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`Macromolecules
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`

`7686
`
`Macromolecules 1997, 30, 7686~7691
`
`
`This material may be protected by Copyright law (Title 17 U.S. Code)
`
`
`New Well-Defined Poly(2,7-fluorene) Derivatives:
`
`Photoluminescence and Base Doping
`
`Maxime Ranger, Dany Rondeau, and Mario Leclerc*
`
`Département de Chimie, Université de Montreal,
`GP. 6128, Succ. Centre-Ville, Montreal, Québec, Canada H3C 3J7
`
`V Received June 24, 1997; Revised Manuscript Received September 29, 19979
`
`ABSTRACT: Well-defined poly(2,7-fluorene) derivatives have been prepared through palladium-catalyzed
`couplings between various 9,9-disubstituted or 9-monosubstituted 2,7-dibromofluorenes and 2,7-bis(4,4,5,5-
`tetramethyl-1,3,2-dioxaborolan-2-yl)—9,9-dioctylfluorene. Using this versatile synthetic method, process-
`able polyfluorenes have been obtained in good yields. In solution, all these neutral yellow polymers exhibit
`blue emission (maximum of emission around 410 nm) with high quantum yields (up to 0.87). Moreover,
`novel acidic polyfluorene derivatives have been synthesized (i.e., poly[2,7’-(alkyl 9,9-dioctyl-7,2’-bifluorene-
`9’-carboxylate)]s) which show, upon base doping, electrical conductivities of 10—6—10’5 S/cm. This new
`doping method for conjugated polymers could open the way to the preparation of air-stable electron-
`injecting electrodes. Both photophysical and electrical properties of these polymers are quite promising
`for the fabrication of efficient blue-light-emitting devices.
`
`Introduction
`
`Great interest has been devoted to conjugated poly-
`mers due to their unusual optical and electrical proper-
`ties. Recently, these polymers have been used in the
`fabrication of light—emitting devices (LEDs and LECs).1“5
`It is believed that the next generation of flat panel
`displays could be fabricated from these polymeric light-
`emitting devices. Along these lines, there is a great
`interest
`to produce efficient and stable blue-light-
`emitting materials to get access to the three primary
`colors. In this regard, it has been shown that polyesters
`derived from bithiophenes or terthiophenes could give
`the desired color emission but their low fluorescence
`
`quantum yields put some limitations on their use in
`optical devices.6 On the other hand, the utilization of
`large-band-gap, conjugated polymer materials can also
`give blue-light—emitting materials. Interesting results
`have been obtained with poly(paraphenylene)s,7 but
`some of these materials show processing problems due
`to their limited solubility in common organic solvents.
`Yoshino et al. reported another class of blue-emitting
`materials based on poly(9-alkylfluorene)s and poly(9,9-
`dialkylfluorene)s.8 These polymers have been obtained
`from a simple chemical oxidation of the monomers using
`F6013, a procedure similar to that developed for the
`preparation of poly(3-alkylthiophene)s.9 However, this
`nonspecific oxidation reaction produces some partially
`cross-linked materials, and the soluble fraction of these
`polyfluorenes shows some evidence of irregular cou-
`plings along the backbone.10 As shown with the prepa-
`ration of well-defined polyacetylene11 and polythiophene
`derivatives,12 a more regular structure can involve a
`significant improvement in the performance of the
`materials and, therefore, it could be expected that the
`preparation of well-defined poly(2,7-fluorene) deriva-
`tives could yield better electrical and optical properties.
`In agreement with this assumption, efficient photolu-
`minescence and electroluminescence have been recently
`reported, by Pei and Yang,13 from a well-defined soluble
`polyfluorene derivative obtained from a nickel-catalyzed
`reductive polymerization of 2,7-dibromo-9,9-bis(3,6—di—
`oxaheptyl)fluorene.
`
`* To whom correspondence should béfladdressed.
`9 Abstract published in Advance ACS Abstracts, November 15,
`1997.
`.
`-
`
`On the other hand, it could be useful to get access to
`. another polymerization method, in particular, if one is
`interested in the preparation of polyfluorenes bearing
`reactive side chains toward a reducing agent (e.g., ester
`groups). Indeed, 9-monosubstituted polyfluorenes bear-
`ing strong electron—withdrawing groups such as ester
`or cyano moieties could become an important class of
`conjugated polymers since they should lead to acidic
`conjugated polymers”,15 It is then believed that the
`preparation of these new polyfluorene derivatives could
`give not only highly luminescent materials in the
`neutral state but also base-dopable conducting poly-
`mers. This novel base-doping approach is the counter-
`part of the acidic doping reported for polyanilines,’ where
`a simple protonation of the imine moieties (without the
`use of any external redox process) leads to an insulating-
`to-conducting transition.16 For this purpose, we have
`recently reported the preparation of a novel acidic
`polyfluorene derivative15 from palladium-catalyzed Su-
`zuki couplings17 between ethyl 2,7-dibromofluorene-9-
`carboxylate and 2,7-bis(4,4,5,5-tetramethyl—1,3,2-diox-
`aborolan-2-yl)-9,9-dioctylfluorene.15 Using this versatile
`synthetic method, we report here the synthesis and
`characterization of various well—defined poly(2,7-fluo-
`rene) derivatives, namely, poly[(1,4—phenylene)—2,7-(9,9-
`dioctylfluorene)] (P1), poly[2,7'-(9,9-dioctyl-7,2’-bifluo—
`rene)] (P2), poly[2,7-(9,9-dioctylfluorene)] (P3), poly[2,7’-
`(diethyl 9,9-dioctyl-7,2'-bifluorene—9’,9’-dicarboxylate)]
`(P4), poly[2,7’-(ethyl 9,9-dioctyl-7,2’-bifluorene-9’-car-
`boxylate)] (P5), and poly[2,7'-[(methoxyethoxy)ethyl 9,9-
`dioctyl-7,2’-bifluorene-9’-carboxylate]] (P6) (see Chart
`1). As mentioned above, the luminescent and electrical
`(through base-doping) properties of these conjugated
`polymers could be very useful for the development of
`light-emitting devices.
`
`Experimental Part
`Instrumentation. 1H and 13C NMR spectra were recorded
`on Bruker AMX300 and AMX400 spectrometers in deuterated
`chloroform solutions at 298 K. Number-average (Mn) and
`weight-average (MW) molecular weights were determined by
`size-exclusion chromatography (SEC) with a HPLC Waters 510
`pump using a Waters 410 differential refractometer. The
`calibration was made with a series of monodispersed polysty-
`rene standards in THF (HPLC grade, Aldrich) at 308 K.
`Fluorescence measurements were carried out with a SpeX
`Fluorolog 1681 spectrometer.
`In all cases, the polymer con-
`
`SOOZ4-9297(97)00920-0 CCC: $14.003 © 1997 American Chemical Society
`
`
`
`3
`
`

`

`Macromolecules, Vol. 30, N0. 25, 1997
`
`New Well—Defined Poly(2,7~fluorene) Derivatives
`
`7687
`
`Chart 1
`
`
`
`“11 C8
`
`CBHH
`
`centration was about 10’6 M (on the basis of one repeat unit),
`giving absorbances always less than 0.06 to avoid any inner
`filter effect. The quantum yields of fluorescence were deter-
`mined in argon-saturated solutions at 298 K in chloroform
`against 9,10-diphenylanthracene (Aldrich) in cyclohexane (45;:
`= 0.90) as the standard.18 All corrected fluorescence excitation
`spectra were found to be equivalent to their respective absorp-
`tion spectra. UV~visible absorption spectra were recorded on
`a Hewlett-Packard diode-array spectrophotometer (Model
`8452A).
`Materials. Fluorene and 1,4-dibromobenzene were ob-
`tained from Aldrich.
`Synthesis. 9,9-Diocty1fluorene (1).9 To a solution of 8.48
`g (51.1 mmol) of fluorene (Aldrich) in THF (120 mL) at —78
`0C was added dropwise, 42.92 mL (107.31 mmol) of n,-
`butyllithium (2.5 M in hexane; Aldrich). The mixture was
`stirred at —78 °C for 45 min, and 22.70 g (117.53 mmol) of
`octyl bromide (Aldrich) in THF (25 mL) was added dropwise
`to the mixture. The solution was allowed to warm to room
`temperature and was stirred for 3 h. The mixture was poured
`into water and extracted with ether. The organic extracts were
`washed with brine and dried over magnesium sulfate. The
`solvent was removed under reduced pressure. The excess of
`octyl bromide was removed by distillation (44 °C/O.3 mmHg)
`to give 19.75 g of 9,9—dioctylfluorene (pale-brown powder) Rf:
`0.87 (silica TLC in hexane). Mp: 34—37 °C.
`13C NMR (75
`MHz, CD013): 6 (ppm) 150.63, 141.15, 126.98, 126.70, 122.78,
`119.64, 55.01, 40.46, 31.84, 30.11, 29.26, 29.05, 23.77, 22.64,
`14.09. 1H NMR (300 MHz, CD013):
`(5 (ppm) 7.82 (dd, 2H, J =
`4.3 Hz), 7.42 (m, 6H), 2.12 (m, 4H, J = 3.8 Hz), 1.35—1.24 (m,
`20H), 0.96 (t, 6H, J : 7.1 HZ), 0.79 (m, 4H, J = 3.8 Hz).
`HRMS. Calcd for C29H42: 390.651. Found: 390.598.
`2,7-Dibromo-9,9-dioctylfluorene (2).19 To a solution of
`9,9-dioctylfluorene (1) (15.01 g, 38.42 mmol) in CH013 (58 mL)
`at 0 °C were added 96 mg (0.59 mmol) of ferric chloride and
`4.14 mL (80.52 mmol) of bromine.
`It is important that the
`reaction proceeds in the dark to avoid any bromination of the
`aliphatic part of the molecule. The solution was warmed to
`room temperature and was stirred for 3 h. The resulting
`slurry was poured into water and washed with sodium
`thiosulfate until the red color disappeared.- The aqueous layer
`was extracted with CHCl3 (two times), and the combined
`organic layers were dried over magnesium sulfate to afford
`21.07 g (>99%) of the title product as a pale-brown solid. Rf:
`0.85 (silica TLC in hexane). Mp; 44-47 °C.
`13C NMR (75
`MHz, CDC13): a (Ppm) 152.44, 138.94, 130.04, 126.07, 121.38,
`120.96, 55.56, 40.02, 31.63, 2978,2904, 29.01, 23.51, 22.47,
`
`
`
`P6
`
`“)7 C8 Can
`
`13.94. 1H NMR (300 MHz, CD013): 6 (13pm) 7.53 (d, 2H, J =
`7.7 HZ), 7.46 (d, 2H, J = 1.8 HZ), 7.44 (d, 2H, J = 1.1 Hz),
`1.91 (m, 4H, J = 3.7 Hz), 1.26~1.05 (m, 20H), 0.83 (t, 6H, J:
`3.6 Hz), 0.58 (m, 4H, J = 3.5 Hz). HRMS. Calcd for ngHmu
`79Br2: 546.150. Found: 546.149.
`Preparation of CuBr2 on Alumina (3).20 To a solution
`of copper(II) bromide (10 g, 44.8 mmol; Aldrich) in distilled
`water (100 mL) was added 20 g of neutral alumina (~150
`mesh; Brockmann I Aldrich). The water was removed under
`reduced pressure, and the dry mixture gave a brown powder.
`The solid is dried at 90 °C below a pressure of 1 mmHg for 4
`h.
`
`2,7-Dibromofluorene (4).20 To a solution of fluorene (1.5
`g, 9.0 mmol; Aldrich) in C014 (80 mL) was added 30 g of copper-
`(II) bromide on alumina (3). The mixture was stirred at reflux
`for 5 h. Then, the solution was cooled to room temperature,
`and the solid material was filtered and washed with CCl4 (50
`mL). The organic solution was dried over magnesium sulfate.
`Removal of solvent gave 287 g (98%) of the title product as
`yellow crystals. Recrystallization was made in a mixture of
`ethyl acetate/ hexane (5:95 v/v). Mp: 159—160 DC (lit. mp 160—
`161 °C). 130 NMR (75 MHz, CD013):
`(5 (ppm) 144.65, 139.55,
`130.01, 128.16, 121.04, 120.82, 36.43.
`1H NMR (300 MHz,
`CDCla):
`(3 (ppm) 7.67 (2H, d, J = 1 Hz), 7.61 (2H, d, J = 8
`Hz), 7.51 (2H, dd, J = 8 Hz), 3.87 (2H, s). HRMS. Calcd for
`C13Hg-79Br2: 321.898. Found: 321.899.
`Diethyl 2,7-Dibromofluorene-Q,9-dicarboxylate (5). To
`a solution of diisopropylamine (1.54 g, 15.1 mmol; Aldrich) in
`THF (7 mL) at —78 °C was added dropwise 5.63 mL (14.07
`mmol) of 11,-butyllithium (2.5 M in hexane; Aldrich). The
`mixture was stirred at —78 °C for 20 min and at 0 °C for 15
`min and cooled again at —78 CC. 2,7-Dibromofluorene (4; 2.165
`g, 6.7 mmol) in THF (70 mL) was added dropwise to the
`lithium diisopropylamide (LDA) solution and stirred for 30 min
`at this temperature. Ethyl chloroformate (3.43 g, 31.55 mmol;
`Aldrich), previously distilled on CaClz, was added to the
`mixture. The solution was allowed to warm to room temper-
`ature and was stirred for 3 h. The mixture was poured into
`water and extracted with ether. The organic extracts were
`washed with brine and dried over magnesium sulfate. The
`solvent was removed, and the residue was purified by column
`chromatography (silica gel, 7% ethyl acetate in hexane, Rf 0.15)
`to provide 2.99 g (95%) of the title product as a pale-white solid.
`Mp: 131—133 °C. 13C NMR (75 MHz, CD013): 6 (ppm) 167.06,
`141.38, 149.11, 132.35, 130.06, 121.63, 121.16, 68.68, 62.2,
`13.83. 1H NMR (300 MHz, CDCl3)Z (3 (ppm) 7.93 (d, 2H, J =
`1.7 Hz), 7.58 (dd, 2H, J = 1.5 and 8.2 Hz), 7.53 (d, 2H, J = 8.2
`
`F—fi
`
`4
`
`

`

`7688 Ranger et a1.
`
`Macromolecules, Vol. 30, No. 25, 1.997
`
`Hz), 4.27 (q, 4H, J = 7.1 Hz), 1.29 (t, 6H, J = 7.1 Hz). HRMS.
`Calcd for C19H1504-79Br2: 466.951. Found: 466.949.
`Ethyl 2,7-Dibromofluorene-9-ca.rboxylate (6). The same
`procedure as that described for diethyl 2,7-dibromofluorene-
`9,9-dicarboxylate (5) was used, but with just 1 equiv of ethyl
`chloroformate. It is necessary to use 2 equiv of LDA to avoid
`the production of diethyl 2,7-dibr0mofluorene-9,9-dicarboxy-
`late. Yield: 96% of yellow solid after purification by column
`chromatography (silica gel, 7% ethyl acetate in hexane, Rf
`0.23). Mp: 98—100 °C. 130 NMR (75 MHz, CDC13)Z (5 (Ppm)
`169.16, 142.01, 139.19, 131.31, 128.93, 121.29, 121.14, 61.78,
`52.81, 14.05.
`1H NMR (300 MHz, CDC13): a (Ppm) 7.81 (d,
`2H, J = 0.7 Hz), 7.57 (d, 4H), 7.55 (d, 2H), 4.82 (s, 1H), 4.27
`(q, 2H, J = 7.2 Hz), 1.32 (t, 3H, J = 7.2 Hz). HRMS. Calcd
`for ClsH1202'79Br2: 394.928. Found: 394.929.
`(Methoxyethoxy)ethyl 2,7-Dibromofluorene-9-carbox-
`ylate (7). To a solution of (diethylene glycol) methyl ether,
`CH3(OCH2CH2)2OH (25 mL; Aldrich), were added 3.85 g (9.7
`mmol) of ethyl 2,7-dibromofluorene-9—carboxy1ate (6) and
`concentrated H2804 (10 mol %). The solution was stirred and
`heated to 60 °C at about 10 mmHg. At this low pressure,
`ethanol was easily removed. The product (viscous limpid oil,
`4.29 g) was purified by column chromatography (silica gel, 15%
`ethyl acetate in hexane, Rf 0.12). Yield: 94%.
`13C NMR (75
`MHz, CDC13):
`(5 (ppm) 168.96, 141.75, 139.07, 131.23, 128.91,
`121.19, 121.03, 71.71, 70.34, 68.68, 64.56, 58.84, 52.58.
`1H
`NMR (300 MHz, CD013):
`(5 (Ppm) 7.80 (d, 2H, J = 0.9 Hz),
`7.49 (m, 4H), 4.81 (s, 1H), 4.35 (q, 2H, J = 4.5 Hz), 3.72 (q,
`2H, J = 3.3 Hz), 3.60 (m, 4H), 3.39 (s, 3H). HRMS. Calcd for
`C19H1804-79Br2: 468.965. Found: 468.964.
`2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-
`dioctylfluorene (8).21 To a solution of 2,7-dibromo-9,9-
`dioctylfluorene (2; 5 g, 9.1 mmol) in THF (70 mL) at —78 °C
`was added, by syringe, 7.64 mL (19.11 mmol) of n-butyllithium
`(2.5 M in hexane; Aldrich). The mixture was stirred at —78
`°C, warmed to 0 °C for 15 min, and cooled again at —78 °C for
`15 min. 2-lsopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
`(4.00 g, 21.5 mmol; Aldrich) was added rapidly to the solution,
`and the resulting mixture was warmed to room temperature
`and stirred for 24 h. The mixture was poured into water and
`extracted with ether. The organic extracts were washed with
`brine and dried over magnesium sulfate. The solvent was
`removed by rotary evaporation, and the residue was purified
`by column chromatography (silica gel, 7% ethyl acetate in
`hexane, Rf 0.20) to provide 3.80 g (65%) of the title product as
`a pale-yellow solid.
`13C NMR (75 MHz, CD013):
`(5 (ppm)
`150.31, 143.78, 133.54, 128.77, 119.23, 83.54, 55.03, 39.36,
`31.65, 29.79, 29.05, 29.00, 24.80, 23.44, 22.45, 13.94. 1H NMR
`(300 MHz, CD013):
`(3 (ppm) 7.84 (d, 2H, J = 7.6 Hz), 7.78 (s,
`2H), 7.75 (d, 2H, J = 7.6 Hz), 2.03 (m, 4H, J = 3.4 Hz), 1.43
`(s, 24H), 1.26—1.04 (m, 20H), 0.83 (t, 6H, J = 6.6 Hz), 0.58
`(In, 4H). HRMS. Calcd for C41H6404-11B2: 642.499. Found:
`642.497.
`Preparation of Tetrakis(triphenylphosphine)pal-
`ladium(0) (PP113)4Pd(0).22 To a solution of palladium dichlo—
`ride (0.25 g, 1.41 mmol; Aldrich) in dimethyl sulfoxide (DMSO,
`17 mL; Aldrich) was added 1.85 g (7.06 mmol) of triph-
`enylphosphine (Aldrich). The system was kept under an argon
`atmosphere. The mixture was heated at 140 °C until complete
`solubilization occurred. The heated bath was then taken away,
`and the solution was rapidly stirred for approximately 15 min.
`Hydrazine hydrate (0.28 mL; Aldrich) was added over 1 min.
`A vigorous reaction took place with evolution of nitrogen. The
`dark solution was immediately cooled with a water bath;
`crystallization began to occur at ~125 °C. At this point the
`mixture is allowed to cool without the use of the water bath.
`After the mixture reached room temperature, it was filtered
`under argon on a coarse, sintered—glass funnel. The solid was
`washed successively with two 15 mL portions of ethanol and
`two 15 mL portions of diethyl ether. The product (yellow
`crystalline solid, 1.53 g) was stored under an inert atmosphere.
`Yield: 94%.
`-
`.
`Polymerization.17 Carefully purified 2,7-dibromofluorene
`derivative (1 equiv), 2,7-bis(4,4,5,5-tetramethyl-1,3,2-diox-
`aborolan-2-y1)-9,9-diocty1fluorene (1 equiv), and (PPh3)4Pd(0)
`(1.5—0.5 mol %) were dissolved. in a mixture of toluene
`
`
`
`([monomer] = 0.5 M) and aqueous 2 M Na2C03 (or K2003) (1;
`1.5 toluene). The solution was first put under a nitrogen
`atmosphere and was refluxed with vigorous stirring for 48 h,
`The whole mixture was then poured into methanol (150 mL)_
`The precipitated material was recovered by filtration through
`a Buchner funnel and washed with dilute HCl. The solid
`material was washed for 24 h in a Soxhlet apparatus using
`acetone to remove oligomers and catalyst residues. The
`resulting polymers were soluble in THF and CHCla. Yields:
`~65—90%.
`
`Poly[(1,4-phenylene)-2,7-(9,9-diocty1fluorene)](P1). 1H
`NMR (400 MHz, CD013):
`(5 (ppm) 7.85 (2H, d), 7.65—7.5 (4H,
`m), 2.1 (4H, In), 1.15 (24H, m), 0.85 (6H, t).
`1H NMR
`Poly[2,7’-(9,9-dioctyl-2',7-bifluorene)] (P2).
`(400 MHz, CD013): 6 (ppm) 7.1—8.0 (12H, m), 4.0 (2H, s), 2.1
`(4H, m), 1.1 (24H, m), 0.8 (6H, t).
`Poly[2,7-(9,9-dioctylfluorene)] (P3). 1H NMR (400 MHz,
`CDC];,):
`(5 (ppm) 7.85 (2H, d), 7.68 (4H, m), 2.15 (4H, m), 1.2
`(24H, m), 0.8 (6H, t).
`Poly-2,7’-(diethyl 9,9-dioctyl-2,7’-bifluorene-9’,9'-dicar-
`boxylate)] (P4). 1H NMR (400 MHz, CD013):
`(5 (ppm) 8.2
`(2H, s), 7.75 (5H, m), 7.65 (5H, m), 4.45-4.2 (4H, m),2.1(4H,
`m), 1.7 (1.5H, m), 1.4—1.0(24H, 111), 0.9-0.6 (6H, 2t).
`Poly[2,7’-(ethyl 9,9-dioctyl-2,7’-bifluorene-9’-carboxy-
`late)] (P5). 1H NMR (400 MHz, CDClg):
`c) (PPm) 8.2 (s, 2H),
`7—7.8 (m, 10H), 4.7 (1H, s), 4—4.4 (2H, m), 1.8—2.2 (4H, m),
`1.6 (3H, m), 0.5—1.4 (30H, m).
`Poly[2,7’-[(methoxyethoxy)ethyl 9,9-dioctyl-2’,7-bifluo-
`rene-9’-carboxylate]] (P6). 1H NMR (400 MHz, CD013): 6
`(ppm) 7.9—7.6 (12H, m), 4.7 (1H, s), 4.45 (2H, m), 3.7 (6H, d),
`3.4-3.1(3H,m), 2.1 (4H, In), 1.4—1.0(24H,m),0.9—0.6(6H,
`m).
`
`Base Doping. Polymer P5 was solubilized in a solution of
`THF (Aldrich). To this solution were added 2 equiv of
`potassium tert-butoxide, and the mixture was warmed slightly
`for activation of the base. The precipitated polymer was
`filtered on nylon filters (0.45 gm) under vacuum and was
`washed with cooled THF. Before electrical measurements on
`pressed pellets, polymers were dried under reduced pressure
`(25 °C/0.1 mmHg).
`
`Results and Discussion
`
`Synthesis and Structural Characterization. As
`shown in Scheme 1, all monomers have been easily
`prepared from fluorene.
`In the synthesis of ethyl 2,7-
`dibromofluorene-9-carboxy1ate, it was necessary to use
`2 equiv of lithium diisopropylamide (LDA) since the pKa
`of this fluorene derivative is about 10 while fluorene has
`
`a pKa of 22.23 With 1 equiv of LDA, the lithium moieties
`migrated to the formed monosubstituted derivative to
`yield almost exclusively the 9,9-disubstituted fluorene.
`Suzuki couplings17 between 2,7—dibromofluorene deriva-
`tives and fluorene derivatives bearing diboronic moieties
`(see Scheme 2) allowed the preparation of all polymers
`shown in Chart 1, including the novel acidic conjugated
`polymers. Because of the use of organolithium com-
`pounds in the synthesis of the boronic derivatives, it was
`impossible to prepare the homopolymers with ester
`substituents. Therefore, with the exception of poly[2,7-
`(9,9—dioctylfluorene)] (P3), this synthetic procedure gives
`alternating polyfluorene derivatives. This alternating
`structure can be, however, very useful for the prepara-
`tion of well-defined amphiphilic conjugated polymers.
`For instance, assuming an anti conformation for poly-
`mer P6 (as shown in Chart 1), it is quite evident that
`this structure should give access to amphiphilic proper-
`ties (and, possibly, P4 and P5) where one side of the
`molecules has a hydrophobic nature whereas the other
`.one can exhibit some hydrophilic properties. These
`interesting properties could be particularly useful for
`the preparation of well-defined polymeric Langmuir—
`
`5
`
`

`

`Macromolecules, Vol. 30, No. 25, 1997
`
`New Well-Defined Poly(2,7—fluorene) Derivatives
`
`7689
`
`Scheme 1
`
`CuBrZ/A1203
`CC|4 reflux 5h
`
`
`l) 2 eqn-B—uLi -“78C
`
`THF
`2) 3 eq C3H17Br
`
`Y:97% (4)
`
`THF, s78°C
`'l) 2.l eq. LDA
`
`2)
`
`1 eq. 0
`/“\
`/\0 Cl
`
`H;
`
`8 03””
`
`FeCl; (2% mol), 24 h
`0°C ->ZS°C
`
`I 2eq. Br;(I), CHCI3
`120.0.Y=99%
`
`H]
`
`a CaHn
`
`1)2.1eqn-BuLi
`
`THF78°C \::>B—O<
`
`Scheme 2
`
`M.H.708 CaH17
`
`+
`
`., 0.0 .
`
`[(PPh3)4]Pd(0) 2% mol
`
`toluene / 2M NaZC03 (aq)
`
`reflux 48h, under Ar
`
` n
`
`
` Y: ~65-90%
`
`Blodgett films and should be tested in the near future
`in different electrical and optical devices.
`On the basis of SEC measurements (with a calibration
`using polystyrene standards), this versatile synthesis
`allows the preparation of polyfluorene derivatives with
`good molecular weights (Table 1);
`Indexes of polydis-
`persity (MW/Mn ) a1ound 2 have been calculated, which
`is consistent with a polycondensation reaction. On the
`
`
`-.o
`7.s
`7'9
`as
`so
`ss
`so
`4:
`40
`:5
`:0 2:
`:'a
`I5
`1.0
`as
`
`Figure 1.1H-NMR spectrum of poly[2 7-(9,9-dioctylfluorene)]
`in CD013 at 298 K.
`
`10,13
`
`11.12
`
`2.7
`
`1,6
`
`1.8
`
`1.5
`
`
` 1
`
`I
`
`1
`
`152
`
`I
`
`'
`144
`
`n
`
`.
`140
`
`145
`
`156
`
`u
`
`r
`1
`1
`136
`(PPM)
`
`1
`132
`
`r
`
`n
`
`1
`125
`
`1
`
`‘
`
`l
`124
`
`u
`120
`
`1
`
`1
`116
`
`v
`
`Figure 2. Aromatic region of the (a) 13C NMR and (b)
`DEPT135 NMR spectra of poly[2,7-(9,9-dioctylfluorene)] in
`CDClg at 298 K.
`
`Table 1. Number-Average (Mn) and Weight-Average (MW)
`Molecular Weights of the Polyfluorene Derivatives
`
` polymer Mn Mw Mw/MI1
`
`
`P1
`4600
`7600
`1.7
`P2
`2400
`2900
`1.2
`P3
`24000
`40000
`1.7
`P4
`14000
`32000
`2.2
`P5
`5600
`7800
`1.4
`P6
`6300
`8900
`1.4
`
`basis of these results, it seems that the presence of
`flexible and solubilizing side chains is required to get
`high molecular weights.
`Indeed, polymers without
`substituents on the 2,7-dibromofluorenes (or 1,4-dibro-
`mobenzene) show systematically lower molecular weights.
`NMR analyses indicate clearly that well-defined poly-
`(2,7-fluorene) derivatives have been indeed obtained. As
`an example and because of its simple repeating unit,
`we show here the 1H (Figure 1) and 13C NMR (Figure
`2) spectra of poly[2,7-(9,9-dioctylfluorene)] (P3). More-
`over, a similar analysis had been previously reported
`by Yoshino et al.10 for FeClg-polymerized poly(9,9-
`dialkylfluorene)s and could serve for comparison pur-
`poses. As shown in Figure 1, the 1H NMR spectrum of
`P3 is consistent with a well-defined structure. The only
`major difference from that published by Yoshino et a1.
`is the lower intensity of the 7.5 ppm peak which had
`been attributed to the terminal units.10 This result is
`in agreement with the higher molecular weight of the
`
`6
`
`6
`
`

`

`7690 Ranger et al.
`
`
`
`
`
`RelativeFluorescenceIntensity
`
`0
`
`300
`
`350
`
`400
`
`450
`
`500
`
`550
`
`600
`
`Wavelength (nm)
`
`Figure 3. Excitation and emission spectra of fluorescence
`poly[(1,4-phenylene)—2,7-(9,9-dioctylfluorene)] in chloroform at
`298 K.
`
`Table 2. Maximum Excitation Wavelength, Maximum
`Emission Wavelength, and Fluorescence Quantum Yield
`for the Polyfluorene Derivatives in Chloroform at 298 K
`
` polymer lexc (nm) Aem (11m) $0
`
`
`P1
`362
`407
`0.87
`P2
`372
`415
`0.71
`P3
`373
`412
`0.79
`P4
`367
`408
`0.36
`P5
`368
`413
`0.50
`P6
`371
`415
`0.16
`
`Macromolecules, Vol. 30, No. 25, 1997
`
`properties should favor good blue-light-emitting proper-
`ties?!24 All polymers of this study ShOW similar absorp.
`tion and emission spectra; all these polyfluorene de-
`rivatives emit in the blue region with a maximum
`around 410 nm (Table 2). All emission spectra exhibit
`also the same vibronic structure which is associated
`with a coupled C=C stretching mode (1550-1600 cm—l)
`(Figure 3).
`In general, the presence of a well-defined
`vibronic structure in the emission spectra indicates that
`the polymers have a rigid and well-defined backbone?’7
`In addition to interesting blue emission, some fluores-
`cence quantum yields are very high (up to 0.87; see
`Table 2). However, it is worth noting that the presence
`of the carbonyl function in P4, P5, and P6 reduces
`strongly the fluorescence quantum yield.
`It is well-
`known that the carbonyl moieties are good fluorescence
`quenchers since an intercrossing process is favored by
`their n—Jr* transition.
`
`Base-Doping and Electrical Properties. Poly-
`mers P5 and P6 possess an acidic proton in the
`9-position which should have, on the basis of studies
`performed on the monomers?”3 a pKa of about 10 in
`DMSO and of about 14 in water. These polymers could
`then be deprotonated (base-doped) and, in principle, this
`'novel doping met