Melting point. 127–128 uC (lit.19 125–126 uC).
filtration and dried in vacuo to give triphenyl(2,3-diphenyl-
quinoxalinylmethyl)phosphonium bromide (1.58 g, 93%. 1H
NMR (CDCl3, 300 MHz) d 7.1–7.8 (m, 29H, aromatic Hs),
2
5.82 (d, JHP 13 Hz, 2H, CH2P).
Synthesis of 6-vinyl-2,3-diphenylquinoxaline. Triphenyl-
(diphenylquinoxalinylmethyl)phosphonium bromide (1.50 g,
2.35 mmol) was dissolved in dichloromethane (3 ml) and
formaldehyde (0.40 ml, 37% solution in water, 4.7 mmol)
added. Aqueous sodium hydroxide (1.5 ml, 50% solution) was
added dropwise over a period of 30 minutes with rapid stirring
and stirred for a further 30 minutes. The solution was diluted
with dichloromethane, washed with water, dried over MgSO4
and evaporated to dryness to give a pale yellow solid. This solid
was purified by column chromatography on silica with hexane
as the eluent to give white crystals, 10.5 g, 50% (mp 122–123 uC,
lit.21 122–123 uC. Found C, 85.69; H, 5.19; N, 9.12%. C22H16N2
requires C, 85.69; H, 5.23; N, 9.08%). 1H NMR (CDCl3,
300 MHz) d 8.11 (d, 3JHH 8.7 Hz, 1H, quinoxaline H), 8.10 (br,
Synthesis of 2-(3-vinylphenyl)-5-phenyl-1,3,4-oxadiazole.
2-(3-Bromophenyl)-5-phenyl-1,3,4-oxadiazole (2.0 g, 6.64 mmol)
was dissolved in degassed toluene (30 ml). Pd(PPh3)4 (0.15 g,
0.133 mmol) and nBu3Sn(CHCH2) (2.11 g, 6.64 mmol) were
added under dry nitrogen. The solution was refluxed for
1
4 hours after which time a H NMR spectrum of a sample of
the solution showed total consumption of the starting
materials. The solution was evaporated to give a yellow solid
which was recrystallised from hexane to give a yellow oil. This
was redissolved in toluene and passed through a silica packed
column giving a strong yellow band. The column was eluted
with toluene until the yellow band reached the bottom of the
column. The toluene collected was evaporated and shown to
contain only nBu3SnBr. The column was stripped with
methanol, the methanol evaporated and the residue recrys-
tallised from hexane to give white crystals (0.9 g, 54%) which
were shown by 1H NMR to be 2-(3-vinylphenyl)-5-phenyl-
3
4
1H, quinoxaline H), 7.90 (dd, JHH 8.7 Hz, JHH 2.1 Hz,
quinoxaline H), 7.45–7.55 (m, 4H, phenyl H), 7.28–7.38 (m,
3
6H, phenyl H), 6.95 (dd, JHH(cis) 11.1 Hz, JHH(trans)
3
3
17.7 Hz, 1H, vinylic H), 6.00 (d, JHH(trans) 17.7 Hz, 1H,
3
vinylic H), 5.47 (d, JHH(cis) 11.1 Hz, 1H, vinylic H).
n
1,3,4-oxadiazole with only traces of Bu3SnBr.
Copolymerisation of 4-vinyltriphenylamine with 2-phenyl-5-
(3-vinylphenyl)-1,3,4-oxadiazole. 2-Phenyl-5-(3-vinylphenyl)-
1,3,4-oxadiazole (0.60 g, 2.4 mmol), 4-vinyltriphenylamine
(0.60 g, 2.2 mmol) and AIBN (19.71 mg, 120 mmol) were
placed in an ampoule and benzene (5 ml) condensed into the
ampoule under vacuum. The solution was then heated in the
ampoule to 70 uC for 10 hours, cooled and the product poured
into methanol (50 ml). The polymer which precipitated was
collected by filtration and dried under vacuum to yield 0.80 g of
a white powder.
1H NMR (CDCl3, 300 MHz). d 8.1–8.2 (m, 3H, aromatic
CH), 8.02 (dt, 1H, aromatic CH), 7.6–7.4 (m, 5H, aromatic
3
CH), 6.80 (dd, JHH 17.7 Hz and 10.8 Hz, CHCH2), 6.90 (d,
3
3JHH 17.7 Hz, CHCH2), 5.39 (dd, JHH 0.8 Hz, CHCH2).
Synthesis of 6-methyl-2,3-diphenylquinoxaline. 1,2-Diamino-
4-methylbenzene (25.0 g, 0.20 mol) and benzil (43 g, 0.20 mol)
were refluxed in ethanoic acid (250 ml) overnight. The solvent
was evaporated in vacuo and the black residue recrystallised
three times from ethanol to give pale brown crystals of
6-methyl-2,3-diphenylquinoxaline (39.6 g, 65%).
1H NMR (CDCl3, 300 MHz) d 8.08 (d, J 8.4 Hz, 1H, Hs of
quinoxaline), 7.97 (br s, 1H, Hs of quinoxaline), 7.60 (dd, J 8.4,
J 1.8Hz, 1H, Hs of quinoxaline), 7.50–7.58 (m, 4H, phenyl
rings), 7.30–7.38 (m, 6H, phenyl rings), 2.62 (s, 3H, CH3).
¯
¯
¯
¯
GPC analysis (CHCl3): Mn 15,700, Mw 53,000, Mw/Mn /3.4
Other polymers were prepared from the corresponding
monomers under the same conditions.
2.2 Organic device fabrication and test
The polymers under investigation are charge-transport
materials with negligible emission properties. In order to
assess their performance in emissive devices, each was doped at
a concentration of 0.5% (by weight) with the pyromethene laser
dye PM580 supplied by Exciton (Fig. 2).
Melting point. 114.5–116 uC (lit.20 115–116 uC).
Synthesis of 6-bromomethyl-2,3-diphenylquinoxaline.
6-Methyl-2,3-diphenylquinoxaline (5.0 g, 16.9 mmol) was dis-
solved in dry, oxygen free benzene (50 ml). The solution was
brought to reflux and a mixture of NBS (3.00 g, 16.9 mmol)
and AIBN (0.1 g) added as a solid over a period of 30 minutes.
The solution was then refluxed for 2 h, cooled, washed
with water (36100 ml), dried over MgSO4 and evaporated
to leave a pale brown solid. This was recrystallised from
hexane–toluene (1 : 1, 80 ml) to yield 6-bromomethyl-2,3-
diphenylquinoxaline (3.5 g, 56%. Calc. for C21H15N2Br C,
67.21; H, 15.12; N, 7.47%. Found C, 67.17; H, 3.95; N, 7.41%
despite the fact that traces of 6-methyl-2,3-diphenylquinoxaline
Light-emitting diode devices based on doped single organic
layers were fabricated on 24 mm square pieces of 10 V ITO
coated glass (Balzers). Prior to use, the ITO was washed and
UV–ozone treated. Polymer layers were deposited by spin
coating from 1,2-dichlorobenzene, followed by a 10 minute
hotplate bake at 75 uC to remove the solvent. Polymer concen-
trations of 4–5%, with spin speeds of 2000 to 3000 rpm
provided dry layer thicknesses in the range 75 nm–140 nm.
˚
Cathode metalisation comprising 1000 A of Mg followed by
˚
1000 A of Ag as a protective layer was deposited by thermal
evaporation at a pressure of 261026 Torr. The cathode was
patterned by use of a shadow mask which defined circular
devices each of area 9.61 mm2.
1
were shown to be present by H NMR).
1H NMR (CDCl3, 300 MHz) d 8.16 (d, J 8.7 Hz, 1H, Hs of
quinoxaline), 8.16 (d, J 2.2 Hz, 1H, Hs of quinoxaline), 7.78
(dd , J 8.7, J 2.2 Hz, 1H, Hs of quinoxaline), 7.48–7.56 (m, 4H,
phenyl ring), 7.30–7.40 (m, 6H, phenyl ring), 4.71 (s, 2H,
CH2Br).
Devices were driven using a computer-controlled Keithley
236 Source-Measure unit, while the brightness and spectral
Synthesis of triphenyl(2,3-diphenylquinoxalinylmethyl)phos-
bromide. 6-Bromomethyl-2,3-diphenylquinoxaline
phonium
(1.0 g, 2.7 mmol) and triphenylphosphine (0.70 g, 2.7 mmol)
were dissolved in toluene (50 ml) and the solution refluxed
overnight. The white solid that precipitated was recovered by
Fig. 2 Structure of luminescent dopant PM580.
2240
J. Mater. Chem., 2001, 11, 2238–2243