Macromolecules
Article
temperature). Differential scanning calorimetry (DSC) studies were
carried out on a TA Instruments with a 5 °C/minute ramp from −50
to +220 °C under both N2 and ambient atmosphere.
Syntheses. The monomers 9,9-dihexyl-fluorene-2,7-diamine (1),
9,9-dioctyl-fluorene-2,7-dicarbaldehyde, diethyl 2,5-diaminothiophene-
3,4-dicarboxylate, and 2,3-dihydrothieno[3,4-b][1,4]dioxine-5,7-dicar-
baldehyde were synthesized according to previously reported
procedures.39−42 Similarly, PFl-co-Fl was prepared according to
known methods.37
2.02 (m, −CH2), 1.33 (m, −CH2−CH2−), 0.80 (m, −CH2−), 0.59
(m, −CH3).
Poly(2,3-dihydrothieno[3,4-b][1,4]dioxine)-co-9,9-dihexylfluore-
nylazomethine (PFl-co-EDOT). The copolymerization was similar to
that above with 2,3-dihydrothieno[3,4-b][1,4]dioxine-5,7-dicarbalde-
hyde (163 mg, 0.882 mmol) and 1 (300 mg, 0.882 mmol) in CHCl3
(6 mL) in a pressure tube at 90 °C for 48 h. The reaction was then
cooled to room temperature and it was poured into a methanol/water
mixture. The resulting red precipitate was filtered. It was then washed
consecutively with methanol, water and acetone. The title polymer was
isolated as a red solid (60%, 140 mg) after drying under vacuum
Experimental Procedures. 3-(2-Ethylhexyl) thiophene. In
anhydrous THF (50 mL) was dissolved magnesium (2.65 g, 109
mmol) and 2-ethylhexyl bromide (15 g, 77 mmol). The reaction
mixture was stirred for 30 min at 0 °C. The temperature was then
gradually warmed to room temperature until most of the magnesium
reacted, followed by refluxing for 2 h. In another flask was dissolved 3-
bromothiophene (7.0 g, 43 mmol) to which was then added [1, 3-bis
(diphenylphosphino) propane] nickel(II) chloride (200 mg, 0.4
mmol) in anhydrous THF (100 mL). Three cycles of freeze−
pump−thaw were performed to ensure complete removal of oxygen.
The prepared 2-ethylhexyl magnesium bromide Grignard reagent was
added by cannula to the red colored solution of nickel catalyst and the
resulting brown solution was then refluxed for 18 h. The reaction
mixture was washed with aqueous HCl (10% w/w) after cooling to
room temperature. The organic phase was extracted with ethyl acetate,
dried with MgSO4, and the solvent was evaporated after removing the
MgSO4. The crude product was chromatographed on silica with 100%
hexanes to afford a colorless oil (4.9 g, 58%). 1H NMR (CDCl3): δ =
7.23 (d, 1H), 6.94 (d, 2H), 2.53 (t, 2H), 1.44 (m, 1H), 1.30 (bs, 8H),
0.91 (t, 6H).
3-(2-Ethylhexyl)thiophene-2,5-dicarbaldehyde (5). To a solution
of 3-(2-ethylhexyl) thiophene (7.5 g, 38 mmol) and freshly distilled
TMEDA (9.8 g, 84 mmol) diluted in anhydrous hexanes (50 mL)
under nitrogen, was added dropwise a solution of 2 M n- BuLi in
hexane (42 mL, 84 mmol). After refluxing for 1.5 h, THF (40 mL) was
added and the solution was cooled to −50 °C. Anhydrous DMF (14
mL, 190 mmol) was then added dropwise, after which the reaction
mixture was allowed to warm to room temperature. After 2.5 h at
room temperature, the reaction mixture was hydrolyzed with water (60
mL) and the mixture was extracted with ether. The organic layers were
dried over MgSO4 and concentrated. The crude product was purified
by column chromatography with hexanes/ethyl acetate (90/10 v/v) to
give the product as a colorless oil (5.8 g, 61%). 1H NMR (CDCl3), δ,
ppm: 10.09 (s, 1H), 9.56 (s, 1H), 7.16 (s, 1H), 2.61 (t, 2H), 1.59
(septet, 1H), 1.31 (qt, 2H), 1.04 (bs, 6H), 0.92 (t, 6H). HR−MS(+):
calculated for [C14H20O2S + H]+, 253.12840; found, 253.12842.
Poly(3-(2-ethylhexyl)thiophene)-co-9,9-dihexylfluorenylazome-
thine (PFl-co-Th). The copolymerization was done by mixing 1 (100
mg, 0.27 mmol) and 3-(2-ethyl-hexyl)-thiophene-2,5-dicarbaldehyde
(68 mg, 0.27 mmol) in CHCl3 (3.0 mL) in a pressure tube. A catalytic
amount of diluted TFA (30 μL) was then added. The pressure tube
was sealed and heated to 90 °C for 48 h. The reaction mixture was
cooled to room temperature and the polymer was precipitated from a
methanol/water mixture. The resulting red solid (60%, 80 mg) was
filtered and washed with methanol, water and acetone and then dried
under vacuum overnight. 1H NMR (400 MHz, CDCl3), δ, ppm: 10.41
(m, CHO), 8.95 (m, −-NCH−), 8.40 (s, −Th−H) 7.34−7.71 (m,
Fl−H), 6.71 (b, NH2), 2.82 (m, −CH2), 1.31 (m, −CH−CH2−), 1.93
(m, −CH2−), 0.77 (m, −CH3).
1
overnight. H NMR (400 MHz, CDCl3) δ ppm: 10.01 (m, CHO),
8.75 (m, −NCH−), 7.31−7.71 (m, Fl−H), 6.7 (b, NH2), 4.44−4.47
(m, O−CH2, EDOT), 1.99 (m, −CH2), 1.05 (m, −CH2−CH2−), 0.78
(m, −CH2−), 0.64 (m, −CH3).
9,9-Dihexyl-N,N′-bisthiophen-2-ylmethylenefluorene-2,7-dia-
mine (Th-Fl-Th1). In ethanol (20 mL) were dissolved 1 (40.0 mg, 0.1
mmol) and thiophene-2-carbaxyldehyde (36 mg, 0.32 mmol) to which
was then added a 1 M solution of TFA (20 μL). The solution was
stirred at room temperature for 12 h, after which the solvent was
evaporated and the product was extracted into ethyl acetate. The
organic layer was washed with a brine solution and dried over Na2SO4.
After filtering, the solvent was removed under reduced pressure and
the crude product was purified by silica gel column chromatography
with hexanes/ethyl acetate (80/20% v/v). The product was obtained
as an orange solid (32 mg, 58% yield). 1H NMR (CDCl3), δ, ppm: 8.7
(s, 2H), 7.68 (d, 2H), 7.53 (d, 4H), 7.23−7.29 (m, 4H), 7.01 (s, 2H),
1.99 (t, 4H), 1.25 (p, 4H), 1.11 (m, 4H), 0.78 (t, 6H), 0.66 (t, 4H).
13C NMR (acetone), δ, ppm: 164.9, 164.3, 161.5, 147.0, 144.1, 140.4,
133.4, 131.0, 102.2, 61.1, 60.1, 32.2, 32.0, 26.7, 22.9, 14.4, 14.1, 13.9.
HR−MS (+): calculated for [C35H40N2S2 + H]+, 553.27089; found,
553.27089.
9,9-Dihexyl-N,N′-bis(5-butylthiophen-2-ylmethylene)fluorene-
2,7-diamine (Th−Fl−Th2). In ethanol (40 mL) were dissolved 1
(110.0 mg, 0.41 mmol) and 5-butylthiophene-2-carbaxyldehyde (222
mg, 1.32 mmol) to which was then added a 1 M solution of TFA (60
μL). The solution was stirred at room temperature for 12 h. The
solvent was then removed under reduced pressure and the crude
product was extracted into ethyl acetate. The organic layer was washed
with a brine solution and dried over Na2SO4. After filtering and then
removing the solvent under reduced pressure, the crude product was
purified by silica gel column chromatography with hexanes/ethyl
acetate (70/30% v/v). The product was obtained as an orange solid
1
(212 mg, 78% yield). H NMR (acetone-d6), δ, ppm: 8.78 (s, 2H),
7.78 (d, 2H), 7.46 (d, 2H), 7.37 (d, 2H), 7.25 (d, 2H), 6.94 (d, 2H),
2.88 (t, 4H), 1.73 (p, 4H), 1.30 (t, 4H), 1.08 (p, 8H), 0.95 (t, 6H),
0.74 (t, 12H). 13C NMR (acetone), δ, ppm: HR−MS (+): calculated
for [C43H56N2S2 + H]+, 665.39840; found, 665.39751.
DISCUSSION AND RESULTS
■
The polymers presented in Chart 1 were targeted for examining
the effect of incorporating different thiophenes on the
polymer’s opto-electronic properties. The particular properties
of interest are the emission colors and fluorescence quantum
yields, given that previously investigated polyazomethines were
all nonfluorescent. The exception is PFl-co-Fl that fluoresces in
appreciable amounts (Table 2).37 The additional benefit of
incorporating thiophene into the polymers is that significant
spectral changes for both the absorbance and emission are
expected relative to the all-fluorene PFl-co-Fl polymer.
Significant spectral changes are additionally expected between
PFl-co-Th vs PFl-co-EDOT, owing to the electronic differences
of the EDOT and thiophene moieties. Meanwhile, the effect of
the azomethine placement on the opto-electronic properties is
expected by comparing the measured properties of PFl-co-DAT
relative to both PFl-co-Th and PFl-co-EDOT.
Poly(thiophene-3,4-dicarboxylic acid diethyl ester)-co-9,9-dio-
ctylfluorenylazomethine (PFl-co-DAT). The copolymerization was
done similar to that above with 1 (485 mg, 1.88 mmol) and 9,9-
dioctyl-fluorene-2,7-dicarbaldehyde (840 mg, 1.88 mmol) in CHCl3
(10 mL) in a pressure tube at 90 °C for 48 h. The reaction mixture
was cooled to room temperature and it was poured into a methanol/
water mixture. The resulting precipitate was filtered and it was washed
with methanol, water and then acetone. The title polymer was isolated
as a red solid (70%, 120 mg) after drying under vacuum overnight. 1H
NMR (400 MHz, CDCl3) δ ppm: 10.1 (m, CHO), 8.52 (m, −N
CH−), 7.53−7.91 (m, Fl-H), 6.35 (b, NH2), 4.24−4.49 (m, O−CH2),
The monomers required for synthesizing the targeted
copolymers were prepared by known means as outlined in
1167
dx.doi.org/10.1021/ma2024304 | Macromolecules 2012, 45, 1165−1173