New Base-Dopable Well-Defined Polys-2,7s-Fluorene Derivatives
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0 H
C5H1 1
H17C8 C8 H1 7
H
Pd(PPh 3 )4 /toluene
0
C5H1
K2CO3/H20 95*C
n
HrýC8 C8 H17
P9KF 0 H
0C 6 H1 3
P9EF H17gC8 8 H17
n
Scheme 1. Preparation of alternating polyfluorene derivatives by Suzuki couplings. RESULTS The results of the polymerization reactions are summarized in Table 1. P9EF and P9KF (Scheme 1) are soluble in common organic solvents such as THF, toluene and CHCI3. Table 1. Results of the polymerization reactions
Polymers
Rx Time(h)
Yield(%)
Mn
M.
DP
P9EF
48
75
7800
14000
12
P9KF
48
72
10000
21000
15
DP=degree of polymerization, M,=Number-average molecular weight, Mw=Weight-average molecular weight. All data were evaluated by GPC against polystyrene standards in THF. The chemical structure of the copolymers was identified by NMR spectroscopy (Figures 1 and 2). As an example, the 'H NMR spectrum of P9KF shows an acidic proton at 5.05 ppm. The evaluation of the degree of polymerization (DP) by NMR analysis from terminal protons at 7.49 and 7.38 ppm gave the same value as that estimated by GPC. Figure 2 shows 12 peaks associated to the 12 different carbon atoms in P9KF and confirms that the copolymer has a well-defined structure. This regioregularity should contribute to a better intramolecular transport of the charge carriers (by allowing the resonance between benzoid and quinoid forms). By 2D-NMIR analysis,
836
the two peaks (having an asterisk), at 128.68 and 127.11 ppm, were associated to carbon atoms of end groups.
CDCI3
I
I
8.0
7.8
I
7.6
7.4
(ppm) acetone
8
7
6
5
4
3
1
2.
0
(ppm)
Figure 1. The 'H NMR spectrum of P9KF in CDCI3.
*
l
l
l
11
II 15514
Figure 2. Aromatic region of the
10
13C
140
135
NMR of P9KF, in CDCI3. 837
30
15
'[II
12
Photoluminescence measurements have revealed that these copolymers emit strongly in the blue range. Excitation fluorescence spectra correspond perfectly with absorption spectra (Figure 3). P9KF shows an emission maximum at 412 nm and a fluorescence quantum yield of 0.20. P9EF exhibits the same emission spectrum with a quantum yield of 0.50. The apparent Stokes shift of polyfluorene was small with a average value of 2000 cm'1. This value of Stokes shift is associated to a rigid polymer and could indicate that similar geometries exist in both the ground and excited states. The emission fluorescence spectra showed a vibronic structure associated to the coupling of a C=C vibration mode.
1
Ui 300
I
350
3I 40I
400
4,50
SC X0
550
600
650
WaMenrfh (rim) Figure 3. Relative excitation and emission spectra for P9KF in chloroform at room temperature. Moreover, upon deprotonation, P9KF and P9KF show interesting conductivities of 10"'-10"' and 10"2_10"3 S/cm respectively. These conductivities are significant if one compares those obtained with oxidized polyfluorenes [3,4], which are around of 10-3 S/cm and considering the fact that all measurements were carried out in air. The higher conductivity of P9KF can be explained by a better stability of the generated anion since the ketone group is a bette
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