Synthesis, characterization and photoconductive properties of optically active methacrylic polymers bearing side-chain 9-phenylcarbazole moieties

Article abstract of DOI:10.1016/j.polymer.2009.11.054

The synthesis of two novel optically active monomers containing 9-phenylcarbazole moieties, such as (S)-(+)-2-methacryloyloxy-N-[4-(9-carbazolyl)phenyl]succinimide [(S)-(+)-MCPS] and (S)-(+)-3-methacryloyloxy-N-[4-(9-carbazolyl)phenyl]pyrrolidine [(S)-(+)

Full text of DOI:10.1016/j.polymer.2009.11.054

Polymer 51 (2010) 368–377
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Polymer
journal homepage: www.elsevier.com/locate/polymer
Synthesis, characterization and photoconductive properties of optically active
methacrylic polymers bearing side-chain 9-phenylcarbazole moieties
,
a
b
b
a
Luigi Angiolini a , Loris Giorgini , Huawei Li , Attilio Golemme , Francesco Mauriello ,
*
Roberto Termine c
a Dipartimento di Chimica Industriale e dei Materiali and INSTM UdR-Bologna, University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
b INSTM UdR-Calabria, Centro di Eccellenza CEMIF.CAL, Dipartimento di Chimica, University of Calabria, 87036 Rende (CS), Italy
c Laboratorio Licryl INFM-CNR and Centro di Eccellenza CEMIF.CAL, 87036 Rende (CS), Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of two novel optically active monomers containing 9-phenylcarbazole moieties, such as
(S)-(þ)-2-methacryloyloxy-N-[4-(9-carbazolyl)phenyl]succinimide [(S)-(þ)-MCPS] and (S)-(þ)-3-metha
cryloyloxy-N-[4-(9-carbazolyl)phenyl]pyrrolidine [(S)-(þ)-MCPP], is described. Each monomer has been
radically homopolymerized to afford the corresponding optically active polymeric derivatives, which
have been fully characterized. Their spectroscopic, thermal and photoconductive properties were
compared to those of the new achiral homopolymer poly[N-(2-methacryloyloxyethyl)-N-[4-(9-carb-
azolyl)phenyl]ethylamine] {poly[MCPE]}, devised as an optically inactive macromolecular model
compound, as well as to analogue polymeric derivatives containing side-chain optically active carbazolyl
moieties. The chiroptical properties of the chiral polymers are quantitatively higher than in the corre-
sponding monomers. Owing to the substantially stereoirregular structure of the main chain, this suggests
that the overall optical activity is mainly due to conformational dissymmetry of the macromolecules.
Spectroscopic evidence suggests the presence in all polymeric derivatives of dipole–dipole interactions
between the 9-phenylcarbazolyl chromophores, occurring as a consequence of their anchorage to the
polymer backbone, which favours their aggregation and justifies their high decomposition temperatures.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 3 September 2009
Received in revised form
21 November 2009
Accepted 25 November 2009
Available online 3 December 2009
Keywords:
Chiroptical properties
Photoconductive polymers
Multifunctional materials
1. Introduction
because of their possible use in the general topic dealing with chiral
nanotechnology [12,13].
Carbazole has attracted considerable interest as building block
in material science for its well known hole-transporting and elec-
troluminescence properties [1].
Within this context, stereoregular helical polyacetylenes con-
taining in the side chain the carbazole group functionalized with
chiral minidendrons and with chiral menthyl, bornyl and triphenyl-
amine groups [14–16] and optically active vinyl homo- and copoly-
mers with side-chain carbazole moieties [17–20] have been reported.
To this regard, we have recently investigated the first example of
optically active methacrylic polymers containing side-chain
carbazole linked at their 3-position to the macromolecular
main chain through an optically active group of one absolute
configuration such as poly[(S)-(þ)-2-methacryloyloxy-N-[3-(9-
ethylcarbazole)]succinimide] {poly[(S)-(þ)-MECSI]} and poly-
[(S)-(ꢀ)-3-methacryloyloxy-N-[3-(9-ethylcarbazole)]pyrrolidine]
{poly[(S)-(ꢀ)-MECP]} [21].
Among various classes of photoconductive and photorefractive
materials, carbazole-containing polymers are promising, since they
possess outstanding and unique advantages over inorganic and
organic crystals, such as the highest figure of merit, versatility in
structural design, and good processability [2]. Such polymers have
been used in advanced micro- and nanotechnologies as photocon-
ductive and photorefractive media, in electroluminescent devices, as
blue emitting materials and in holographic memories [3,4].
On the other hand, an intense interest has currently arisen into
investigations concerning the amplification of chirality in poly-
meric materials, in solution as well as in the solid state [5–11],
These materials are characterized, in solution, by chiral confor-
mations related to the combined effects of the strongly dipolar
conjugated carbazole system with the conformational stiffness of
optically active rings, favouring the instauration of a conforma-
tional arrangement with a prevailing handedness, at least for chain
sections of the macromolecules [21].
* Corresponding author. Tel./fax: þ39 051 2093687.
E-mail address: luigi.angiolini@unibo.it (L. Angiolini).
0032-3861/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2009.11.054

L. Angiolini et al. / Polymer 51 (2010) 368–377
369
Meanwhile, a wide range of vinyl monomers and their poly-
2. Experimental section
meric derivatives bearing various photo-active or electro-active
chromophores have been extensively studied and applied in the
field of advanced composites, optoelectronic materials and devices
[22,23]. To this regard, polyacrylates and polymethacrylates with
pendand 9-phenylcarbazolyl moiety have been largely studied in
order to correlate the architecture of the chromophores to the
photochemical and photophysical properties [24].
2.1. Materials and reagents
Methacryloyl chloride (Aldrich) was distilled (b.p. ¼ 95 ꢁC)
under dry nitrogen in the presence of traces of 2,6-di-tert.butyl-p-
cresol as polymerization inhibitor just before use.
Triethylamine (TEA) (Aldrich) was refluxed over dry CaCl2 for
8 h, then distilled (bp 89 ꢁC). 2,20-Azobisisobutyronitrile (AIBN)
(Aldrich) was crystallized from abs. ethanol before use.
The optically active intermediate (S)-(þ)-5-carboxymethyl-2-
trichloromethyl-4-oxo-1,3-dioxolane (malic acid chloralide) was
prepared starting from (S)-(ꢀ)-malic acid by reaction with chloral
hydrate, according to literature procedures [25].
Toluene, chloroform, dichloromethane and tetrahydrofuran
(THF) were purified and dried according to the reported procedures
[26] and stored over molecular sieves (4 Å) under nitrogen.
Carbazole (Aldrich), N-ethyl-N-(2-hydroxyethyl)amine (Aldrich)
and all other reagents and solvents (Aldrich) were used as received
without further purification.
N-(4-aminophenyl)carbazole was prepared starting from crude
carbazole with a synthetic procedure reported in literature [27].
(S)-(ꢀ)-3-Hydroxy-N-phenylpyrrolidine [(S)-(ꢀ)-HPP] [28] and
2-bromo-(N-ethylamine)ethanol [29] have been prepared as
previously reported.
In the present study, in order to investigate how the macro-
molecular structure affects the hole transport mechanism and the
photoconductive properties, we have envisaged the synthesis of
polymeric derivatives bearing in the side chain a 9-phenyl-
carbazole moieties linked to the (S)-2-hydroxy-succinimide, or
the (S)-3-hydroxy-pyrrolidinyl ring, as chiral moieties covalently
linked to the main chain through ester bonds, such as poly[(S)-
(þ)-2-methacryloyloxy-N-[4-(9-carbazolyl)phenyl]succinimide]
{poly[(S)-(þ)-MCPS]} and poly[(S)-(þ)-3-methacryloyloxy-N-[4-
(9-carbazolyl)phenyl]pyrrolidine] {poly[(S)-(þ)-MCPP]} (Fig. 1).
The presence of a strong electron-withdrawing or donating
group such as the five membered cyclic succinimide moiety or the
pyrrolidine residue, respectively, should induce highly conjugated
system, potentially suitable to be used as photoconductive mate-
rials, electroluminescent devices, data storage, chemical photore-
ceptors, NLO, blue emitting materials and holographic memory.
Furthermore, the replacement of the alkyl substituent usually
bound to the N atom of carbazole by a phenyl group, is also
expected to expand the electronic conjugation in the molecules
and to increase the glass transition temperature (Tg) of these
macromolecules.
(S)-(ꢀ)-3-Hydroxy-N-(4-bromophenyl)pyrrolidine [(S)-(ꢀ)-HPP-
Br] and 2-hydroxyethyl-N-ethyl-N-(4-bromophenyl)amine have
been prepared as previously reported [30].
Finally, the influence of chirality on the properties of the
macromolecules was tested. This can be achieved by comparison
with an analogous achiral polymeric derivative obtained by radical
polymerization of the new monomer N-(2-methacryloyloxyethyl)-
N-[4-(9-carbazolyl)phenyl]ethylamine [MCPE]. The structure
of this polymeric model, poly[N-(2-methacryloyloxyethyl)-N-
[4-(9-carbazolyl)phenyl]ethylamine] {poly[MCPE]} is reported in
Fig. 1.
All the polymeric derivatives have been fully characterized and
their spectroscopic properties compared to those of the corre-
sponding monomers with the aim of evaluating the effect of the
macromolecular structure on their physico-chemical properties.
Photoconductivity measurements as a function of applied electric
field under irradiation at fixed wavelength have been performed on
the polymeric samples to investigate the effect of the presence of
different electron-donating or withdrawing moieties linked to the
carbazole group.
2.2. Measurements
1H and 13C NMR spectrawere obtained at room temperature on 5–
10% CDCl3 solutions using a Varian NMR Gemini 300 spectrometer.
Chemical shifts are given in ppm from tetramethylsilane (TMS) as the
internal reference.1H NMR spectra were run at 300 MHz by using the
following experimental conditions: 24 000 data points 4.5-kHz
spectral width 2.6-s acquisition time 128 transients. 13C NMR spectra
were recorded at 75.5 MHz, under full proton decoupling, by using
the following experimental conditions: 24,000 data points, 20 kHz
spectral width, 0.6 s acquisition time, 64,000 transients.
FT-IR spectra were carried out on a Perkin–Elmer 1750 spec-
trophotometer equipped with an Epson Endeavor II data station on
sample prepared as KBr pellets.
Number average molecular weight (Mn) and polydispersity
(Mw=Mn) were determined in THF solution by SEC using an HPLC
Lab Flow 2000 apparatus, equipped with an injector Rheodyne
7725i, a Phenomenex Phenogel 5
m MXL column and a UV–Vis
detector Linear Instruments model UVIS-200, working at 254 nm.
Calibration curves were obtained by using several monodisperse
polystyrene standards.
UV–Vis absorption spectra were recorded at 25 ꢁC on a Perkin
Elmer Lambda 19 spectrophotometer on CHCl3 solutions by using
cell path lengths of 1 and 0.1 cm for the 500–320 and 320–250 nm
spectral regions, respectively. Carbazole chromophore concentra-
tions of about 5$10ꢀ4 mol Lꢀ1 were used.
Fluorescence spectra were recorded between 300 and 700 nm at
25 ꢁC in 1 cm quartz cells with a Perkin Elmer LS55 spectro-
fluorimeter.
Optical activity measurements were accomplished at 25 ꢁC on
CHCl3 solutions with a Perkin Elmer 341 digital polarimeter,
equipped with a Toshiba sodium bulb, using a cell path length of 1
dm. Specific and molar rotation values at the sodium D line
are expressed as deg dmꢀ1 gꢀ1 cm3 and deg dmꢀ1 molꢀ1 dL,
respectively. Molar rotation for polymers refers to the molecular
weight of the repeating unit.
CH3
C
CH3
C
CH3
C
CH2
CH2
CH2
n
n
n
C
O
O
C
O
O
C
O
O
*
*
N
N
N
N
O
O
N
N
Poly[MCPE]
Fig. 1. Chemical structures of the investigated polymers.
Poly[(S)-(+)-MCPP]
Poly[(S)-(+)-MCPS]

370
L. Angiolini et al. / Polymer 51 (2010) 368–377
Circular dichroism (CD) spectra were carried out at 25 ꢁC on
CHCl3 solutions on a Jasco 810 A dichrograph, using the same path
lengths and solution concentrations as for the UV–Vis measure-
ments. D3 values, expressed as L molꢀ1 cmꢀ1 were calculated from
After evaporation of the solvent under reduced pressure, 4.8 g of
sodium fluoride in dist. water (40 ml) were cautiously added to the
solid residue, then the mixture was made acidic (pH 2) with conc.
aq. HCl and refluxed 2 h. After treatment with 30% aq. NaOH (pH 10),
the precipitated crude product was filtered and finally crystallized
from hexane to afford 3.2 g of pure (S)-(þ)-HCPP (yield 72%).
the following expression: D3 ¼ [
Q]/3300, where the molar ellip-
ticity [
Q
] in deg cm2 dmolꢀ1 refers to one carbazole chromophore.
The glass transition temperature (Tg) values were determined by
differential scanning calorimetry (DSC) on a TA Instrument DSC
2920 Modulated apparatus at a heating rate of 10 ꢁC/min under
nitrogen atmosphere on samples of 5–9 mg.
The initial thermal decomposition temperature (Td) was deter-
mined on the polymeric samples with a Perkin–Elmer TGA-7
thermogravimetric analyzer by heating in air at a rate of 20 ꢁC/min.
Samples for photoconductivity measurements were prepared by
squeezing the material between two hot conductive (ITO) glasses,
½
aꢂ2D5 ¼ þ2:6ꢁ ðc ¼ 0:542 in CHCl3Þ:
2.3.2.2. Method B. A mixture of 7.12 g (0.024 mol) of carbazole,
0.55 g of trans-cyclohexanediamine (10% mol) and 0.46 g of air-
stable CuI (10% mol) was prepared in 15 ml of dry dioxane (1 M) in
the presence of 7 g di K2CO3 (2 equiv). Then, 6.92 g (0.029 mol) of
(S)-(ꢀ)-3-hydroxy-N-(4-bromophenyl)pyrrolidine [(S)-(ꢀ)-HPP-Br]
in dry dioxane (10 ml) were added and the resulting solution heated
at reflux under inert atmosphere for 24 h. The cooled mixture was
filtered-off and the organic solution washed with 0.1 M HCl, 5%
Na2CO3 and finally with water, in that order. After drying the organic
phase over anhydrous Na2SO4 and evaporation of the solvent under
reduced pressure, the crude reaction product was purified by column
chromatography (SiO2, CH2Cl2/EtOAc 1:1 v/v as eluent), followed by
crystallization from abs. ethanol to give 6.8 g of pure product (yield
82.0%).
adjusting the thickness with glass spacers to 10 or 5 mm. The cells
were then quickly cooled to room temperature and the final real
thickness measured by interferometry [31]. The samples containing
diphenyl phthalate (DPP) (from Sigma–Aldrich, purified by
recrystallization) as plasticizer, were prepared by first dissolving
the components in chloroform and processing the resulting blend,
after solvent evaporation, according to the method described
above.
Photoconductivity data were obtained by applying a DC voltage
to the sample and measuring the current with a Keithley 6517A
Electrometer in the dark and under illumination. The illuminating
light was provided by a Newport-Oriel 250 W Xenon lamp, coupled
½
a 2D5
ꢂ
¼ þ2:6ꢁ ðc ¼ 0:525 in CHCl3Þ:
1H NMR (CDCl3): 8.30–8.20 (d, 2H, arom. 2,7-H carbazole), 7.60–
7.35 (m, 8H, arom. 1,3,4,5,6,8-H carbazole and 15,19-H phenyl), 6.90
(d, 2H,16,18-H phenyl), 4.90 (m,1H, 3-CH), 3.60–3.50 (m, 4H, 2- and
5-CH2), 3.40 (s, 1H, OH), 2.40–2.20 (m, 2H, 4-CH2) ppm.
with
a Newport-Oriel monochromator (mod 74,100), with
a resulting light intensity I w 3 mW/cm2 or, alternatively, by a laser
light at 532 nm (from Laser Quantum, mod. Torus), with a light
intensity I w 1 W/cm2.
FT-IR (KBr): 3425 (nOH), 3050 (nCH arom.), 2967 (nCH aliph.), 1605
(
nC]C arom.), 1519 (dCH), 1205 (dC–O), 852 and 815 (dCH 1,4-disubst.
arom. ring), 748 (dCH 1,2-disubst. arom. ring) cmꢀ1
.
2.3. Synthesis of intermediate alcohols and monomers
2.3.3. N-(2-Hydroxy)-N-[4-(9-carbazolyl)phenyl]ethylamine
[HCPE]
2.3.1. (S)-(þ)-2-Hydroxy-N-[4-(9-carbazolyl)phenyl]succinimide
[(S)-(þ)-HCPS]
A mixture of 7.12 g (0.024 mol) of carbazole, 0.55 g of trans-
cyclohexanediamine (10% mol) and 0.46 g of air-stable CuI (10%
mol) was prepared in 15 ml of dry dioxane (1 M) in the presence of
7 g di K2CO3 (2 equiv). Then, 7.00 g (0.029 mol) of 2-hydroxyethyl-
N-ethyl-N-(4-bromophenyl)amine in dry dioxane (10 ml) were
added and the resulting solution heated at reflux under inert
atmosphere for 24 h. The cooled mixture was filtered-off and the
organic solution washed with 0.1 M HCl, 5% Na2CO3 and finally with
water, in that order. After drying the organic phase over anhydrous
Na2SO4 and evaporation of the solvent under reduced pressure, the
crude reaction product was purified by column chromatography
(SiO2, CH2Cl2/EtOAc 1:1 v/v as eluent) followed by crystallization
from abs. ethanol to give 3.8 g of pure product (yield 48.0%).
1H NMR (CDCl3): 8.20 (d, 2H, arom. 2,7-H carbazole), 7.40–7.20
(m, 8H, arom. 1,3,4,5,6,8-H carbazole and 15,19-H phenyl), 6.90 (d,
2H, 16,18-H phenyl), 3.95 (d, 2H, N–CH2–CH2), 3.50 (m, 4H, N–CH2),
1.80 (m, 1H, OH), 1.20 (t, 3H, N–CH2–CH3) ppm.
Malic acid chloralide (9.9 g 0.0376 mol) was submitted to chlo-
rination with excess of SOCl2 (0.400 mol) to give, according to the
reported procedure [25], the intermediate acid chloride which was
directly submitted to the cyclization step. After evaporation under
reduced pressure of any unreacted thionyl chloride, dry toluene
(140 mL) and 9.7 g (0.0376 mol) of N-(4-aminophenyl)carbazole
were added and the mixture heated at reflux under inert
atmosphere for 12 h. The solvent was then evaporated under
reduced pressure and the crude product purified by column
chromatography (SiO2, eluent EtOAc/CH2Cl2 1:1 v/v) to give 5.6 g of
pure (S)-(þ)-HCPS (yield 52%).
½
a 2D5
ꢂ
¼ þ5:9ꢁ ðc ¼ 0:603 in CHCl3Þ:
1H NMR (CDCl3): 8.20–8.10 (d, 2H, arom. 2,7-H carbazole), 7.70–
7.65 (d, 2H, arom. 4,5-H carbazole), 7.60–7.55 (d, 2H, 15,19-H
phenyl), 7.40 (m, 4H, arom. 1,3,6,8-H carbazole), 7.30 (m, 2H, 16,18-
H phenyl), 4.85 (m, 1H, 2-CH), 3.40 (s, 1H, OH), 3.35 and 2.94 (2dd,
2H, 3-CH2) ppm.
FT-IR (KBr): 3420 (nOH), 3050 (nCH arom.), 2967 (nCH aliph.), 1605
(
nC]C arom.), 1360 (nCHs CH3), 1231(nC-O alcohol), 847 and 816 (dCH
1,4-disubst. arom. ring), 746 (dCH 1,2-disubst. arom. ring) cmꢀ1
.
FT-IR (KBr): 3458 (nOH), 3050 (nCH arom.), 2967 (nCH aliph.), 1706
(
(
nC]O imide), 1600 (nC]C arom.), 1514 (dCH), 1205 (nC–O), 850 and 830
dCH 1,4-disubst. arom. ring), 744 (dCH 1,2-disubst. arom. ring) cmꢀ1
.
2.3.4. (S)-(þ)-2-methacryloyloxy-N-[4-(9-carbazolyl)phenyl]succi
nimide [(S)-(þ)-MCPS]
To an ice-cooled, vigorously stirred solution of (S)-(þ)-HCPS (2 g,
0.0047 mol), triethylamine (0.79 ml, 0.0057 mol), dimethylamino
pyridine (0.1 g) as catalyst, and 2,6-di-tert-butyl-4-methyl phenol
(0.1 g) as polymerization inhibitor, in anhydrous THF (150 mL),
methacryloyl chloride (0.79 ml, 0.0057 mol) in THF (5 ml) was
added dropwise, under nitrogen atmosphere. The mixture was kept
2.3.2. (S)-(þ)-3-Hydroxy-N-[4-(9-carbazolyl)phenyl]pyrrolidine]
[(S)-(þ)-HCPP]
2.3.2.1. Method A. A 2 M solution of borane-dimethyl sulfide
complex in THF (14.1 ml) was added dropwise, under inert atmo-
sphere, to a stirred solution of (S)-(þ)-HCPS (4 g, 0.00938 mol) in
dry THF (45 ml) and the mixture kept under reflux for one night.

L. Angiolini et al. / Polymer 51 (2010) 368–377
371
ice-cooled for 2 h, then left at room temperature for one night,
2.4. General polymerization procedure
concentrated at reduced pressure and the crude product dissolved
in chloroform. The chloroformic solution was washed with 0.1 M
HCl, 5% Na2CO3 and finally with water, in that order.
After drying the organic phase over anhydrous Na2SO4 and
evaporation of the solvent under reduced pressure, the crude
reaction product was purified by column chromatography (SiO2,
CH2Cl2/EtOAc 4:1 v/v as eluent) followed by crystallization from
abs. ethanol to give 1.70 g of pure product (yield 70.0%).
The polymerization of the monomers was carried out in glass
vials using AIBN as free radical initiator and THF as solvent. The
reaction mixture (1.0 g of monomer, 2% weight of AIBN in 25 ml of
THF) was introduced into the vial under nitrogen atmosphere,
submitted to several freeze–thaw cycles and heated at 60 ꢁC for
72 h. The reaction was then stopped by pouring the mixture into
a large excess (200 ml) of methanol, and the coagulated polymer
filtered-off. The solid polymeric product was repeatedly redissolved
in THF at room temperature and reprecipitated again with meth-
anol. The last traces of unreacted monomers and oligomeric
impurities were eliminated by Soxhlet continuous extraction with
methanol followed by acetone. The material was finally dried at
60 ꢁC under vacuum for several days to constant weight.
Relevant data for the synthesized homopolymers are reported in
Table 1.
½
a 2D5
ꢂ
¼ þ2:0ꢁðc ¼ 0:996 in CHCl3Þ:
1H NMR (CDCl3): 8.20–8.10 (d, 2H, arom. 2,7-H carbazole), 7.80–
7.70 (d, 2H, arom. 4,5-H carbazole), 7.60–7.55 (d, 2H, 15,19-H
phenyl), 7.40 (m, 4H, arom.1,3,6,8-H carbazole), 7.30 (m, 2H,16,18-H
phenyl), 6.35 and 5.75 (2dd, 2H, CH2 methacrylic), 5.60 (m, 1H, 2-
CH), 3.40 and 2.95 (d, 2H, 3-CH2), 2.00 (s, 3H, CH3 methacrylic) ppm.
FT-IR (KBr): 3050 (nCH arom.), 2967 (nCH aliph.), 1716 (nC]O
ester), 1705 (nC]O imide), 1633 (nC]C methacrylic), 1600 (nC]C
arom.), 1512 (dCH2), 1460 (nCHas CH3), 1356 (nCHs CH3), 1230(dC–O),
1161 (nC–O), 832 and 810 (dCH 1,4-disubst. arom. ring), 751 (dCH 1,2-
2.5. Spectroscopic data of polymers
disubst. arom. ring) cmꢀ1
.
2.5.1. Poly[(S)-(þ)-MCPS]
1H NMR (CDCl3): 8.20–7.80 (d, 2H, arom. 2,7-H carbazole), 7.80–
6.90 (m, 10H, arom. 1,3,4,5,6-H carbazole and 15,16,18,19-H
phenyl.), 5.60 (m, 1H, 2-CH2), 3.40–2.95 (m, 2H, 3-CH2), 2.10–1.00
(m, 3H, CH3 and CH2 backbone) ppm.
2.3.5. (S)-(þ)-3-methacryloyloxy-N-[4-(9-carbazolyl)phenyl]
pyrrolidine [(S)-(þ)-MCPP]
The same procedure adopted for (S)-(þ)-MCPS was followed
starting from (S)-(þ)-HCPP (3.5 g, 0.0107 mol), triethylamine
(1.8 ml, 0.0128 mol), dimethylamino pyridine (0.2 g) and 2,6-di-
tert-butyl-4-methyl phenol (0.2 g) in THF (150 ml). The acylation
reaction was performed by using methacryloyl chloride (1.24 ml,
0.0128 mol). Pure (S)-(þ)-MCPP was obtained in 71.0% yield (2.25 g)
by column chromatography purification (SiO2, CH2Cl2/EtOAc 1:1 v/v
as eluent) followed by crystallization from abs. ethanol.
FT-IR (KBr): 3050 (nCH arom.), 2967 (nCH aliph.), 1724 (nC]O
ester), 1600 (nC]C arom.), 1512 (dCH2), 1365 (nCHs CH3), 1200 (nC-O
ester), 850 and 834 (dCH 1,4-disubst. arom. ring), 748 (dCH 1,2-dis-
ubst. arom. ring) cmꢀ1
.
½
a 2D5
ꢂ
¼ þ6:4ꢁ ðc ¼ 0:806 in CHCl3Þ:
2.5.2. Poly[(S)-(þ)-MCPP]
1H NMR (CDCl3): 8.20–8.00 (d, 2H, arom. 2,7-H carbazole), 7.40–
7.00 (m, 8H, arom. 1,3,4,5,6,8-H carbazole and 15,19-H phenyl),
6.80–6.40 (m, 2H, 16,18-H phenyl), 5.40–5.00 (m, 1H, 3-CH), 3.70–
3.00 (m, 4H, 2- and 5-CH2), 2.40–0.80 (m, 7H, 4-CH2 and backbone
CH3 and CH2) ppm.
½
a 2D5
ꢂ
¼ þ9:3ꢁðc ¼ 0:994 in CHCl3Þ:
1H NMR (CDCl3): 8.20–8.10 (d, 2H, arom. 2,7-H carbazole), 7.40–
7.20 (m, 8H, arom. 1,3,4,5,6,8-H carbazole and 15,19-H phenyl), 6.80
(d, 2H, 16,18-H phenyl), 6.15 and 5.60 (2dd, 2H, CH2 methacrylic),
5.55 (m, 1H, 3-CH), 3.60–3.40 (m, 4H, 2 and 5-CH2), 2.40–2.30 (m,
2H, 4-CH2), 1.95 (s, 3H, CH3 methacrylic) ppm.
FT-IR (KBr): 3050 (nCH arom.), 2967 (nCH aliph.), 1737 (nC]O
ester) 1608 (nC]C arom.), 1519 (nCH2), 1451 (nCHas CH3), 1365 (nCHs
CH3), 1161 (nC–O ester), 851 and 814 (dCH 1,4-disubst. arom. ring),
FT-IR (KBr): 3050 (nCH arom.), 2967 (nCH aliph.), 1718 (nC]O
ester), 1608 (nC]C arom.), 1519 (dCH2), 1450 (nCHas CH3), 1356 (nCHs
CH3), 1231 (nC–O alcohol), 1161 (nC–O ester) 850 and 815 (dCH 1,4-
746 (dCH 1,2-disubst. arom. ring) cmꢀ1
.
disubst. arom. ring), 748 (dCH 1,2-disubst. arom. ring) cmꢀ1
.
½
a 2D5
ꢂ
¼ þ9:0ꢁ ðc ¼ 0:792 in CHCl3Þ:
2.3.6. N-(2-methacryloyloxyethyl)-N-[4-(9-carbazolyl)phenyl]
ethylamine [MCPE]
2.5.3. Poly[MCPE]
1H NMR (CDCl3): 8.20–8.00 (d, 2H, arom. 2,7-H carbazole), 7.40–
6.40 (m, 18H, arom. 1,3,4,5,6,8-H carbazole and 15,19-H phenyl),
6.80 (m, 2H, 16,18-H phenyl), 3.95 (m, 2H, N–CH2–CH2), 3.70–3.50
(m, 4H, N-CH2), 2.10–0.80 (m, 8H, N–CH2–CH3 and backbone CH2
and CH3) ppm.
The same procedure adopted for (S)-(þ)-MCPS was followed
starting from HCPE (3.3 g, 0.0097 mol), triethylamine (1.63 ml,
0.0128 mol), dimethylamino pyridine (0.2 g) and 2,6-di-tert-butyl-
4-methyl phenol (0.2 g) in THF (100 ml). The acylation reaction was
performed by using methacryloyl chloride (1.14 ml, 0.0117 mol).
Pure MCPE was obtained in 55.0% yield (2.1 g) by column chro-
matography (SiO2, CH2Cl2/EtOAc 1:1 v/v as eluent) followed by
crystallization from abs. ethanol.
Table 1
Characterization data of polymeric derivatives.
b
b
c
d
Sample
Yielda
Mn
M
w=Mn
Tg
Td
1H NMR (CDCl3): 8.20 (d, 2H, arom. 2,7-H carbazole), 7.40–7.20
(m, 8H, arom. 1,3,4,5,6,8-H carbazole and 15,19-H phenyl), 6.90
(d, 2H, 16,18-H phenyl), 6.15 and 5.60 (d, 2H, CH2 methacrylic), 4.50
(d, 2H, N–CH2–CH2), 3.70–3.50 (m, 4H, N–CH2), 2.00 (s, 3H, CH3
methacrylic), 1.20 (t, 3H, N–CH2–CH3).
Poly[(S)-(þ)-MCPS]
Poly[(S)-(þ)-MCPP]
Poly[MCPE]
83
80
80
11400
7000
10100
1.9
1.9
1.9
244
194
129
336
343
320
a
Calculated as (g polymer/g monomer)$100.
Determined by GPC in THF solution at 25 ꢁC, expressed in g molꢀ1
b
c
.
FT-IR (KBr): 3048 (nCH arom.), 2978 (nCH aliph.), 1716 (nC]O),
1623 (nC]C methacrylic),1605 (nC]C arom.),1520 (dCH2), 1450 (nCHas
CH3), 1371 (nCHs CH3), 1169 (nC–O ester), 852 and 814 (dCH 1,4-dis-
Glass transition temperature determined by DSC at 10 ꢁC/min heating rate
under nitrogen flow, expressed in ꢁC.
d
Initial decomposition temperature as determined by TGA at 20 ꢁC/min heating
ubst. arom. ring), 753 (dCH 1,2-disubst. arom. ring) cmꢀ1
.
rate under air flow, expressed in ꢁC.

372
L. Angiolini et al. / Polymer 51 (2010) 368–377
CH3
C
CH2
C
O
O
CH3
C
OH
CH2
O
O
NH2
*
Cl3C
*
C
O
*
O
O
O
Cl
CH2COCl
N
N
O
O
TEA DMAP
N
N
N
(S)-(+)-HCPS
(S)-(+)-MCPS
.
(CH3)2S BH3
CH3
CH2
C
C
O
O
CH3
OH
OH
*
OH
CH2
C
NH2
NH2
*
*
*
C
O
CuI /
N
N
N
N
N
N
Cl
Br2 / CH2Cl2
H
N
Bu4NBr / MeOH
TEA DMAP
Br
(S)-( )-HPP-Br
Dioxane 110°C
−
(S)-(−)-HPP
(S)-(+)-HCPP
(S)-(+)-MCPP
CH3
C
CH2
C
O
O
CH3
OH
OH
OH
CH2
C
NH2
C
O
CuI /
N
N
N
N
NH2
Cl
Br2 / CH2Cl2
H
N
Bu4NBr / MeOH
TEA DMAP
N
Br
N
Dioxane 110°C
MCPE
HCPE
Scheme 1. Synthesis of monomers.
FT-IR (KBr): 3048 (nCH arom.), 2978 (nCH aliph.), 1716 (nC]O
The aromatic amine was submitted to reaction with the acyl
chloride obtained by chlorination of (S)-malic acid chloralide,
derived in turn from (S)-(ꢀ)-malic acid by reaction with chloral
hydrate [25], to give the key intermediate (S)-(þ)-2-hydroxy-N-[4-
(9-carbazolyl)phenyl]succinimide [(S)-(þ)-HCPS].
ester), 1605 (nC]C arom.), 1520 (nCH2), 1450 (nCHas CH3), 1371 (nCHs
CH3), 1169 (nC–O ester.), 852 and 814 (dCH 1,4-disubst. arom. ring),
753 (dCH 1,2-disubst. arom. ring) cmꢀ1
.
(S)-(þ)-HCPS was then selectively reduced to the alcohol (S)-
3. Results and discussion
(þ)-3-hydroxy-N-[4-(9-carbazolyl)phenyl]pyrrolidine
[(S)-(þ)-
HCPP] with a synthetic procedure used for analogous chiral
derivatives [28].
3.1. Synthesis of monomers
N-(2-hydroxy)-N-[4-(9-carbazolyl)phenyl]ethylamine [HCPE]
(Scheme 1) was instead prepared starting from N-(4-bromo-
phenyl)-N-ethyl-N-(2-hydroxyethyl)amine, derived in turn from
the bromination of N-ethyl-N-(2-hydroxyethyl)phenylamine. This
compound was coupled with carbazole, under Ullmann’s condi-
tions [27], to provide the desired alcohol.
The synthesis of (S)-(þ)-MCPS and (S)-(þ)-MCPP was carried
out according to Scheme 1, starting from the N-(4-amino-
phenyl)carbazole, obtained by Ullmann reaction [27] of carbazole
with 1-bromo-4-nitrobenzene, followed by selective reduction to
amine of the nitro group.

L. Angiolini et al. / Polymer 51 (2010) 368–377
373
Table 2
UV–vis spectra in CHCl3 solution at 25 ꢁC of monomers and polymeric derivates.
Sample
1st band
2nd band
3rd band
4th band
5th band
a
b
a
b
a
b
a
b
a
b
lmax
3max
lmax
3max
lmax
3max
lmax
3max
lmax
3max
(S)-(þ)-MCPS
Poly[(S)-(þ)-MCPS]
(S)-(þ)-MCPP
Poly(S)-(þ)-MCPP]
MCPE
–
–
268
269
268
269
–
–
283
280
283
283
283
283
14700
15500
21500
20400
24400
20100
292
293
292
293
292
293
18600
19600
20000
18900
22150
18500
325
325
328
329
326
327
3000
4500
3200
4100
3800
3900
338
339
341
342
340
341
3200
3600
3000
4600
3400
3200
25400
22800
27900
22200
Poly[MCPE]
a
Wavelength of maximum absorbance, expressed in nm.
b
Calculated for one single chromophore, expressed in Lmolꢀ1cmꢀ1
.
The synthesis of (S)-(þ)-HCPP was also carried out with the
the contemporary appearance of the band at 1728–1731 cmꢀ1
,
same synthetic procedure adopted for HCPE (Scheme 1) starting
from the alcoholic intermediate (S)-(ꢀ)-3-hydroxy-N-phenyl-
pyrrolidine [(S)-(ꢀ)-HPP], prepared as previously reported [28],
giving essentially similar results as the above described synthetic
method (see experimental part), with the aim to verify the occur-
rence of partial racemization in the course of the synthesis.
The three novel monomers (S)-(þ)-2-methacryloyloxy-N-[4-(9-
carbazolyl)phenyl]succinimide [(S)-(þ)-MCPS], (S)-(þ)-3-metha-
cryloyloxy-N-[4-(9-carbazolyl)phenyl]pyrrolidine [(S)-(þ)-MCPP]
and N-(2-methacryloyloxyethyl)-N-[4-(9-carbazolyl)phenyl]ethyl-
amine [MCPE] were finally obtained with good yields by esterifi-
cation of the related alcohols with methacryloyl chloride.
related to the carbonyl stretching vibration of the a,b saturated
methacrylic ester group, shifted to higher frequency by ca. 10 cmꢀ1
with respect to the corresponding band of the monomeric
precursors.
The 1H NMR spectra of polymers, as compared to those of
monomers (see experimental part), are also in agreement with the
proposed structures. In accordance with FT-IR data, the resonances
at 5.60 and 6.15 ppm, related to the methacrylic CH2 protons, are
absent in the 1H NMR spectra of the polymers, and the methacrylic
CH3 resonance is shifted from 1.95 ppm to higher field. It is also to
be noted that the resonances of the polymeric aromatic protons are
shifted upfield to a variable extent with respect to the monomers,
thus indicating the presence of shielding interactions between the
side-chain chromophores in solution (see experimental part).
The microtacticity of synthesized polymers, as evaluated by
integration of the 13C NMR signals related to the methacrylic
methyl group at about 20 and 18 ppm, belonging to heterotactic
meso-racemo (mr) and syndiotactic racemo–racemo (rr) triads [32],
respectively, indicates a content of rr triads around 51–55%, with
a probability of formation of meso and racemo dyads of 0.24–0.27
and 0.73–0.76, respectively, in agreement with literature reports
concerning the radical polymerization of analogous methacrylic
derivatives containing carbazole [21,33]. Thus, the main chain
The structures of all novel intermediates and final products were
confirmed by 1H NMR and FT-IR spectroscopy.
3.2. Synthesis of polymers
The polymerization of the monomers, carried out in solution
under free radical conditions by using AIBN as a thermal initiator,
produced the corresponding polymeric derivatives in acceptable
yields after purification, with average molecular weight and poly-
dispersity values, as determined by gel permeation chromatography
(GPC), in the range expected for this type of process. The polymeric
products are completely soluble in common organic solvents such as
CHCl3 and THF, this feature favouring the possibility of their appli-
cation as thin films.
Relevant data for the synthesized homopolymers are reported in
Table 1.
The occurred polymerization was also proved by IR spectros-
copy by checking the disappearance in the spectra of the absorption
at 1630–1635 cmꢀ1, related to the methacrylic double bond, and
25000
20000
15000
10000
5000
0
350
400
450
500
550
(nm)
250
300
350
400
450
500
Fig. 3. Fluorescence spectra of poly[(S)-(þ)-MCPS] (---), poly[(S)-(þ)-MCPP] (d),
poly[MCPE] (d), (S)-(þ)-MCPS (-,-), (S)-(þ)-MCPP (...) and MCPE (.) in CHCl3,
excited at 293 nm (concentration about 10ꢀ5 mol/L). The intensities are normalized to
the concentration of carbazole unit.
.
Fig. 2. UV–vis spectra in CHCl3 solution of poly[(S)-(þ)-MCPP]
(þ)-MCPS (d).
(
)
and poly[(S)-

374
L. Angiolini et al. / Polymer 51 (2010) 368–377
Table 3
the polymers investigated containing the residue of 9-phenyl-
carbazole are considerably higher than those of analogous poly-
mers with aliphatic linear spacers between the carbazole
chromophore and the methacrylic main chain [33,35–37].
The noticeable high thermal stability and Tg values suggest that
these polymeric materials may be promisingly tested for
commercial applications, besides the optical ones, where thermal
stability is a fundamental requirement.
Specific and molar optical rotation data of the synthesized compounds in CHCl3
solution at 25 ꢁC.
Sample
½
a 2D5
ꢂ
½ ꢂ
F 2D5
a
b
(S)-(þ)-MCPS
þ2.0
þ6.4
þ9.3
þ9.0
þ8.5
Poly[(S)-(þ)-MCPS]
(S)-(þ)-MCPP
þ27.2
þ38.2
þ36.9
Poly[(S)-(þ)-MCPP]
a
Specific optical rotation, expressed in deg$dmꢀ1 gꢀ1$dL.
Molar optical rotation, calculated as ð½a D25
ꢂ
$M=100Þ, where M represents the
b
molecular weight of the monomer or the molecular weight of the repeating unit of
the polymer, in other word the molar optical rotation for carbazole unit, expressed
in deg$dmꢀ1$molꢀ1$dL.
3.4. UV–Vis and fluorescence properties
The UV–vis absorption spectra in CHCl3 solution of monomers
and polymers (Table 2 and Fig. 2) exhibit, in the region 250–
microstructure is essentially atactic, with a predominance of syn-
diotactic triads, suggesting a substantial low stereoregularity of the
main chain.
500 nm, evident absorption bands attributed to
p-p* electronic
transitions of the carbazole chromophore [38]. In accordance with
Platt notation, these bands are related to three spectral regions,
located between 350 and 315 nm (1Lb ) 1A1 electronic transition),
310–280 nm (1La ) 1A1 electronic transition) and 280–260 nm
(1B2 ) 1A1 electronic transition) [39].
3.3. Thermal properties
The thermal stability of all polymeric derivatives, one of the
most important features for the applicability of these materials, as
determined by thermogravimetric analysis (TGA), resulted very
high, with onset decomposition temperatures (Td) in the range
320–343 ꢁC (Table 1), much higher than those reported for the
classic polyvinylcarbazole (PVK) (227 ꢁC) [34], deeply investigated
as polymeric material for photorefractive applications [1], and
other methacrylic carbazole-containing polymers [35] and is
indicative of strong dipolar interactions in the solid state between
the chromophores located in the macromolecular side chains. The
highest Td value (343 ꢁC) displayed by poly[(S)-(þ)-MCPP] can be
thus attributed to increased inter- and/or intramolecular polar
interactions between the neighbouring side-chain moieties.
As expected, only second-order transitions originated by glass
transitions (Tg), with no melting peaks, are observed in the DSC
thermograms of the investigated polymers (Table 1), thus con-
firming that the macromolecules are substantially amorphous in
the solid state. The high Tg values displayed by poly[(S)-(þ)-MCPS]
and poly[(S)-(þ)-MCPP], as measured by DSC (224 and 194 ꢁC,
respectively) can be of interest for applications in optoelectronics
and photonics (more stable photorefractivity, holographic storage,
etc.); high values of Tg being in fact required in order to achieve
enhanced temporal stability at room temperature of the electrically
oriented dipoles in the bulk.
The UV–vis absorption spectra of (S)-(þ)-MCPP and poly[(S)-
(þ)-MCPP] display five absorption bands with maxima centered
about at 268, 283 (shoulder), 292, 328 e 341 nm related to
p–p*
electronic transitions. By contrast, (S)-(þ)-MCPS and poly[(S)-
(þ)-MCPS] show only four absorption bands of similar intensity
centered at about 280 (shoulder), 293, 325 e 339 nm, related to the
above mentioned electronic transitions of carbazole. The dissimilar
nature of the bands can be ascribed to the presence of the succi-
nimide residue, characterized by electron-withdrawing capability,
originating lower electron density in the conjugated chromophoric
system with respect to the pyrrolidine ring.
Achiral poly[MCPE] shows analogue absorptions bands as
optically active poly[(S)-(þ)-MCPP] (Table 2). This behaviour can be
attributed to similar architectures of the phenylcarbazole moiety
and electron-donating power of the amine nitrogen atoms located
in the N-ethyloxy-N-ethylamine and pyrrolidine residues, respec-
tively, which increase the electron density in the carbazole moiety.
In these last systems, while the maximum absorption wave-
lengths (Table 2) do not substantially change in going from the
monomers to the related polymers, a remarkable hypochromic
effect is observed when the spectra of (S)-(þ)-MCPP and MCPE,
where the lack of structural restraints originates a random distri-
bution of the chromophores in dilute solution, are compared with
those of the related polymers (Table 2).
In particular, the Tg of poly[(S)-(þ)-MCPP] is considerably
higher, by about 65 ꢁC, than that measured for poly[MCPE]. This
behaviour is indicative of a reduced mobility of the macromolecular
chains containing (S)-(þ)-MCPP due to the presence of the con-
formationally rigid pyrrolidine ring interposed between the back-
bone and the 9-phenylcarbazole chromophore. Accordingly,
poly[(S)-(þ)-MCPS] containing the even more rigid succinimide
ring, shows the highest Tg value. Again, in accordance with
a reduced mobility of the macromolecular chains originated by
their dipolar structure and conformational stiffness, the Tg values of
This behaviour, frequently noticed in polymeric derivative
bearing side-chain aromatic chromophores [19,30,33], is attributed
to the presence of electrostatic dipole–dipole interactions between
the neighbouring aromatic moieties [40–42] and confirms the
occurrence of interactions between the side-chain carbazole groups
(particularly in poly[MCPE]), which appear promising for achieving
good photoconductivity even in the absence of dopants.
Fig. 3 shows the fluorescence spectra of synthesized polymers
and relative monomers in CHCl3 dilute solution (concentration of
carbazole chromophore about 10ꢀ5 mol/L) excited at 293 nm.
Table 4
CD spectra in CHCl3 solution at 25 ꢁC of monomers and polymeric derivatives.
Sample
1st band
2nd band
3rd band
4th band
5th band
a
b
a
b
a
b
a
b
a
b
l1
D31
l2
D32
l3
D33
l4
D34
l5
D35
(S)-(þ)-MCPS
266
268
269
269
þ0.42
þ0.81
ꢀ0.24
ꢀ1.56
286
278
290
288
þ0.94
þ0.70
þ0.56
þ0.57
–
308
–
–
–
–
324
334
–
–
338
342
–
þ0.21
þ0.40
–
þ0.23
Poly[(S)-(þ)-MCPS]
(S)-(þ)-MCPP
þ2.21
–
–
þ0.23
Poly[(S)-(þ)-MCPP]
–
þ0.25
347
a
Wavelength of maximum dichroic absorption, expressed in nm.
b
Calculated for one repeating unit in the polymer, expressed in Lmolꢀ1cmꢀ1
.

L. Angiolini et al. / Polymer 51 (2010) 368–377
375
more intense than those measured on the corresponding mono-
mers. The imperfect correspondence of the bands between the CD
and UV–vis spectrum can be explained by considering that they are
originated by a sum of electronic transitions which can be differ-
ently influenced by the chirality of the macromolecules.
0,5
0,0
In particular, the CD spectra of poly[(S)-(þ)-MCPP] and (S)-
(þ)-MCPP exhibit four and three dichroic bands, respectively (Fig. 4
and Table 4). The monomer shows one negative signal at 269 nm
and two positive signals at 290 and 324 nm of low intensity, while
the polymer shows more intense signals at the same wavelengths
(particularly relevant the negative dichroic absorption around
269 nm) and one additional positive dichroic band around 347 nm
with respect to the monomer.
-0,5
-1,0
-1,5
The CD spectrum of poly[(S)-(þ)-MCPS] exhibits four relevant
positive dichroic bands (lmax ¼ 342, 308, 278 and 268 nm) in the
spectral region related to the
p-p* electronic transition of the
250
300
350
400
450
500
carbazole chromophore (Table 4). Significantly, the CD spectrum of
the corresponding monomer (S)-(þ)-MCPS displays only three
weak positive dichroic signals (lmax ¼ 338, 286 and 266 nm),
related to its UV–vis absorptions (Fig. 5 and Table 4).
Fig. 4. CD spectra in CHCl3 solution of (S)-(þ)-MCPP (- - - -) and poly[(S)-(þ)-MCPP] (d).
It appears, therefore, that the presence of an optically active
cyclic residue of one prevailing absolute configuration, interposed
between the main chain and the 9-phenylcarbazole residue,
favours to some extent the establishment of conformational
dissymmetry in the macromolecules and chiral perturbation on the
electronic transitions of the 9-phenylcarbazole chromophore [30].
These effects, previously observed in several polymers bearing
optically active side-chain carbazole [21] or azocarbazole [30,33]
chromophores arranged in a mutual chiral geometry of one pre-
vailing handedness, at least for chain segments of the macromol-
ecules in solution [9,43–45], should be due to the presence of
dipole–dipole interactions between neighbouring carbazole
groups, as suggested by the UV–vis spectra in solution. Indeed,
similar dipolar interactions are absent in the spectrum of mono-
mers, that do not have any structural restriction in dilute solution
and thus are unable to produce cooperative chiral interactions
between the chromophores.
Both the solutions of (S)-(þ)-MCPP and MCPE emit strong
fluorescence in the blue region with maximum wavelength at about
407 and 408 nm, respectively. Poly[(S)-(þ)-MCPP] and poly[MCPE]
emit in a similar manner, with a small intensity quenching with
respect to the related monomers. This similar fluorescence spec-
troscopic pattern suggests that the 9-phenylcarbazole moieties in
the side-chain emit regardless the presence of the poly-
methacrylate backbone, at least in dilute solution, and the different
electron-donating properties of amine and pyrrolidine nitrogen
atoms.
The fluorescence spectra of (S)-(þ)-MCPS and poly[(S)-
(þ)-MCPS] show two strong emission bands at lmax values of about
348 and 362 nm, with a shoulder at about 383 nm which should be
due to fluorescence of the carbazole chromophore (Fig. 3). Clearly,
the fluorescence efficiency is significantly lower for the polymeric
sample (quenching) than for the monomer. This behaviour is due to
the existence of intramolecular interactions between neighbouring
carbazole chromophores along the polymer chains [24].
The CD spectra of poly[(S)-(þ)-MCPS] and poly[(S)-(þ)-MCPP]
registered in the temperature range 10–40 ꢁC at concentrations
of carbazole repeating unit varying within 10ꢀ6–10ꢀ2 mol Lꢀ1
,
The above results clearly demonstrate that the strength and the
type of the inter- and intrachromophoric interactions in carbazole-
containing polymers can be tuned by the electron-withdrawing
and donating properties of the substituent at carbazole so as to give
rise to different photoconductive mechanisms.
3,0
1,5
3.5. Chiroptical properties
The dependence of optical activity on the macromolecular
structure was assessed by measuring the specific f½a D25
ꢂ
g and molar
f½F 2D5
ꢂ
g optical rotation in chloroform solution at the sodium
D
line
of monomers and related polymers (Table 3).
Poly[(S)-(þ)-MCPS] shows higher specific and molar optical
rotation values than the corresponding monomer, thus suggesting
a conformational contribution to the overall optical activity by the
macromolecules with respect to (S)-(þ)-MCPS. Instead, poly[(S)-
(þ)-MCPP] and (S)-(þ)-MCPP display substantially similar optical
activity.
0,0
To investigate in more detail their chiroptical properties,
monomers and polymers have been submitted to CD spectroscopy
in chloroform solution in the spectral region between 250 and
650 nm (Table 4, Figs. 4 and 5).
-1,5
The CD spectra of poly[(S)-(þ)-MCPS] and poly[(S)-(þ)-MCPP]
are characterized by dichroic signals in correspondence to the UV–
Vis absorption bands. These signals, which are related to the elec-
tronic transitions of the 9-phenylcarbazolyl chromophores, are
250
300
350
400
450
500
(nm)
Fig. 5. CD spectra in CHCl3 solution of (S)-(þ)-MCPS (- - -) and poly[(S)-(þ)-MCPS] (d).

376
L. Angiolini et al. / Polymer 51 (2010) 368–377
for poly[(S)-(þ)-MCPP] and
a
¼ 118 cmꢀ1 for poly[(S)-(þ)-MCPS]
2,5
2,0
1,5
1,0
0,5
0,0
(85 wt % þ 15 wt % DPP). The difference between the samples has
therefore to be more likely attributed to the presence of a charge-
transfer (CT) complex [24] between the strong electron donator
pyrrolidine and carbazole in poly[(S)-(þ)-MCPP], as evidenced by
the emission band at 407 nm in the fluorescence spectrum. In fact,
CT process can positively affect photoconductivity by two different
mechanisms: photogeneration efficiency, due to the stabilization of
charged species, and transport parameters, which can be favoured
by more efficient holes hopping between more electron-rich
carbazole moieties.
0,4
0,2
0,0
0
15 30 45 60
By contrast, poly[MCPE] (85 wt % þ 15 wt % DPP) (Fig. 6 and
Table 5) shows a considerable higher value of photoconductivity
with respect to poly[(S)-(þ)-MCPS] and the analogous poly[(S)-
(þ)-MCPP]. This behaviour can be ascribed to the different struc-
ture of the repeating units: in poly[MCPE], the 9-phenylcarbazole
residue is linked to the backbone through a flexible spacer, whereas
in (S)-(þ)-MCPS and (S)-(þ)-MCPP units, the conformational
freedom of the carbazole chromophore is limited by the five
membered succinimide and pyrrolidine rings, so as to reduce the
mobility of the side chains. These results suggest that the appro-
priate flexibility of the spacer connecting the carbazole moiety to
the main chain may favour the adoption of a convenient mutual
geometry of the neighbouring 9-phenylcarbazole chromophores,
thus allowing a better carrier transport via hopping process with
consequent improvement of the photoconductive properties of the
material.
0
10
20
30
40
50
60
70
Fig. 6. Photoconductivity vs. the electric field at 532 nm of poly[MCPE] mixed with
15% w/w of DPP (:), pure poly[(S)-(þ)-MCPP] ( ) and poly[(S)-(þ)-MCPS] mixed
6
with 15% w/w of DPP (C). Inset: enlargement of pure poly[(S)-(þ)-MCPP] (
6) and
poly[(S)-(þ)-MCPS] with 15% w/w of DPP (C).
resulted, in the limit of experimental errors, practically unchanged.
This confirms the presence of intramolecular interactions between
side-chain chromophores which appear stable at least in the range
of temperatures investigated.
However, the contribution by conformational dissymmetry to
the overall optical activity of the synthesized polymers appears of
limited extent with respect to the previously investigated [21]
4. Conclusions
poly[(S)-(þ)-MECSI] ðf½F D25
ꢂ g ¼ þ668:0Þ and poly[(S)-(ꢀ)-MECP]
ðf½F 2D5
ꢂ g ¼ þ200:7Þ, as suggested also by the specific optical rota-
Novel chiral homopolymeric methacrylates, poly[(S)-(þ)-MCPS]
and poly[(S)-(þ)-MCPP] have been obtained by radical polymeri-
zation of the related novel monomers, bearing the optically active
residues of (S)-2-hydroxy-succinimide and (S)-3-hydroxy-pyrroli-
dine, respectively, interposed between the main chain and the
9-phenylcarbazole chromophore.
In order to evaluate the influence of the chirality on the prop-
erties of these macromolecules, an analogous achiral new polymer
{poly[MCPE]} has been also synthesized.
tory power at the sodium D line. In fact, the homopolymers bearing
the 9-phenylcarbazolyl group linked to the nitrogen atom of the
pyrrolidine or succinimide ring through the phenyl substituent
display ½F 2D5
ꢂ
values about one order of magnitude lower than the
derivatives having the chiral succinimide and pyrrolidine residues
directly linked to the carbazole chromophore, thus indicating that
in the latter a much more efficient chirality induction on the
carbazole moiety takes place.
The presence of strong dipolar interactions between the side-
chain 9-phenylcarbazole groups in the solid state also produces
relevant thermal properties with high values of Tg and Td which can
be of interest for nanoscale technological applications.
Absorption and fluorescence spectra confirm the presence of
dipolar interaction between neighbouring 9-phenylcarbazole
moieties.
The optical activity shown by the chiral homopolymers with
respect to the related monomers indicates that the macromolecules
assume, in solution, conformations with a prevailing chirality, at
least for chain sections of the macromolecules, as demonstrated by
the presence in the CD spectra of dichroic signals, related to the
electronic transitions of the 9-phenylcarbazole chromophores.
However this effect is remarkably reduced with respect to previ-
ously investigated analogous polymeric derivatives bearing the
chiral moiety directly linked to the carbazole group.
3.6. Photoconductive properties
All the polymeric samples, given the presence of the carbazole
moiety which is well known for its hole conducting properties [1],
do not require the addition of dopants in order to exhibit photo-
conductivity. The main results obtained are shown in Fig. 6 and
Table 5.
As reported in the inset of Fig. 6, pure poly[(S)-(þ)-MCPP] shows
higher photoconductivity than poly[(S)-(þ)-MCPS] (85 wt
% þ 15 wt % DPP). This different behaviour cannot be ascribed to the
presence of the plasticizer DPP and to the absorption coefficients of
the materials at
l
¼ 532 nm, that appear quite similar,
a
¼ 147 cmꢀ1
Table 5
Photoconductivity of the investigated polymers.
The photoconductivity measurements indicate that the pres-
ence of a flexible spacer interposed between the main chain and the
9-phenylcarbazole chromophore favours the adoption of chromo-
phore conformations suitable to provide a better carrier transport
via hopping process.
The properties of this class of optically active carbazole poly-
mers, bearing at the same time different chemical functionalities,
may allow a variety of potential applications based on photocon-
ductive properties.
Sample (% DPP)a
s
/Ib
s
/Ic
ad
s/a
Ie
Poly[(S)-(þ)-MCPS] (15%)
Poly[(S)-(þ)-MCPP]
Poly[MCPE] (15%)
3.5ꢃ10ꢀ13
7.8ꢃ10ꢀ13
1.3ꢃ10ꢀ11
8.3ꢃ10ꢀ13
1.6ꢃ10ꢀ12
2.4ꢃ10ꢀ11
118
147
78
7.0ꢃ10ꢀ15
1.1ꢃ10ꢀ14
3.1ꢃ10ꢀ13
a
Weight % of plasticizer (DPP) in the sample.
b
c
Photoconductivity expressed in
Photoconductivity expressed in
s
s
/I (S cm Wꢀ1) at 18 V/
/I (S cm Wꢀ1) at 35 V/
m
m
m.
m.
d
e
Absorption coefficient at 532 nm expressed in cmꢀ1
.
Photoconductivity expressed in s/a W mm.
I (S cm2 ꢀ1) at 35 V/

L. Angiolini et al. / Polymer 51 (2010) 368–377
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