Facile synthesis of 3,8-dibromo-substituted phenanthridine derivatives and their conjugated polymers

Article abstract of DOI:10.1021/ma902375a

We present an efficient and convenient synthesis of 3, 8- dibromophenanthridine derivatives and their conjugated polymers and demonstrate that phenanthridine-containing conjugated polymers can be used as luminescent chemosensor materials. High molecular w

Full text of DOI:10.1021/ma902375a

Macromolecules 2010, 43, 1349–1355 1349
DOI: 10.1021/ma902375a
Facile Synthesis of 3,8-Dibromo-Substituted Phenanthridine Derivatives
and Their Conjugated Polymers
Yulan Chen,† Fenghong Li,‡ and Zhishan Bo*,†
†Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100190, P. R. China and ‡Department of Physics,
€
€
Chemistry and Biology, Linkoping University, SE-58183, Linkoping, Sweden
Received October 26, 2009; Revised Manuscript Received December 21, 2009
ABSTRACT: We present an efficient and convenient synthesis of 3,8-dibromophenanthridine derivatives
and their conjugated polymers and demonstrate that phenanthridine-containing conjugated polymers can be
used as luminescent chemosensor materials. High molecular weight poly(phenanthridine-co-fluorene)s
(P1, P2) and poly(phenanthridine-co-p-phenylene) (P3) were synthesized by palladium-catalyzed Suzuki-
€
Miyaura-Schluter polycondensation (SMSPC). These phenanthridine-containing polymers are of high
quantum yields in solution and show reversible optical response to protonation and deprotonation of the
phenanthridine rings.
9,9-dioctylfluorene-2,7-diboronic pinacol ester (5),10 and 2,5-di-
hexylphenyl-1,4-diboronic acid ester (6)11 were prepared accord-
Introduction
Conjugated polymers have received a great deal of interest for
a variety of potential applications, such as optoelectronics,
microelectronics,1 and chemical and biological sensors.2 To meet
diverse demands for different uses, incessant exploration of new
conjugated polymer materials is highly required.3 Phenanthridine
is a fused aromatic compound with an electron-withdrawing
nitrogen atom in scaffold,4 which has been synthesized in 1930s.5
However, there is no report on this chromophore as a building
block for the construction of conjugated polymers.
Bischler-Napieralski cyclization was first reported more than a
century ago6 and has been widely used in synthesis of pharmaceu-
tically interesting nitrogen-containing heterocyclic compounds
in synthetic organic and medical chemistry.7 Here, we report
the facile synthesis of 3,8-dibromo-substituted phenanthridine
derivatives using Bischler-Napieralski cyclization as the key step.
A set of 6-substituted 3,8-dibromophenanthridine monomers has
ing to literature procedures.
Characterization. 1H and 13C NMR spectra were recorded on
a Bruker AV400 or an AV600 spectrometer. Gel permeation
chromatography (GPC) measurements were performed on
Waters 410 system against polystyrene standards with THF as
an eluent. UV-vis absorption spectra were obtained on a
Shimadzu UV-vis spectrophotometer (model UV-1601 PC).
Fluorescence spectra were recorded on a Hitachi F-4500 fluore-
scence spectrophotometer. Fluorescence quantum yields (ΦF)
of the samples in THF were measured by using 9,10-diphenyl-
anthracene (ΦF = 0.9) as a standard.12 Elemental analyses were
performed on a Flash EA 1112 analyzer. Thermal gravimetric
analysis (TGA) and differential scanning calorimetry (DSC)
measurements were performed on TA2100 and Perkin-Elmer
Diamond DSC instrument, respectively, under a nitrogen
atmosphere at a heating rate of 10 °C/min to record TGA and
DSC curves. The powder X-ray diffraction (XRD) patterns
were collected using monochromated Cu KR radiation (λ =
1.540 56 A) on a Rigaku D/max-2500 diffractometer. Polarized
light micrography was performed on an Olympus BH-2 optical
microscope with a Mettler hot stage (FP-52) and an automatic
camera (heating rate: 10 °C/min). HOMO levels of the polymers
were determined by the ultraviolet photoelectron spectroscopy
(UPS) measurements of a bulk thin film spin-coated on ITO.
UPS characterizations (binding energy error of about 100 meV)
were carried out with monochromatized HeI radiation at
21.2 eV in ultrahigh vacuum. The highest occupied molecular
orbital (HOMO) values are here defined as the vertical ioniza-
tion potential derived from UPS.
€
been synthesized. Suzuki-Miyaura-Schluter polycondensation
(SMSPC) of 3,8-dibromophenanthridine-based monomers and
aryldiboronic ester monomers afforded high molecular weight
conjugated polymers with phenanthridine units in polymer main
chains. Photophysical properties of these polymers were also
studied. To the best of our knowledge, this is the first report on
the synthesis of phenanthridine-containing conjugated polymers.
Experimental Section
Materials. Unless otherwise noted, all chemicals were pur-
chased from commercial suppliers and used without further
purification. Phosphoryl trichloride was freshly distilled before
use. Tetrahydrofuran (THF) was distilled over sodium and
benzophenone. All reactions were performed under an atmo-
sphere of nitrogen and monitored by TLC with silica gel 60 F254
(Merck, 0.2 mm). Column chromatography was carried out on
silica gel (200-300 mesh). The catalyst precursor Pd(PPh3)4
was prepared according to the literature8 and stored in a
Schlenk tube under nitrogen. 2-Nitro-4,40-dibromobiphenyl (1),9
2-Amino-4,40-dibromobiphenyl (2). To a solution of 1 (15.0 g,
42.0 mmol) in 160 mL of ethanol was added aqueous HCl
(80 mL, 32%). Tin powder (10.0 g, 84.0 mmol) was then
added portionwise over 10 min, and the reaction mixture was
heated to reflux overnight. After cooling, the mixture was
poured into ice water (400 mL) and then made alkaline with
aqueous NaOH solution (20%) until the pH was 9.0. The
precipitate was collected by filtration and dried under vacuum
to give the product as a colorless solid that could be used for
*Corresponding authors: Fax þ86-10-82618587; e-mail zsbo@iccas.
1
ac.cn.
next step without further purification (13 g, 95%). H NMR
r 2010 American Chemical Society
Published on Web 01/08/2010
pubs.acs.org/Macromolecules

1350 Macromolecules, Vol. 43, No. 3, 2010
Chen et al.
(CDCl3, 400 MHz): δ 7.57 (d, 2H, ArH), 7.29 (d, 2H, ArH), 6.93
(s, 2H, ArH), 6.91 (s, 1H, ArH), 3.77 (s, 2H, NH2). 13C NMR
(CDCl3, 100 MHz): δ 144.85, 137.46, 132.25, 131.63, 130.75,
125.20, 122.52, 121.75, 121.70, 118.29. Anal. Calcd for
C12H9NBr2: C, 44.07; H, 2.77; N, 4.28. Found: C, 44.21; H,
2.86; N, 4.12.
General Procedure for Synthesis of Amide-Substituted Biphe-
nyl Derivatives 3a-g. To a dry THF solution of 2 and triethyl-
amine (3 mL) was added dropwise a dry THF solution (35 mL)
of the respective acyl chloride at 0 °C. After stirring at room
temperature for 24 h, the solution was poured into water
(80 mL) and extracted with diethyl ether (2 ꢀ 50 mL). The
combined organic extracts were dried over anhydrous Na2SO4
and evaporated to dryness. The residue was purified by recrys-
tallization from CH2Cl2/n-Hex or chromatography on silica gel
column eluting with petroleum ether/CH2Cl2.
7.28 (d, 2H, ArH), 7.14 (d, 1H, ArH). 13C NMR (CDCl3, 100
MHz): δ 162.98, 149.83, 139.54, 135.61, 135.07, 132.70, 131.20,
130.69, 130.27, 128.38, 127.98, 124.56, 124.17, 123.15, 122.71.
Anal. Calcd for C19H12N2Br2O2: C, 47.93; H, 2.54; N, 5.88.
Found: C, 47.58; H, 2.71; N, 5.79.
3f. Compound 2 (2.0 g, 6.1 mmol) and thiophene-2-carbonyl
chloride (1.2 g, 8.1 mmol) were used. The crude product was
recrystallized from CH2Cl2/n-Hex and dried under high vacuum
to afford 3f as a colorless solid (2.0 g, 75%). 1H NMR (CDCl3,
400 MHz): δ 8.69 (s, 1H, NH), 7.71 (s, 1H, ArH), 7.67 (d, 2H,
ArH), 7.52 (d, 1H, ArH), 7.34 (dd, 1H, ArH), 7.29 (d, 2H, ArH),
7.23 (d, 1H, ArH), 7.11(d, 1H, ArH), 7.07 (t, 1H, ArH). 13C
NMR (CDCl3, 100 MHz): δ 159.41, 138.68, 135.78, 135.52,
132.59, 131.30, 130.98, 130.84, 129.45, 128.45, 128.02, 127.52,
124.06, 122.89, 122.68. Anal. Calcd for C17H11NBr2SO: C,
46.71; H, 2.54; N, 3.20. Found: C, 46.38; H, 2.57; N, 3.33.
3g. Compound 2 (1.2 g, 3.7 mmol) and 5-bromothiophene-2-
carbonyl chloride (1.0 g, 4.4 mmol) were used. The crude
product was recrystallized from CH2Cl2/n-Hex and dried under
3a. Compound 2 (4.0 g, 12.2 mmol) and decanoyl chloride
(3.5 g, 18.3 mmol) were used. The crude product was recrystal-
lized from CH2Cl2/n-Hex and dried under high vacuum to
1
1
high vacuum to afford 3g as a colorless solid (1.0 g, 53%). H
afford 3a as a colorless solid (4.3 g, 73%). H NMR (CDCl3,
NMR (CDCl3, 400 MHz): δ 8.59 (s, 1H, NH), 7.66 (d, 2H, ArH),
7.60 (s, 1H, ArH), 7.34 (d, 1H, ArH), 7.27 (d, 2H, ArH), 7.11 (d,
1H, ArH), 7.02 (d, 1H, ArH), 6.9 (d, 1H, ArH). 13C NMR
(CDCl3, 100 MHz): δ 158.33, 140.13, 135.65, 135.13, 132.63,
131.05, 130.97, 130.77, 129.60, 128.17, 127.79, 124.21, 122.99,
122.67, 119.57. Anal. Calcd for C17H10NBr3SO: C, 39.57; H,
1.95; N, 2.71. Found: C, 39.33; H, 2.23; N, 2.88.
General Procedure for Synthesis of 3,8-Dibromo-6-Substituted
Phenanthridine Derivatives 4a-g. A solution of amide-substi-
tuted biphenyl derivatives (3a-g) and P2O5 in freshly distilled
POCl3 was stirred under reflux for 30 h. The mixture was
concentrated under vacuum, the residue was diluted with ethyl
acetate (15 mL), and water (15 mL) was added slowly. The
aqueous layer was adjusted to pH = 10 with NaOH solution
(5 M) and extracted with ethyl acetate (2 ꢀ 15 mL). The
combined organic layers were dried over anhydrous Na2SO4
and evaporated to dryness. The crude product was chromato-
graphically purified on silica gel column eluting with petroleum
ether/CH2Cl2.
400 MHz): δ 8.53 (s, 1H, NH), 7.62 (d, 2H, ArH), 7.30 (dd, 1H,
ArH), 7.21 (d, 2H, ArH), 7.05 (d, 1H, ArH), 7.00 (s, 1H, ArH),
2.20 (t, 2H, CH2), 1.56 (m, 2H, CH2), 1.32-1.25 (m, 12H, CH2),
0.88 (t, 3H, CH3). 13C NMR (CDCl3, 100 MHz): δ 171.37,
136.21, 135.89, 132.57, 131.08, 130.90, 129.69, 127.47, 124.64,
122.81, 122.65, 37.83, 31.97, 29.51, 29.43, 29.38, 29.21, 25.47,
22.78, 14.22. Anal. Calcd for C22H27NBr2O: C, 54.90; H, 5.65;
N, 2.91. Found: C, 54.94; H, 5.72; N, 2.76.
3b. Compound 2 (0.5 g, 1.5 mmol) and 4-methylbenzoyl
chloride (0.35 g, 2.3 mmol) were used. The crude product was
purified by chromatography on silica gel column eluting with
petroleum ether/CH2Cl2 (v:v, 1:1) to afford 3b as a colorless
solid (0.61 g, 90%). 1H NMR (CDCl3, 400 MHz): δ 8.72 (s, 1H,
NH), 7.82 (s, 1H, ArH), 7.64 (d, 2H, ArH), 7.49 (d, 2H, ArH),
7.33 (dd, 1H, ArH), 7.28 (d, 2H, ArH), 7.22 (d, 2H, ArH), 7.10
(d, 1H, ArH), 2.39 (s, 3H, CH3). 13C NMR (CDCl3, 100 MHz):
qδ 165.10, 142.93, 136.19, 136.09, 132.68, 131.43, 131.14,
130.96, 129.93, 129.73, 127.58, 126.93, 124.47, 122.94, 122.79,
21.59. Anal. Calcd for C20H15NBr2O: C, 53.96; H, 3.40; N, 3.15.
Found: C, 54.03; H, 3.44; N, 2.92.
3c. Compound 2 (1.2 g, 3.7 mmol) and 4-tert-butylbenzoyl
chloride (1.2 g, 6.1 mmol) were used. The crude product was
recrystallized from CH2Cl2/n-Hex and dried under high vacuum
to afford 3c as a colorless solid (1.6 g, 89%). 1H NMR (CDCl3,
400 MHz): δ 8.75 (s, 1H, NH), 7.87 (s, 1H, ArH), 7.65 (d, 2H,
ArH), 7.54 (d, 2H, ArH), 7.44 (d, 2H, ArH), 7.33 (dd, 1H, ArH),
7.29 (d, 2H, ArH), 7.10 (d, 1H, ArH), 1.33 (s, 9H, CH3). 13C
NMR (CDCl3, 100 MHz): δ 165.11, 156.08, 136.33, 136.21,
132.81, 131.42, 131.29, 131.08, 129.99, 127.66, 126.91, 126.15,
124.54, 123.06, 122.91, 35.26, 31.33. Anal. Calcd for C23H23-
NBr2O: C, 56.70; H, 4.34; N, 2.87. Found: C, 56.62; H, 4.35; N,
2.87.
4a. Compound 3a (0.98 g, 2.0 mmol), P2O5 (2.2 g, 15.5 mmol),
and POCl3 (40 mL) were used. Chromatography on silica gel
eluting with petroleum ether/CH2Cl2 (v:v, 2:1) afforded 4a as a
1
colorless solid (0.920 g, 98%). H NMR (CDCl3, 400 MHz):
δ 8.39 (d, 1H, ArH), 8.33 (d, 1H, ArH), 8.28 (d, 1H, ArH), 8.27
(d, 1H, ArH), 7.89 (dd, 1H, ArH), 7.68 (dd, 1H, ArH), 3.27 (t,
2H, CH2), 1.88 (m, 2H, CH2), 1.51 (m, 2H, CH2), 1.38 (m, 2H,
CH2), 1.36-1.27 (m, 8H, CH2), 0.88 (t, 3H, CH3). 13C NMR
(CDCl3, 100 MHz): δ 162.58, 144.70, 133.89, 132.38, 131.27,
129.92, 129.06, 126.67, 124.31, 123.30, 122.77, 121.94, 121.78,
36.15, 32.01, 29.91, 29.65, 29.61, 29.43, 29.08, 22.80, 14.24.
Anal. Calcd for C22H25NBr2: C, 57.04; H, 5.44; N, 3.02. Found:
C, 56.98; H, 5.51; N, 3.07.
4b. Compound 3b (0.4 g, 0.90 mmol), P2O5 (1.0 g, 7.0 mmol),
and POCl3 (20 mL) were used. Chromatography on silica gel
eluting with petroleum ether/CH2Cl2 (v:v, 2:1) afforded 4b as a
3d. Compound 2 (1.0 g, 3.1 mmol) and 4-bromobenzoyl
chloride (1.0 g, 4.5 mmol) were used. The crude product was
purified by chromatography on silica gel column eluting with
petroleum ether/CH2Cl2 (v:v, 1:1) to afford 3d as a colorless
solid (1.2 g, 77%). 1H NMR (CDCl3, 400 MHz): δ 8.65 (s, 1H,
NH), 7.80 (s, 1H, ArH), 7.64 (d, 2H, ArH), 7.56 (d, 2H, ArH),
7.45 (d, 2H, ArH), 7.35 (dd, 1H, ArH), 7.27 (d, 2H, ArH), 7.11
(d, 1H, ArH). 13C NMR (CDCl3, 100 MHz): δ 164.33, 136.10,
135.77, 133.15, 132.85, 132.43, 131.33, 131.00, 130.31, 128.59,
128.12, 127.26, 124.76, 123.20, 122.90. Anal. Calcd for
C19H12NBr3O: C, 44.74; H, 2.37; N, 2.75. Found: C, 44.77; H,
2.57; N, 2.82.
1
colorless solid (0.350 g, 91%). H NMR (CDCl3, 400 MHz):
δ 8.49 (d, 1H, ArH), 8.40 (d, 1H, ArH), 8.38 (d, 1H, ArH), 8.28
(d, 1H, ArH), 7.94 (dd, 1H, ArH), 7.76 (dd, 1H, ArH), 7.60 (d,
2H, ArH), 7.39 (d, 2H, ArH), 2.49 (s, 3H, CH3). 13C NMR
(CDCl3, 100 MHz): δ 161.41, 144.81, 139.42, 135.98, 134.21,
132.99, 131.96, 131.50, 130.51, 129.71, 129.49, 126.66, 124.09,
123.36, 123.03, 122.06, 121.69, 21.54. Anal. Calcd for
C20H13NBr2: C, 56.24; H, 3.07; N, 3.28. Found: C, 56.05; H,
3.09; N, 3.13.
3e. Compound 2 (1.0 g, 3.1 mmol) and 4-nitrobenzoyl chlor-
ide (0.74 g, 4.0 mmol) were used. The crude product was
recrystallized from CH2Cl2/n-Hex and dried under high vacuum
to afford 3e as a yellow solid (1.06 g, 73%). 1H NMR (CDCl3,
400 MHz): δ 8.66 (s, 1H, NH), 8.28 (d, 2H, ArH), 7.84(s, 1H,
ArH), 7.77 (d, 2H, ArH), 7.66 (d, 2H, ArH), 7.40 (dd, 1H, ArH),
4c. Compound 3c (0.24 g, 0.49 mmol), P2O5 (0.4 g, 2.8 mmol),
and POCl3 (12 mL) were used. Chromatography on silica gel
eluting with petroleum ether/CH2Cl2 (v:v, 2:1) afforded 4c as a
colorless solid (0.230 g, 100%). 1H NMR (CDCl3, 400 MHz): δ
8.49 (d, 1H, ArH), 8.40 (d, 1H, ArH), 8.38 (d, 1H, ArH), 8.33 (d,
1H, ArH), 7.94 (dd, 1H, ArH), 7.76 (dd, 1H, ArH), 7.65 (d, 2H,

Article
Macromolecules, Vol. 43, No. 3, 2010 1351
ArH), 7.60 (d, 2H, ArH), 1.42 (s, 9H, CH3). 13C NMR (CDCl3,
100 MHz): δ 161.40, 152.54, 144.81, 135.93, 134.23, 132.99,
131.96, 131.51, 130.49, 129.49, 126.60, 125.85, 124.10, 123.36,
123.02, 122.04, 121.69, 34.98, 31.46. Anal. Calcd for C23H19-
NBr2: C, 58.87; H, 4.08; N, 2.99. Found: C, 58.27; H, 4.10; N,
3.12.
Scheme 1. Synthesis of 3,8-Dibromo-6-Substituted Phenanthridine
Derivatives
4d. Compound 3d (0.3 g, 0.59 mmol), P2O5 (0.42 g, 2.9 mmol),
and POCl3 (12 mL) were used. Chromatography on silica gel
eluting with petroleum ether/CH2Cl2 (v:v, 2:1) afforded 4d as a
1
colorless solid (0.277 g, 96%). H NMR (CDCl3, 400 MHz):
δ 8.50 (d, 1H, ArH), 8.40 (d, 1H, ArH), 8.38 (d, 1H, ArH), 8.19
(d, 1H, ArH), 7.96 (dd, 1H, ArH), 7.79 (dd, 1H, ArH), 7.73 (d,
2H, ArH), 7.59 (d, 2H, ArH). 13C NMR (CDCl3, 100 MHz):
δ 159.92, 144.47, 137.54, 134.33, 132.87, 131.89, 131.84, 131.26,
130.86, 130.76, 126.10, 124.10, 123.79, 123.27, 123.10, 121.98,
121.78. Anal. Calcd for C19H10NBr3: C, 46.38; H, 2.05; N, 2.85.
Found: C, 45.95; H, 2.03; N, 2.74.
4e. Compound 3e (0.3 g, 0.63 mmol), P2O5 (0.45 g, 3.2 mmol),
and POCl3 (12 mL) were used. Chromatography on silica gel
eluting with petroleum ether/CH2Cl2 (v:v, 2:3) afforded 4e as a
yellow solid (0.197 g, 68%). 1H NMR (CDCl3, 400 MHz): δ 8.55
(d, 1H, ArH), 8.46 (d, 2H, ArH), 8.44 (d, 1H, ArH), 8.39 (d, 1H,
ArH), 8.11 (d, 1H, ArH), 8.00 (dd, 1H, ArH), 7.59 (d, 2H, ArH),
7.84 (dd, 1H, ArH). 13C NMR (CDCl3, 100 MHz): δ 158.64,
148.31, 144.87, 144.29, 134.67, 132.99, 131.89, 131.32, 130.75,
130.34, 125.76, 124.30, 123.91, 123.36, 122.15, 122.08. Anal.
Calcd for C19H10N2Br2O2: C, 49.81; H, 2.20; N, 6.12. Found: C,
49.84; H, 2.11; N, 5.83.
4f. Compound 3f (0.31 g, 0.71 mmol), P2O5 (0.51 g, 3.6 mmol),
and POCl3 (12 mL) were used. Chromatography on silica gel
eluting with petroleum ether/CH2Cl2 (v:v, 2:1) afforded 4f as a
yellow solid (0.256 g, 86%). 1H NMR (CDCl3, 400 MHz): δ 8.70
(s, 1H, ArH), 8.46 (d, 1H, ArH), 8.35 (d, 1H, ArH), 8.34 (d, 1H,
ArH), 7.95 (d, 1H, ArH), 7.74 (d, 1H, ArH), 7.64 (d, 1H, ArH),
7.61 (d, 1H, ArH), 7.27 (t, 1H, ArH). 13C NMR (CDCl3, 100
MHz): δ 154.55, 145.21, 142.61, 134.97, 133.45, 132.70, 131.36,
131.32, 130.55, 129.76, 128.62, 126.49, 124.84, 123.93, 123.90,
122.89, 122.43. Anal. Calcd for C17H9NSBr2: C, 48.72; H, 2.16;
N, 3.34. Found: C, 48.94; H, 2.38; N, 3.32.
4g. Compound 3g (0.3 g, 0.58 mmol), P2O5 (0.42 g, 2.9 mmol),
and POCl3 (12 mL) were used. Chromatography on silica gel
eluting with petroleum ether/CH2Cl2 (v:v, 2:1) afforded 4g as a
yellow solid (0.212 g, 73%). 1H NMR (CDCl3, 400 MHz): δ 8.67
(d, 1H, ArH), 8.48 (d, 1H, ArH), 8.34 (d, 1H, ArH), 8.32 (d, 1H,
ArH), 7.96 (dd, 1H, ArH), 7.75 (dd, 1H, ArH), 7.41 (d, 1H,
ArH), 7.21 (d, 1H, ArH). 13C NMR (CDCl3, 100 MHz):
δ 152.52, 144.33, 143.59, 134.35, 132.65, 132.60, 132.11,
130.76, 130.60, 130.07, 129.86, 125.29, 124.25, 123.19, 122.17,
121.73, 116.69. Anal. Calcd for C17H8NSBr3: C, 41.00; H, 1.62;
N, 2.81. Found: C, 40.95; H, 1.63; N, 2.95.
General Procedure for Synthesis of Phenanthridine-Containing
Polymers P1-3. A mixture of 2,8-dibromophenanthridines,
aryldiboronic acid esters, NaHCO3, THF, toluene, and H2O
was carefully degassed before and after Pd(PPh3)4 was added.
The mixture was heated to reflux and stirred under nitrogen
for 96 h. The reaction mixture was extracted with CHCl3 (2 ꢀ
50 mL), and the combined organic layers were dried over
anhydrous Na2SO4. After the removal of most of solvent, the
residue was precipitated into methanol, and the resulted pre-
cipitate was collected by filtration and dried under vacuum to
give polymers P1-3.
Polymer P1. Compound 4a (0.10 g, 0.22 mmol), 9,9-dioctyl-
fluorene-2,7-diboronic pinacol ester (0.14 g, 0.22 mmol),
NaHCO3 (0.73 g), Pd(PPh3)4 (2.49 mg), THF (10 mL), toluene
(10 mL), and H2O (6 mL) were used. P1 was obtained as an off-
white solid (0.14 g, 93%). 1H NMR (CDCl3, 400 MHz): δ
8.76 (broad, 1H), 8.65 (broad, 1H), 8.55 (broad, 2H), 8.19
(broad, 1H), 8.03 (broad, 1H), 7.91-7.39 (broad, 6H), 3.53
(broad, 2H), 2.08 (broad, 4H), 1.64 (broad, 8H), 1.31-1.14
(broad, 30H), 0.90 (broad, 3H), 0.79 (broad, 6H). 13C NMR
(CDCl3, 150 MHz): δ 163.52, 152.37, 152.20, 151.95, 144.34,
141.77, 140.65, 139.57, 132.03, 130.02, 128.95, 127.38, 126.71,
125.77, 124.78, 123.36, 122.74, 121.94, 120.59, 55.68, 40.73,
36.94, 32.10, 31.94, 30.28, 29.81, 29.55, 29.44, 24.15, 22.88,
22.76, 14.30, 14.22, 14.07.
Polymer P2. Compound 4b (0.10 g, 0.23 mmol), 9,9-dioctyl-
fluorene-2,7-diboronic pinacol ester (0.15 g, 0.23 mmol),
NaHCO3 (0.78 g), Pd(PPh3)4 (2.70 mg), THF (10 mL), toluene
(10 mL), and H2O (6 mL) were used. P2 was obtained as an off-
white solid (0.15 g, 97%). 1H NMR (CDCl3, 400 MHz): δ 8.84
(broad, 1H), 8.73 (broad, 1H), 8.64 (broad, 1H), 8.47 (broad,
1H), 8.23 (broad, 1H), 8.10 (broad, 1H), 7.89-7.80 (broad, 4H),
7.79 (d, 2H),7.65 (broad, 2H), 7.44 (d, 2H), 2.52 (s, 3H), 2.08
(broad, 4H), 1.56 (broad, 4H), 1.26-1.10 (broad, 20H), 0.78
(broad, 6H). 13C NMR (CDCl3, 100 MHz): δ 162.30, 152.29,
144.55, 140.78, 140.58, 130.14, 129.96, 129.74, 129.55, 129.43,
128.32, 127.44, 126.35, 125.99, 123.08, 122.93, 122.77, 122.05,
122.00, 121.90, 120.59, 55.65, 40.79, 31.98, 30.30, 30.14, 29.92,
29.76, 29.47, 24.16, 22.82, 21.67, 14.27.
Polymer P3. Compound 4a (0.10 g, 0.22 mmol), 2,5-dihexyl-
phenyl-1,4-diboronic 1,3-propanediol ester 6 (0.09 g, 0.22 mmol),
NaHCO3 (0.73 g), Pd(PPh3)4 (2.49 mg), THF (10 mL), toluene
(10 mL), and H2O (6 mL) were used. P3 was obtained as a grayish
solid (0.10 g, 84%). 1H NMR (CDCl3, 400 MHz): δ 8.80 (broad,
1H), 8.68 (broad, 1H), 8.29 (d, 2H), 7.95 (s, 1H), 7.76 (s, 1H),
7.40-7.35 (broad, 2H), 3.45 (broad, 2H), 2.73 (broad, 4H), 2.02
(broad, 2H), 1.59 (broad, 8H), 1.28-1.19 (broad, 20H), 0.87
(broad, 3H), 0.78 (broad, 6H). 13C NMR (CDCl3, 150 MHz):
δ 163.03, 143.82, 142.64, 140.82, 138.04, 131.98, 131.59, 131.45,
129.97, 128.13, 126.76, 125.16, 122.37, 121.62, 36.70, 32.86, 31.94,
31.61, 30.15, 29.90, 29.72, 29.67, 29.40, 22.74, 22.56, 14.17, 14.06.
Results and Discussion
Synthesis of 3,8-Dibromo-6-Substituted Phenanthridine
Derivatives. As shown in Scheme 1, the synthetic route
for 3,8-dibromophenanthridines is rather straightforward.
Starting from 4,40-dibromo-2-nitrobiphenyl (1), reduction of
the nitro group with Sn/Hþ afforded the corresponding
2-amino-4,40-dibromobiphenyl (2) in a yield of 95%. The
reaction of compound 2 with acyl chlorides in a solvent
mixture of tetrahydrofuran (THF) and triethylamine (TEA)
afforded amides 3 in yields of 53-90%. The conversion
of compounds 3 to 3,8-dibromophenanthridines 4 was ac-
complished with Bischler-Napieralski cyclization. The con-
version of 3b to 4b was investigated using different reaction
conditions. The cyclization was screened using POCl3 as
15
the solvent and PCl3,13 PCl5,14 or P2O5 as the catalyst
at refluxing. The cyclization is very sensitive to the catalyst.
No product was detected, when PCl3 or PCl5 was used as the
catalyst; whereas when P2O5 was used as the catalyst, the
cyclization yields were in the range of 90% to almost 100%.
The optimized cyclization conditions are feasible for the
synthesis of various 3,8-dibromophenanthridine derivatives.
The results are shown in Table 1. The cyclization yields
range between 68 and 99% for various substituents in the

1352 Macromolecules, Vol. 43, No. 3, 2010
Chen et al.
6-position of phenanthridine.7f ,16 The purification of
3,8-dibromophenanthridine derivatives only requires simple
chromatography on silica gel column. All compounds
was carried out in a biphasic mixture of aqueous NaHCO3
and THF/toluene with freshly prepared Pd(PPh3)4 as the
catalyst precursor. The reaction was kept stirring under N2 at
reflux for 4 days. During the reaction, only P2 precipitated
from the reaction mixture in about 2 days. And all precipi-
tated polymers could be fully redissolved in common organic
solvents, such as chloroform and THF. Standard work-up
afforded polymers P1, P2, and P3 as amorphous, gray solids
in yields of 93%, 97%, and 84%, respectively. The molecular
weights determined by gel permeation chromatography
(GPC) against polystyrene standards are shown in Figure 1
and Table 2. These data show that high molecular weights
were achieved. The weight-average molecular weights (Mw)
for P1, P2, and P3 were found up to 82, 180, and 67 kg/mol,
respectively. GPC is known not to be a good method to
determine the actual molecular weight of rodlike polymers;
the number presented here should be treated with careful-
ness. The polymers were unambiguously characterized with
1H and 13C NMR spectroscopy.
1
obtained were unambiguously characterized with H and
13C NMR spectroscopy and elemental analysis. This
approach is suitable for the preparation of 3,8-dibromophe-
nanthridine derivatives on a large scale.
Synthesis of Phenanthridine-Containing Polymers. As
shown in Scheme 2, three phenanthridine-containing con-
jugated polymers were prepared by palladium-catalyzed
€
Suzuki-Miyaura-Schluter polycondensation. The poly-
merization of 6-substituted 3,8-dibromophenanthridines
with 9,9-dioctylfluorene-2,7-diboronic pinacol ester (5) or
2,5-dihexylphenyl-1,4-diboronic 1,3-propanediol ester (6)
Table 1. Isolated Yields of 3,8-Dibromo-6-Substituted Phenanthri-
dines (4a-g) by Cyclization of 4,40-Dibromo-2-acylbiphenyls (3a-g)
The thermal properties of the polymers were investigated
using thermogravimetric analysis (TGA) and differential
scanning calorimetry (DSC). As shown in Figure 2, all these
polymers P1-3 exhibit good thermal stability. They showed
less than 5% decomposition up to 400 °C and a residual
weight of about 50-60% at 800 °C under a nitrogen atmo-
sphere at a heating rate of 10 °C/min. The 5% weight loss
temperatures (Td) of polymers are also included in Table 2.
For P1 and P2, no distinct glass transition was observed
from 35 to 350 °C in their DSC curves of the second heating
and cooling runs (10 °C/min), which suggested that they were
amorphous (Figure S1).17 As shown in Figure S1c, P3
exhibited a distinct endothermal peak at about 106 °C in
the DSC trace of second heating and a distinct exothermic
peak at about 93 °C in the trace of second cooling at a rate of
10 °C/min. However, no distinct morphology change was
observed by polarized light micrography in the second cool-
ing and heating runs from the temperature range of 35-
320 °C (Figure S2). Therefore, the above observed endother-
mal and exothermic peaks are probably ascribed to an
undefined solid to solid transition.18
Optical and Electrical Properties of Polymers P1-3. All
the three polymers could be readily dissolved in common
organic solvents, such as methylene chloride, chloroform,
toluene, and THF. The UV-vis absorption and photolumi-
nescent (PL) spectra of P1-P3 in dilute THF solution are
shown in Figure 3a. P1 and P2 exhibit strong absorption in
the ultraviolet region ranging from 320 to 410 nm with a
maximum at around 386 nm. P3 absorbs in the range
of 250-370 nm with two peaks at about 284 and 305 nm.
Scheme 2. Synthesis of Phenanthridine-Containing Polymers

Article
Macromolecules, Vol. 43, No. 3, 2010 1353
In THF solution, P1 and P2 emit in blue region with a
maximum at 409 and 411 nm and a shoulder at about 431 and
434 nm, respectively. P3 emits in the ultraviolet region with a
maximum of 369 nm and a shoulder at around 386 nm. The
introduction of fluorene unit instead of 1,4-phenylene one
into the polymer backbone results in obvious red-shifting of
the absorption and emission spectra.12,19 The quantum
yields of P1, P2, and P3 in dilute THF solution were
measured to be 99%, 96%, and 81%, respectively, by using
9,10-diphenylanthracene as a reference standard (ΦF = 0.9).
Solid films on quartz plates used for UV-vis absorption and
fluorescence spectroscopy measurements were prepared by
spin-coating with THF solutions of P1-3 (1.0 mg/mL).
Figure 3b shows the UV-vis absorption and fluorescence
spectra of P1-3 in films. The results are also listed in Table 3.
In comparison with their absorption spectra in solution, the
absorption peaks of all polymers P1-3 are slightly broad-
ening and red-shifted. In film, P1 exhibits a featureless
emission peak with a maximum at about 505 nm, which is
red-shifted for about 96 nm in comparison with its solution
emission spectrum. P2 in film also displays a featureless
emission spectrum peaked at about 452 nm, which is red-
shifted for about 41 nm in comparison with its solution one.
P3 in film shows a very broad emission spectrum with two
peaks at about 388 and 438 nm, which is also red-shifted in
comparison with its solution one. The broadening and
red-shifting of the absorption and emission spectra of
conjugated polymers in film are usually ascribed to the
formation of aggregation for conjugated polymer chains
in the solid state.2g,19,20 In THF solution, the PL spectra
of P1 and P2 are similar because their chemical structures are
almost the same except that the substituent on 6-position is
different. However, the PL spectra of P1 and P2 in films are
quite different, with P1 emits much longer wavelength light
than P2. This is probably due to the 6-position-substituted
aryl group that usually has a dihedral angle with the phenan-
thridine ring, which can change the packing style of polymer
chains in the solid state; thus, the formation of exciplexes
may occur to a greater or lesser extent depending on the
polymer structures.2g As revealed by the X-ray diffraction
(XRD) patterns of the powdery sample of these polymers (as
shown in Figure S3), the 6-position alkyl-substituted P1 has
apparently different packing style in comparison with the
6-position aryl-substituted P2.3e Therefore, it is possible
to finely adjust the emission color and even to tune the
morphological and charge transporting properties of phe-
nanthridine-based conjugated polymers by selecting appro-
priate substituents on phenanthridine moiety.
Figure 1. GPC elution traces of polymers P1-3.
Table 2. Molecular Weights and Thermal Properties of Polymers
P1-3
polymer
Mn
Pn
Mw
Pw
Mw/ Mn
Tg
Td
P1
P2
P3
41 000
83 000
25 000
59
126
45
82 000
180 000
67 000
118
287
122
2.0
2.3
2.7
-
-
-
424
417
404
The HOMO energy levels of P1-3 bulk thin films spin-
coated on ITO were estimated by ultraviolet photoelectron
spectroscopy (UPS) to be -5.8 ( 0.1, -5.9 ( 0.1, and -6.4 (
0.1 eV, respectively. The band gaps (Eg) were determined
from the onset of the UV-vis absorption spectra, and the
data are summarized in Table 3. According to the equation
ELUMO = EHOMO þ Eg, the LUMO energy levels were
calculated to be 2.94 eV for P1, 3.03 eV for P2, and
2.91 eV for P3. These results imply that the three polymers
have a similar electron-withdrawing ability while P3 is poor
in terms of electron-donating.21
Figure 2. TGA traces of polymers P1-3.
Figure 3. (a) Normalized solution absorption and PL spectra of polymers P1-3 (10-5 M for repeating units) in THF. (b) Normalized film absorption
and PL spectra of polymers P1-3.

1354 Macromolecules, Vol. 43, No. 3, 2010
Chen et al.
Table 3. Summary of UV-vis Absorption and PL Maxima (λ), PL Quantum Yields (ΦF), Optical Bandgaps (ΔE ), and HOMO and LUMO
Levels of Polymers P1-3
λ
abs (nm)
λPL (nm)
solutiona
films
solutiona
films
ΦF
ΔE (eV)b
HOMOc ( 0.1 (eV)
LOMO (eV)
a
polymer
P1
P2
P3
385
386
284, 305
392
398
292, 311
409
411
369, 386
505
452
388, 438
0.99
0.96
0.81
2.86
2.87
3.49
-5.8
-5.9
-6.4
-2.94
-3.03
-2.91
a Measured in THF. b Estimated from absorption onset. c Estimated from UPS.
Figure 4. Changes in (a) UV-vis absorption and (b) PL spectra of P1 (10-6 M (repeating unit)) in THF at various concentrations of TFA: [TFA] = 0,
4.0 ꢀ 10-3, 6.0 ꢀ 10-3, 8.0 ꢀ 10-3, 2.4 ꢀ 10-2, and 1.6 ꢀ 10-1 M. Dotted lines represent the partial recovery of the optical properties when the
protonated P1 solution in THF was titrated with a droplet of TEA. Inset shows the fluorescence images of P1 in THF as the TFA concentration
increased (taken under the illumination with 365 nm UV light).
Optical Response to Protic Acid. The nitrogen atom on
the phenanthridine ring can be easily protonated and depro-
tonated, which should cause significant changes of their
photoluminescent spectra due to the fact that the phenan-
thridine ring is in the polymer main chain.2a,f ,g,22 All the
polymers can be effectively protonated with trifluoroacetic
acid (TFA) and deprotonated with triethylamine (TEA). As
shown in Figure 4 and Figure S4, the color changes of
polymer solution and film upon the addition of TFA and
TEA can be clearly seen by the naked eye. When adding TFA
(from 0 to 1.6 ꢀ 10-1 M) to a solution of P1 in THF (10-6
M), the color of polymer solution changed from colorless to
orange. The color change is more evident under the illumina-
tion of UV light at the wavelength of 365 nm. UV-vis
absorption spectra of P1 in THF solution titrated with
trifluoroacetic acid (TFA) are shown in Figure 4a. The
intensity of absorption peak at 384 nm decreased upon the
titration of the THF solution of P1 with TFA. The photo-
luminescent spectra of polymer P1-3 in THF solution
titrated with trifluoroacetic acid (TFA) are shown in
Figure 4b. When titrated with TFA, the intensity of the blue
emission peak decreased dramatically and finally disap-
peared, and a new long wavelength emission band peaked
at about 540 nm appeared and its intensity increased gradu-
ally. Partial recovery of the blue emission and complete
disappearance of the long wavelength emission were ob-
served, when the protonated P1 solution in THF was titrated
with a droplet of TEA. The appearance of the polymer
solution changed from orange back to colorless. P2 and P3
also displayed similar optic properties (Figure S4). Our
investigations have illustrated that these phenanthridine-
containing polymers are promising light-emitting and protic
acid sensitive materials.
polycondensation of 3,8-dibromophenanthridine monomers with
9,9-dioctylfluorene-2,7-diboronic ester or 2,5-dihexylphenyl di-
boronic acid ester afforded high molecular weight conjugated
polymers with phenanthridine units in the polymer main chain.
Photophysical studies indicated that these phenanthridine-con-
taining polymers are promising light-emitting materials and pH
sensors.
Acknowledgment. Financial support by the NSF of China
(20834006 and 20774099) and National Basic Research Program
of China (973 Program 2009CB623601) is gratefully acknow-
ledged.
Supporting Information Available: DSC data of P1-3,
polarizing optical micrographs of P3, X-ray diffraction patterns
of P1-3, and optical response to protic acid for P2-3. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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