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Synthetic Metals 161 (2011) 188–195

Contents lists available at ScienceDirect

Synthetic Metals

journa l homepage: www.e lsev ier .com/ locate /synmet

onducting polynaphthalenes from 1,1′-binaphthyl and,1′-bi-2-naphthol via electropolymerization

aoyang Lu, Congcong Liu, Yuzhen Li, Jingkun Xu ∗, Guodong Liuchool of Pharmacy, Jiangxi Science & Technology Normal University, Nanchang 330013, China

r t i c l e i n f o

rticle history:eceived 21 May 2010eceived in revised form 24 August 2010ccepted 12 November 2010vailable online 13 December 2010

a b s t r a c t

Polynaphthalene films with electrical conductivity of 10−3 S cm−1 were successfully electrosynthesizedby direct anodic oxidation of 1,1′-binaphthyl (BN) and 1,1′-bi-2-naphthol (BNO) in CH2Cl2 contain-ing additional boron trifluoride diethyl etherate (BFEE). The introduction of BFEE greatly lowered theonset oxidation potentials of the monomers compared with other supporting electrolytes. The resultingpoly(1,1′-binaphthyl) (PBN) films exhibited good redox activity and stability in different monomer-free

eywords:onducting polymerslectrosynthesisolynaphthalenesluorescence

electrolytes. Moreover, FT-IR spectra and quantum chemistry calculation results proved that PBN andpoly(1,1′-bi-2-naphthol) (PBNO) were both synthesized mainly through the coupling of the monomersat �-positions of the naphthalene ring. Fluorescence spectral determination showed that the polymerswere typical blue light-emitters with solution quantum yields of 0.17 and 0.13, respectively. The sub-stitution of hydroxyl and naphthyl groups did not change the emission wavelength of polynaphthalene(about 417 nm). Surface morphology determination revealed that regular particles with different sizes

n ITO

were orderly assembled o

. Introduction

The field of conjugated polymers continues to attract greatnterest of many scientists due to their potential applications inhe development and the construction of new advanced materials1–4]. As a useful and widely applied technique, the electrosyn-hesis of conducting polymers on the electrode surface has been

very active research area in electrochemistry [5] because ofhe outstanding properties of these materials, which allow theolymer-modified electrode to be used as sensors, catalysts, elec-rochromic materials, batteries, microelectronic devices [1–4], andlso as corrosion inhibitors to protect semiconductors and metals6,7].

Naphthalene and their derivatives are very promising blocks foruilding high-quality conducting polymers due to the extended �-lectron systems in their molecules. Compared to polythiophenes,olypyrroles, polyanilines, and polyphenylenes, less attentionas been paid to the electrosynthesis of polynaphthalenes inhe field of synthetic metals [8–18]. However, polynaphthalene

nd its derivatives exhibit unique non-linear optical propertiesnd can be widely used in various domains [8–18], such asabrication of sensors, second batteries, electrochromic and elec-roluminescence devices, and anticorrosion coatings. Hence, the

∗ Corresponding author. Tel.: +86 791 8537967; fax: +86 791 3823320.E-mail address: xujingkun@tsinghua.org.cn (J. Xu).

379-6779/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rioi:10.1016/j.synthmet.2010.11.021

electrode after electrochemical growth.Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.

electrodeposition of high-quality polymer films of novel polynaph-thalenes with improved properties is still quite necessary andessential.

Among the derivatives of naphthalene, 1,1′-binaphthyl (BN),1,1′-bi-2-naphthol (BNO), and 1,1′-bi-2-naphthyl dimethyl ether(BNME) (Scheme 1), which are widely employed in enantiose-lective catalysis, metallo-supramolecular chemistry and materialsciences, have not attracted considerable interests for synthesiz-ing inherently conducting polymers. Meana-Esteban et al. havereported the electrosynthesis of poly(1,1′-binaphthyl) (PBN) bycyclic voltammetry in nitrobenzene–Bu4NPF6 and the propertiesof the resulting oligonaphthalene films obtained were presentedsystematically [18]. Additionally, Dietrich and Heinze reportedthe determination of redox potentials of �,�′-binaphthyl and�,�′-binaphthyl [19]. However, the quality of the oligomer filmsneeds to be improved and their properties, such as electri-cal and optical properties, have not been studied. In presentstudy, we report the electrochemical polymerization of BNand BNO in BFEE-based electrolytes. More importantly, proper-ties of the obtained polynaphthalenes, such as electrochemicalbehavior, structural information, solubility, optical properties, elec-trical conductivity, and morphologies, were also investigated indetail.

ghts reserved.

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2

2

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2

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Scheme 1. Chemical structures of naphthalene and its derivatives.

. Experimental

.1. Materials

1,1′-Binaphthyl (BN, 98+%; TCI-GR), (±)-1,1′-bi-2-naphtholBNO, 99%; Alfa Aesar), 25% ammonia (Ji’nan Chemical Reagentompany, Shandong, China) and concentrated sulfuric acid (SA,8%; Ji’nan Chemical Reagent Company, Shandong, China) weresed as received. Dichloromethane (analytical grade) was the prod-cts of Tianjin Bodi Chemicals Co., Ltd. and used after refluxistillation. BFEE (1.12–1.14 × 103 g L−1, BF3 = 48.24%; Changyanghemical Plant, Beijing, China) was purified by distillation andtored at 0 ◦C before use. Dimethyl sulfoxide (DMSO, analyticalrade; Tianjin Bodi Chemicals Co., Ltd., China) was used directlyithout further purification. Tetrabutylammonium tetrafluorobo-

ate (TBATFB, 98%; Acros Organics) was dried under vacuum at 60 ◦Cor 24 h before use. Other reagents were all A.R. grade and used aseceived without further treatment.

.2. Electrosynthesis and electrochemical tests

The electrochemical tests and polymerization of theonomers were performed in a one-compartment cell usingpotentiostat–galvanostat (Model 263A, EG&G Princeton Appliedesearch) under computer control. For electrochemical tests, theorking and counter electrodes were Pt wire with diameter of

.5 mm and stainless steel wire with diameter of 1 mm, respec-ively. They were placed 5 mm apart during the tests. To obtainufficient amount of the polymer films for characterization, ITO ort and stainless-steel sheets with surface areas of 4 and 6 cm2 eachere used as the working and counter electrodes, respectively.

hese electrodes were carefully polished with abrasive paper1500 mesh), cleaned successively with water and acetone, andhen dried in air before each experiment. An Ag/AgCl electrodeirectly immersed in the solution served as the reference electrodend it revealed sufficient stability during the experiments. All theolutions were deaerated by a dry nitrogen stream and maintainednder a slight overpressure through all the experiments. The poly-er films were grown potentiostatically and their thickness was

ontrolled by the total charge passed through the cell, which wasead directly from current–time (I–t) curves by computer. After

olymerization, the polymer films were washed repeatedly withnhydrous diethyl ether to remove the electrolyte. For spectralnalyses, they were dedoped with 25% ammonia for three days,ashed repeatedly with pure water, and then dried at 60 ◦C under

acuum for 24 h.

161 (2011) 188–195 189

2.3. Characterization

The electrical conductivities of the obtained polymer films weredetermined by applying the conventional four-probe techniquewith free-standing films or pressed pellets of the samples. Infraredspectra were recorded using a Bruker Vertex 70 Fourier trans-form infrared (FT-IR) spectrometer with samples in KBr pellets.Ultraviolet–visible (UV–vis) spectra were measured with a Perkin-Elmer Lambda 900 UV–vis–near-infrared (NIR) spectrophotometer.Fluorescence spectra were determined with an F-4500 fluorescencespectrophotometer (Hitachi). Scanning electron microscopy (SEM)measurements were made with a Scanning Electron MicroscopeVEGA\\LSU (Tescan).

2.4. Details of computations

All calculations were carried out using the Gaussian 03 program[20]. BN and BNO were optimized without symmetry constraintsusing a hybrid density functional [21] and Becke’s three parameterexchange functional combined with the LYP correlation functional(B3LYP) [22] and with the 6-31G(d,p) basis set (B3LYP/6-31G(d,p)).Vibrational frequencies were evaluated at the same level to identifythe real minimal energy structures.

3. Results and discussion

3.1. Optimized conditions for electrochemical polymerization

Fig. S1 represents the anodic polarization curves of BN and BNOin different solvents and electrolytes for comparison. As seen fromthe figure, the oxidation of BNO was much easier than that of BNdue to the strong electron-donating effect of hydroxyl group sub-stitution. Additionally, with the introduction of BFEE, the onsetoxidation potentials of the two monomers (about 0.94 V for BNand 0.65 V for BNO, respectively) were both decreased considerablycompared with those using Bu4NBF4 as the supporting electrolyte(1.51 V for BN and 1.18 V for BNO). These potentials were alsomuch lower than those reported in nitrobenzene–Bu4NPF6 (about1.35 V for BN) [18] and SO2–Bu4NPF6 (about 1.58 V for BN) [19].This phenomenon was attributed to the interaction of BFEE withthe aromatic rings of the monomers, which reduced their reso-nance stability through the formation of �-complexes between themonomers and BFEE, thus making electron loss from them mucheasier.

Successive cyclic voltammograms (CVs) of the monomers werealso performed utilizing the same solvent–electrolyte couples,respectively, as shown in Fig. 1 (BN) and Fig. 2 (BNO). For BN, noapparent redox waves were found in CH2Cl2–Bu4NBF4 (Fig. 1A) andalso no film was formed on the electrode surface. However, whenchanging the supporting solvent/electrolyte from Bu4NBF4 to BFEE,CVs of BN (Fig. 1B and C) showed the characteristic features ofconducting polymers during potentiodynamic synthesis and free-standing metallic black films could be easily obtained, similar tothe results reported previously [18]. The increase in the redox wavecurrents implied that the amount of the polymer on the electrodewas increasing gradually. The broad redox waves of as-formedpolymer film may be ascribed to the wide distribution of thepolymer chain length or the conversion of conductive species onthe polymer main chain from the neutral state to polarons, from

polarons to bipolarons, and finally from bipolarons to the metallicstate. The potential shift of the current wave maximum providedinformation about the increase in the electrical resistance of thepolymer film and the over-potential needed to overcome this resis-tance.

190 B. Lu et al. / Synthetic Metals 161 (2011) 188–195

F(

rCgbsm

csoBtoIppeiFfi

F(

Fig. 3. Cyclic voltammograms of PBN films electrochemically synthesized inCH2Cl2 + BFEE (1:1, by volume) on the Pt electrode in monomer-free CH2Cl2 + BFEE

ig. 1. Cyclic voltammograms of 0.01 mol L−1 BN in CH2Cl2 + 0.1 mol L−1 Bu4NBF4

A), CH2Cl2 + BFEE (1:1, by volume) (B), and BFEE (C). Potential scan rate: 100 mV s−1.

On the other hand, CVs of BNO in CH2Cl2–Bu4NBF4 showedeversible redox couple (Fig. 2A) while nothing could be found inH2Cl2–BFEE (Fig. 2B) although the onset oxidation potential wasreatly lowered. It was very difficult to get sufficient PBNO films inoth systems, mainly because the protons ionizing from BNO in theolution inhabited polymerization according to the radical cationechanism.After further optimization by cyclic voltammetry (Fig. S2) and

onsidering the quality of the obtained polymer films, the binaryolvent system consisting of CH2Cl2 and BFEE with a volume ratiof 1:1 was selected for the electropolymerization of BN and BNO.esides the choice of solvents and electrolytes, the applied elec-rical conditions have been shown to influence the structures andrientation of the electrogenerated conducting polymers seriously.n present work, potentiostatic electrolysis was employed to pre-are the polymer films for characterization. To optimize the appliedotentials for polymerization, a set of current transients during the

lectropolymerization of BN and BNO at different applied potentialsn different electrolytes were recorded for comparison, as shown inig. S3. By considering the overall factors affecting the quality of thelm, such as moderate polymerization rate, negligible overoxida-

ig. 2. Cyclic voltammograms of 0.01 mol L−1 BNO in CH2Cl2 + 0.1 mol L−1 Bu4NBF4

A) and CH2Cl2 + BFEE (1:1, by volume) (B). Potential scan rate: 100 mV s−1.

(1:1, by volume) (A) and BFEE (B) at potential scan rates of 50 (a), 100 (b), 150 (c),200 (d), 250 (e), and 300 mV s−1 (f). Inset: plots of redox peak current densities vs.potential scan rates. jp is the peak current density, and jp,a and jp,c denote the anodicand cathodic peak current densities, respectively.

tion, regular morphology, and good adherence against the workingelectrode, the applied potentials were optimized to be 1.2 V for BNin BFEE and 1.3 V and 1.0 V in CH2Cl2–BFEE (1:1) for BN and BNO,respectively.

3.2. Electrochemistry of PBN

The electrochemical behavior of PBN and PBNO films was deter-mined carefully by cyclic voltammetry in different monomer-freeelectrolytes. It can be clearly seen that the steady-state CVs of PBNfilms represented broad anodic and cathodic peaks in the elec-trolytes (Fig. 3). The peak current densities were proportional topotential scanning rates (insets of Fig. 3), indicating that the redoxprocesses were non-diffusional and the electroactive polymer waswell adhered to the working electrode surface. Furthermore, thefilms could be cycled repeatedly between the conducting (oxidized)and insulating (neutral) state without significant decomposition ofthe materials, indicating high redox stability of the polymer. How-ever, CVs of PBNO-coated electrode still showed no obvious redoxwaves, indicating its poor electroactivity.

PBN films from CH2Cl2–BFEE could be oxidized and reducedfrom 0.70 V (anodic peak potential, Ea) to 0.33 V (cathodic peakpotential, Ec) in monomer-free CH2Cl2–BFEE (1:1) and from 0.67 V(Ea) to 0.29 V (Ec) in BFEE at the potential scan rate of 50 mV s−1.Compared to the results reported in nitrobenzene–Bu4NPF6 (with-

B. Lu et al. / Synthetic Metals 161 (2011) 188–195 191

S LUM(

o(t

3

pa5iwhotedtcftfo8ffCbp

tetpvdaatt

cheme 2. Optimized geometries, composition of the frontier orbitals (HUMO andwithout H atoms).

ut well-defined redox peaks) [18] and SO2–Bu4NPF6 [from 1.70 VEa) to 1.45 V (Ec)] [19], as-formed PBN exhibited much better elec-roactivity and much lower redox potentials.

.3. Structural characterization

In order to elucidate the structure of the polymers and inter-ret the polymerization mechanism, FT-IR spectra of the monomersnd doped polymer films in the wavenumber range from 1200 to50 cm−1 were recorded, as shown in Fig. 4. BN monomer gave

ts characteristic bands in the regions 800–775 and 780–760 cm−1,here the out-of-plane C–H bending of three and four adjacentydrogen atoms took place, respectively. In addition, the spectrumf the monomer had a peak at 618 cm−1, which could be assignedo the ring stretching of mono-substituted naphthalenes. How-ver, in the spectrum of the film the number of strong IR modesecreased in comparison to the spectrum of the monomer. Fur-hermore, the spectrum of the electrosynthesized film had someharacteristic bands at 760 and 839 cm−1 which could also beound in the spectra of poly(1,4-naphthalenes) [12–14], implyinghat as-formed PBN showed the same structure as that obtainedrom nitrobenzene–Bu4NPF6 [18]. In the spectrum of BNO, theut-of-plane vibration of the two adjacent C–H bonds appeared at66 cm−1, 825 cm−1, 783 cm−1, and 775 cm−1 peaks, and that of theour adjacent C–H bonds was at 750 cm−1 and 723 cm−1. However,or the doped polymer, the 814 cm−1 band could be ascribed to the–H wagging and ring deformation vibration of pentasubstitutedenzene, indicating the polymerization may occur at C(4) and C(4′)ositions.

Moreover, the augmented width and shifts of these bands fromhe monomer to doped polymers manifested the occurrence of thelectrochemical polymerization of BN and BNO. The broadening ofhe IR bands in the experimental spectra is due to the resultingroduct composed of oligomers with wide chain dispersity. Theibrational peaks of the oligomers with different polymerization

egrees have different IR shifts. These peaks overlap one anothernd produce broad bands with hyperstructures. Furthermore, therere chemical defects on the polymer chains, which resulted fromhe inevitable overoxidation of the polymer. This also contributeso the band broadening of the experimental IR spectra. On the other

O) in BN and BNO and atomic electron spin densities (ESD) of their radical cations

hand, the peaks in the region 1090–1050 cm−1 corresponded to thecharacteristic vibration bands of the doping anions (B–F bonds).

To further explore the structures of PBN and PBNO, the atomicelectron density population and proportion of the frontier orbitalsof the monomers, together with the electron spin density of theirradical cations, were calculated using Gaussian 03 software [20].Optimized geometries of BN and BNO by quantum chemistry cal-culations are shown in Scheme 2. BNO exhibited a larger dihedralangle between the two naphthalene rings (89.3◦) than that of BN(75.2◦) owing to the hydroxy group substitution and their radi-cal cations showed more planar structures with smaller dihedralangles (49.3◦ for BN•+ and 63.3◦ for BNO•+, respectively). Calcu-lations for atomic electron density populations of BN (Table S1)showed similar negative electrons on C(4), C(5), C(8), C(4′), C(5′), andC(8′), while for BNO (Table S2), the negative charge was mainly con-centrated on C(3), C(4), C(5), C(8), C(3′), C(4′), C(5′), and C(8′), whichimplied that these atoms would donate electrons during the elec-trochemical polymerization. According to the frontier molecularorbital theory, the reaction between the active molecules mainlyhappens on the highest frontier molecular orbitals. HOMO propor-tions of �-positions on the naphthalene ring in BN and BNO weremuch higher than those of other atoms on �-positions (Scheme 2).It should be emphasized here that there was considerable sterichinderance on C(8) and C(8′) sites.

By analogy with benzenes, pyrroles and thiophenes as couplinginvolves monomer radical cations during electrochemical polymer-ization, the most likely coupling sites are believed to be those withthe largest electron spin densities (ESD), where there will be thehighest propensity for radical-coupling and bond formation. Thecalculated electron spin density distribution in their radical cations(Scheme 2) showed the highest unpaired ESD at C(4) and C(4′) posi-tions in both BN•+ and BNO•+. Based on these calculated results,it can be reasonably deduced that the polymerization sites wouldhappen preferentially at C(4) and C(4′) positions for BN and BNO.

3.4. Solubility and UV–vis spectra

As-formed PBN and PBNO films were both in the doped stateand metallic dark in color. After dedoping with 25% ammonia, theircolors changed to brown and dark gray, respectively. Both doped

192 B. Lu et al. / Synthetic Metals 161 (2011) 188–195

oped

amd

eb

FP

Fig. 4. FT-IR spectra of BN, d

nd dedoped PBN and PBNO films were partly soluble in many com-

on organic solvents, such as tetrahydrofuran, acetonitrile, DMSO,

ichloromethane, and chloroform.UV–vis spectra of PBN and PBNO deposited on the ITO transpar-

nt electrode are depicted in Fig. 5A and B. The doped PBN showedroad absorption centered at 514 nm and the absorption peaks

ig. 5. UV–vis spectra of the monomers and polymers in the solid state (A and B) and inBNO; (e) BN; (f) doped PBN; (g) dedoped PBN; (h) BNO; (i) doped PBNO; and (j) dedoped

PBN, BNO, and doped PBNO.

of PBNO located 524 nm and 646 nm, which could be attributable

to the characteristics of the existence of conductive species, suchas polarons or bipolarons. UV–vis spectra of the monomers andthe resulting polymers in DMSO were also examined, as shownin Fig. 5C and D. BN showed a characteristic absorption peak at286 nm while BNO at 341 nm (a single electron �–�* transition).

DMSO (C and D). (a) Doped PBN; (b) dedoped PBN; (c) doped PBNO; (d) dedopedPBNO.

B. Lu et al. / Synthetic Metals 161 (2011) 188–195 193

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ig. 6. Fluorescence spectra of the monomers and polymers in the solid state (A andBNO; (e) BN; (f) doped PBN; (g) dedoped PBN; (h) BNO; (i) doped PBNO; and (j) de

t can be clearly seen that, due to the increase in the conjugatedhain length, the overall absorption of the polymers tailed off toore than 620 nm for PBN (Fig. 5A-b) and about 460 nm for PBNO

Fig. 5B-d) in comparison with those of the monomers (339 nm forN and 361 nm for BNO, respectively). These spectral results con-rmed the occurrence of electrochemical polymerization amonghe monomers and the formation of a conjugated polymer withroad molar mass distribution. Moreover, UV–vis spectra of dopednd dedoped PBN and PBNO in DMSO were quite similar, mainlyepending on the automatic dedoping process of the polymer, con-erning dopant removal.

.5. Fluorescence spectra

The fluorescence emission spectra of the polymers in the dopednd dedoped states were determined both in solid state and inMSO, as shown in Fig. 6. The emission peaks of doped and dedopedBN emerged at 391 nm and 397 nm (Fig. 6A) on the ITO electrodehereas maximum emission peaks at 406 nm and 411 nm charac-

erized the spectra of doped and dedoped PBNO, respectively.In DMSO, BN exhibited a strong emission peak at 371 nm under

xcitation at 311 nm, while the emission of its polymer centeredt 417 nm at 321 nm excitation (Fig. 6C). The emission spectrumf BNO (Fig. 6D) emerged at 370 nm in DMSO when excited at11 nm whereas doped and dedoped PBNO showed their maxi-um emission at around 418 nm (excited at 342 nm). Large red

hifts between the monomers and the polymers (about 50 nm) cane clearly seen from the figure, which is mainly attributable to thelongation of the polymer’s delocalized �-electron chain sequence.

t should be noted here that PBN and PBNO exhibited samemission wavelengths with electropolymerized polynaphthalene417 nm), implying that the substitution of hydroxyl and naphthylroups does not change the emission wavelength of polynaph-halene. Besides, compared with those in DMSO, hypsochromic

in DMSO (C and D). (a) Doped PBN; (b) dedoped PBN; (c) doped PBNO; (d) dedopedPBNO.

shifts of 9–18 nm in the emission of solid state were probablyattributed to the interaction of adjacent polymer chains in polymermatrix.

The fluorescence quantum yields (�overall) of the soluble sam-ples were measured using anthracene in acetonitrile (standard,�ref = 0.27) as a reference and calculated according to the well-known method based on the expression [23]:

�overall = n2ArefI

n2refAIref

× �ref (1)

where n, A, and I denote the refractive index of the solvent, theabsorbance at the excitation wavelength, and the intensity of theemission spectrum, respectively. In DMSO, the fluorescence quan-tum yield (�overall) of PBN was calculated to be 0.17, whereas that ofsoluble PBNO films was 0.13, both higher than that of PDHN (0.11)[17].

3.6. Conductivity and morphology

As-formed PBN was free-standing films but fragile, whereasPBNO was in the powder state. The electrical conductiv-ity of the pressed pellets of doped PBN was measured tobe 4.8 × 10−3 S cm−1, while that of PBNO pellets was only6.3 × 10−4 S cm−1 as free-standing films, both lower than thoseof poly(naphthalene) (5.9 × 10−2 S cm−1), poly(�-naphthalene sul-fonic acid) (0.95 S cm−1), and poly(1,5-dihydroxynaphthalene)(0.46 S cm−1) [12–17]. This phenomenon can be correlated to adecrease in the average length of the conjugated � system in PBNand PBNO compared with polynaphthalene. The monomers BN and

BNO has relatively lower reactivity than naphthalene owing to thedelocalization of � electrons over the entire molecules. Namely, theoverall reactivity of the monomers decreases or, in other words,the stability of the corresponding radical cations increases, whichcauses a decrease in polymerizability. On the other hand, the strong

194 B. Lu et al. / Synthetic Metals 161 (2011) 188–195

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ig. 7. SEM images of PBN and PBNO films deposited electrochemically on ITO eleBNO.

lectron-donating nature of the hydroxyl group substitution onNO further stabilizes its radical cations.

The surface morphology of the resulting polymer filmseposited on the ITO electrodes was observed by scanning electronicroscope (SEM), as shown in Fig. 7. Macroscopically, as-formed

BN appeared to be flat, compact and could be peeled from thelectrode into a free-standing film. Microscopically, at high magni-cations (×50,000), both doped and dedoped PBN films (Fig. 7A and) resembled ordered arrangements of nanoparticles with diame-er in the range from 20 to 100 nm, extremely different from thatf PBN reported previously [18]. This growth mode is a feature oftronger interactions between deposited molecules than betweenhe film and substrate. This morphology facilitates the movementf doping anions in and out of the polymer films during dopingnd dedoping processes, in well accordance with the good redoxctivity of PBN films in different monomer-free electrolytes. Themooth and homogeneous structures of compact PBN films werextremely beneficial to improve their electrical conductivity andlectron transfer capability and also make them good candidates forotential applications, such as ion-selective electrodes, ion-sieving

lms, and matrices for hosting catalyst particles.

However, SEM pictures (Fig. 7C and D) demonstrated that PBNOlms displayed sphere-type growth processes on ITO electrodehereby a number of regular nanospheres with different sizes were

bserved. Note here that the doped and dedoped polymers showed

e for 400 s. (A and B) Doped and dedoped PBN and (C and D) doped and dedoped

no obvious difference, implying that the dedoping processes did notdestroy the surface morphologies of the doped polymers. However,for PBNO, it was very difficult to get sufficient polymer films, mainlybecause of the following factors:

(1) The strong electron-donating effect of hydroxyl group substi-tution can stabilize the corresponding radical cations of BNO;

(2) The protons ionizing from BNO in the solution inhabitelectrochemical polymerization according to radical cationmechanism.

During electrochemical polymerization, there are two competi-tive pathways: the growth of polymer chains on the anode surfaceand the parallel formation of soluble oligomers. In the case of BNO,this latter process is favored because of the above reasons. There-fore, it is difficult for BNO to grow sufficient amount of polymerfilms, leading to the observed morphology of isolated nanospheres.

4. Conclusions

To summarize, low-potential electrochemical polymerizationof BN and BNO has been systematically investigated in CH2Cl2containing additional BFEE and direct anodic oxidation of themonomers led to successful deposition of their polymer films.As-formed PBN showed much better electroactivity and sta-

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B. Lu et al. / Synthetic

ility in different monomer-free electrolytes and lower redoxotentials than the results reported previously. Both experi-ental and computational results indicated that PBN and PBNOere likely deposited via the coupling of the monomers at C(4)

nd C(4′) positions. Moreover, PBN exhibited favorable electri-al and optical properties, with conductivity of 10−3 S cm−1 andolution fluorescence quantum yields up to 0.17. PBNO dis-layed inferior electrochemical, electrical, and optical propertieso PBN. Both PBN and PBNO kept the same emission wave-ength (417 nm) of electrosynthesized polynaphthalenes. SEMhotographs demonstrated that uniform polymer films could beirectly obtained on the electrode surface. Many potential applica-ions may be pursued with these favorable electroactivity, electricalnd optical properties, and regular morphologies of as-formedolynaphthalenes.

cknowledgements

NSFC (50963002, 51073074 and 60767001) and Jiangxi Jinggangtar Project are acknowledged for their financial supports.

ppendix A. Supplementary data

Supplementary data associated with this article can be found, inhe online version, at doi:10.1016/j.synthmet.2010.11.021.

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[

[[

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