Alternatively linking fullerene and conjugated polymers

Alternatively Linking Fullerene and Conjugated Polymers

ROGER C. HIORNS,1 PIERRE IRATCABAL,1 DIDIER BEGUE,1 ABDEL KHOUKH,1 REMI DE BETTIGNIES,2

JOCELYNE LEROY,3 MURIEL FIRON,4 CAROLE SENTEIN,3* HERVE MARTINEZ,1 HUGUES PREUD’HOMME,1

CHRISTINE DAGRON-LARTIGAU1

1IPREM CNRS-UMR 5254, Universite de Pau et des Pays de l’Adour, Helioparc, 2 avenue President Angot,64053 Pau Cedex 9, France

2INES-RDI DRT/LITEN/DTS/LCS Savoie Technolac, 50 Avenue du lac Leman, 73377 Le Bourget du Lac, France

3CEA-DRT/LITEN, CEA-Saclay, 91191 Gif-sur-Yvette, France

4DEN/DDIN/DPCD/CESD, CEA-Saclay, 91191 Gif-sur-Yvette, France

Received 30 November 2008; accepted 16 January 2009DOI: 10.1002/pola.23311Published online in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: The stereo-electronic control over bisadditions of conjugated polymers tofullerene (C60) is explored in the formation of alternating copolymers. The chemistry,resulting configuration, and properties of poly(3-hexylthiophene)-alt-C60 copolymersprepared by either classic pyrrolidine ring formation or an atom transfer radicaladdition are compared. Both routes result in controlled additions of polymers to C60.Extensive macromolecular modeling through PM6 methods indicate that there is noconjugation between P3HT and C60 in the systems studied. This along with 2D-NMR, AFM, and photovoltaic characterizations of the materials indicate the impor-tance of the structure of the modified C60 and the nature of the linking groupbetween C60 and P3HT segments in determining the morphology of the copolymersin the solid state. VVC 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2304–

2317, 2009

Keywords: computer modeling; conjugated polymers; copolymerization; fullerenes;poly(3-hexylthiophene); polymer photovoltaic devices

INTRODUCTION

The chemistry of fullerene and its incorporationinto macromolecules has evolved to yield a consid-erable number of structures over recent years.1 The

major stimulation for this effort has been the possi-bility of combining the electronic,2 optoelectronic,3

superconducting,4 and even biological5 properties ofC60 with the beneficial characteristics of polymers,such as their mechanical strength and ease ofmanipulation.6 These benefits may be multipliedwhen devising copolymers because of their tend-ency to form nanoscale domains of like-polymers inwell-ordered microstructures.7–9 This level of orga-nization10 can be determinant in rheology,11 opto-electronics,12 electronics,13 and, in particular, pho-tovoltaics.14

Previous work has shown that a variety ofstructures incorporating C60 into polymers, such

Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 47, 2304–2317 (2009)VVC 2009 Wiley Periodicals, Inc.

Additional Supporting Information may be found in theonline version of this article.

Correspondence to: R. C. Hiorns, Laboratoire de Chimiedes Polymeres Organiques, ENSCPB, Universite deBordeaux, Pessac Cedex F33607, France (E-mail: [email protected])

*Presentaddress:DEN/DMN/SRMA/LTMEX,bat. 460Pointcourrierno.52,CEASaclay,F91191Gif-sur-Yvette,France

2304

as star-like,15 dumbbell,16 and chain-end cappedpolymers,17 are attainable through multiple ormono-additions to C60. The high degree of controlover the number of additions to C60 is mostly dueto the stereo-electronic characteristics of theformed molecule, that is, once an addition hasbeen made it will influence the direction andnumber of the following additions. Two of themost widely practiced reactions are the Prato-based and radical additions. The Prato reaction istraditionally used with small molecule additionsto C60, but it has been extended to preparing mac-romolecules containing fullerene and conjugatedsegments.1,15(b),18 It has been particularly ex-ploited in the preparation of materials for photo-voltaic devices in which the polymers are gener-ally expected to act as chromophoric electrondonors that absorb light, attain excited states,and donate electrons to C60 so that in the pres-ence of electrodes, an electric current can be gen-erated.14,19 These systems have yet to demon-strate high efficiencies for several reasons, includ-ing but not limited to their poor structural order.In the case of radical polymer chain additions, ithas been demonstrated that paired additions pref-erentially result in 1,4-bis adducts. The numberof additions to C60 can be raised to 4 by simplyaltering the ratio of the starting materials.20

Changing the reaction solvent from toluene tochlorobenzene reduces the formation of bisad-ducts and results in mono-chain addition to theC60.

17,21 This has been used to effect in preparing,most notably, materials for electroluminescentapplications.

It has been demonstrated that alternatingmulti-block copolymers incorporating conjugatedsegments22 may give rise to better long-rangeorder of self-assembled nanostructures than theirlower order equivalents.22(a) This may be of impor-tance to a number of systems, but more specificallyhere to photovoltaics where like-polymer nanodo-mains of well-organized copolymers parallel to theelectrodes may possibly enhance interface interac-tions and increase current flow (Fig. 1). Given theimportance of fullerene and conjugated polymersin such devices, it was surprising for us to notethat in the literature we could not find examplesof copolymers that incorporated fullerene as analternating repeated moiety in a conjugated copol-ymer structure. Furthermore, the geometry andorientation of the bisadditions of pairs of like-con-jugated polymers to C60 have not been, to ourknowledge, explored. As a starting point, we weretherefore interested to see if it might be possible to

make a system based on alternating fullerene-con-jugated polymer structures so as to explore andcompare the principal chemistries used (Prato andradical addition) and then to study any particular-ities of their self-assembly. We were also interestedto see if there is an influence made by the linkinggroup between the conjugated polymer and theC60 on the self-assembly and optoelectronic proper-ties. With this reasoning, we propose, to the bestof our knowledge, the first two examples of con-trolled bisadditions of photoactive polymers to C60

to yield alternating polymers (Scheme 1).

EXPERIMENTAL

Polymer Characterization

Polymer molecular weights were estimated againstpolystyrene standards by gel permeation chroma-tography (GPC) using a bank of four columns (HR0.5, 2, 4, and 6V

R

) of 300-mm 5-lm Styragel at40 �C, THF eluent at a flow rate of 1.0 mL min�1

controlled by a WatersVR

2690 pump, an ERCVR INC7515A refractive index detector, and a Waters 996multiple wavelength UV–visible photodiode arraydetector, unless otherwise indicated. 13C (100MHz) and 1H (400 MHz) NMR were recorded on aBrukerV

R

Avance 400 spectrometer in CDCl3 at am-bient temperature, unless otherwise noted. UV–visible near IR absorption spectra were recordedusing the GPC detector so as to obtain curvesat Mps. Photovoltaic characterizations were per-formed as detailed in the Supporting Information

Figure 1. A highly idealized example of an aimed-for photovoltaic device made using conjugated multi-block copolymers that may exhibit high degrees oflong range order and lie parallel to the substrate.22(a)

Positively, this self-enforced crystallinity may enhancep–p stacking of adjacent conjugated segments, improveelectrode-active mass p-orbital interactions, and resultin improved charge mobilities perpendicular to theelectrodes.

ALTERNATING FULLERENE AND CONJUGATED POLYMERS 2305

Journal of Polymer Science: Part A: Polymer ChemistryDOI 10.1002/pola

and elsewhere.23 AFM samples were drop castfrom toluene solutions (ca. 10 mg mL�1) onto micaplates and dried at ambient temperature undernitrogen. Images were recorded at ambient tem-perature using a Nanoscope IIIa multimode(Veeco, Santa Barbara, CA) in the tapping mode. Astandard silicon cantilever (Veeco) was used with aresonance frequency at about 300 kHz. All images(512 lines of 512 data points) are presented asreceived, except that a flatten command was usedto remove background slope.

Materials

All materials were used as received and obtainedfrom Aldrich (France), except fullerene which wasobtained from MER (USA). Solvents were distilledfrom over their respective drying agents underdry nitrogen. Reactions were performed in flame-dried and dry nitrogen flushed glass reactorsunless otherwise stated. In the text, discussionsare based on polystyrene-calibrated GPC-indicatedvalues of molar masses. Note that N-methylglycineis also known as sarcosine.

Synthesis of a,x-DiH-P3HT

This is a representative method. Isopropyl magne-sium chloride (2 M in THF, 0.0388 mol) was added

to 2,5-dibromo-3-hexylthiophene (0.0388 mol) andTHF (380 mL) in a 1-L flask and stirred for 3 h at29 �C. The polymerization started on addingNi(dppp)Cl2 (1.29 � 10�3 mol); it was allowed torun for 24 h at 28 �C. Termination and theremoval of bromine chain ends was accomplishedby the slow addition of LiAlH4 (0.02 mol). Afteranother 16 h, excess LiAlH4 was quenched bydropwise addition of HCl (20 mL, 1 M), the poly-mer was recovered by precipitation in ethanol(2 L) and centrifugation. Following extensiveSoxhlet washing with methanol, a,x-diH-P3HTwas recovered from the Soxhlet with chloroform.Following precipitation in ethanol and centrifuga-tion it was dried under reduced pressure for 1 hat 70 �C, 3 h at 80 �C, and 1 h at 130 �C (yield:2.86 g, 44%). GPC: Mn ¼ 4500 g mol�1, D (¼Mw/Mn) ¼ 1.22. 1H and 13C NMR data as same asthat of P3HT-1 in ref. 23.

Synthesis of a,x-Diformyl-poly(3-hexylthiophene)

The polymer of interest was prepared followinga method described elsewhere.24 Briefly, a,x-diH-P3HT (Mn ¼ 4500 g mol�1, D ¼ 1.22, 0.3 g)was stirred in toluene (80 mL) with N-methylfor-manilide (0.016 mol) and POCl3 (0.014 mol) at

Scheme 1. Synthetic routes for P(P3HT-PyC60) and P(P3HT-CH2C60): (a) N-Methyl-formanilide, POCl3, 75

�C, 42 h; (b) LiAlH4, room temperature, 3.5 h, then HCl (aq.);(c) DDQ, triphenyl phosphine, tetra-n-butyl ammonium bromide, room temperature,30 min; (d) C60,N-methylglycine, reflux, 24 h; and (e) C60, CuBr, bypyridine, 120

�C, 70 h.

2306 HIORNS ET AL.


75 �C for 42 h. Once cooled to room temperature,the solution was stirred with sodium acetate(100 mL, saturated aq.) for 4 h. Following precipi-tation in ethanol (1 L), recovery by filtration,extensive Soxhlet washing with ethanol, anddrying under reduced pressure at 40 �C for 24 h,0.29 g (97%) of a,x-diCHO-P3HT was recovered.GPC: Mn ¼ 4250, Mp ¼ 4550 g mol�1, D ¼ 1.22.

1H NMR (minor peaks in italics): 10.04, 10.02and 9.85 (sum to 2 H); 7.07, 7.02, 7.00 (sum to 25H); 2.96, 2.84, 2.65 (sum to 60 H) 1.73, 1.58, 1.45,1.37, 1.28 (sum to 240 H), 0.93 (90 H) ppm (seeSupporting Information Figs. S1 and S2). 13CNMR: 182.1, 182.0, 154.0, 145.9, 142.5, 140.3,136.6, 136.3, 134.8, 134.7, 134.4, 134.1, 130.9,130.6, 130.2, 129.9, 129.3, 129.0, 128.5, 32.0, 31.9,30.9, 30.7, 30.2, 29.9, 29.7, 29.4, 28.9, 23.1, 23.0,and 14.6 ppm.

Synthesis of a,x-Dihydroxymethyl-poly(3-hexylthiophene)

The polymer of interest was prepared followingthe method given elsewhere.24 Representatively,a,x-diCHO-P3HT (Mn ¼ 7440 g mol�1, D ¼ 1.22,1.39 g) dissolved in THF (300 mL) was stirredwith LiAlH4 (1 M in THF, 12 mL) for 3.5 h. Thereaction was terminated with the addition of HCl(1 M, 5 mL) and the polymer recovered followingprecipitation in ethanol (2.5 L). Soxhlet washingwith methanol, reprecipitation from dichloro-methane (DCM) (120 mL) in ethanol (1 L), anddrying under reduced pressure overnight at 40 �Cgave a,x-diHOCH2-P3HT (0.93 g, 67%). GPC:Mn ¼ 8110 g mol�1, D ¼ 1.19.

1H NMR: 7.00, 4.80 (doublet, J ¼ 6 Hz), 4.77(doublet, J ¼ 6 Hz), 2.81, 1.73, 1.17, 1.46, 1.36,and 0.93 ppm (see Supporting InformationFig. S3).

Synthesis of a,x-Dibromomethyl-poly(3-hexylthiophene)

In a 500-mL flask flushed with nitrogen, DCM(240 mL), DDQ (0.0192 mol), and triphenyl phos-phine (0.012 mol) were stirred for 3 min. To thisred mixture was added tetra-n-butyl ammoniumbromide (0.012 mol) and, after 2 min, was addeda,x-diCH2OH-P3HT (Mn ¼ 5540 g mol�1, D ¼ 1.4,0.52 g) dissolved in DCM (40 mL). After 30 min atambient temperature the solution was droppedinto ethanol, the precipitate was recovered andwashed in a Soxhlet with methanol. Drying underreduced pressure gave a,x-diBrCH2-P3HT (82%

yield). GPC indicated Mn ¼ 5600 g mol�1 andMw/Mn ¼ 1.4.

1H NMR: 7.00 (s, 1 H), 4.62 (s), 4.60 (s), 2.81 (t,J ¼ 6.7 Hz, 2 H), 2.63 ppm (t, J ¼ 7.7 Hz, withlower lying m), 1.72 (m, 2H), 1.46 (m, 2H), 1.37(m, 4 H), and 0.94 ppm (m, 3 H) (SupportingInformation Fig. S4).

Synthesis of Poly{poly(3-hexylthiophene)-alt-[bis(N-methylpyrrolidine) fullerene]}

a,x-DiCHO-P3HT (Mn ¼ 4250, Mp ¼ 4550 gmol�1, D ¼ 1.21, 0.2 g, 4.7 � 10�5 mol), C60 (4.7 �10�5 mol) and N-methylglycine (9.4 � 10�5 mol)were dissolved in 6 mL of chlorobenzene at 50 �C.The mixture was then refluxed for 24 h, and pre-cipitated in ethanol. Sequential ethanol and hex-ane Soxhlets removed excess N-methylglycine,and then unreacted a,x-diCHO-P3HT and C60,respectively. P(P3HT-PyC60) was recovered usinga DCM Soxhlet (yield: 62%). GPC indicated Mn ¼10,600 g mol�1, Mp ¼ 19,870 g mol�1, and D ¼2.13 (see Supporting Information Fig. S5).

1H NMR (CDCl3, ambient, D1 ¼ 10 s) showedbroad peaks due to P3HT at 7.02 (1 H), 2.84 (2 H),1.75 (2 H), 1.48 (2 H), 1.39 (4 H), and 0.95 ppm (3H), and due to the pyrrolidine ring at 5.39 (s,[CHA), 4.62 (dd, J ¼ 300 Hz, J ¼ 9.65 Hz,ACH2A), 4.61 (dd, J ¼ 300 Hz, J ¼ 9.65 Hz,ACH2A), about 4.3 (only just discernable broadd), and 3.7 ppm (possible trisadduct methylenes).13C NMR (CDCl3, ambient; Supporting Informa-tion Fig. S6) showed peaks due to C60 at 147.7,146.71, 146.55, 146.33, 146.1, 146.05, 146.02,145.97, 145.88, 145.83, 145.79, 145.75, 145.64,145.56, 145.49, 145.04, 145.00, 144.68, 142.97,142.63, 142.51, 142.38, 142.24, 142.16, and 142.00ppm, along with peaks due to P3HT at 140.3,134.12, 130.91, 129.00, 32.15, 30.95, 29.92, 29.72,23.11, and 14.59 ppm, and peaks due to the pyr-rolidine ring at 77.66, 70.38, and 63 ppm. Also seeSupporting Information Figure S7 for corrobora-tive indications from 13C DEPT-1H HSQC NMR.

Synthesis of Poly{[a,x-dimethylene-poly(3-hexylthiophene)]-alt-fullerene}

a,x-DiBrCH2-P3HT (Mn ¼ 5960, Mp ¼ 4990 gmol�1, D ¼ 1.41, 0.08 g, estimated 2.6 � 10�5 mol,equivalent to 5.2 � 10�5 mol of active chain ends)and C60 (1.28 � 10�4 mol, ca. 2.5 times the num-ber of a,x-diBrCH2-P3HT chain ends) were dis-solved in toluene (35 mL) at 80 �C. After the addi-tion of CuBr (3.5 � 10�5 mol) and bipyridine



(7.0 � 10�5 mol), the mixture was heated to120 �C. After 70 h, the solution was dropped intoethanol (300 mL) and the precipitate was recov-ered and washed in a hexane Soxhlet to removeunreacted P3HT and C60. The treatment of thesame Soxhlet filter with THF yielded a brown or-ange solution. Precipitation in ethanol gaveP(P3HT-CH2C60) (yield: 10%). GPC indicated Mn

¼ 15,200 g mol�1, Mp ¼ 24,900 g mol�1, and Mw/Mn ¼ 2.0 (see Supporting Information Fig. S8).

1H NMR (D1 ¼ 10 s): 7.00 (s), 4.62 (s), 4.60 (s),3.60 (dd, gemJ ¼ 9 Hz), 3.44 (s), 3.27 (s), 2.82, 2.6(m), 1.72, 1.45, 1.37, and 0.93 ppm. 13C DEPTNMR (Supporting Information Fig. S9; 135� thus Cnot bonded to H unseen, ACHA and ACH3 up andACH2A down; scans ¼ 33,628, D1 ¼ 2 s): 129.00(up), 32.12 (down), 30.93 (down), 29.88 (down),29.68 (down), 23.07 (down), and 14.56 ppm (up).

RESULTS AND DISCUSSION

The chain growth polymerization of 2-bromo-5-chloromagnesium-3-hexylthiophene with 1,3-bis(diphenylphosphino)propane nickel(II) chloride[Ni(dppp)Cl2] permits a certain degree of prede-termination of P3HT molecular weights.23,25,26

Although below the optimum value for maximump-conjugation,23 P3HTs with about 20 repeatunits were prepared to facilitate this demonstra-tion of chain-end chemistry. The steps of debromi-nation to prepare a,x-diH-P3HT,26 formylationto yield a,x-diformyl-poly(3-hexylthiophene) (a,x-diCHO-P3HT),24 and hydrogenation to givea,x-dihydroxymethyl-P3HT (a,x-HOCH2-P3HT)24

were carried out using known methods. It is inter-esting to note the TOCSY 2-D NMR of a partiallychain-end formylated P3HT (see SupportingInformation Fig. S2) which indicates that onlychain-end a-methylene protons undergo through-space 4J correlations with 4-thiophene protons;mid-chain groups did not register similar correla-tions, perhaps because of restrained relaxations.COSY 2-D NMR characterization of a,x-HOCH2-P3HT unequivocally showed the presence ofhydroxyl groups by correlations of chain-endmethylene and hydroxy protons (see SupportingInformation Fig. S3).

The conversion of a,x-HOCH2-P3HT to a,x-diBrCH2-P3HT proved more problematic. Ini-tially, HBr or SOBr2 were used but the former ledto uncontrolled brominations and the latter a deg-radation of the polymer.27 However, the reactionwith tetra-n-butyl ammonium bromide in the

presence of 2,3-dichloro-5,6-dicyano-1,4-benzoqui-none (DDQ) and triphenylphosphine went to nearcompletion.28 The few remaining hydroxyl groupswere not converted, as excessive brominationcould invite the addition of DDQ moieties to theP3HT backbone.15(d) The 1H NMR in the Support-ing Information shows two peaks at 4.62 and 4.60ppm due to chain-end ACH2Br groups. Therespective ratio of their areas, at about 80-20, istypical of P3HT chain-end isomers.26

Preparation of Poly{poly(3-hexylthiophene)-alt-[bis(N-methylpyrrolidine) fullerene]}

The first example of an alternating polymer struc-ture containing C60, P(P3HT-PyC60), was preparedby the equimolar reaction of a,x-diCHO-P3HTwith C60 in the presence of excess N-methylgly-cine.18 As the P3HT has functional groups at bothchain-ends, it was expected that the reactionwould yield a mixture of linear chains, as shown inScheme 1, some mono-C60 addition products andsome insoluble three-dimensional branched struc-tures due to numerous reactions about the C60.

It should be noted that the product was exten-sively purified by precipitation and Soxhlet wash-ing so as to remove unreacted C60 and most of theunreacted P3HT. The recovered product was wellsoluble in THF, which would tend to indicate thatthe presence of crosslinked material was very low.Assuming that the steric exclusion behavior ofP(P3HT-PyC60) does not differ from that of a,x-diCHO-P3HT, the GPC of P(P3HT-PyC60) can bedeconvoluted to divulge the component copoly-mers, as shown in Figure 2. It should be notedthat the deconvoluted curves show only the mostprobable (and not necessarily actual) macromole-cules present; they serve to give a qualitativerather than a quantitative indication.22(d) Itshould be made extremely clear that the molecu-lar weight of fullerene is not included in these cal-culations because its contribution to the curve isnegligible under the conditions used.17 The threemain constituents exhibit molecular weights cor-responding closely to: peak 3, P3HT-PyC60Py-P3HT; peak 4, P3HT-(PyC60-P3HT)2; and peak 5,(P3HT-PyC60)4-P3HT. This result suggests thatdi-additions are well favored. MALDI-TOF wasapplied to P(P3HT-PyC60), using techniquesdetailed elsewhere,23 however, the results wereinconclusive because of a well-recognised frag-mentation of weak polymer-C60 bonds.29 UV–visi-ble spectroscopy confirmed the incorporation ofC60 by way of an increase in absorbance at about

2308 HIORNS ET AL.


320 nm (see Supporting Information). Theextremely minor absorptions around 600–700 nmassociated with pyrrolidine modification of C60

were eclipsed by the presence of P3HT and thelow concentration of C60 units in the chain.

Given the low concentrations of C60 in thecopolymers, and their low solubilities, it wasfound all the more necessary to seek a model toguide NMR peak attributions. A comparablemodel was found wherein N-methylpyrrolidinebisadducts were formed with various isomers,namely, cis-3, trans-3, trans-2, trans-4, trans-1,and equatorial in that order of preference.30 Fromthis work it was supposed that the most probableP(P3HT-PyC60) bisadduct isomers and mono- andtris-adducts could be summed up as shown in Fig-ure 3. It should be noted that the isomers that themacromolecules can take up around the methyl-pyrrolidine cycle [such as a trans (equatorial–equatorial) structure, as discussed below in thesection on modeling] are not taken into accountbecause of the inability of the NMR, when dealingwith necessarily low concentrations of relativelyinsoluble copolymers, to make such attributionspossible. Because of the low ratio of C60 to P3HTin the copolymers, the long relaxation times of theinferred nuclei, and the relatively limited solubil-ities of the samples in NMR solvents, extremelylong 1H NMR experiments were performed (typi-cally of the order of 36 h). Peaks due to unreactedP3HT chain-end formyl groups were negligible,indicating that their concentration was extremely

Figure 2. Deconvoluted GPC of P(P3HT-PyC60) (UV,254 nm) with Mp ¼ 18,830 g mol�1 showing: (2) Mp ¼4560 g mol�1 due to unreacted a,x-di-CHO-P3HT; (3)Mp ¼ 9120 g mol�1; (4) Mp ¼ 14,350 g mol�1; and (5)Mp ¼ 27,300 g mol�1. Note that Mp is used as it isderived directly from inflections in the parent curve.

Figure 3. Various possible structures of P(P3HT-PyC60). Note that the stereoiso-mers of each structure are not considered here but in the modeling detailed else-where in the text.



low and that the copolymers had relatively highdegrees of repetition. The 2-D HMQC 13C(DEPT)-1H NMR of P(P3HT-PyC60) (Fig. 4) showsa peak at 70.38 ppm (ACH2A) which correlateswith double-doublets at 4.62 ppm (J ¼ 300 Hz,J ¼ 9.65 Hz). Each of these doublets is replicatedby similar but smaller double-doublets at 4.61ppm (J ¼ 300 Hz, J ¼ 9.65 Hz). This repetition isdue to the aforementioned effect of P3HT chain-end isomers, and unequivocally associates thesecorrelations with the pyrrolidine methylene pro-tons in P(P3HT-PyC60). As there are no compara-ble singlet peaks, as have been observed forknown single additions,18(i) it can be stated thatthe symmetrical mono- and trans-1 bisadductsare not present. This is not surprising given thatthe Prato addition often gives low yields for mono-adducts, even when strict attention is paid to stoi-chiometric control so as to minimize multipleadditions.3 The steric bulk of P3HT probablyexcludes formation of cis-3 bisadducts. Therefore,the double-doublets are most likely due to trans-3,trans-2, or trans-4 bisadducts, in that order ofpreference. Given the stereo-electronic preferenceof C60,

31 the trans-3 form is possibly dominant.However, the additional smaller correlationsbetween the same carbon at 70.38 ppm and pro-ton peaks at about 4.1–3.9 ppm give a tentative

indication that the main product is probably thetrans-2 isomer and that the trans-3 isomer is theminor isomer. This is because the model com-pound, as here, shows peaks due to trans-2 isomerprotons being downfield from the trans-3 isomer.On reflection, it could be expected that the first-added bulky P3HT may favor the formation of thetrans-2 isomer through steric inhibition of otherisomers that require closer addends. The pyrroli-dine methine is indicated by the correlation at77.66 (13C) and 5.39 (1H); it is a single peak withan area comparable to each individual peak of thegem ACH2A protons in the 1H spectrum. This sin-glet exhibits a shoulder at 5.36 ppm (1H) becauseof P3HT chain-end isomerism. Integration of theareas of the peaks provide evidence that thetrans-2 bisadduct is present in more than 80% ofthe structure of P(P3HT-PyC60). It is probablethat the trans-3 bis adduct makes up most of theremaining structures. It is possible to speculatethat the correlation at about 3.7 (1H) and 63 (13C)ppm is due to a trisadduct. However, its concen-tration is low. There is no indication of higheradducts. It would seem therefore that the mostdominant reaction is two P3HT additions to eachC60 to form a linear, alternating P(P3HT-PyC60).This may be explained by the steric bulk of thepolymer excluding further reactions around theC60.

15(a) It should be reiterated that these attribu-tions remain tentative given the low concentra-tions of the chain-ends characterized.

The simplest copolymer, P3HT-PyC60Py-P3HT,was modeled using MOPAC PM632 semiempiricaloptimizations carried out with the EigenvectorFollowing method. PM6 was chosen in preferenceto AM1 and PM333 formalisms because it wasfound that, as shown in Table 1,33–38 for a modelcompound 2,20-bithiophene, PM6 faithfully repro-duces both conformational behavior and struc-tural parameters while managing to give resultsthat compare favorably with those obtained by abinitio methods using large basis sets (such asCCSD(T)/aug-cc-pVDZ and MP2/aug-cc-pVTZ).36

This method also permits, with reasonable com-putational effort, an elucidation of the energeti-cally favored torsional disorder of relatively longP3HT chains (in the case of P3HT-PyC60Py-P3HT,a pair of 19 repeat units). It should be noted thatthe requested SCF convergence and threshold val-ues for the RMS gradient were 0.0001 and 0.2kcal mol�1, respectively. The geometry around theC60 unit for trans-2 P3HT-PyC60Py-P3HT struc-tures was initiated from X-ray data gleamed froma closely related pyrrolidine-based structure,

Figure 4. 2D HMQC 13C (DEPT 135�)-1H ofP(P3HT-PyC60). Note that the peak at 49.85 ppm(13C, ACH2A) is due to a minor trace of sarcosine,observed because of the extremely long experimenttimes. [Color figure can be viewed in the online issue,which is available at www.interscience.wiley.com.]

2310 HIORNS ET AL.


namely a pyrrolidine-linked tetraphenylpor-phyrin/C60 dyad.39 Two input structures wereused for PM6 optimizations. The first was takenfrom a MMþ optimization using steepest descentand conjugated gradient methods with a conver-gence threshold set to 0.001 kcal mol�1 A�1. Thesecond input geometry was prepared by stepwiseaddition and optimization40 of 3-hexylthiophenetrimers. A trans (equatorial–equatorial) disposi-tion of the methyl and P3HT substituents withrespect to the CAN bonds of the pyrrolidine ringwas assumed as the starting point for the geome-tries. However, the final structure displayed aninversion of the pyrrolidine ring with both methyland P3HTentities being in an axial position. Opti-mized structures based on twisted [Fig. 5(a–d)] orplanar [Fig. 5(e–h)] P3HT were separated by only3 kcal mol�1. This small difference can explainwhy the macromolecule may easily take up theless stable planar form when packing in the solidcrystalline state. In addition, it is apparent thatthe extension of conjugation throughout the chainis relatively insensitive to slight variations (i.e.,�20�) in planarity. This would tentatively explainwhy fibrillar, twisted structures display relativelyhigh charge mobilities. In both the cases, thedegenerate HOMOs (HOMO and HOMO-1) arelocated on the P3HT segments, whereas theLUMOs (LUMO and LUMO þ 1) are on the fuller-ene moiety, thus indicating that the band struc-

tures are not significantly affected by the confor-mation of the P3HT. Calculations do not discernconjugation between the two P3HTs and the C60.

AFM phase imaging of drop-cast films ofP(P3HT-PyC60), represented in Figure 6, showedfibrils and nanorods of about 14 nm thickness.These characteristics, respectively, resemble thoseof high- (ca. 30,000 g mol�1) and low-molecular-weight (ca. 4000 g mol�1) P3HTs.42 The low-energy barrier between the aforementionedtwisted and planar P3HT structures may be rep-resentative of this solid state morphology. Thenanostructures are dotted with hard nodules thatare several nanometers in diameter and mostlikely made of aggregated C60, indicating thateven though the C60 makes up a very small partof the overall volume of the polymers, it still ini-tiates phase separation even when encumberedwith pyrrolidine links. It is probable thereforethat its incorporation in future structures willhave to be performed with respect to the extentthat it provides the driving force for phase separa-tion. Evidently, the ideal structure shown in Fig-ure 1 is not obtained; this is a model system andit is probable that C60 volumes will have to beincreased for this to happen.

The length of the P3HT and concentration ofC60 were evidently not optimized with regard tophotovoltaic behavior but to explore the feasi-bility of forming multicomponent, alternating

Table 1. Comparison of Bond Lengths and Angles Obtained by Various Methods for the Bithiophene Unit

Method �rC�C (A)a �rC�S (A) aC�S�C (�) sS�C�C�S (�)b

PM6 1.43 1.75 93.0 146.8 152c 142d

HF/3-21G* 146e

B3LYP/6-31G* 1.45 1.75 91.8 157.9B3LYP/SVP 1.45f 1.75f 92.0f �160f

B3LYP/aug-cc-pVTZ 156.2g

MP2/6-31G** 141.7g

MP2/aug-cc-pVTZ 147.5g

CCSD(T)/cc-pVDZ 146.6g

Experimental 1.44–1.45h 1.71–1.72h 92.2–92.5h 148 � 3i

aCAC bond distance between rings.bClose inspection of this table reveals that the bonds lengths and valence angles calculated by the available theoretical

approaches are in good agreement with experimental values. With respect to torsional characteristics, and amongst the varioussemiempirical methods, PM6 gives the results in closest agreement with the most sophisticated of theoretical methods, such asCCSD(T) and MP2.

cDeveloped from AM1 in ref. 33.dDeveloped from PM3 in ref. 33.e From HF/3-21G* in ref. 34.f From B3LYP/SVP in ref. 35.g From ref. 36.h From ref. 37 and references cited therein.i From experimental work in ref. 38.



Figure 5. Frontier orbitals of trans-2 P3HT-PyC60Py-P3HT gained through PM6optimization for the twisted: (a) HOMO; (b) HOMO-1; (c) LUMO; (d) LUMO þ 1; andplanar forms: (e) HOMO; (f) HOMO-1; (g) LUMO; and (h) LUMO þ 1. It should benoted that the images for the geometry and orbitals were generated via Avogadrosoftware,41 unless otherwise stated. [Color figure can be viewed in the online issue,which is available at www.interscience.wiley.com.]

2312 HIORNS ET AL.


structures containing P3HT and C60. Neverthe-less, the temptation to test P(P3HT-PyC60) wasgreat, and therefore it was placed in a typicalsetup (glass/ITO/PEDOT-blend-PSS/P(P3HT-PyC60)/LiF/Al). We found a relatively high mean open cir-cuit voltage (Voc) of 0.58 V, a short circuit current(Jsc) of 0.38 mA cm�2, a fill factor (FF) of 0.25,and efficiencies (g) averaging at 0.05%. The effi-ciency and Jsc is low because of the low molecularweight of the P3HT used (around 20 units leadingto electronic confinement effects23). To explainthis effect it is worth considering that the samestarting material in these reactions, a,x-diH-P3HT [which has the same low molecular weightas the P3HT segments in P(P3HT-PyC60)] whenmixed with PCBM at a 1:1 ratio (i.e., with agreater amount of C60 than in this system) gaveVoc ¼ 0.68 V, Jsc ¼ 1.0 mA cm�2, FF ¼ 0.30, and g¼ 0.2%. The fact that it is the low molecularweight of P3HT that has a considerable effect isfurther confirmed when realizing that a compara-ble device with a higher molecular weight P3HTand PCBM gave yields of the order of 3%.23 So,even though the efficiency of the device is low itcan be explained by the low molecular weight ofthe P3HT and the low volume of C60. What is ofmore interest here is that the model compound,using an original reaction, actually does work tosome extent. It is highly possible that if theamount of C60 and the length of the P3HT can beincreased to attain domains in the solid state thatcan traverse the whole active layer, as shown inFigure 1, then higher efficiencies may well be pos-sible. This argument is reinforced by the notableresult that the relatively high value of the Voc con-firms the result of the computer modeling studies,in that the C60 and the P3HT retain their ownindividual electronically conjugated structures.

Poly{[a,x-dimethylene-poly(3-hexylthiophene)]-alt-fullerene}

P(P3HT-CH2C60) was formed by the atom transferradical addition of a,x-diBrCH2-P3HT to C60.

43,44

Mathis and coworkers unequivocally showed thatthe number of additions of macromolecules to C60

is controlled by the relative concentrations of theactive chain-ends and C60 in toluene.17,20(a) Pairedaddition is favored because of the formation of anactive radical site on the C60. One or two ‘‘pairs’’of polymers may add to the C60 sphere if the ratioof polymer chain ends to C60 is\2 or[4, respec-tively. To our knowledge, the work we presenthere is the first example of this type of additionbeing used to prepare an alternating and linearstructure, which contains conjugated segments.The ratio used in our work, 0.4 polymer chainends to each C60, was well placed to yield the solu-ble linear structure indicated in Scheme 1, ratherthan an insoluble three-dimensional network.Assuming that the steric exclusion profile of thecopolymer did not greatly differ from that of thestarting a,x-diBrCH2-P3HT, the GPC-indicatedvalue of Mp ¼ 24,900 g mol�1 is equivalent to astructure based on 5 P3HT units and 4 C60s [Fig.7(a)]. Furthermore, a shoulder to the main curve,

Figure 6. AFM phase image of P(P3HT-PyC60) filmsurface showing fibrillar structure decorated withnodules. [Color figure can be viewed in the onlineissue, which is available at www.interscience.wiley.com.]

Figure 7. (a) 3D GPC (THF) elution curves ofP(P3HT-CH2C60); and (b) UV–visible absorbance ofa,x-diBrCH2-P3HT, denoted as 1, and P(P3HT-CH2C60), denoted as 2, normalized to P3HT peakmaxima at about 450 nm.



with Mp � 40,000 g mol�1, indicated the forma-tion of much longer polymers, probably aroundtwice those of the main peak given the knownmechanism for this reaction.17,20(a),44 More inter-esting is the formation of aggregates outside ofthe calibration range of the apparatus, that is,[1� 106 g mol�1, when using a concentrated injectedsolution. This indicates the retention of THF-phobic properties by C60 because of the limitedmodification of its structure. The increased ab-sorbance of P(P3HT-CH2C60) with respect to a,x-diBrCH2-P3HT [cf. P(P3HT-PyC60)] at about320 nm confirms the incorporation of C60 [Fig. 7(b)].

17

The result is corroborated by the 13C and 2-D13C (DEPT)-1H NMR shown in Figure 8. Theminor correlation at about 3.6 (1H) and 67 ppmconfirms the 1,4-methylene addition to C60 byway of its small size, and it being a double-doubletin the 1H spectrum.45 It is therefore probable thatthe macromolecule takes up the 1,4-structureabout the C60 rather than the symmetrical 1,2-position due to the steric bulk of the P3HT. A cor-relation arises from chain-end ACH2Br groups at4.62 (1H) and 64.8 ppm (13C). Integration of the

Figure 8. 2D NMR of P(P3HT-CH2C60) with 1H hor-izontal and 13C DEPT vertical. Note the correlationsat about 68 ppm (13C) and 3.75 ppm (1H) due to THF,and about 56.8 ppm (13C) and 3.27 ppm (1H) due tomethanol, arising with the high number of scansrequired for this system.

Figure 9. Frontier orbitals of the 1,4-bis adduct P3HT-CH2C60CH2-P3HT throughPM6 optimization: (a) HOMO; (b) HOMO-1; (c) LUMO; and (d) LUMO þ 1. [Colorfigure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

2314 HIORNS ET AL.


methylene and ACH2Br peaks in the 1H spectrumindicates that there are about 5.7 C60-CH2A to 2ACH2Br, equivalent to a number average chaincontaining about 2.8 C60s, a value in proximity tothat indicated by GPC.

The simplest structure, P3HT-CH2C60CH2-P3HT, was also investigated using PM6 semiem-pirical modeling. The optimization using planarP3HT moieties failed to converge. The same afore-mentioned methodology, namely stepwise optimi-zation, resulted in a structure with similarlytwisted P3HT moieties. The optimized structureis shown in Figure 9. It should be noted that theP3HT HOMO displays a clear separation from theC60 LUMO indicating electronically independentband structures.

Once again, it should be stated that this workwas carried out to demonstrate the feasibility ofthe chemistry and the importance of the P3HT-C60

linking group on the properties of the system.Therefore, the P3HT chains were intentionallyshort and C60 concentrations very low (i.e., one C60

per macromolecular unit). Nevertheless, character-izations were attempted and as expected, low val-ues for photovoltaic activities were found forP(P3HT-CH2C60), as in Voc ¼ 0.31 V, Jsc ¼ 0.16 mAcm�2, FF¼ 0.26, and g ¼ 0.01%. It should be statedthat the films were difficult to prepare because ofthe low solubility of the polymer and the strongtendency of the C60 to aggregate. This led to poorfilm formation and this impinged upon the results.So while the methylene group may be of use for itsretention of the physical properties of C60, it alsoencumbers the copolymer with phase separationproperties that considerably alter its solvent dis-persion by making the C60 harder to dissolve. Thisresult was corroborated by the AFM characteriza-tions represented in Figure 10, in which a dis-

tinctly fibrous structure dotted with bundles ofaggregated C60 is shown. It is apparent thereforethat the character of C60, even when in low concen-trations with respect to the overall structure,impinges very strongly on the behavior of the sys-tem. When compared with P(P3HT-PyC60), theP(P3HT-CH2C60) seems to be much more highlyaffected by the phase separation behavior of C60.

CONCLUSIONS

These experiments demonstrate the preparationof regioselective and controlled additions of conju-gated polymers to C60 to give alternating struc-tures. The ground state electronic bands of C60

and P3HT moieties are found to remain separatefor the pyrrolidine and methylene groups used.Characterization and modeling indicate a greaterretention of the physical properties of C60 whenusing methylene links. The change in going fromthe pyrrolidine to the methylene group impactsheavily upon the properties of the system as itseems that even in low relative concentrations,the character of the C60 strongly influences theself-assembly of the copolymers. The apparentlygreater retention of the spherical character of C60

in a 1,4-bis addition product than in a trans-2 pyr-rolidine product means that the former exhibitsgreater tendencies to phase separate in solid anddispersed states.

These model structures may provide the basisfor future macromolecules for photovoltaic devi-ces; however, it is apparent that the relative vol-umes of C60 in the macromolecules will have toincrease considerably to enhance current flowsand attain structures similar to that shown in theidealized structure in Figure 1. This may be feasi-ble through a variety of routes. It seems that thephase separation of C60 and P3HTwill be assuredusing either of the linking groups discussed here,but most especially when using a methylene link.

The authors thank Melanie Dowling, Farid Ouhib, andmembers of the Cellules Solaires Photovoltaıques Plas-tiques (CSPVP) consortium for their enlightening dis-cussions and warm encouragement. Gerald Clisson andFrancis Ehrenfeld are thanked for their technicalexpertise and assistance. The Centre InformatiqueNational de l’Enseignement Superieur (CINES) isacknowledged for technical support to D. Begue. Theyalso thank the CNRS and the ADEME (CSPVP researchprogram no. 0105148, contract no. 99 05 019) for finan-cial support to R. C. Hiorns.

Figure 10. AFM phase image of P(P3HT-CH2C60)film surface. [Color figure can be viewed in the onlineissue, which is available at www.interscience.wiley.com.]



REFERENCES AND NOTES

1. (a) Giacalone, F.; Martın, N. Chem Rev 2006, 106,5136–5190; (b) Wang, C.; Guo, Z.-X.; Fu, S.; Wu,W.; Zhu, D. Prog Polym Sci 2004, 29, 1079–1141.

2. Newman, C. R.; Frisbie, C. D.; da Silva Filho, D.A.; Bredas, J.-L.; Ewbank, P. C.; Mann, K. R.Chem Mater 2004, 16, 4436–4451.

3. Fullerenes: From Synthesis to OptoelectronicProperties (Developments in Fullerene Science);Guildi, G. M.; Martın, N., Eds.; Kluwer AcademicPublishers: Dordrecht, Netherlands, 2002.

4. (a) Dagotto, E. Science 2001, 293, 2410–2411; (b)Makarova, T. L.; Sundqvist, B.; Hohne, R.; Esqui-nazi, P.; Kopelevich, Y.; Scharff, P.; Davydov, V.A.; Kashevarova, L. S.; Rakhmanina, A. V. Nature(London) 2001, 413, 716–718.

5. Nakamura, E.; Isobe, H.; Tomita, N.; Sawamura,M.; Jinno, S.; Okayama, H. Angew Chem Int EdEngl 2000, 39, 4254–4257.

6. Wang, X.; Yuan-Yong, Y. Polymer 2006, 47, 6267–6271.

7. Lecommandoux, S.; Borsali, R. Polym Int 2006,55, 1161–1168.

8. Klok, H. A.; Lecommandoux, S. Adv Mater 2001,13, 1217–1229.

9. de Cuendias, A.; Le Hellaye, M.; Lecommandoux,S.; Cloutet, E.; Cramail H. J Mater Chem 2005,15, 3264–3267.

10. Lee, M.; Cho, B. K.; Zin, W.-C. Chem Rev 2001,101, 3869–3892.

11. Noshay, A.; McGrath, J. E. Block Copolymers;Academic Press: New York, 1977.

12. Cho, M. J.; Choi, D. H.; Sullivan, P. A.; Akelaitis,A. J. P.; Dalton, L. R. Prog Polym Sci 2008, 33,1013–1118.

13. Ling, Q.-D.; Liaw, D.-J.; Zhu, C.; Chan, D. S.-H.;Kang, E.-T.; Neoh, K.-G. Prog Polym Sci 2008, 33,917–978.

14. (a) Gunes, S.; Neugebauer, H.; Sariciftci, N. S.Chem Rev 2007, 107, 1324–1338; (b) Li, G.; Shro-triya, V.; Yao, Y.; Huanga, J.; Yang, Y. J MaterChem 2007, 17, 3126–3140.

15. (a) Xu, G.; Han, Y.; Sun, M.; Bo, Z.; Chen, C. JPolym Sci Part A: Polym Chem 2007, 45, 4696–4706; (b) Xu, G.; Han, Y.; Sun, M.; Bo, Z.; Chen,C. J Polym Sci Part A: Polym Chem 2007, 45,4696–4706; (c) Picot, C.; Audouin, F.; Mathis,C. Macromolecules 2007, 40, 1643–1656; (d)Mignard, E.; Hiorns, R. C.; Francois, B. Macromo-lecules 2002, 35, 6132–6141.

16. Ederle, Y.; Mathis, C. Macromolecules 1999, 32,554–558.

17. Audouin, F.; Nuffer, R.; Mathis C. J Polym SciPart A: Polym Chem 2004, 42, 3456–3463.

18. (a) Prato, M.; Maggini, M. Acc Chem Res 1998,31, 519–526; (b) Leea, K.-K.; Fujidab, K.; Tsut-suib, T.; Kim, M.-R. Solar Energy Mater Solar

Cells 2007, 91, 892–896; (c) Segura, J. L.; Giac-alone, F.; Gomez, R.; Martın, N.; Guldi, D. M.;Luo, C.; Swartz, A.; Riedel, I.; Chirvase, D.; Par-isi, J.; Dyakonov, V.; Sariciftci, N. S.; Padinger, F.Mater Sci Eng C 2005, 25, 835–842; (d) Negishi,N.; Takimiya, K.; Otsubo, T.; Harima, Y.; Aso. Y.Synth Met 2005, 152, 125–128; (e) Guldi, D. M.;Luo, C.; Swartz, A.; Gomez, R.; Segura, J. L.;Martın, N. J Phys Chem A 2004, 108, 455–467; (f)Nierengarten, J.-F. Solar Energy Mater SolarCells 2004, 83, 187–199; (g) Zhu, D.; Li, Y.; Wang,S.; Shi, Z.; Du, C.; Xiao, S.; Fang, H.; Zhou, Y.Synth Met 2003, 133/134, 679–683; (h) van Hal,P. A.; Knol, J.; Langeveld-Voss, B. M. W.;Meskers, S. C. J.; Hummelen, J. C.; Janssen, R.A. J. J Phys Chem A 2000, 104, 5974–5988; (i)Ouhib, F.; Khoukh, A.; Ledeuil, J.-B.; Martinez,H.; Desbrieres, J.; Dagron-Lartigau, C. Macromo-lecules 2008, 41, 9736–9743.

19. (a) Nunzi, J. M. C. R. Physique 2002, 3, 523; (b)Jaiswal, M.; Menon, R. Polym Int 2006, 55, 1371–1384; (c) Kirova, N. Polym Int 2008, 57, 678–688;(d) Moliton, A.; Hiorns, R. C. Polym Int 2004, 53,1397–1412.

20. (a) Audouin, F.; Nunige, S.; Nuffer, R.; Mathis, C.Synth Met 2001, 121, 1149–1150; (b) Wu, H.-X.;Cao, W.-M.; Cai, R.-F.; Song, Y.-L.; Zhao, L. JMater Sci 2007, 42, 6515–6523.

21. (a) Ravi, P.; Dai, S.; Hong, K. M.; Tam, K. C.; Gan,L. H. Polymer 2005, 46, 4714–4721; (b) Ravi, P.; Dai,S.; Tan, C. H.; Tam, K. C. Macromolecules 2005, 38,933–939; (c) Chochos, C. L.; Kallitsis, J. K.; Gregor-iou, V. G. J Phys ChemB 2005, 109, 8755–8760.

22. (a) Hiorns, R. C.; Martinez, H. Synth Met 2003,139, 463–469; (b) Sommerdijk, N. A. J. M.;Holder, S. J.; Hiorns, R. C.; Jones, R. G.; Nolte, R.J. M. Macromolecules 2000, 33, 8289–8294; (c)Milling, A. J.; Richards, R. W.; Hiorns, R. C.;Jones, R. G. Macromolecules 2000, 33, 2651–2661;(d) Hiorns, R. C.; Holder, S. J.; Schue, F.; Jones,R. G. Polym Int 2001, 50, 1016–1028.

23. Hiorns, R. C.; de Bettignies, R.; Leroy, J.; Bailly,S.; Firon, M.; Sentein, C.; Khoukh, A.; Preud’-homme, H.; Dagron-Lartigau, C. Adv Funct Mater2006, 16, 2263–2273.

24. Liu, J.; McCullough, R. D. Macromolecules 2002,35, 9882–9889.

25. (a) Yokoyama, A.; Miyakoshi, R.; Yokozawa, T. Mac-romolecules 2004, 37, 1169–1171; (b) Sheina, E. E.;Liu, J.; Iovu, M. C.; Darin, W.; Laird, D. W.; McCul-lough, R. D.Macromolecules 2004, 37, 3526–3528.

26. Hiorns, R. C.; Khoukh, A.; Gourdet, B.; Dagron-Lartigau, C. Polym Int 2006, 55, 608–620.

27. Mas, J.-M.; Metivier, P. Synth Commun 1992, 22,2187–2191.

28. Iranpoor, N.; Firouzabadi, H.; Aghapour, Gh.;Vaezzadeh, A. R. Tetrahedron 2002, 58, 8689–8693.

2316 HIORNS ET AL.


29. Pozdnyakov, O. F.; Pozdnyakov, A. O.; Schmaltz,B.; Mathis, C. Polymer 2006, 47, 1028–1035.

30. Lu, Q.; Schuster, D. I.; Wilson, S. R. J Org Chem1996, 61, 4764–4768.

31. Skiebe, A.; Hirsch, A. J. J Chem Soc Chem Com-mun 1993, 335–336.

32. (a) Stewart, J. J. P. J Mol Model 2007, 13, 1173–1213; (b) Stewart, J. J. P. MOPAC2007; StewartComputational Chemistry: Colorado Springs, CO,2007. Available at http://openmopac.net (accessedJanuary 2009).

33. Oliveira, M. A.; Duarte, H. A.; Pernaut, J.-M.; DeAlmeida,W. B. J PhysChemA2000, 104, 8256–8262.

34. Di Cesare, N.; Belletete, M.; Durocher, G.;Leclerc, M. Chem Phys Lett 1997, 275, 533–539.

35. Beeken, W. J. D. Chem Phys 2008, 349, 250–255.36. Raos, G.; Famulari, A.; Marcon, V. Chem Phys

Lett 2003, 379, 364–372.37. Lukevics, E.; Barbarella, G.; Arsenyan, P.; Belya-

kov, S.; Pudova, O. Chem Heterocycl Compd 2000,36, 630–662.

38. Samdal, S.; Samuelsen, E. J.; Volden, H. V. SynthMet 1993, 59, 259–265.

39. Sun, Y.; Drovetskaya, T.; Bolskar, R. D.; Bau, R.;Boyd, P. D. W.; Reed, C. A. J Org Chem 1997, 62,3642–3649.

40. Ouhib, F.; Dkhissi, A.; Iratcabal, P.; Hiorns, R. C.;Khoukh, A.; Desbrieres, J.; Pouchan, C.; Dagron-Lartigau, C. J Polym Sci Part A: Polym Chem2008, 46, 7606–7516.

41. Hutchison, G. Avogadro 0.8.0, released May 19,2008; GNU General Public License.

42. Kline, R. J.; McGehee, M. D.; Kadnikova, E. N.;Liu, J.; Frechet, J. M. J.; Toney, M. F. Macromole-cules 2005, 38, 3312–3319.

43. Matyjaszewski, K.; Patten, T. E.; Xia, J. J AmChem Soc 1997, 119, 674–680.

44. Mathis, C.; Schmaltz, B.; Brinkmann, M. C. R.Chimie 2006, 9, 1075–1084.

45. (a) Subramanian, R.; Kadish, K. M.; Vijayash-ree, M. N.; Gao, X.; Jones, M. T.; Miller, M.;Krause, K. L.; Suenobu, T.; Fukuzumi, S. J PhysChem 1996, 100, 16327–16335; (b) Kadish, K.M.; Gao, X.; Van Caemelbecke, E.; Suenobu, T.;Fukuzumi, S. J Phys Chem A 2000, 104, 3878–3883.



Documents

Alternatively linking fullerene and conjugated polymers