Novel bifluorene based conjugated systems: synthesisand properties

Roberto Grisorio,a Antonio Dell’Aquila,a Giuseppe Romanazzi,b Gian Paolo Suranna,a

Piero Mastrorilli,a Pynalisa Cosma,c Domenico Acierno,d Eugenio Amendola,e

Giuseppe Ciccarellaf and Cosimo Francesco Nobilea,*

aDepartment of Water Engineering and Chemistry (DIAC), Polytechnic of Bari, via Orabona, 4 I-70125 Bari, ItalybDepartment of Civil and Enviromental Engineering (DICA), Polytechnic of Bari, via Orabona, 4 I-70125 Bari, Italy

cDepartment of Chemistry, University of Bari, via Orabona 4, I-70125 Bari, ItalydDepartment of Materials and Production Engineering (DIMP), University of Naples Federico II, p.le Tecchio 80, I-80125 Naples, Italy

eInstitute of Composite and Biomedical Materials (IMCB), Italy’s National Research Council, p.le Tecchio 80, I-80125 Naples, ItalyfDipartimento di Ingegneria dell’Innovazione, University of Lecce, Via Monteroni, I-73100 Lecce, Italy

Received 29 July 2005; revised 29 September 2005; accepted 6 October 2005

Available online 2 November 2005

Abstract—A series of novel bifluorene based systems was synthesised by a convergent approach by means of a Suzuki cross-couplingbetween 7,7 0-bis-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-9,9,9 0,9 0-tetraoctyl-2,2 0-bifluorene and suitable aryl-bromides. All theoligomers have been characterized by 1H, 13C NMR, FT-IR, UV–vis, PL spectroscopy and mass analyses. In particular, it has beendemonstrated that the presence of strong electron donor (amines) or withdrawing (carboxylic esters) groups causes a bathochromic shift ofthe optical properties with respect to those of unsubstituted molecules. The effects of these functional groups on the HOMO–LUMO energylevels were investigated by cyclic voltammetry. Remarkably, the LUMO energy level of 7,7 0-bis-[5 0-carbodecaoxy-2,2 0-bithiophen-5-yl]-9,9,9 0,9 0-tetraoctyl-2,2 0-bifluorene (K3.07 eV) is strongly influenced by the presence of the ester functional group.q 2005 Elsevier Ltd. All rights reserved.

1. Introduction

During the last two decades, organic semiconductingmaterials have been the subject of great interest aspotentially active layers in opto-electronic devices, inparticular in light emitting diodes (LEDs).1 The easy controlof the optical properties and the solubility of the organicmaterials offers the possibility of lowering the manufactur-ing costs of the devices and improving, in comparison withthose based on inorganic substances, some technologicalaspects. Aiming at a close control both of the physicalproperties and of the purity of the materials, research effortshave been focused on the synthesis of monodisperseoligomers and well-defined molecules.2 In particular,oligofluorenes have recently attracted the scientific com-munity, because of their high solubility, good film-formingcapability, high luminescence efficiencies3 and liquid-crystal properties,4 which make them promising materials

0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.tet.2005.10.010

Keywords: Functionalised oligofluorenes; Suzuki coupling; Yamamotocoupling; Photoluminescence.* Corresponding author. Tel.: C39 080 5963605; fax: C39 080 5963611;

e-mail: nobile@poliba.it

for the fabrication of low-cost organic opto-electronicdevices.5 Very recently, circularly polarized light-emission6

and field effect modulation7 of oligofluorenes have alsobeen explored. However, the possibility of modulating theirfeatures by means of the introduction of specific functionalgroups has thus far received little attention.

In this paper, we propose the synthesis of novelp-conjugated systems based on a bifluorene core substitutedin the 7,7 0 positions with different moieties, aiming atinvestigating how the optical and electrochemical propertiesare affected by the substituents on the bifluorene core.

2. Results and discussion

2.1. Synthesis and characterization

The synthesis of the bis(diphenylamino)-quaterfluoreneBF1 is described in Scheme 1. The commercially available2,7-dibromofluorene (1) was easily converted into thecorresponding dioctyl derivative 2, which was used in thesynthesis of the boronic ester 3. A Ni(COD)2 promoted

Tetrahedron 62 (2006) 627–634

Scheme 1. Synthetic sequence for the obtainment of BF1.

Scheme 2. Synthetic sequences for the preparation of BF2–5.

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Figure 1. Absorption and emission spectra of BF1–3 (A) and BF4–5 (B) inchloroform solution (concentration: 1.0!10K5 M for absorption and1.0!10K6 M for fluorescence).

R. Grisorio et al. / Tetrahedron 62 (2006) 627–634 629

dimerization of 3 in toluene at 80 8C afforded the bifluorenederivative 4 in 87% yield.8 The protocol allowed us to avoidbifluorene bromination, which can lead to impurities whichare difficult to remove.

The bis(trimethylsilyl)-quaterfluorene 5 was synthesised in57% yield submitting 2-bromo-7-trimethylsilyl-9,9-dioctyl-fluorene and 4 to a Suzuki cross-coupling. The reaction wasperformed using Pd(PPh3)4 as catalyst, Na2CO3 as base andtetrabutylammonium bromide (TBAB) in toluene. Thepresence of a phase transfer agent in a Suzuki couplinginvolving 4 was necessary to warrant a complete conver-sion. Interconversion of the trimethylsilyl groups of 5 intoreactive iodides by ICl afforded the diiodo quaterfluorene 6in 71% yield. The subsequent Pd-catalyzed amino-dehalo-genation of 6 with diphenylamine gave BF1 in 42% yield.

Differently from BF1, the synthesis of BF2–3 was achievedby a direct cross-coupling between 4 and a suitablecarbazolyl bromide (Scheme 2). The bromo-carbazolederivative 7 was synthesized in 90% yield submitting3-bromocarbazole to alkylation with 1-bromooctane.Compound 8 was synthesized by selective bromination ofN-phenylcarbazole by N-bromosuccinimide (NBS). Theyields of the Suzuki cross-couplings between 4 and therelevant bromo-carbazole derivatives (7 or 8) were 21 and27%, respectively. Such yields are similar to those reportedin the literature for analogous reactions involving 3-bromo-carbazole derivatives.9

The synthesis of the bithiophene functionalised compoundsBF4–5 was then addressed. To this purpose, the bithiophenesystems 9 and 11 were synthesized, as reported in Scheme 2.5 0-Bromo-2,2 0-bithiophene-5-carbonyl chloride was readilyconverted into the corresponding ester 9 by reaction with1-decanol. The synthesis of 11 required metallation ofbithiophene with 1 equiv n-BuLi and reaction with1-bromododecane, yielding the alkyl derivative 10. Sub-sequent bromination with NBS gave 11 in 85% yield. Cross-coupling between 4 and the bithiophene derivatives 9 and 11afforded BF4 and BF5 in 68 and 50% yield, respectively.

BF1–5 are soluble in all common solvents and theirstructures were confirmed by 1H, 13C NMR and atmosphericpressure chemical ionization (APCI) mass analyses. More-over, their purity was confirmed by gel permeationchromatography (GPC) and found higher than 99% in allcases.

2.2. Optical properties

We gained insight into the physical properties of BF1–5 byinvestigating their absorption and emission behaviour.Figure 1A shows UV–vis and photoluminescence (PL)spectra of BF1–3, recorded in chloroform. The absorptioncurve of the quaterfluorene BF1 shows a maximum at384 nm, ascribed to the p–p* transition of the conjugatedbackbone, and a band corresponding to the n–p* transitionof the triarylamine moieties at 310 nm. The BF1 emission ischaracterized by two maxima at 438 and 455 nm, fullylocalized in the blue region. Both the absorption and theemission are markedly red-shifted with respect to quater-fluorene (labsZ361 nm, lemZ403, 427 nm).10 This aspect

could be due to the energy gap reduction caused by thepresence of the diphenylamino groups, which differentlyinfluence the HOMO and LUMO energy levels of thequaterfluorene backbone.

The same consideration can be drawn for BF2–3. Theirspectra, reported in Figure 1A, evidence an absorptionmaximum at 357 nm and emission peaks at 407 and 430 nm.The introduction of carbazol-3-yl moieties, which shouldhave lowered the p-conjugation degree of the system,11 didnot cause the expected blue-shift with respect to quater-fluorene. In fact, the absorption curves of BF2–3 had a smallband at 288 nm, which could be attributed to the p–p*transitions of isolated carbazole. Moreover, phenyl or alkylsubstitution at the nitrogen atom did not sensibly affect theiroptical properties. The quantum yields of BF1–3 withrespect to 9,10-diphenyl-anthracene (FZ0.83)12 have alsobeen evaluated (FZ0.77–0.81).

The optical properties of BF4–5 are reported in Figure 1B.The presence of the ester functionality on the bithiophenemoieties is responsible for the red-shift of the BF4absorption (lmaxZ408 nm) with respect to BF5 (lmaxZ397 nm) bearing alkyl substituents. This bathochromic shiftis the result of the extention of p-conjugation on thecarboxylic groups and of the different influence of theelectron withdrawing carboxylic esters on the HOMO andLUMO energy levels. The same effect is observed for thePL features: BF4 emits into the green region (lemZ467,485 nm) while the alkyl functionalized BF5 is characterizedby a blue fluorescence (lemZ441, 468 nm).

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Remarkably, the presence of bithiophene moieties did notaffect the fluorescence quantum yields of BF4 and BF5(0.74 and 0.73, respectively), which are uncommonly highfor thiophene-containing molecules.13

The optical properties of the oligomers were alsoinvestigated in the solid state. The absorption spectra ofBF1–3 reveal no substiantial changes with respect to thoserecorded in solution (Fig. 2A). On the contrary, the emissionfeatures of the compounds show only a change of therelative intensity of the vibronic peaks with maximalocalized at 455 nm for BF1 and at 434 nm for BF2–3.This behaviour could be ascribed to some conformationalrearrangements of these oligomers in the solid state, whichmight render the S1–0–S0–1 transition more probable. Theseresults allow us to hypothesise that the molecular design ofBF1–3 avoids the formation of intermolecular interactionsin the solid state, which could modify the blue-emissionproperties of these molecules.

Figure 2. Absorption and emission spectra of BF1–3 (A) and BF4–5 (B) inthe solid state (films obtained by spin coating from 5 mg/ml chloroformsolutions).

Table 1. Electrochemical and thermal properties of BF1–5

Entry E1/2 (V)a HOMO (eV) Energy gap (eV)b LUM

BF1 0.85 K5.55 2.92 KBF2 1.10 K5.60 3.06 KBF3 1.18 K5.69 3.06 KBF4 1.24 K5.74 2.67 KBF5 1.06 K5.56 2.78 K

a Half-wave oxidation potentials.b Estimated from the onset of absorption in the UV–vis spectrum.c Decomposition temperature at 5% weight loss, revealed by TGA.d Minor endothermic events detected during the first DSC scan.e Melting point as determined by DSC.

The absorption curves of BF4–5 in the solid state are shownin Figure 2B and are characterized by a slight bathochromicshift with respect to those recorded in solution. Theabsorption maxima of BF4–5 at 414 and 401 nm,respectively, are accompanied by a shoulder at longerwavelength, deriving from their tendency to intermolecularinteractions in the solid state. In fact, the emission propertiesof BF4–5 in the solid state are characterized by a consistentred-shift of their maxima (lmax at 500 and 479 nm,respectively) with respect to those in solution and by theloss of their vibronic structure.

2.3. Electrochemical properties

In order to investigate the redox properties of BF1–5 and theinfluence of the functional groups on their HOMO–LUMOenergy levels, cyclic voltammetry (CV) measurements wereperformed. Cyclic voltamograms were measured in CH2Cl2using n-Bu4NClO4 as supporting electrolyte (0.1 M) andAgC/Ag as the reference electrode. The results are collectedin Table 1. The evaluation of the HOMO level was carriedout by measuring the half-wave oxidation potential14 andthe onset of UV–vis absorption was used for the calculationof the energy gaps. All compounds showed reversibleoxidation peaks, suggesting that BF1–5 can be good andstable hole-carrying materials, while no reduction peak wasobserved.

In the case of nitrogen-containing compounds BF1–3, theHOMO levels appear to depend on the position of thenitrogen atom on the formal octa(p-phenylene) structure andon its substitution. The HOMO energy level of BF1 is atK5.55 eV, which is slightly higher than those of BF2 andBF3 (K5.60 and K5.69 eV, respectively). Interestingly,notwithstanding the fact that BF2 and BF3 have the sameenergy gap (3.06 eV), the HOMO energy value of BF3 isslightly lower than that of BF2. This result can be due to thehigher electron donating ability of the carbazole alkylgroups with respect to the aryl ones, which makes BF2 moreeasily oxidizable.

In the case of BF4 and BF5, substituents in the terminalpositions of the p-conjugated backbone have a markedeffect on the HOMO and LUMO energy levels. Thepresence in BF4 of an electron withdrawing functionalitylowers the HOMO energy (K5.74 eV) with respect to thatof BF5 (K5.56 eV). A more pronounced effect can beobserved by considering the LUMO energy level of BF4(K3.07 eV), which considerably differs from that of theother four compounds and which should better match the

O (eV) Td (8C)c Secondary melting (8C)d Tm (8C)e

2.63 411 89.0 39.92.54 407 — 121.42.63 391 — 51.83.07 372 57.6 72.92.78 415 67.4/74.0 50.4

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energy level of high work-function cathodes used in LEDs,such as aluminium.

2.4. Thermal properties

In order to investigate the thermal behaviour of oursystems, thermogravimetric analyses (TGA) and differ-ential scanning calorimetry (DSC) measurements werecarried out. TGA and DSC results are summarized inTable 1. The thermogravimetric analyses revealed thatBF1–5 are highly stable materials, which decomposeat temperatures higher than 370 8C. All compoundsexhibited a clear endothermic melting peak during thefirst heating scan. Other minor phase transitions weredetected by DSC (first scan). Polarised opticalmicroscopy (POM) observation for BF1, BF4 and BF5confirmed that these minor transitions consisted in themelting of small mass fractions of the sample, and couldnot be attributed to glass transition events. During thecooling, no recrystallization was observed for any of theoligomers, consequently, second DSC traces did notshow any transition. Presumably, the oligomers aresupercooled liquids or metastable glasses with anegligible glass transition.

3. Conclusions

The properties of novel bifluorene-based p-conjugatedsystems prepared by a simple and practical convergentapproach were investigated. The presence of thebifluorene core offers the possibility of spanning theblue-green region and modulating the HOMO–LUMOenergy levels of the corresponding materials by choosingsuitable aryl end-groups and functional substituents.Remarkably, the presence of n-octyl chains and themolecular design of BF1–3 inhibits the intermolecularinteractions in the solid state, preserving the blue-emission of these systems.

4. Experimental

4.1. General remarks

All manipulations were carried out under an inert nitrogenatmosphere using Schlenk techniques. All solvents werecarefully dried and freshly distilled according to commonlaboratory techniques. All reactants were purchased byAldrich, Acros or Fluka and used without furtherpurification. 1H and 13C{1H} NMR spectra were recordedat 295 K on a Bruker Avance 400 MHz. UV–vis spectrawere recorded on a Kontron Uvikon 942 instrument;fluorescence spectra were obtained on a Varian CaryEclipse spectrofluorimeter; FT-IR spectra were recordedon a Bruker Vector 22 spectrometer. GC–MS data (EI,70 eV) were acquired on a HP 6890 instrument equippedwith a HP-5MS 5% phenyl methyl siloxane (30.0 m!250 mm!0.25 mm) coupled with a HP 5973 mass spectro-meter. Mass analyses were performed by direct injection onan Agilent 1100 LC-MS SL series instrument using an APCIinterface. GPC analyses were carried out on a Agilent Series1100 instrument equipped with a Pl-gel 10 mm. THF

solutions for GPC analysis were eluted at 25 8C at a flowrate of 1 ml/min and analyzed using a multiple wavedetector. Cyclic voltammetry measurements were carriedout under inert nitrogen atmosphere with an Autolabpotentiostat PGSTAT 10 using a three-electrode cell (aglassy carbon as working electrode, an Ag wire as referenceelectrode, and a platinum counter electrode). The rate scanwas 200 mV/s and the supporting electrolyte was a n-Bu4NClO4 (0.1 M) solution in CH2Cl2. Thermogravimetricanalyses (TGA) were carried out with a thermobalance TAInstruments 2590; differential scanning calorimetry (DSC)was measured on a TA Instruments 2920 calorimeter. Boththermal analyses were carried out under a nitrogen flow andwith a heating scan of 10 8C/min. C,H,N,S elementalanalyses were carried out with a Eurovector CHNS-OElemental Analyser. The synthesis of 2,7-dibromo-9,9-di(octyl)-fluorene15 (2), 7-bromo-9,9-di(octyl)-fluoren-2-yl-4,4,5,5-tetramethyl-[1,3,2]-dioxaborolane16 (3), 2-bromo-7-trimethylsilyl-9, 9-di(octyl)-fluorene,15 3-bromocar-bazole,17 N-phenylcarbazole,18 and 5 0-bromo-2,20-bithio-phene-5-carbonyl chloride19 were carried out by followingor slightly adapting literature procedures.

4.2. Synthetic procedures

4.2.1. 7,7 0-Bis-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-9,9,9 0,9 0-tetraoctyl-2,2 0-bifluorene (4). A mixture of3 (4.40 g, 7.40 mmol), Ni(COD)2 (2.44 g, 8.88 mmol),bipyridine (1.39 g, 8.88 mmol), COD (0.80 g, 7.40 mmol)and toluene (40 ml) was stirred at 80 8C overnight. Aftercooling down to room temperature, the solution was filteredon a Celite plug with petroleum ether 40–60 8C as eluent.After solvent evaporation, the residue was purified by ashort silica gel plug using CH2Cl2 as eluent, to give 4 as paleyellow solid (yield: 87%). 1H NMR (400 MHz, CDCl3):d 7.89–7.44 (m, 8H), 7.70–7.62 (m, 4H), 2.12–2.04 (m, 8H),1.43 (s, 24H), 1.25–1.02 (m, 40H), 0.83 (t, JZ6.7 Hz, 6H),0.75–0.66 (m, 8H); 13C{1H} NMR (101 MHz, CDCl3):d 152.1, 150.2, 143.8, 141.0, 140.2, 133.8, 128.9, 128.7,126.1, 121.5, 120.3, 119.0, 83.9, 55.2, 40.2, 31.8, 30.0, 29.2,28.0, 24.9, 823.7, 22.6, 14.1; MS (APCI): m/z calculated:1030.8, found: 1031.7 (MCH)C. Anal. Calcd forC70H104B2O4: C, 81.53; H, 10.17. Found: C, 81.60; H,10.14.

4.2.2. 7,7 000-Bis-trimethylsilyl-9,9,9 0,9 0,9 00,9 00,9 000,9 000-octaoctyl-2,2 0;7 0,2 00;7 00,2 000-quaterfluorene (5). A mixtureof 4 (0.82 g, 0.80 mmol), 5 (1.04 g, 1.92 mmol),TBAB (0.15 g, 0.48 mmol), Pd(PPh3)4 (0.046 g, 4.00!10K2 mmol), toluene (6.5 ml), and a 2.0 M Na2CO3

aqueous solution (2.4 ml) was refluxed overnight. Afterthe solution was cooled down to room temperature, diethylether (10 ml) was added to the reaction mixture. The organiclayer was separated, washed with water and dried overNa2SO4. After solvent evaporation, the residue was purifiedby flash chromatography (silica gel, petroleum ether 40–60 8C/CH2Cl2Z9:1) giving 5 as pale yellow viscous solid(yield: 57%). 1H NMR (400 MHz, CDCl3): d 7.89–7.80 (m,6H), 7.77–7.64 (m, 14H), 7.57–7.50 (m, 4H), 2.20–2.01 (m,16H), 1.30–1.06 (m, 80H), 0.92–0.69 (m, 40H), 0.36(s, 18H); 13C{1H} NMR (101 MHz, CDCl3): d 151.7,150.2, 141.4, 140.5, 140.0, 139.0, 131.8, 127.6, 126.0,121.5, 120.0, 118.9, 55.3, 55.1, 40.4, 40.1, 31.8, 30.0, 29.9,

R. Grisorio et al. / Tetrahedron 62 (2006) 627–634632

29.2, 23.9, 23.8, 22.6, 14.1, K0.8; MS (APCI): m/zcalculated: 1699.3, found: 1700.2 (MCH)C. Anal. Calcdfor C122H178Si2: C, 86,15; H, 10,55. Found: C, 88.17; H,10.54.

4.2.3. 7,7 000-Diiodo-9,9,9 0,9 0,9 00,9 00,9 000,9 000-octaoctyl-2,2 0;7 0,2 00;7 00,2 000-quaterfluorene (6). To a solution of 5(0.73 g, 0.43 mmol) in CH2Cl2 (3 ml), an ICl solution(1.0 M in CH2Cl2, 0.92 ml, 0.92 mmol) was slowly added at0 8C over 30 min. The mixture was then stirred for 1 h atroom temperature. The reaction was quenched by adding anaqueous Na2S2O3 solution (10% w/w), until discolorationwas observed. After extraction with CH2Cl2 and solventremoval, the crude product was purified by flash chromato-graphy (silica gel, petroleum ether 40–60 8C/CH2Cl2Z9:1)giving 6 as pale yellow viscous solid (yield: 71%). 1H NMR(400 MHz, CDCl3): d 7.89–7.75 (m, 6H), 7.74–7.60(m, 16H), 7.55–7.48 (m, 2H), 2.19–1.94 (m, 16H),1.29–1.06 (m, 80H), 0.91–0.67 (m, 40H); 13C{1H} NMR(101 MHz, CDCl3): d 153.4, 151.8, 150.9, 141.5, 140.1,139.2, 135.9, 132.1, 126.3, 121.3, 119.8, 92.0, 55.5, 55.3,40.4, 40.3, 31.8, 30.0, 29.2, 23.9, 23.8, 22.6, 14.1; MS(APCI): m/z calculated: 1807.1, found: 1808.0 (MCH)C.Anal. Calcd for C116H160I2: C, 77.05; H, 8.92. Found:C, 77.01; H, 8.94.

4.2.4. 7,7 000-Bis-diphenylamino-9,9,9 0,9 0,9 00,9 00,9 000,9 000-octaoctyl-2,2 0;7 0,2 00;7 00,2 000-quaterfluorene (BF1). A mix-ture of 6 (0.53 g, 0.29 mmol), diphenylamine (0.15 g,0.87 mmol), Pd(OAc)2 (52.1 mg, 2.30!10K2 mmol), tri-(tert-butyl)phosphane (9,4 mg, 4.64!10K2 mmol), sodiumtert-butoxide (0.25 g, 2.61 mmol) and toluene (4 ml) waskept under vigorous stirring at 80 8C overnight. Aftercooling the solution to room temperature, CH2Cl2 wasadded. The organic layer was separated, washed with waterand dried over Na2SO4. After solvent evaporation, theresidue was purified by flash chromatography (silica gel,petroleum ether 40–60 8C/CH2Cl2Z10:1) to afford BF1 aspale yellow solid (yield: 42%). 1H NMR (400 MHz,CDCl3): d 7.88–7.81 (m, 4H), 7.75–7.59 (m, 16H),7.32–7.24 (m, 8H), 7.20–7.14 (m, 10H), 7.10–7.00(m, 6H), 2.19–1.85 (m, 16H), 1.39–1.05 (m, 80H),0.93–0.72 (m, 40H); 13C{1H} NMR (101 MHz, CDCl3):d 152.4, 151.8, 151.4, 148.0, 174.1, 140.5, 140.1, 140.0,139.9, 139.7, 136.0, 129.2, 126.1, 123.8, 123.6, 122.5,121.5, 121.4, 121.2, 120.4, 119.9, 119.5, 119.3, 55.3, 55.2,40.4, 40.3, 31.8, 30.0, 29.2, 23.9, 22.6, 14.1; IR (KBr)n [cmK1] 3034, 2924, 2852, 1587, 1492, 1457, 1274, 812,750, 695; MS (APCI): m/z calculated: 1889.4, found: 1890.3(MCH)C. Anal. Calcd for C140H180N2: C, 88.92; H, 9.59;N, 1.48. Found: C, 88.90; H, 9.58; N, 1.51.

4.2.5. 3-Bromo-N-octyl-carbazole (7). A mixture of3-bromocarbazole (1.30 g, 5.20 mmol) and 1-bromooctane(1.06 g, 5.50 mmol) in DMSO (10 ml) and a NaOH aqueoussolution (50% w/w, 5 ml) was stirred at room temperatureovernight. Then, 20 ml of water was added andthe resulting mixture extracted with diethyl ether. Aftersolvent evaporation, the crude was purified by flashchromatography (silica gel, petroleum ether 40–60 8C)giving 7 as colorless oil (yield: 90%). 1H NMR(400 MHz, CDCl3): d 8.24 (d, JZ1.6 Hz, 1H) 8.08 (d, JZ7.6 Hz, 1H), 7.59–7.40 (m, 3H), 7.34–7.24 (m, 2H), 4.28

(t, JZ7.3 Hz, 2H), 1.87 (pseudoquint, JZ7.3 Hz, 2H),1.44–1.22 (m, 10H), 0.91 (t, JZ6.7 Hz, 3H); 13C{1H} NMR(101 MHz, CDCl3): d 140.7, 139.1, 128.2, 126.3, 124.5,123.0, 121.8, 120.5, 119.2, 111.5, 110.1, 109.0, 43.2, 31.8,29.4, 29.2, 28.9, 27.3, 22.6, 14.1; MS (EI, 70 eV): m/z 357(MC).

4.2.6. 3-Bromo-N-phenylcarbazole (8). To a mixture ofN-phenylcarbazole (1.00 g, 4.10 mmol) in DMF (5 ml), asolution of NBS (0.73 g, 4.10 mmol in 5 ml DMF) wasadded dropwise at 0 8C. The mixture was then stirredovernight at room temperature. The solution was dilutedwith water (20 ml) and extracted with diethyl ether. Aftersolvent removal, the crude product was purified by flashchromatography (SiO2, petroleum ether 40–60 8C) to afford8 as colorless oil (yield: 42%). 1H NMR (400 MHz, CDCl3):d 8.30–8.22 (m, 1H), 8.20–8.10 (m, 1H), 7.97–7.39 (m, 8H),7.36–7.28 (m, 2H); 13C{1H} NMR (101 MHz, CDCl3):d 141.2, 139.6, 137.2, 130.0, 128.5, 127.8, 127.1, 126.6,125.9, 125.1, 123.0, 120.4, 120.3, 119.3, 112.9, 112.6,111.3, 110.0, 109.7; MS (EI, 70 eV): m/z 321 (MC).

4.2.7. 7,7 0-Bis-[N-octyl-carbazol-3-yl]-9,9,9 0,9 0-tetraoc-tyl-2,2 0-bifluorene (BF2). A mixture of 4 (0.52 g,0.50 mmol), 7 (0.42 g, 1.20 mmol), Pd(PPh3)4 (69.0 mg,0.06 mmol), TBAB (96.7 mg, 0.30 mmol), toluene (4 ml)and a 2.0 M Na2CO3 solution (1.5 ml) was refluxedovernight. After cooling down to room temperature, diethylether was added. The organic layer was separated, washedwith brine and dried over Na2SO4. After solvent evapora-tion, the crude product was purified by flash chromatog-raphy (silica gel, petroleum ether 40–60 8C/CH2Cl2Z7:1)to give BF2 as pale yellow solid (yield: 21%). 1H NMR(400 MHz, CDCl3): d 8.44 (s, 2H), 8.25 (d, JZ8.5 Hz, 2H),7.91–7.82 (m, 6H), 7.80–7.68 (m, 8H), 7.58–7.45 (m, 6H),7.35–7.27 (m, 2H), 4.39 (t, JZ7.3 Hz, 4H), 2.22–2.11(m, 8H), 1.95 (pseudoquint, JZ7.3 Hz, 4H), 1.51–1.10(m, 60H), 0.96–0.80 (m, 26H); 13C{1H} NMR (101 MHz,CDCl3): d 151.7, 141.1, 141.0, 140.3, 140.2, 139.9, 139.3,132.8, 126.1, 125.7, 125.3, 123.4, 123.0, 121.7, 121.4,120.5, 120.0, 119.8, 118.9, 108.9, 55.3, 43.2, 40.5, 31.8,30.1, 29.4, 29.3, 29.1, 27.4, 23.9, 22.6, 14.1; IR (KBr)n [cmK1] 3055, 2925, 2851, 1599, 1348, 1225, 806, 744,727; MS (APCI): m/z calculated: 1333.0, found: 1333.9(MCH)C. Anal. Calcd for C98H128N2: C, 88.23; H, 9.67;N, 2.10. Found: C, 88.20; H, 9.68; N, 2.12.

4.2.8. 7,7 0-Bis-[N-phenyl-carbazol-3-yl]-9,9,9 0,9 0-tetra-octyl-2,2 0-bifluorene (BF3). A mixture of 4 (0.52 g,0.50 mmol), 8 (0.39 g, 1.20 mmol), Pd(PPh3)4 (69.0 mg,0.06 mmol), TBAB (96.7 mg, 0.30 mmol), toluene (4 ml)and a 2.0 M Na2CO3 solution (1.5 ml) was refluxedovernight. After cooling to room temperature, CH2Cl2 wasadded. The organic layer was separated, washed with waterand dried over Na2SO4. After solvent removal, the residuewas purified by flash chromatography (silica gel, petroleumether 40–60 8C/CH2Cl2Z9:1) to give BF3 as pale yellowsolid (yield: 27%). 1H NMR (400 MHz, CDCl3): d 8.48(s, 2H), 8.30 (d, JZ8.5 Hz, 2H), 7.90–7.85 (m, 4H),7.82–7.64 (m, 20H), 7.57–7.45 (m, 8H), 2.21–2.12(m, 40H), 0.94–0.80 (m, 20H); 13C{1H} NMR (101 MHz,CDCl3): d 151.8, 151.7, 141.4, 140.9, 140.4, 140.3, 140.2,139.5, 137.7, 134.0, 130.0, 127.5, 127.1, 126.2, 126.1, 126.1

R. Grisorio et al. / Tetrahedron 62 (2006) 627–634 633

(two overlapped signals), 125.7, 124.0, 123.5, 124.8, 121.5,120.5, 120.1, 120.0, 119.8, 118.8, 110.1, 110.0, 55.3, 40.5,31.8, 30.1, 29.3, 29.2, 24.0, 22.6, 14.1; IR (KBr) n [cmK1]3043, 2923, 2850, 1597, 1501, 1453, 1230, 806, 744, 696;MS (APCI): m/z calculated: 1260.8, found 1261.7 (MCH)C. Anal. Calcd for C94H104N2: C, 89.47; H, 8.31; N, 2.22.Found: C, 89.50; H, 8.30; N, 2.20.

4.2.9. 5-Bromo-5 0-carbodecaoxy-2,2 0-bithiophene (9). Asolution containing 5 0-bromo-2,2 0-bithiophene-5-carbonylchloride (1.01 g, 3.29 mmol), decan-1-ol (0.52 g,3.29 mmol) and pyridine (0.30 g, 3.79 mmol) in toluene(17 ml) was refluxed overnight. After cooling to roomtemperature, the solution was poured into water forextraction with diethyl ether. The organic extracts weredried over Na2SO4. After solvent evaporation, the residuewas purified by flash chromatography (silica gel, CH2Cl2)affording 9 as pale yellow solid (yield: 98%). 1H NMR(400 MHz, CDCl3): d 7.67 (d, JZ3.9 Hz, 1H), 7.07 (d, JZ3.9 Hz, 1H), 7.03–6.99 (m, 2H), 4.28 (t, JZ6.4 Hz, 2H),1.74 (pseudoquint, JZ6.4 Hz, 2H), 1.45–1.27 (m, 14H),0.88 (t, JZ7.0 Hz, 3H); 13C{1H} NMR (101 MHz, CDCl3):d 162.0, 142.7, 137.8, 134.0, 132.3, 130.9, 125.2, 124.1,112.9, 65.4, 31.9, 29.5, 29.5 (overlapped signals), 29.3,29.2, 28.7, 25.9, 22.7, 14.1; MS (EI, 70 eV): m/z 430 (MC).Anal. Calcd for C19H25BrO2S2: C, 53.14; H, 5.87; S, 14.93.Found: C, 53.15; H, 5.88; S, 14.91.

4.2.10. 5-Dodecyl-2,2 0-bithiophene (10). To a solution of2,2 0 bithiophene (2.99 g, 18.02 mmol) in THF (75 ml) a1.6 M solution of n-BuLi in hexane (11.2 ml, 18.02 mmol)was added at K70 8C. After 30 min, the mixture waswarmed to K15 8C and 1-bromododecane (4.50 g,18.02 mmol) was added. The mixture was warmed toroom temperature and stirred for 2 h. Then a saturatedNH4Cl solution was added for extraction with diethyl ether.After solvent removal, the residue was purified bychromatography (RP 18 silica gel, methanol/hexaneZ1:2)yielding 10 as pale yellow solid (yield: 83%). 1H NMR(400 MHz, CDCl3): d 7.19 (m, 2H), 7.04 (m, 2H), 6.73 (m,1H), 2.78 (t, JZ7.6 Hz, 2H), 1.67 (m, 2H), 1.45–1.20 (m,18H), 0.88 (t, JZ6.9 Hz, 3H); 13C{1H} NMR (101 MHz,CDCl3): d 146.0, 139.5, 133.7, 130.5, 124.8, 123.8, 123.0,110.1, 31.9, 31.6, 30.1, 29.7, 29.5, 29.4, 29.1, 22.7, 14.1;MS (EI, 70 eV): m/z 334 (MC). Anal. Calcd for C20H30S2:C, 71.79; H, 9.04; S, 19.17. Found: C, 71.74; H, 9.04; S,19.22.

4.2.11. 5-Bromo-5 0-dodecyl-2,2 0-bithiophene (11). To asolution of 10 (4.84 g, 14.45 mmol) in CH2Cl2 (75 ml), NBS(2.57 g, 14.45 mmol) was added stepwise at 0 8C. Thereaction mixture was stirred for 4 h at room temperature andthen poured into a flask containing ice for extraction withdichloromethane. The organic extracts were washed withwater and dried over Na2SO4. Upon solvent removal, theresidue was recrystallized from ethanol to afford 11 as paleyellow solid (yield: 85%). 1H NMR (400 MHz, CDCl3):d 6.93 (d, JZ3.7 Hz, 1H), 6.91 (d, JZ3.0 Hz, 1H), 6.82(d, JZ3.7 Hz, 1H), 6.66 (d, JZ3.0 Hz, 1H), 2.77(t, JZ7.6 Hz, 2H), 1.67 (m, 2H), 1.20–1.45 (m, 18H),0.88 (t, JZ6.9 Hz, 3H); 13C{1H} NMR (101 MHz, CDCl3):d 146.0, 139.5, 133.7, 130.5, 124.8, 123.8, 123.0, 110.1,31.9, 31.6, 30.1, 29.7, 29.5, 29.4, 29.1, 22.7, 14.1; MS (EI,

70 eV): m/z 412 (MC). Anal. Calcd for C20H29BrS2: C,58.10; H, 7.07; S, 15.51. Found: C, 58.14; H, 7.08; S, 15.50.

4.2.12. 7,7 0-Bis-[5-carbodecaoxy-2,2 0-bithiophen-5 0-yl]-9,9,9 0,9 0-tetraoctyl-2,2 0-bifluorene (BF4). A mixture of 4(0.52 g, 0.50 mmol), 9 (0.52 g, 1.20 mmol), Pd(PPh3)4

(69.0 mg, 0.06 mmol), TBAB (96.7 mg, 0.30 mmol), tolu-ene (4 ml) and a 2.0 M Na2CO3 solution (1.5 ml) was stirredat reflux overnight. After cooling down to room tempera-ture, diethyl ether was added. The organic layer wasseparated and dried over Na2SO4. After solvent evaporation,the crude product was purified by flash chromatography(silica gel, petroleum ether 40–60 8C/CH2Cl2Z2:1) toafford BF4 as pale yellow solid (yield: 68%). 1H NMR(400 MHz, CDCl3): d 7.84–7.60 (m, 14H), 7.37 (d, JZ3.7 Hz, 2H), 7.33 (d, JZ3.7 Hz, 2H), 7.22 (d, JZ3.7 Hz,2H), 4.33 (t, JZ6.1 Hz, 4H), 2.16–2.06 (m, 8H), 1.79(pseudoquint, JZ6.1 Hz, 2H), 1.52–1.02 (m, 68H), 0.92(t, JZ6.7 Hz, 6H), 0.84–0.76 (m, 20H); 13C{1H} NMR(101 MHz, CDCl3): d 162.2, 152.0, 151.7, 145.8, 144.1,141.0, 140.7, 139.7, 135.3, 134.2, 132.4, 131.6, 126.3,126.2, 124.8, 123.8, 123.6, 121.4, 120.3, 120.0, 65.4, 55.4,40.4, 31.9, 31.8, 30.0, 29.6, 29.2, 28.7, 26.0, 23.8, 22.6,14.1; IR (KBr) n [cmK1] 2954, 2923, 2851, 1692 (C]O),1452, 1281, 1099, 794, 747; MS (APCI): m/z calculated:1474.9, found: 1475.8 (MCH)C. Anal. Calcd forC96H130O4S4: C, 78.10; H, 8.88; S, 8.69. Found: C, 78.14;H, 8.90; S, 8.70.

4.2.13. 7,7 0-Bis-[5 0-dodecyl-2,2 0-bithiophen-5-yl]-9,9,9 0,9 0-tetraoctyl-2,2 0-bifluorene (BF5). A mixture of 4(0.52 g, 0.50 mmol), 11 (0.50 g, 1.20 mmol), Pd(PPh3)4

(69.0 mg, 0.06 mmol), TBAB (96.7 mg, 0.30 mmol),toluene (4 ml) and a 2.0 M Na2CO3 solution (1.5 ml) wasrefluxed overnight. After cooling down to room tempera-ture, diethyl ether was added. The organic layer wasseparated and dried over Na2SO4. After solvent evaporation,the crude product was purified by flash chromatography(silica gel, petroleum ether 40–60 8C/CH2Cl2Z8:1) to giveBF5 as pale yellow solid (yield: 50%). 1H NMR (400 MHz,CDCl3): d 7.83–7.58 (m, 12H), 7.32 (d, JZ3.6 Hz, 2H),7.13 (d, JZ3.6 Hz, 2H), 7.06 (d, JZ3.6 Hz, 2H), 6.74(d, JZ3.6 Hz, 2H), 2.84 (t, JZ7.4 Hz, 4H), 2.14–2.04(m, 8H), 1.73 (pseudoquint, JZ7.4 Hz, 4H), 1.47–1.05(m, 76H), 0.92 (t, JZ6.1 Hz, 6H), 0.86–0.73 (m, 20H);13C{1H} NMR (101 MHz, CDCl3): d 151.9, 151.7, 145.5,143.2, 140.5, 140.4, 139.8, 137.0, 134.9, 132.9, 126.2,124.8, 124.5, 123.9, 123.4, 123.2, 121.4, 120.1, 119.9,119.8, 55.3, 40.4, 31.9, 31.8, 31.6, 30.2, 30.0, 29.7, 29.6,29.4, 29.2, 29.1, 23.8, 22.7, 22.6, 14.2, 14.1; IR (KBr)n [cmK1] 2953, 2924, 2850, 1460, 1375, 876, 814, 791; MS(APCI): m/z calculated: 1443.0, found: 1443.9 (MCH)C.Anal. Calcd for C98H138S4: C, 81.49; H, 9.63; S, 8.88.Found: C, 81.47; H, 9.69; S, 8.85.

Acknowledgements

This work was financially supported by italian MIUR (FIRBproject MICROPOLYS).

R. Grisorio et al. / Tetrahedron 62 (2006) 627–634634

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