><p>J. Lee et al. / Synthetic Metals 156 (2006) 590596 591</p><p>POSS units retain their nanoscale dimensions in a polymermatrix [14,15]. Heeger et al. demonstrated that thermal sta-bilities andpolymers mend-cappertially insulhave enhanreducing inpaper, we rPFs with esmall amoution of PFsand thus lidation andexpected, trevealed strthermal ox</p><p>2. Experim</p><p>2.1. Instru</p><p>1H NMRAVANCE 3ethylsilanements, chlospectra weeter with sweight-avemined by gGPC-150Cas standardtial scanninwere perfoof 10 C mwere meas</p><p>spectra of ta Spex Fluspin-coated1000. Thetics were rand a lumiEL measurcorrespondFilm thicknsurface pro</p><p>2.2. Mater</p><p>2,7-Dibtetrahydro-platinum(0(Pt(dvs)) s15-heptacyoxane, 2,2Aldrich ChBis(1,5-cyc</p><p>Chemicals. Sodium hydroxide was purchased from JunseiChemical Co. and all other reagents and solvents were pur-</p><p>com</p><p>t fur</p><p>2-[2ro-2as s</p><p>ratu</p><p>2-(2as s</p><p>ratu</p><p>1-[2-eneas s</p><p>ratu</p><p>2,7-as s</p><p>ratu</p><p>2,7-3 g ((4),5,7,7,13]</p><p>e, ansultiul ofroom</p><p>hrouhe muo a</p><p>n chr(1/3</p><p>t asH, 6): 0..84t, 2HMR22.439.4, 138</p><p>Polyixtuof</p><p>f anargonom</p><p>lfluor rate waC folight-emitting device performances of conjugatedight be enhanced by introduction of POSS as an[16a]. Recently, Cacialli et al. illustrated that par-</p><p>ated conjugated polymers with cyclodextrins shouldced luminescence efficiencies and stabilities throughteractions of the polymer chains [10,17]. In this</p><p>eport a novel method for preparing POSS-substitutednhanced optical properties. We hypothesized thatnts of nanoscale POSSs attached to the C-9 posi-would reduce the intermolecular interactions,</p><p>mit the aggregation and/or thermal oxidative degra-crosslinking between polymer chains [7,8,10,12]. Ashe PL and EL studies of POSS-functionalized PFsongly suppressed intermolecular aggregation and/or</p><p>idation and crosslinking [16].</p><p>ental</p><p>mentation</p><p>and 13C NMR spectra were recorded on a Bruker00 and 400 spectrometer, respectively, with tetram-as an internal reference. For the NMR measure-roform-d (CDCl3) was used as the solvent. FT-IR</p><p>re obtained using a Nicolet Model 800 spectrom-amples prepared as KBr pellets. The number- andrage molecular weights of the polymers were deter-el permeation chromatography (GPC) on a Watersinstrument, using THF as eluent and polystyrene</p><p>. Thermogravimetric analysis (TGA) and differen-g calorimetry (DSC) measurements of the polymersrmed under a nitrogen atmosphere at a heating ratein1 using a Dupont 9900 analyzer. UVvis spectraured on a Jasco V-530 UVvis Spectrometer and PLhe polymers were measured at room temperature onorolog-3 spectrofluorometer (model FL3-11) usingfilms. EL spectra were obtained with a Minolta CS-</p><p>voltageluminance and voltagecurrent characteris-ecorded on a currentvoltage source (Keithley 238)nance detector (Minolta LS-100). Polymer films forement were prepared by spin-coating solutions of theing polymers (1 wt.% in chlorobenzene (Aldrich)).ess were measured with a TENCOR alpha-step 500filer.</p><p>ials</p><p>romofluorene, 1-bromohexane, 2-(2-bromoethoxy)2H-pyran, tetrabutylammonium bromide (TBAB),) 1,3-divinyl-1,1,3,3-tetramethyldisiloxane complexolution, 1-(hydridodimethylsilyloxy)-3,5,7,9,11,13,clopentylpentacyclo-[9.5.1.13,9.15,15.17,13]-octasil--dipyridyl, 1,5-cyclooctadiene, were obtained fromemical Co. and used without further purification.looctadienyl)nickel(0) was purchased from STREM</p><p>chasedwithou</p><p>2.2.1.perhyd</p><p>It wthe lite</p><p>2.2.2.It w</p><p>the lite</p><p>2.2.3.prop-2</p><p>It wthe lite</p><p>2.2.4.It w</p><p>the lite</p><p>2.2.5.1.2</p><p>poundoxy)-315,15. 1toluenThe respoonftion attered tAfter tin vaccolumhexaneproduc49.91; ppm3H), 02.28 (13C N22.39,31.40,130.42</p><p>2.2.6.A m</p><p>0.417 g5 mL ounderof modihexya molatoluenat 80 mercially as analytical-grade quality, and usedther purification.</p><p>-(2,7-Dibromo-9-hexyluoren-9-yl)ethoxy]H-pyran (2)ynthesized according to the procedures outlined inres [18].</p><p>,7-Dibromo-9-hexyluoren-9-yl)ethan-1-ol (3)ynthesized according to the procedures outlined inres [18].</p><p>-(2,7-Dibromo-9-hexyluoren-9-yl)ethoxy](4)ynthesized according to the procedures outlined inres [18].</p><p>Dibromo-9,9-dihexyluorene (6)ynthesized according to the procedures outlined inres [18].</p><p>Dibromo-9-hexyl-9-POSSuorene (5)2.50 mmol) of allyl-functionalized fluorene com-and 2.61 g (2.55 mmol) of 1-(hydridodimethylsilyl-9,11,13,15-heptacyclopentyl pentacyclo-[9.5.1.13,9.-octasiloxane were dissolved in 20 mL of anhydrous</p><p>d 0.5 mL of the toluene solution of Pt(dvs) was added.ng solution was stirred at 60 C for 24 h, and then aactivated carbon was dispersed into the reaction solu-</p><p>temperature for 1 h. The mixture solution was fil-gh a medium-size glass filter packed with Celite-545.ixture had been filtered, the toluene was evaporated</p><p>nd the concentrated crude product was purified byomatography using a mixture of ethyl acetate and n-0) as the eluent, yielding 2.88 g (yield 78.5%) of the</p><p>a white solid: Anal. Calcd. for C61H98Br2O14Si9: C,.73. Found: C, 50.27; H, 6.79. 1H NMR (CDCl3,</p><p>07 (m, 6H), 0.39 (m, 2H), 0.59 (b, 2H), 0.76 (t,1.20 (m, 13H), 1.291.83 (m, 58H), 1.93 (m, 2H),), 2.73 (t, 2H), 2.97 (t, 2H), 7.397.56 (m, 6H),</p><p>(CDCl3, ppm): 0.38, 13.84, 13.88, 22.28, 22.34,8, 23.23, 23.42, 27.03, 27.05, 27.33, 27.36, 29.46,4, 40.48, 53.92, 66.64, 73.52, 121.07, 121.58, 126.57,.87, 152.00.</p><p>merizationre of 0.735 g of bis(1,5-cyclooctadienyl)nickel(0),2,2-dipyridyl, 0.2 mL of 1,5-cyclooctadiene, andhydrous DMF was maintained at 80 C for 30 minn atmosphere. To this solution, a total of 1.8 mmolers, comprising a mixture of 2,7-dibromo-9,9-rene (6) and POSSs-functionalized fluorene (5) inio of 95:5, 90:10, and 80/20, dissolved in 15 mL ofs added dropwise. The resulting solution was stirredr 3 days. Then, 0.1 g of 9-bromoanthracene (the end</p></li><li><p>592 J. Lee et al. / Synthetic Metals 156 (2006) 590596</p><p>capper) in 5 mL of anhydrous toluene was added to the polymersolution, and the resulting solution was stirred at 80 C for a fur-ther 24 h. The polymer was precipitated in 400 mL of a mixtureof HCl, acetone, and methanol (vol.% of 1:1:2). The filteredcrude polymer was extracted with chloroform from NaHCO3aq. solution, washed with distilled water, and dried over anhy-drous magnesium sulfate. The organic layer was concentratedin vacuo, dissolved in chloroform, and precipitated in methanolagain. The resulting polymer was purified by Soxhlet extractionin methanol (80 C, 3 days) and dried under vacuum. Finally,the dried polymer was dissolved in chloroform, precipitated inmethanol, and dried in vacuo to give 0.61 g (yield 91%) of whitepolymer. Anal. Calcd. for PF-POSS05: C, 88.59; H, 9.59. Found:C, 88.84; H, 9.75; Anal. Calcd. for PF-POSS10: C, 86.87; H,9.49. Found: C, 86.12; H, 9.38; Anal. Calcd. for PF-POSS20:C, 83.44; H, 9.27. Found: C, 82.79; H, 9.18. 1H NMR (CDCl3, ppm): 0.03 (m), 0.42 (m), 0.78 (t), 1.13 (m), 1.54 (m), 1.70(m), 2.11 (m), 7.448.01 (m). FT-IR (KBr, cm1): 2952, 2928,2858, 1458, 1402, 1377, 1251, 1118, 885, 813, 749, 507.</p><p>3. Results</p><p>3.1. Synthe</p><p>The moPOSS-contpounds 2 aconditions,tions. As wcable interCompoundCompoundwas preparfunctionaliNi(0)-mediize 5 and 6POSSs (PFmolecular swith 1H NM</p><p>a) 1H NMR spectrum of monomer 1 in the range 1 to 9 ppm. (b) 1Hectrum of polymers.</p><p>esis.and discussion</p><p>sis and characterization</p><p>lecular structures and synthetic procedures for theaining PFs are shown in Schemes 1 and 2 [18]. Com-nd 6 were synthesized by alkylation of 1 under basicand 2 was deprotected to yield 3 under acidic condi-e previously reported, 3 is a useful and easily appli-</p><p>mediate to prepare asymmetric fluorene derivatives.4 was prepared by alkylation of 3 with allyl bromide.5, the mono-POSS-substituted fluorene monomer,</p><p>ed using a hydrosilation reaction between POSS-zed hydrido siloxane and 4 with a Pt catalyst. Theated coupling reaction was employed to copolymer-(2,7-dibromo-9,9-dihexylfluorene) to produce PF-</p><p>-POSS05, PF-POSS10, and PF-POSS20) [18]. Thetructures of monomers and polymers were confirmedR, 13C NMR, and FT-IR spectroscopy and elemental</p><p>Fig. 1. (NMR sp</p><p>Scheme 1. Monomer synth</p></li><li><p>J. Lee et al. / Synthetic Metals 156 (2006) 590596 593</p><p>esis.</p><p>analysis (Fshown in Stional prototo POSS un</p><p>As thesignals fromthe polymea weak Sithe FT-IRstretchingat 110011good solubroform, tetout any gelevels ofbility is punits, in wgroups. ThThe molecgel permestandardsMw = 56,00PF-POSS1POSS20 (M</p><p>The thedifferential10 C minrate of 10 sition temp</p><p>Vvis absorption and PL spectra of the polymers as spin-coated filmslene).</p><p>104, and 105 C for PF-POSS05, PF-POSS10, and PF-0, respectively. The decomposition temperatures for 5%loss of the polymers (Td) were above 420 C for all the</p><p>mers.</p><p>Table 1Physical and</p><p>Polymer</p><p>PF-POSS05PF-POSS10PF-POSS20</p><p>a Content rfluorine [18].</p><p>b TemperatuScheme 2. Polymer synth</p><p>ig. 1). The results were consistent with the moleculescheme 1. For monomers and polymers, the conven-n and carbon signals of the SiCH3 groups adjacentits, near 0 ppm, were observed in 1H NMR spectra.</p><p>amount of 5 in the copolymers was increased, thethese groups significantly increased. For 5 and all</p><p>rs, a strong SiO stretching band at 1118 cm1 andC stretching band at 1251 cm1 were observed in</p><p>spectra. Grill and Neumayer reported that SiOSibands in cage structures like POSS are observed50 cm1 [19]. All the copolymers showed veryility in common organic solvents such as chlo-rahydrofuran (THF), toluene, and p-xylene with-l formation, and, notably, copolymers with higherPOSS showed better solubility. This good solu-robably due to the introduction of soluble POSShich each POSS unit supports seven cyclopentyle copolymers easily formed films by spin-coating.ular weights of the polymers were determined byation chromatography (GPC) against polystyrenewith THF as eluent. PF-POSS05 (Mn = 27,000;0; PDI = 2.1) had a higher molecular weight than0 (Mn = 24,000; Mw = 53,000; PDI = 2.2) and PF-</p><p>n = 19,000; Mw = 50,000; PDI = 2.6).</p><p>Fig. 2. U(in p-xy</p><p>be 99,POSS2weightcopolyrmal properties of the polymers investigated usingscanning calorimetry (DSC; heating rate of</p><p>1) and thermogravimetric analysis (TGA; heatingC min1) are summarized in Table 1. The glass tran-eratures (Tg) of the copolymers were measured to</p><p>3.2. Optica</p><p>The UVthin films oabsorption</p><p>optical properties of the polymers</p><p>Feed ratio (x:y) Content ratioa (x:y) Yield (%)95/5 96.3/5.7 9190/10 88.1/11.9 8580/20 75.8/24.2 63</p><p>atios were calculated by NMR-assignment of the polymers, and x:y indicates the ra</p><p>re resulting in 5% weight loss based on initial weight.l properties</p><p>vis absorption and PL spectra of the PF-POSSs asn quartz plates are shown in Fig. 2. The maximumand the maximum emission of the copolymers are</p><p>Mw (104) PDI Tg (C) Tdb (C)5.6 2.1 99 4295.3 2.2 104 4245.0 2.6 105 420</p><p>tio of 2,7-dibromo-9,9-dihexylfluorene to the POSS-substituted</p></li><li><p>594 J. Lee et al. / Synthetic Metals 156 (2006) 590596</p><p>Table 2Optical properties of the polymers</p><p>Polymer max (UV, nm) max (PL, nm) max (PL, nm), annealed (150 C)Solut...</p></li></ul>

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