Preparation of a new polymer containing photoluminescent pyrazoline unit in the main chain

Preparation of a New Polymer ContainingPhotoluminescent Pyrazoline Unit in the Main Chain

QIANG FANG, TAKAKAZU YAMAMOTO

Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan

Received 19 September 2003; accepted 3 February 2004DOI: 10.1002/pola.20136Published online in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: A novel photoluminescent polymer (PPyne) containing a 2-pyrazoline unitin the molecular main chain was prepared (for the first time) by polycondensationbetween a 2-pyrazoline monomer [an adduct of 2,6-bis(4-bromobenzylidene)cyclohex-anone with phenylhydrazine] and 2,5-dihexyloxy-p-phenylene diboric ester in the pres-ence of Pd(PPh3)4. PPyne had a number-average molecular weight of 7800 and apolydispersity index of 1.99 and showed good solubility in common organic solvents. Intoluene PPyne exhibited an intrinsic viscosity [�] of 0.42 dL g�1 at 30 °C. The polymerwas photoluminescent (PL) in both the chloroform solution and the solid state; thequantum yield of PL in the solution was 40%. In the two states, PPyne gave the sameultraviolet–visible (UV–vis) peak at 368 nm and the same PL peak at 512 nm. DSCtraces indicated that PPyne had a melting temperature of 168 °C, and thermogravi-metric analysis revealed that the polymer had good thermal stability with a 5 wt % losstemperature of 376 °C under N2. Electrochemical oxidation of PPyne started at about0.5 V versus Ag/AgNO3 and gave a peak at 0.98 V versus Ag/AgNO3 with a color changeof the film from yellow to black green. The color change was followed by UV–visspectroscopy. The corresponding reduction peak appeared at 0.80 V versus Ag/AgNO3.Treatment of PPyne with HCl led to dehydrogenating transformation of the polymer toa new cross-conjugated polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: PolymChem 42: 2686–2697, 2004Keywords: luminescence polymer; pyrazoline derivatives; polycondensation; redoxpolymers; dehydrogenating transformation

INTRODUCTION

Organic luminescent materials have many impor-tant usages in industry and in the theoreticalresearch fields because of their good optic electri-cal properties.1–7 In particular, since the effectiveand practical electroluminescent materials werereported8,9 in 1987 and 1990, respectively, thegood development prospect1–7 of the luminescentmaterials in organic light-emitting diodes(OLED) and other optic electronic fields has pro-

moted many researchers to converge on findingthe new luminescent materials with good opticelectrical properties. Therefore, numerous re-search reports and patents concerning the mate-rials have been found in the literature in the pasttwo decades.1–7,10–17

A new class of organic luminescent materials,1,3,5-triaryl-2-pyrazolines, have been reported.18–24

The compounds had good hole-transporting abilityand high light-emitting brightness and could beused in OLED.22–24 Moreover, pyrazoline has aninteresting ring unit containing both the electron-accepting imine OCANO group and the electron-donatingON(Ar1)O group. Therefore, it is expectedthat the compounds can be used as a new class of

Correspondence to: T. Yamamoto (E-mail: [email protected])Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 42, 2686–2697 (2004)© 2004 Wiley Periodicals, Inc.

2686

optic electric materials in a broader application fieldvia adjusting the electron-donating or electron-withdrawing ability of Ar1, Ar2, and Ar3 in the ring(see Structure 1).18–24

Several reports concerning the polymers con-taining pyrazoline units in molecular side chainshave been found.25,26 However, there is no prece-dent of the synthesis of the polymer containing apyrazoline unit in the main chain. For practicaluse, especially in optic electric devices, polymericmaterials are superior to small-molecule com-pounds in many cases. For example, polymericfilms are easily fabricated with a simple spin-coating method or an ink-jet printing method, and

polymeric materials have a longer lifetime thanthat of the small-molecule compounds duringlong-time use. Under these circumstances, it isdesired to study the synthesis and optic electricproperties of the polymers containing the pyrazo-line unit in the main chain.

We reported27 the preparation and propertiesof a new, soluble, unsaturated polyketone withphotoluminescence (PL) and electroactivity. Thepolymer was synthesized by a Pd-catalyzed cou-pling between monomers 1 and 4 (shown inScheme 1). As an extension of the research, wecarried out the reaction of 1 with phenylhy-drazine to yield the adduct 2, which exhibitedgood PL in both solutions and the solid state.Structurally, adduct 2 had the pyrazoline struc-ture and two reactive bromo groups, which en-couraged us to prepare a new polymer, PPyne,consisting of 2-pyrazoline units in the macromo-lecular main chains via polycondensation be-tween the pyrazoline monomer (2) and p-phe-nylene diboric ester (4). The polymer had good PL,film-forming ability, electroactivity, and higherheat resistance. Herein, we report the results.

Scheme 1. Preparation procedure of the novel polymer.

PHOTOLUMINESCENT PYRAZOLINE POLYMERS 2687

EXPERIMENTAL

Materials

2,6-Bis(4-bromobenzylidene)cyclohexanone (1)and 1,4-dibromo-2,5-bis(hexyloxy)benzene (3)were prepared by the method described in theliterature.27 [Bu4N]BF4 (Bu � butyl) was purifiedby recrystallizing three times from a mixture ofethyl acetate and ethanol (20:1, v/v) and wasdried over P2O5 in vacuo at room temperature for5 days.

Instruments1H NMR spectra were recorded on a JEOL P-300spectrometer. IR spectra were taken with a JascoFT/IR 410 plus spectrophotometer with KBr pel-lets. The molecular weight was measured by gelpermeation chromatography (GPC) with a Shi-madzu LC-9A liquid chromatograph equippedwith a UV detector (eluent: chloroform). The datawere relative to polystyrene standards. Ultravio-let–visible (UV–vis) absorption spectra were mea-sured with a Shimadzu UV 3000 spectrophotom-eter. PL was measured with a Hitachi modelF4010 fluorescence spectrophotometer. X-ray dif-fraction patterns were recorded with a RigakuRINT 2000 Ultima �/PC X-ray diffractometer.Thermal stability of the polymers was determinedon a Shimadzu TGA-50 thermogravimetric ana-lyzer (TGA) at a heating rate of 10 °C min�1 innitrogen. Cyclic voltammograms (CVs)for the castpolymer films on a platinum plate (1 � 1 cm) wereobtained in an acetonitrile solution of [Bu4N]BF4(0.10 M) under N2 with (0.10 M AgNO3)/Ag andplatinum wire as a reference and counterelec-trodes, respectively. A Solartron S-1260 analyzerwas used for CV. Viscosity was measured with anUbbelohde viscometer with toluene at 30 °C.

3-(4-Bromophenyl)-7-[(4-bromophenyl)methylene]-3,3a,4,5,6,7-hexahydro-2-phenyl-2H-indazole (2)

This monomer was prepared by modifying a methodreported for preparation of an adduct of 2,6-diben-zylidenecyclohexanone with hydrazine.28

To a suspension solution of 1 (3.0 g, 6.94 mmol)in 100 mL of ethanol was added 0.9 g of phenyl-hydrazine (98% content, 8.2 mmol). The mixturewas allowed to reflux for 24 h. After cooling toroom temperature, the resulting yellow turbid so-lution was kept at 0 °C for 24 h. Crude 2 wascollected by filtration and washed with water and

methanol, respectively. After recrystallizationfrom a mixed solvent of chloroform and methanol,2 was obtained as bright yellow needles.

Yield: 57%; mp: 196 °C (DSC). IR (cm�1): 1600.1H NMR (CDCl3): � 1.34–2.31 (m, 5H), 2.81 (dddd,2H), 4.46 (d, J � 12 Hz, 1H), 6.74–7.13 (m, 5H,aromatic H of the phenyl group), 7.19 (s, 1H,vinylic H), 7.29–7.45 (m, 8H, aromatic H in thep-phenylene units). ELEM. ANAL. Calcd. forC26H22Br2N2: C, 59.79%; H, 4.25%; N, 5.36%; Br,30.60%. Fond: C, 59.87%; H, 4.27%; N, 5.25%; Br,30.82%.

Bis(2,2-dimethylpropane-1,3-diyl)-1,4-dihexyloxyphenylene-2,5-diborate (4)

This monomer was prepared by modifying theprocedure described in the literature.27

Iodine-activated magnesium turnings (2.4 g,100 mmol) in 50 mL of dry tetrahydrofuran (THF)were heated briefly to 60 °C. Then the solution of17.5 g of 3 (40 mmol) in 100 mL of THF was addeddropwise over 30 min, and the reaction mixturewas thereafter kept for 8 h at reflux temperature.After cooling, the Grignard solution was addedover 1 h to a solution of trimethyl borate (41 mL,400 mmol) in 200 mL of THF at �60 °C. When theaddition was completed, the mixture was stirredfor an additional 1 h at that temperature. Thenthe mixture was warmed to room temperature,stirred for 24 h, poured into 800 mL of 2 M HCl,and stirred for 24 h at room temperature. 2,5-Dihexyloxy-p-phenylenediboric acid, as a whitecrystalline solid, was obtained by filtration, wash-ing with water and cold acetone, and drying invacuo. Yield: 75%. The 1H NMR data of the com-pound agreed with the reported data.27

2,5-Dihexyloxy-p-phenylenediboric acid thusprepared and 2,2-dimethyl-l,3-propanediol (10.4g, 100 mmol) were mixed in 100 mL of dry tolu-ene, and the mixture was allowed to react underreflux for 10 h. The solvent was removed by evap-oration, and the residue was recrystallized fromhexane to obtain 4 as white crystalline rods.

Yield: 40%. The IR and 1H NMR data of thecompound agreed with the reported data.27 ELEM.ANAL. Calcd. for C28H48B2O6: C, 66.95%; H,9.63%. Found: C, 66.87%; H, 9.62%.

Polymer Synthesis

The polymer was synthesized in a way analogousto that described in our previous research.27

2688 FANG AND YAMAMOTO

To a 200-mL Schlenk tube charged with 2 (986mg, 1.89 mmol), 4 (949 mg, 1.89 mmol), and Pd-(PPh3)4 (66 mg, 0.0571 mmol) were added a de-gassed mixed solvent of 20 mL of toluene and 75mL of THF. The mixture was stirred for 20 min atroom temperature under N2. Then, 9.5 mL of adegassed 2 M K2CO3 aqueous solution (19 mmol)were added to the Schlenk tube, and the reactionmixture was heated to reflux. After maintainingthis temperature for 72 h under intensive stir-ring, the mixture was cooled to room temperatureand diluted with 300 mL of chloroform. The or-ganic layer was washed with water and dried overanhydrous Na2SO4. After evaporation of the sol-vents, the residue was redissolved in 10 mL ofchloroform and poured into 200 mL of methanolto give a polymer precipitate. After filtration anddrying in vacuo, PPyne was obtained as a brightyellow powder (904 mg, yield: 75%).

Number-average molecular weight (Mn)� 7800 (GPC, CHCl3); molecular weight distribu-tion (Mw/Mn) � 1.99. Intrinsic viscosity: [�] � 0.42dL g�1 (toluene, 30 °C). IR (cm�1): 2925, 1600. 1HNMR (CDCl3): � 7.35–7.55 (m, 8H, aromatic H inthe p-phenylene unit), 7.29 (s, 1H, vinylic H), 6.93(s, 2H, aromatic H in the 2,5-hexyloxy-1,4-phe-nylene unit), 6.75 and 7.05–7.2 (m, 5H, aromaticH of the phenyl group), 4.57 (d, J � 12 Hz, 1H, Hat the 3-position of the pyrazoline ring), 3.80 (t,4H, OOCH2O), 1.9–3.2 (m, 5H), 1.19–1.61 (m,18H, 2H in the cyclohexyl unit and OCH2O hy-drogens in the side chains), 0.79 (t, 6H). ELEM.ANAL. Calcd. for (C44H50N2O2 � H2O)n: C, 80.49%;H, 7.93%; N, 4.27%; Br, 0%; Found: C, 80.81%; H,7.93%; N, 4.10%; Br, 0.57%.

RESULTS AND DISCUSSION

Synthesis and Characterization of Ppyne

With the method similar to that used for thesynthesis of unsaturated polyketone depicted inour previous work,27 PPyne was prepared in agood yield from 2 and 4, as shown in Scheme 1.The polymer showed Mn and Mw/Mn values of7800 and 1.99, respectively, in the GPC analysis.The polymer exhibited an [�] of 0.42 dL g�1 intoluene at 30 °C.

PPyne is easily soluble in common organic sol-vents and had good film-forming ability when castfrom either chloroform or toluene solutions.

The chemical structure of the polymers wascharacterized by IR, 1H NMR, and elemental

analysis. In the IR spectrum of PPyne, a charac-teristic � (CAN) peak appeared at 1600 cm�1. The1H NMR spectrum of the polymer is depicted inFigure 1. The axial and equatorial hydrogens inthe cyclohexane ring gave their peaks at differentpositions and are assigned as depicted in Figure1. A large coupling constant, 12 Hz, observed withthe peak at � 4.57 (cf. Experimental and Fig. 1),indicates that the hydrogens at the Hb- and Hc-positions, as shown in Figure 1, were in a transconfiguration. Comparison of the 1H NMR datawith those of monomer 2 (cf. Experimental) showsthat there was no difference between PPyne andmonomer 2 for the coupling constant (12 Hz) ob-served with the Hb signals at � 4.57 and 4.46 for2 and PPyne, respectively, suggesting that thegeometric configuration of the pyrazoline ringwas maintained during polymerization.

All of the detected peaks and rations betweentheir peak areas were consistent with the pro-posed structure.

Optical Properties

The chloroform solution of PPyne was yellow andexhibited a strong green PL under irradiationwith long UV light (336 nm). Figure 2 shows theUV–vis spectra of PPyne in chloroform and in thesolid state. Comparison of the UV–vis data withthose of monomer 2 indicates that the maximumabsorption peak of PPyne in chloroform had aredshift of 10 nm from that of 2. This seemed to bedue to expansion of the �-conjugation system ofthe pyrazoline ring in PPyne, similar to that ofthe ladder polymers without large, extended�-conjugated units.29

PPyne exhibited PL at 512 nm in both chloro-form and in the solid state, as shown in Figure 3.The difference of the PL spectra between the twostates is that the excitation peak was broader inthe solid state. The quantum efficiency of PL ofPPyne in the solution was measured at 40% witha 1 N H2SO4 solution of quinine (10�5 M) as areference. The corresponding monomer 2 demon-strated PL at 508 nm in chloroform at an excita-tion wavelength of 358 nm. The quantum effi-ciency of 2 in the solution was 38%, indicating thePL features of 2 were maintained in PPyne, whichhad a �-conjugation system constituting the pyra-zoline unit and terphenyl unit. Pyrazolines andterphenyl compounds (or the polymers containingterphenyl groups in side chains) showed PL at440–500 and 390–400 nm, respectively.24–26,30,31


Treatment with Acids

The optical properties of acid-treated PPyne werealso investigated. Figure 4 shows the changes inUV–vis spectra of THF solution of PPyne by addingdifferent acids. Compared with the UV–vis spec-trum of the solution of the neat PPyne, the maxi-mum absorption peak of the acid-treated PPyneexhibited a blueshift of about 20 nm. Figure 5 showsthe influence of concentration of hydrochloric acidon the maximum absorption peak of the neatPPyne. The maximum absorption peak changedfrom 368 to 345 nm with an increase in the acidconcentration, and when the acid concentration washigher than 1.8 � 10�4 M, the change was satu-rated. The cast film obtained from the toluene solu-tion of the HCl-treated PPyne32 showed the sameUV–vis spectrum as that of the polymer in THF(Fig. 5). No electric conductivity of the cast film ofthe HCl-treated PPyne was observed.

The chloroform and THF solutions of the acid-treated PPyne obtained with different acids ex-hibited the same PL spectra. Figure 6 gives thePL spectra of the acid-treated PPyne in chloro-form and on a quartz glass plate. Compared withthe PL spectrum of the original PPyne (cf. Fig. 3),that of the acid-treated PPyne showed a shift of

about 7 nm to a longer wavelength. Although theacid-treated PPyne showed an IR spectrum simi-lar to that of the neat PPyne, its 1H NMR spec-trum (Fig. 7) indicated that the peaks at � 4.57(Hb in Fig. 1) and one peak in the region of �1.9–3.2 disappeared. The original two peaks ofPPyne at � 2.42 and 2.21 were shifted to � 2.99and 2.78, respectively. These NMR results sug-gested that the pyrazoline was changed to pyra-zole with the loss of Hb and Hc hydrogens ofPPyne in Figure 1 to form a new OCACO bond.

Usually, pyrazoline is converted to the corre-sponding pyrazole on exposure to light and oxy-gen.30 A recent report33 revealed that the changealso occurs in acetic acid in the presence of palla-dium catalyst. Our results indicated that thechemical structure change occurs even in thestrong acids such as hydrochloric acid without thepalladium catalyst (see Structure 2).

Figure 1. 1H NMR spectrum of PPyne.


In our case, the chemical structure change wasconsidered to result in a shift of the UV–vis ab-sorption band to a longer wavelength because offorming a more expanded, �-conjugated system.However, as previously described, the UV–vis ab-sorption shifted to a shorter wavelength. Thismay be due to the formation of the HCl salt in the

HCl-treated PPyne, as revealed by elementalanalysis.32

However, even after removing HCl with ammo-nia,32 the HCl-free product gave the same 1HNMR and UV–vis spectra as those of the HCl-treated PPyne. The reason for the blueshiftcaused by the dehydrogenation is not clear. ThePL spectra of HCl-free product, as shown in Fig-ure 8, were different from those of HCl-treatedPPyne and original PPyne. Compared with the PLspectrum of the original PPyne (cf. Fig. 3), that ofthe HCl-free product (ammonia-treated PPyne)showed a shift of about 90 nm to a short wave-length. The quantum efficiency of the HCl-freeproduct in the solution was by about 10% lessthan that of original PPyne. The dehydrogenationpolymer has a pyrrole-like structure in molecularmain chains, and it has been reported that suchstructure gives a lower quantum efficiency.30

Analyses of the X-ray Diffraction (XRD) Data

Powder XRD patterns of PPyne in the originalstate and after annealing at 170 °C are given inFigure 9, which indicates that the polymer waspartly crystalline in the original state [Fig. 9(A)],whereas it became almost amorphous after being

Figure 2. UV–vis spectra of monomers 2 and 4 and PPyne.

Figure 3. PL and excitation (EX) spectra of PPyne inchloroform and on a quartz glass plate. The polymergave the same emission spectrum in chloroform and inthe solid state. The solid and dashed EX lines exhibitedexcitation spectra in the chloroform solution and in thesolid state, respectively.


Figure 4. UV–vis spectra of the acid-treated PPyne in THF.

Figure 5. Changes in UV–vis spectrum of a THF solution of PPyne (concentration ofthe repeat unit: 3.92 � 10�5 M) on addition of hydrochloric acid. Concentration (M) ofhydrochloric acid: a, 0; b, 0.6 � 10�4; c, 1.2 � 10�4; and d, 1.8 � 10�4. e is the cast filmobtained from a toluene solution of the HCl-treated PPyne.


annealed at 170 °C and quickly cooled to roomtemperature [Fig. 9(B)]. When compared withthat of the previously reported unsaturatedpolyketone with long side chains,27 the XRD peakof PPyne became obscure, suggesting that PPynedid not form a well-packed structure. As dis-cussed in our previous work,27 the unsaturatedpolyketone has a quasi-�-conjugated structureand forms a �-staked solid structure characteris-tic of �-conjugated polymers with long side

chains.34 In the case of PPyne, it does not seem toform a crystalline well-packed structure in thesolid state. The XRD data agreed with the negli-gible shift of the UV–vis peak of the film PPynefrom that in the solution and revealed that thereis no significant �-� interaction between the poly-mer chains, which leads to changes in the elec-tronic state of the polymer.

Redox Properties

The electrochemical properties of PPyne werecharacterized by CV with its cast films, and theresults are shown in Figure 10. As depicted in

Figure 6. PL and EX spectra of the HCl-treatedPPyne in chloroform (the solid line) and on a quartzglass plate (the dashed line).

Figure 7. 1H NMR spectrum of the HCl-treated PPyne.

Figure 8. PL and EX spectra of the HCl-free productobtained by removing HCl in the HCl-treated PPyne32

[in chloroform (the solid line) and a film on a quartzglass plate (the dashed line)].


Figure 10, scanning in a range from 0 to 1.2 Vversus Ag�/Ag showed redox peaks with colorchanges. Electrochemical oxidation of the poly-mer started at about 0.3 V versus Ag�/Ag andgave two peaks at about 0.6 V (br) and 0.98 Vversus Ag�/Ag, respectively. The color of the filmchanged from yellow to black green through redon oxidation. The corresponding reduction ap-peared at 0.80 V. No peaks were observed whenthe sweep was carried out in the range from 0 to�2.5 V.

This electrochemical behavior of PPyne waspartly similar to that of pyrazoline compounds,which usually give the oxidation peak in therange of 0.3–0.7 V versus Ag�/Ag, and the oxida-tion was partially reversible.24–26,30

Optoelectrochemical spectra of the cast film ofPPyne on an indium–tin oxide (ITO) glass platewere measured in an acetonitrile solution of 0.10M [Bu4N]BF4 by applying the desired potential,and changes of the spectrum are displayed inFigure 11. When the applied potential was �0.5,�1.5, and �2.5 V, respectively, the absorptionbands of the film were not changed.

In the oxidation region, when the applied po-tential was 0.6 V, where the oxidation starts (cf.Fig. 10), the absorption peak at 368 nm disap-peared, and a new absorption band appeared atabout 700 nm (chart c in Fig. 11). This absorptionband change was attributed to the oxidation ofthe amine at the 1-position of the pyrazoline ring,as shown in Scheme 2, similar to the case oftrisubstituted arylamines that show oxidationpeaks at 0.6–0.8 V versus Ag�/Ag.35,36 On appli-cation of a higher positive potential of 1.2 V, the

intensity of the absorption band at about 700 nmincreased (chart d). When a reverse potential of0.8 V was applied, chart d in Figure 9 changed tochart e, which is similar to chart c obtained in theinitial oxidation sweep (0–0.6 V). On applying areverse potential of 0.5 V, the absorption peak atabout 700 nm became obscure (chart f). Finally,when the sweep returned to 0 V (chart b), theUV–vis spectrum was similar to that of the initialfilm.

However, the absorption peak at 368 nmshifted to about 350 nm (chart b), indicating thatthe electrochemical process of PPyne is not fullyreversible and quasi-reversibile, which may bedue to a strong interaction of the anion dopant(BF4

� in this case) with the alkoxy side chain.Similar electrochemical irreversibility has beenobserved with poly(p-phenylene)s, poly(arylene-ethynylene)s, and poly(diarylidenecyclohex-anone) with alkyloxy side chains.27,34,37 In thiswork, the oxidation peak of PPyne at 0.98 V ver-sus Ag�/Ag seemed to be related to this type ofirreversible oxidation.

Thermal Properties

DSC traces of PPyne are depicted in Figure 12.Curve A represents the DSC trace at the first scanfrom �100 to 250 °C. The peaks appearing at 168°C were assigned to a melting temperature, whichwas confirmed with a micro-melting-point appa-ratus. Curve B represents the second scan ob-tained after the first scan. Comparison of curve A

Figure 10. CV chat of the cast film of PPyne on a Ptelectrode (1 � 1 cm) in an acetonitrile solution of 0.10 M[Bu4N]BF4 (Bu � butyl).

Figure 9. XRD powder patterns of PPyne in (A) theoriginal state and (B) after annealing at 170 °C.


with curve B indicates that the peak at 168 °Cobserved in the first scan became broad, suggest-ing changes in morphology after the first scan. Atthe first scan, the polymer with a semicrystallinestructure [cf. Fig. 9(A)] seemed to show melting ofthe crystalline area. After being cooled, themelted crystalline area was not able to recover to

the original state and seemed to be changed to theamorphous state, similar to the reported pyrazo-line compounds.23 Some changes in the XRD pat-terns of the polymer (especially the disappear-ance of the peak at 2� � 7°) were observed afterannealing at 170 °C as depicted in Figure 9. As aresult, at the second scan, the amorphous poly-

Figure 11. Changes in the UV–vis spectrum of a film of PPyne on an ITO glasselectrode at various applied potentials versus Ag/Ag�. Curve a displays the UV–visspectrum of the cast film of PPyne. Applied potential (V): chat a (0.0)3 c (0.6)3 d (1.2)3 e (0.8) 3 f (0.5) 3 b (0.0) [in a CH3CN solution of [Bu4N][BF4] (0.10 M)].

Scheme 2. Oxidation process of PPyne.


mer showed a broad melting peak in its DSCtraces.

PPyne is stable under air at ambient tempera-ture. No changes were observed in its 1H NMR,IR, and UV–vis spectra after the solid sample waskept for 6 months at room temperature, and itshowed 5 wt % loss temperature at 376 °C undernitrogen in TGA.

CONCLUSIONS

A novel polymer (PPyne) containing the pyrazo-line unit in the molecular main chain was pre-pared (for the first time) by polycondensation be-tween a functional 2-pyrazoline monomer and anaromatic diboric ester in the presence of Pd-(PPh3)4. The polymer demonstrated good solubil-ity in common organic solvents and had high ther-mal and environmental stability. PPyne showedexcellent PL properties originating from the2-pyrazoline unit and was electrochemically ac-tive. Such main-chain-type pyrazoline polymersare expected to be good materials for optic elec-trical devices.

Financial support from the Japan Society for Promo-tion of Science (JSPS) is gratefully acknowledged.

REFERENCES AND NOTES

1. Krasovitskii, B. M.; Bolotin, B. M. Organic Lumi-nescent Materials; VCH: Weinheim, 1998.

2. Li, X.-C.; Moratti, S. C. In Photonic Polymer Sys-tems: Fundamentals, Methods, and Applications;Wise, D. L.; Wnek, G. E.; Trantolo, D. J.; Cooper,T. M.; Gresser, J. D., Eds.; Marcel Dekker: NewYork, 1998; Chapter 10, pp 335–371.

3. Bernius, M. T.; Inbasekaran, M.; O’Brien, J.; Wu,W. Adv Mater 2000, 12, 1737–1750.

4. Yamamoto, T. Prog Polym Sci 1992, 17, 1153–1205.5. Yamamoto, T. Bull Chem Soc Jpn 1999, 72, 621–

638.6. Yamamoto, T. Macromol Rapid Commun 2002, 23,

583–606.7. Kim, D.; Cho, H.; Kim, C. Prog Polym Sci 2000, 25,

1089–1139.8. Tang, C. W.; VanSlyke, S. A. Appl Phys Lett 1987,

51, 913–915.9. Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.;

Marks, R. N.; Mackay, K.; Friend, R. H.; Burn,P. L.; Holmes, A. B. Nature 1990, 347, 539–541.

10. Welter, S.; Brunner, K.; Hofstraat, J. W.; DeCola,L. Nature 2003, 421, 54–57.

11. Lavastre, O.; Illitchev, I.; Jegou, G.; Dixneuf, P. H.J Am Chem Soc 2002, 124, 5278–5279.

12. Kraft, A.; Grimsdale, A. C.; Holmes, A. B. AngewChem Int Ed Engl 1998, 37, 402–428.

13. Braun, D.; Heeger, A. J. Appl Phys Lett 1991, 58,1982–1984.

14. Kim, S. T.; Hwang, D. H.; Li, X. C.; Gruner, J.;Friend, R. H.; Holmes, A. B.; Shim, H. K. AdvMater 1996, 8, 979–982.

15. Tasch, S.; Niko, A.; Leising, G.; Scherf, U. ApplPhys Lett 1996, 68, 1090–1092.

16. Yang, Y.; Pei, Q.; Heeger, A. J. J Appl Phys 1996,79, 934–939.

17. Greenham, N. C.; Moratti, S. C.; Bradley, D. D. C.;Friend, R. H.; Holmes, A. B. Nature 1993, 365,628–630.

18. Zhang, X. H.; Lai, W. Y.; Gao, Z. Q.; Wong, T. C.;Lee, C. S.; Kwong, H. L.; Lee, S. T.; Wu, S. K. ChemPhys Lett 2000, 320, 77–80.

19. Xiao, D.; Xi, L.; Yang, W.; Fu, H.; Shuai, Z.; Fang,Y.; Yao, J. J Am Chem Soc 2003, 125, 6740–6745.

20. Gao, X.-C.; Cao, H.; Zhang, L.-Q.; Zhang, B.-W.;Cao Y.; Huang, C.-H. J Mater Chem 1999, 9, 1077–1080.

21. Barbera, J.; Clays, K.; Gimenez, R.; Houbrechts, S.;Persoonsb, A.; Serrano, J.-L. J Mater Chem 1998,8, 1725–1730.

22. Zhang, X. H.; Lai, W. Y.; Wong, T. C.; Gao, Z. Q.;Jiang, Y. C.; Wu, S. K.; Kwong, H. L.; Lee, C. S.;Lee, S. T. Synth Met 2000, 114, 115–117.

23. Ma, C.-Q.; Zhang, L.-Q.; Zhou, J.-H.; Wang, X.-S.;Zhang, B.-W.; Cao, Y.; Bugnon, P.; Scher, M.;Nusch, F.; Zhang, D.-Q.; Qiu, Y. Chin J Chem 2002,20, 929–932.

24. Ma, C.-Q.; Zhang, L.-Q.; Li, X.-H.; Wang, X.-S.;Zhang, B.-W.; Cao, Y.; Wang, D.-M.; Jiang, X.-Y.;

Figure 12. DSC curves of PPyne at a heating rate of10 °C min�1 (A, first scan; B, second scan).


Zhang, Z. L.; Zhang, D.-Q.; Qiu, Y. Acta ChimSinica 2002, 60, 847–853.

25. Kaufman, F. B.; Engler, E. M. J Am Chem Soc1979, 101, 547–549.

26. Kaufman, F. B.; Schroeder, A. H.; Engler, E. M.;Patel, V. V. Appl Phys Lett 1980, 36, 422–425.

27. Fang, Q.; Yamamoto, T. Polymer 2003, 44, 2947–2956.

28. Khalaf, A. A.; El-Shafei, A. K.; El-Sayed, A. M.J Heterocycl Chem 1982, 19, 609–612.

29. Advincula, R. C.; Xia, C.; Inaoka, S. Polym Prepr(Am Chem Soc Div Polym Chem) 2000, 41, 859–860.

30. Matsubara, Y.; Matsuda, T.; Hatta, S.; Yamaguchi,Y.; Yoshida Z.-I. Adv Mater 2002, 14, 1211–1213.

31. Kallitsis, J. K.; Gravalos, K. G.; Hilberer, A.;Hadziioannou, G. Macromolecules 1997, 30, 2989–2996.

32. HCl-treated PPyne was prepared according to thefollowing procedure: To a 50-mL sample tubecharged with a magnetic bar and PPyne (20 mg)was added 10 mL of chloroform. When the polymerwas dissolved, 2 mL of concentrated hydrochloricacid were added dropwise to the flask with stirringat 0 °C. After stirring for 1 h at that temperature,the solvent was evaporated in vacuo at room tem-perature. The red-brown residue was redissolved in2 mL of chloroform and was poured into 100 mL of

the mixture of hexane and ether (1:1, V/V) to give adeep yellow precipitate. After filtration and dryingin vacuo, the HCl-treated PPyne was obtained as adeep yellow powder, whose 1H NMR (cf. the text)and analytical data agreed with a dehydrogenatedstructure of PPyne and formation of a salt withHCl. ELEM. ANAL. Calcd. for (C44H48N2O2 �0.3HCl)n: C, 81.61%; H, 7.47%; N, 4.33%; Cl, 1.65%.Found: C, 80.48%; H, 7.59%; N, 4.31%; Cl, 1.40%.The HCl salt was dissolved into THF (20 mL) andcooled to 0 °C. To the solution thus obtained wasadded dropwise 5 mL of 30% aqueous ammonia.After stirring for 2 h at 0–5 °C, the solvent wasevaporated in vacuo at room temperature. The res-idue was treated according to the same procedureas that of preparation of the HCl-treated PPynepreviously mentioned. The HCl-free PPyne was ob-tained as a deep yellow powder.

33. Nakamichi, N.; Kawashita, Y.; Hayashi, M. OrgLett 2002, 4, 3955–3957.

34. Yamamoto, T.; Fang, Q.; Morikita, T. Macromole-cules 2003, 36, 4262–4267.

35. Inbasekaran, M.; Woo, E.; Wu, W.; Bernius, M.;Wujkowski, L. Synth Met 2000, 111–112, 397–401.

36. Neher, D. Macromol Rapid Commun 2001, 22,1365–1385.

37. Schiavon, G.; Zotti, G.; Bontempelli, G. J Electro-anal Chem 1984, 161, 323–335.


Documents

Preparation of a new polymer containing photoluminescent pyrazoline unit in the main chain