Synthesis and characterization of fluorescent graft fluorene-co-polyphenol derivatives: The effect of substituent on solubility, thermal stability, conductivity, optical and electrochemical properties

Article abstract of DOI:10.1016/j.reactfunctpolym.2010.07.013

A series of fluorene Schiff bases and their oligophenol derivatives were successfully synthesized using the condensation and graft copolymerization reactions, respectively. The synthesized compounds were good soluble in common organic solvents. Photoluminescence (PL) properties of the synthesized materials were determined in solution forms. As to the fluorene copolymers (FPs), higher PL intensities were obtained when compared with the monomeric models. Solvent effects on the fluorescence spectra and possible usages in spectrofluorometric ion sensors of the FPs were discussed. Optical and electrochemical band gaps of the polymers were lower than those of the Schiff bases indicating the more conjugated structures of the FPs. The oxidized states of the novel fluorene compounds were also examined by cyclic voltammetry (CV) technique. The solid state conductivity measurements showed that the synthesized FPs were semiconductors and when exposed to the iodine vapour their conductivities could be increased up to four orders of magnitude. The polymer having the lower band gap (FP-3) had also the highest undoped conductivity. Thermal characterizations of the synthesized compounds were carried out by TG-DTA and DSC methods. The initial degradation temperatures of the FPs were found quite high in the range of 220-300 °C.

Full text of DOI:10.1016/j.reactfunctpolym.2010.07.013

Reactive & Functional Polymers 70 (2010) 815–826
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Synthesis and characterization of fluorescent graft fluorene-co-polyphenol
derivatives: The effect of substituent on solubility, thermal stability,
conductivity, optical and electrochemical properties
_
*
Ismet Kaya , Mehmet Yıldırım, Aysel Aydın, Dilek Sßenol
Çanakkale Onsekiz Mart University, Faculty of Sciences and Arts, Department of Chemistry, 17020 Çanakkale, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of fluorene Schiff bases and their oligophenol derivatives were successfully synthesized using the
condensation and graft copolymerization reactions, respectively. The synthesized compounds were good
soluble in common organic solvents. Photoluminescence (PL) properties of the synthesized materials
were determined in solution forms. As to the fluorene copolymers (FPs), higher PL intensities were
obtained when compared with the monomeric models. Solvent effects on the fluorescence spectra and
possible usages in spectrofluorometric ion sensors of the FPs were discussed. Optical and electrochemical
band gaps of the polymers were lower than those of the Schiff bases indicating the more conjugated
structures of the FPs. The oxidized states of the novel fluorene compounds were also examined by cyclic
voltammetry (CV) technique. The solid state conductivity measurements showed that the synthesized
FPs were semiconductors and when exposed to the iodine vapour their conductivities could be increased
up to four orders of magnitude. The polymer having the lower band gap (FP-3) had also the highest
undoped conductivity. Thermal characterizations of the synthesized compounds were carried out by
TG-DTA and DSC methods. The initial degradation temperatures of the FPs were found quite high in
the range of 220–300 °C.
Received 26 February 2010
Received in revised form 12 July 2010
Accepted 13 July 2010
Available online 21 July 2010
Keywords:
Graft copolymer
Oligophenol
Fluorescence
Conjugated polymers
Polyfluorene
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
the condensation reaction of FDA with aromatic dialdehydes
containing carbazole or thiophene units [12]. The obtained poly-
Polyfluorenes (PFs) and their derivatives have attracted much
attention of researchers due to their interesting properties like
high luminescence efficiency, thermal stability, and low band gaps
[1–4]. Different methods have been reported for preparing of PFs
such as oxidative polymerization in presence of FeCl3 [5,6], electro
polymerization [7,8] and transition-metal-catalyzed reactions
(Yamamoto’s and Suzuki’s coupling reactions) [9]. Fukuda et al. re-
ported the first soluble PFs at the end of 1980s using FeCl3-cata-
lyzed oxidative coupling polymerization reaction [9]. However,
the first regio-regular synthesis of PFs were accomplished by nick-
el-catalyzed Yamamoto coupling and palladium-catalyzed Suzuki
coupling reactions of 2,7-dibromofluorene and 2,7-diboronylfluo-
rene derivatives [10]. Nowadays, both methods represent the most
important routes to obtain the PFs. The another methodology occa-
sionally used is Stille coupling [11].
mers were observed to have both fine thermal stability and high
solubility in common organic solvents. Bruma et al. reported FDA
co-polyazomethines as blue light emitting polymers with the oxa-
diazole rings as the side groups [13]. Polyamide derivatives of FDA
were investigated with their photoluminescence, electrochemical,
optical, and thermal properties [14] and quite high-thermal-stabil-
ity and luminescence efficiency were recorded. Co-polyazomethine
derivatives of 2,7-diaminofluorene were also synthesized with
dodecyl-substituted 2,5-diformylthiophene [15] and 2,5-difor-
myl-3-hexylthiophene [16]. However, in all mentioned studies flu-
orene moiety was in successive co-polymer structures. In the
present study we proposed graft co-polyazomethine derivatives
of FDA with oligophenol structures and investigated the effects of
fluorene moiety as a side chain. A typical structure of a basic poly-
azomethine (PAM), FDA, and the graft copolymerization of FDA
were shown in Scheme 1.
Fluorene moiety was also used in synthesizing of polyazometh-
ines as hole-facilitating unit. Soluble kinds of azomethine copoly-
mers of 9,90-bis(4-aminophenyl)fluorene (FDA) were obtained by
Schiff base substituted oligophenol derivatives were studied by
Kaya et al. with their useful properties including optical, electro-
chemical, electrical, and thermal characteristics [17–22]. This class
of oligophenols is generally synthesized by oxidative polyconden-
sation reaction (OP) of the corresponding Schiff base using cheap
* Corresponding author. Tel.: +90 286 218 00 18; fax: +90 286 218 05 33.
_
E-mail address: kayaismet@hotmail.com (I. Kaya).
1381-5148/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.reactfunctpolym.2010.07.013

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I. Kaya et al. / Reactive & Functional Polymers 70 (2010) 815–826
Scheme 1. The structures of a typical PAM, FDA, and graft copolymerization of FDA.
oxidants like NaOCl, H2O2, and air. The OP reaction was monitored
by examining the growth of new absorption peaks over time [23].
The electrical conductivity of the azomethine bonds in these kinds
of polymers can be increased by doping with iodine [24]. Graft co-
polyphenol derivatives of polyazomethines were also synthesized
using melamine as the grafting agent [25]. Melamine co-polyphe-
nol derivatives were found as thermally stable and semi-conduc-
tive after a long time doping with iodine.
In this study we aimed to combine the advantages of the fluo-
rene moiety and oligophenol based polyazomethines. For this pur-
pose we grafted FDA units onto aromatic oligohydroxy aldehydes
(OSA, O-4-HBA, and O-3,4-HBA) by azomethine linkages which re-
sulted in the polyconjugated fluorene polymers. The Schiff base
models of FDA were also prepared by condensation reaction with
salicylaldehyde, 4-hydroxybenzaldehyde, and 3,4-dihydroxybenz-
aldehyde. Characterization was made by UV–vis, FT-IR, NMR, and
SEC analyses. Fluorescence characteristics were determined in five
different solvents and a blue light emission for the presented
fluorene polymers was obtained as in the literature [13]. Electrical
conductivities, electrochemical analyses, and the thermal charac-
teristics were also investigated.
(1.740 g, 0.005 mol) was placed into a 250 ml three-necked round-
bottom flask which was fitted with condenser, thermometer and
magnetic stirrer. Fifty milliliters of methanol was added into the
flask and reaction mixture was heated up to 60 °C. A solution of
salicylaldehyde (1.83 g, 0.015 mol), 4-hydroxybenzaldehyde (1.83 g,
0.015 mol), or 3,4-dihydroxybenzaldehyde (2.07 g, 0.015 mol) in
20 ml methanol was added into the flask. Reactions were main-
tained for 3 h under reflux (Scheme 2). The precipitated monomers
was filtered, recrystallized from acetonitrile and dried in a vacuum
desiccator. (yields: 85%, 74%, and 81% for FM-1, FM-2, and FM-3,
respectively).
2.3. Syntheses of the FPs
Oligosalicylaldehyde (OSA), oligo-4-hydroxybenzaldehyde
(O-4-HBA), and oligo-3,4-dihydroxybenzaldehyde (O-3,4-HBA)
were synthesized by oxidative polymerization reaction of the cor-
responding monomers (salicylaldehyde, 4-hydroxybenzaldehyde,
and 3,4-dihydroxybenzaldehyde, respectively) in an aqueous alka-
line medium using NaOCl oxidant, as in the literature [26]. At the
second step the fluorene co-polyphenols (FPs), FP-1, FP-2, and
FP-3, were synthesized by grafting of FDA onto OSA, O-4-HBA,
and O-3,4-HBA, respectively [25]. Reactions were made as follows:
FDA (0.044 g, 0.003 mol) was placed into a 250 ml three-necked
round-bottom flask which was fitted with condenser, thermometer
and magnetic stirrer. 50 ml THF was added into the flask. Reaction
mixture was heated up to 60 °C. OSA, O-4-HBA, and O-3,4-HBA
(1.200 g, containing nearly 0.01 mol aldehyde groups) was sepa-
rately solved in 20 ml THF and added into the flask. Reactions were
maintained under reflux for 5 h and the reaction mixtures were
cooled at the room temperature followed by evaporating in a vac-
uum evaporator (Scheme 3). The obtained products were washed
with methanol and toluene (3 ꢀ 10 ml for each polymer) to sepa-
rate from the unreacted FDA. Then, they were dried in a vacuum
desiccator (yields: 57%, 62%, and 75% for FP-1, FP-2, and FP-3,
respectively).
2. Experimental
2.1. Materials
9,90-bis(4-aminophenyl)fluorene (FDA), salicylaldehyde, 4-hydro-
xybenzaldehyde, 3,4-dihydroxybenzaldehyde, dimethylformamide
(DMF), dimethylsulfoxide (DMSO), tetrahydrofurane (THF), diox-
ane, methanol, ethanol, acetonitrile, acetone, toluene, ethyl acetate,
heptane, hexane, CCl4, CHCl3, H2SO4, KOH and HCl were supplied
from Merck Chemical Co. (Germany) and they were used as
received. 30% aqueous solution of sodium hypo chloride, NaOCl
was supplied by Paksoy Chemical Co. (Turkey).
2.2. Syntheses of the fluorene Schiff bases
2.4. Characterization techniques
Fluorene Schiff bases abbreviated as FM-1, FM-2, and FM-3
were synthesized by the condensation reaction of FDA with
salicylaldehyde, 4-hydroxybenzaldehyde, and 3,4-dihydroxybenz-
aldehyde, respectively. Reactions were performed as follows: FDA
The solubility tests were done in different solvents by using
1 mg sample and 1 ml solvent at 25 °C. The infrared and ultravi-
olet–visible spectra were measured by Perkin Elmer FT-IR Spec-

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I. Kaya et al. / Reactive & Functional Polymers 70 (2010) 815–826
817
Scheme 2. Syntheses of the monomers.
trum one and Perkin Elmer Lambda 25, respectively. The FT-IR
spectra were recorded using universal ATR sampling accessory
(4000–550 cmꢁ1). 1H and 13C NMR spectra (Bruker AC FT-NMR
spectrometer operating at 400 and 100.6 MHz, respectively) were
also recorded by using deuterated DMSO-d6 as a solvent at 25 °C.
The tetramethylsilane was used as internal standard. Thermal
data were obtained by using a Perkin Elmer Diamond Thermal
Analysis system. TG-DTA measurements were made between 20
and 1000 °C (in N2, rate 10 °C/min). DSC analyses were carried
out by using Perkin Elmer Pyris Sapphire DSC. DSC measurements
were made between 25 and 420 °C (in N2, rate 20 °C/min). The
number-average molecular weight (Mn), weight average molecu-
lar weight (Mw) and polydispersity index (PDI) were determined
by size exclusion chromatography (SEC) techniques of Shimadzu
Co. For SEC investigations a SGX (100 Å and 7 nm diameter load-
ing material) 3.3 mm i.d. ꢀ 300 mm column was used; eluent:
ment. The process has been carried out by successive dipping
and withdrawal of ITO glass plates in homogenous solutions of
FP-1, FP-2, and FP-3 in THF (50 mg/ml for each solution) for
250 times. After each dipping the films were kept for 1 min for
drying [27].
Conductivities of the synthesized polymers were measured on a
Keithley 2400 Electrometer, using four point probe technique.
Instrument was calibrated with ITO glass plate. Iodine doping
was carried out by exposure of the polymer films to iodine vapour
at atmospheric pressure in a desiccator at 25 °C [19,25]. Absorption
spectra of the polymer films were measured before and after
iodine doping by ‘‘Analytikjena Specord S 600” single beam
spectrophotometer.
2.7. Fluorescence measurements
DMF (0.4 ml/min), polystyrene standards.
A refractive index
detector (RID) and UV detector were used to analyze the products
at 25 °C.
A Shimadzu RF-5301PC spectrofluorophotometer was used
in fluorescence measurements. Emission and excitation spectra
of the synthesized compounds were obtained in different sol-
vents with the concentration of 0.01 mg/ml. The optimum
emission and excitation wavelengths in each solvent were
determined. Also, optimizations of the concentrations to obtain
maximal emission intensity values were investigated in DMF
(for FM-1, FM-2, FP-2, and FP-3) and acetonitrile (for FM-3
and FP-1).
2.5. Optical and electrochemical properties
Ultraviolet–visible (UV–vis) spectra were measured by Perkin
Elmer Lambda 25. The absorption spectra were recorded by using
DMSO at 25 °C. The optical band gaps (Eg) were calculated from
their absorption edges.Cyclic voltammetry (CV) measurements
were carried out with a CHI 660 C Electrochemical Analyzer (CH
Instruments, Texas, USA) at a potential scan rate of 20 mV/s. All
the experiments were performed in a dry box filled with argon at
room temperature. The electrochemical potential of Ag was cali-
brated with respect to the ferrocene/ferrocenium (Fc/Fc+) couple.
The half-wave potential (E1/2) of (Fc/Fc+) measured in acetonitrile
solution of 0.1 M tetrabutylammonium hexafluorophosphate
(TBAPF6) was found to be 0.39 V with respect to Ag wire. The vol-
tammetric measurements were carried out in acetonitrile for the
Schiff bases and acetonitrile/DMSO mixture (v/v: 10/1) for the
polymers. The HOMO–LUMO energy levels and electrochemical
band gaps (E0g) were calculated from the oxidation and reduction
onset values [23].
3. Results and discussion
3.1. Solubilities and structures of the compounds
The synthesized fluorene Schiff bases have light color-powder
forms whereas their co-polyphenol derivatives are dark colored.
The solubility test results are shown in Table 1. According to Table
1, FM-2 and FM-3 are fine soluble monomers in many employed
solvents with exception some apolar solvents like benzene and
n-hexane. However, their graft copolymers (FP-2 and FP-3) are
only soluble in highly polar solvents like DMSO, DMF, and H2SO4.
Whereas FM-1 is insoluble in methanol, ethylacetate and apolar
solvents like benzene, dioxane, and n-hexane, it is completely sol-
uble in chloroform, DMSO, DMF, and H2SO4. In addition, FP-1 is
partially soluble in methanol, ethylacetate, benzene, and dioxane
as different from FM-1.
2.6. Electrical properties
Polymer films were prepared on indium–tin–oxide (ITO) glass
plates by dip-coating technique using a KSV Dip Coater instru-

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I. Kaya et al. / Reactive & Functional Polymers 70 (2010) 815–826
Scheme 3. Syntheses of the FPs (a) and possible structure of FP-2 including both inter-chain and intra-chain condensations of FDA with O-4-HBA chains (b).
The FT-IR spectra of the synthesized compounds are obtained.
In all spectra new peak appears in the range of 1608–
1618 cmꢁ1 indicating the imine bond formation (HC@N stretch
vibration). The characteristic ANH2 and C@O stretch vibrations of
FDA and the aromatic aldehydes disappear after the condensation
reactions confirming the Schiff bases’ structures. However, the FPs’
a

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I. Kaya et al. / Reactive & Functional Polymers 70 (2010) 815–826
819
Table 1
spectra have still aldehyde and amine stretch vibrations at 1690
and 3595–3659 cmꢁ1 indicating the free amine and aldehyde
groups after the graft copolymerization. OAH stretch vibrations
of all synthesized compounds are seen in the range of 3300–
3375 cmꢁ1 as a widespread peak. Aromatic CAH and C@C vibra-
tions are also observed between 3027 and 3058 and 1498–
1600 cmꢁ1, respectively. In addition, CAO bending vibrations are
Solubility test results of the synthesized compounds.
Solvents
FM-1
FM-2
FM-3
FP-1
FP-2
FP-3
DMSO
Methanol
THF
Ethylacetate
DMF
H2SO4
+
+
+
+
+
+
+
+
+
ꢁ
+
ꢁ
+
+
+
+
+
+
+
+
+
ꢁ
+
ꢁ
+
+
\
+
\
+
+
\
\
\
\
ꢁ
\
+
+
ꢁ
\
\
ꢁ
+
ꢁ
\
–
+
+
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
+
ꢁ
+
+
\
\
ꢁ
ꢁ
ꢁ
+
+
placed in the range of 1274–1285 cmꢁ1
.
1H and 13C NMR analyses results of the synthesized com-
pounds are given in Table 2. At the 1H NMR spectrum of FP-1
the peaks at 12.99, 8.91, and 5.00 ppm indicate the phenolic
AOH, CH@N, and ANH2 protons which confirm the proposed
structure. The peaks indicating the free aldehyde groups (HC@O)
of the FPs are observed at 9.79 and 9.26 ppm for FP-2 and FP-3,
CH3CN
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
Toluene
Benzene
1,4-Dioxane
n-Hexane
Chloroform
+: Soluble, \: partially soluble, ꢁ: insoluble.
Table 2
NMR analyses data of the synthesized compounds.
Compounds Spectral data (d ppm)
FM-1
FM-2
FM-3
FP-1
FP-2
FP-3
1H NMR (DMSO): 13.05 (s, AOH), 9.02 (s, ACH@NA), 7.97 (d, AHk), 7.62 (d, AHd), 7.50 (d, AHg), 7.42 (t, AHj), 7.38 (t, AHi,), 7.33 (d, AHf), 7.22 (d, AHe), 6.97 (m, AHa, AHc)
13C NMR (DMSO): 163.91 (C1-ipso), 160.73 (C7AH), 150.78 (C8-ipso), 147.25 (C11-ipso), 144.65 (C13-ipso), 140.02 (C18-ipso), 133.77 (C3AH), 133.00 (C5AH), 129.18 (C10AH), 128.45
(C14,C15AH), 126.47 (C16,C17AH), 121.91 (C9AH), 121.18 (C4AH), 119.61 (C6-ipso), 117.06 (C2AH), 64.87 (C12-ipso)
1H NMR (DMSO): 10.29 (s, AOH), 8.41 (s, ACH@NA), 7.88 (d, AHi), 7.78 (d, AHb), 7.49 (d, AHe), 7.36 (m, AHf, AHg), 7.18 (d, AHd), 7.12 (d, AHc), 6.92 (d, AHa).
13C NMR (DMSO): 163.86 (C1-ipso), 160.38 (C5AH), 151.06 (C6-ipso), 148.00 (C9-ipso), 143.11 (C11-ipso), 139.89 (C16-ipso), 132.62 (C3AH), 131.17 (C8AH), 128.80 (C4-ipso), 128.15
(C12AH), 127.99 (C13AH), 121.35 (C14AH), 120.82 (C15AH), 116.37 (C7AH), 114.22 (C2AH), 64.80 (C10-ipso)
1H NMR (DMSO): 9.61 (s, AOH), 8.36 (s, ACH@NA), 7.88 (d, AHj), 7.48 (d, Hf), 7.42 (t, AHi), 7.31 (d, AHa), 7.16 (s, AHc), 6.94 (d, AHe), 6.86 (t, AHg), 6.77 (d, AHb), 6.49 (d, AHd)
13C NMR (DMSO): 160.58 (C7AH), 152.66 (C3-ipso), 152.00 (C8-ipso), 146.16 (C4,C11-ipso), 143.04 (C13-ipso), 140.00 (C18-ipso), 132.97 (C6-ipso), 129.37 (C10AH), 128.93 (C14AH),
128.16 (C15AH), 126.44 (C16AH), 125.09 (C17AH), 122.97 (C1AH), 121.34 (C9AH), 116.04 (C2AH), 114.62 (C5AH), 64.44 (C12-ipso).
1H NMR (DMSO): 12.99 (s, AOH), 8.91 (s, ACH@NA), 7.86–6.40 (m, aromatic), 5.00 (s, ANH2).
13C NMR (DMSO): 175.24 (s, ACH@O), 159.25 (C1-ipso), 153.00 (C7AH), 148.50 (C8-ipso), 145.23 (C11-ipso), 140.29 (C13,C18-ipso), 133.72 (C3,C4-ipso), 130.01 (C10AH), 129.30
(C14AH), 128.27 (C15AH), 127.75 (C5AH), 126.70 (C16AH), 126.24 (C2-ipso,C17AH), 121.25 (C9AH), 114.69 (C6-ipso), 64.25 (C12-ipso).
1H NMR (DMSO): 10.23 (s, AOH), 9.79 (s, ACH@O), 8.43 (s, ACH@NA), 7.86 (d, AHg), 7.77 (d, AHd), 7.35 (t, Hf), 7.28 (t, AHe), 6.93 (d, AHa), 6.81 (d, AHc), 6.53 (d, AHd)
13C NMR (DMSO): 191.46 (ACH@O), 160.99 (C5AH), 152.16 (C1-ipso), 151.73 (C6-ipso), 143.61 (C9-ipso), 139.89 (C11,C16-ipso), 132.58 (C12AH), 131.22 (C3AH), 128.84 (C8AH),
128.07 (C13AH), 126.36 (C14,C15AH,C4-ipso), 120.92 (C2-ipso), 116.34 (C7AH), 64.44 (C10-ipso)
1H NMR (DMSO): 9.70 (s, ACH@O), 9.26 (s, AOH), 8.33 (s, ACH@NA), 7.85 (d, AHf), 7.34 (d, AHc), 7.27 (t, AHe), 7.09 (t, AHd), 6.76 (d, AHb), 6.42 (d, AHa)
13C NMR (DMSO): 160.77 (C7AH), 152.71 (C3-ipso), 147.30 (C8-ipso), 146.67 (C11-ipso), 144.36 (C2-ipso), 139.75 (C13,C18-ipso), 133.48 (C5-ipso), 128.68 (C10AH), 127.90 (C14AH),
127.42 (C15AH), 126.35 (C16,C17AH), 124.87 (C1-ipso), 123.85 (C4AH), 120.63 (C6-ipso), 114.11 (C9AH), 64.04 (C12-ipso).

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I. Kaya et al. / Reactive & Functional Polymers 70 (2010) 815–826
Table 3
SEC analyses results of the synthesized polymers.
Molecular weight distribution parameters
Compounds Total
Fraction II
Mn Mw
2550
2750
Fraction III
Mn Mw
Fraction IV
Fraction V
Mn
Mw
PDI
PDI
%
PDI
%
Mn
Mw
PDI
%
Mn
Mw
PDI
%
FP-1a
FP-1b
FP-2a
FP-2b
FP-3a
FP-3b
350
950
580 1.657
1100 1.294
4100 1.608 03
3200 1.164 04
300
800
500 1.667 97
1000 1.250 96
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
30,000 31,400 1.047 48,500 49,800 1.027 54 15,700 18,600 1.185 22
37,550 38,400 1.023 58,000 58,700 1.012 58 15,200 18,900 1.243 21
25,000 30,550 1.222 52,700 79,300 1.505 13 45,500 52,750 1.159 22 16,000 17,350 1.078 39 7200 8800 1.222 26
28,800 35,600 1.236 56,200 79,250 1.410 21 46,000 52,350 1.138 21 15,900 17,600 1.107 36 7400 7500 1.014 22
1500
1850
1650 1.100 24
1900 1.027 21
a
Determined by RI detector.
Determined by UV detector.
b
respectively. Also, according to the 13C NMR results the peaks at
175.24 and 191.46 ppm for FP-1 and FP-2, respectively, indicate
the free aldehyde carbons (HC@O). Moreover, according to the
13C NMR spectra chemical shift values of the coupling carbons
of the FPs are higher than those of the Schiff bases due to the
increasing conjugation length [22,25]. For example, in comparison
of FM-1 and FP-1, after the copolymerization the peak values of
C2 and C4 shift from 117.00 and 121.18 ppm to 126.24 and
133.72 ppm, respectively. Similarly, C2 peak value of FM-2 shifts
from 114.22 to 120.92 ppm and C1, C2, and C5 peak values of FM-
3 shift from 122.97, 116.01, and 114.62 ppm to 133.48, 123.85,
and 124.87 ppm, respectively, after the copolymerization. The
mentioned chemical shifts are also evidence of the polymer struc-
tures: oxidative polycondensation reaction of the phenolic com-
Table 4
Electronic structure parameters of the synthesized compounds.
aHOMO
bLUMO
cEg
ekmax
dE0g
Compounds
FM-1
FP-1
FM-2
FP-2
FM-3
FP-3
ꢁ5.79
ꢁ5.40
ꢁ5.42
ꢁ5.65
ꢁ5.37
ꢁ5.39
ꢁ2.75
ꢁ3.37
ꢁ2.60
ꢁ3.25
ꢁ2.94
ꢁ3.79
3.14
2.37
3.25
2.91
3.21
2.21
3.04
2.03
2.82
2.40
2.43
1.60
347
418
327
330
336
426
a
b
c
Highest occupied molecular orbital.
Lowest unoccupied molecular orbital.
Optical band gap.
Electrochemical band gap.
Maximum absorbance wavelength.
d
e
Fig. 1. Absorption spectra of FM-1 and FP-1 (a), FM-2 and FP-2 (b), and FM-3 and FP-3 (c).

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I. Kaya et al. / Reactive & Functional Polymers 70 (2010) 815–826
821
Fig. 3. Electrical conductivity changes of the I2-doped and undoped compounds vs.
doping time at 25 °C.
Fig. 2. Cyclic voltammograms of FM-1 and FP-1.
pounds proceeds via combination of the monomers by coupling of
the phenylene (-ortho and -para positions of phenol) and oxi-
phenylene radicals. These combinations result in CAC and
CAOAC couplings and the increasing conjugation. As a result,
the coupling carbons in the polymer structures have lower elec-
tron densities and resultantly higher chemical shifts than those
in their monomer compounds [23].
indicates the electronic transition start wavelength. The calculated
band gap values are given in Table 4. These results show that the
synthesized polymers have lower optical band gaps when com-
pared to the monomers, as expected.
Cyclic voltammograms of FM-1 and FP-1 are given in Fig. 2. As
seen in these voltammograms both materials have two oxidation
steps. At the voltammogram of FM-1 the peak at 1400 mV indi-
cates the oxidation of the phenolic AOH group, agreed with the
literature data [16]. That peak disappears at the voltammogram
of FP-1 due to CAOAC coupling. Kaya et al. have previously pro-
posed that oxidative polycondensation reaction of phenol deriva-
tives could proceed by two mechanisms: CAC and CAOAC
coupling of the monomer units [23]. Seo et al. investigated anodic
oxidation pathways of aromatic amine compounds [29]. The peak
at 1015 mV at the voltammogram of FP-1 indicates the oxidation
of free ANH2 groups, agreed with the mentioned study, while in
the voltammogram of FM-1 that peak disappears, as expected.
Additionally, the oxidations of the fluorene rings are seen at
1848 and 1980 mV for FM-1 and FP-1, respectively. It is known
that the fluorene compounds can be oxidatively degraded at the
potentials upon 1700 mV and an irreversible oxidation process
is observed [30].According to the cyclic voltammetry (CV) mea-
surements, the HOMO–LUMO energy levels and the electrochem-
ical band gaps (E0g) are calculated as in the literature [31] and
shown in Table 4. As seen in Table 4 the optical band gaps are
a bit higher than the electrochemical band gaps. This result is
in agreement with the literature [23]. However, the orders of
the band gaps calculated from both optical and electrochemical
data are same. According to these data the order of the fluorene
co-polyphenols’ band gaps is as follows: FP-3 < FP-1 < FP-2. Lower
band gaps facilitate the electronic transitions between HOMO–
LUMO energy levels and make the polymers more electro-con-
ductive than the monomers.
According to the SEC chromatograms, the calculated number-
average molecular weight (Mn), weight average molecular weight
(Mw), and polydispersity index (PDI) values of the FPs measured
using both RI and UV detectors are given in Table 3. As seen in
Table 3 the obtained FP-1, FP-2, and FP-3 have 2, 3, and 4 main
fractions. According to the total values the molecular weight of
FP-1 is lower than 1000 g molꢁ1, whereas the total molecular
weights of FP-2 and FP-3 are approximately 30,000 g molꢁ1
.
These results also agree with the solubility tests. FP-1 with its
low molecular weight is a fine-soluble polymer in common or-
ganic solvents and the others have lower solubilities due to their
high-molecular weighted structures. Lower molecular weight of
FP-1 could be attributed to mainly two factors: the first is low
molecular weight of oligosalicylaldehyde used and the second
is lower grafting capability of FDA onto OSA. As emphasized be-
fore the grafting of FDA onto OSA, O-4-HBA, and O-3,4-HBA is
carried out by condensation reaction and new imine bonds for-
mation. On the contrary of the others OSA has ortho AOH sub-
stituents of the aldehyde groups which may cause the steric
hindrance and low grafting yield. As a result, FDA could be more
easily grafted onto O-4-HBA and O-3,4-HBA due to their non-
substituted structures at ortho-positions which results in higher
molecular weights.
3.2. Optical and electrochemical properties
The UV–vis spectra of the synthesized compounds are shown
in Fig. 1. According to these spectra, a red shift occurs at the
absorption edges of the synthesized polymers in comparison to
the Schiff bases. This is because of the polyconjugated structures
of the polymers which increase HOMO and decrease LUMO en-
ergy levels thus result in lower band gaps. The optical band gaps
(Eg) could be obtained by using the following equation as in the
literature [28]:
3.3. Electrical conductivities
Electrical conductivities of the synthesized FPs and the changes
of these values related to doping time with iodine are shown in
Fig. 3. As well known, there is an opposite tendency between the
HOMO–LUMO band gap and the conductivity. As stressed before
lower band gap facilitates the electronic transition from bulk to
vacuum energy level. This results in higher conductivity. FP-3 with
the lowest band gap has also the highest undoped conductivity.
However, the conductivity of FP-3 increases approximately two or-
ders of magnitude whereas three and four orders for FP-2 and FP-1,
Eg ¼ 1242=konset
ð1Þ
where konset is the onset wavelength which can be determined by
intersection of two tangents on the absorption edges. konset also

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I. Kaya et al. / Reactive & Functional Polymers 70 (2010) 815–826
Fig. 4. The effect of doping procedure on the absorption spectra of the polymers: (a) the absorption spectra of doped (for between 1 and 24 h) and undoped states of FP-1, (b)
FP-2, and (c) FP-3.
respectively. Maximum conductivity increasing is obtained for FP-
1 via iodine doping. As a result FP-1 has the highest saturated con-
ductivity. This is possibly because of the steric effect of the higher
number of AOH substituents of FP-3 which prevent the penetrat-
ing of iodine molecule into the polymer chain. Diaz et al. suggested
the doping mechanism of Schiff base polymers [32]. According to
doping mechanism, nitrogen, being a very electronegative element,
is capable of coordinating with an iodine molecule. As a result, a
charge-transfer complex between imine compound and dopant io-
dine is formed and a considerable increase in conductivity can be
observed [25]. However, steric hindrance of the substituents bound
with the phenol ring prevents the iodine coordination and conse-
quently could decrease the doping level of the polymer [22]. Hind-
son et all. synthesized triphenylamine-based poly(azomethine)s
with wholly aromatic structures as the new opto-electronic mate-
rials [33]. The optical band gaps of their synthesized PAMs were
found as 2.3–2.6 eV. They produced a newly photovoltaic device
using the synthesized PAMs showing an external quantum effi-
ciency (EQE) of 20% at 500 nm. The device had also an open-circuit
voltage of 0.41 V and a short circuit current of 1.23 mA cmꢁ2. In an-
other study the opto-electronic applications of some polymer
charge complexes were investigated by Liu et al. [34]. They used
the polymers with carbazole based side groups in device prepara-
tion. The relationship between the conductivity and polymer ratio
in device was also studied. The obtained polymers were found to
have potential use for low cost-printed electronics. Similarly, the
presented FPs have quite low band gaps (2.20–2.90 eV) and these
energy gaps become less after doping. Fluorene structure is similar
to carbazol ring structure and the presented PFs including the flu-
orene side groups could also be useful materials in electronic or
opto-electronic studies after a long time iodine doping. Conductiv-
ity measurements of imine polymers were previously studied and
considerable increases were reported when they were doped with
iodine [21–25,32].
The absorption spectra of the polymer films before and after
doping are also given in Fig. 4. Red shifts in the absorption spectra
are recorded when the polymers are exposed to iodine vapour. The
growing peaks observed between 400 and 450 nm are attributed to
the polaron band transitions of the imine nitrogen [35]. These new
bands show that the doping procedure is successfully carried out
followed by polaron formation as well as the increasing conductiv-
ity. As a result of the polaron band formation the optical band gap
becomes lower which supports the increasing conductivity.
Doping procedure of conducting polymers has attracted much
attention of researchers into this field, so far [36,37]. This proce-
dure produces a lot of application fields for conducting polymers.
With these properties conducting polymers are used in gas sens-
ing materials against several kinds of electro-donor (such as CO,
CO2, NH3 and H2S) and electro-acceptor (such as I2 and NO2)
gases [38–42]. These studies show that the doping level and
electrical conductivities of a conducting polymer can be changed
considerable by doping with chemical vapours. The sensing pro-
cess of the conductive/semi-conductive polymers generally de-
pends on the electron transferring mechanism from and to the
analytes [42]. Electron transferring causes changes in resistance
and work function (Wf) of a conducting polymer as well as shift-
ing of absorption edge. These kinds of polymers can be used to
develop a gas sensor by measuring of the mentioned physical
changes. The proposed fluorene co-polyphenols, thus, could also
be used as an active layer in gas sensors for detection of electro-
acceptor gases like iodine vapour by measuring of the conductiv-
ity change.

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I. Kaya et al. / Reactive & Functional Polymers 70 (2010) 815–826
823
Fig. 5. Emission and excitation spectra of the synthesized compounds in various solvents. Conditions: slit: kEx 5 nm, kEm 5 nm; concentration of the compounds: 0.01 mg/ml.
3.4. Fluorescence characteristics
ring into the oligohydroxy aldehyde chain followed by a blue
emitting.
Fluorene polymers are known as good candidates for blue emit-
ting materials due to their unique combination of high-thermal-
stability, versatile processability, and high-photoluminescence
(PL) quantum yield in the solid state [43,44]. In the presented
PFs fluorene unit acts as electro-donor and oligohydroxy aldehydes
with the polyconjugated structures are electro-acceptors. The elec-
tron density of the fluorene ring could be transferred into the elec-
tro-acceptor oligohydroxy aldehyde chain by azomethine linkage.
With UV absorption an energy transfer carries out from fluorene
Fluorescence characteristics of the synthesized materials are
determined using five separate solvents. Solvent effects on the
fluorescence properties are seen in Fig. 5. It is clearly seen at
the first glance into the fluorescence spectra that the synthesized
FPs are highly fluorescent. On the contrary of their monomer
models the quantum yields of the FPs are quite high. DMF and
acetonitrile solutions of the all FPs show fine fluorescence charac-
teristics. However, a reverse solvent effect could be observed for
different FPs. For instance; at the CH2Cl2 solution of FP-1 a

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I. Kaya et al. / Reactive & Functional Polymers 70 (2010) 815–826
Table 5
bathochromic shift is observed in comparison to the DMF solu-
tion, while for the FP-2’s solutions a reverse tendency is observed.
On the other hand, polarity and hydrogen bonding capacity of the
solvents could influence the fluorescence properties [45]. CH2Cl2
has lower polarity than DMF and MeOH, as well as having no
hydrogen bonding structure. CH2Cl2 solutions of the synthesized
compounds have generally lower emission wavelengths due to
the mentioned properties (with exception of FM-1 and FP-1).
Also, the emission wavelengths of methanol solutions are higher
than those of the DMF solutions. This is because of the hydrogen
bonding capacity of methanol. The synthesized materials have
hydroxy substituents having hydrogen bonding capacity with
methanol. In addition, FM-3 with its higher number of hydroxyl
substituents shows higher fluorescence intensities in all solvents
as well as higher red shifted spectra from CH2Cl2 to DMF and
MeOH, depending on the polarity and hydrogen bonding. However,
the reverse effects of the solvents on the fluorescence spectra of
Fluorescence spectral data of the synthesized compounds in some employed solvents.
Compound
akEx
bkEm
ckmax
dkmax
eIEx
fIEm
gDkST
(Ex)
(Em)
1FM-1
1FP-1
1FM-2
2FP-2
1FM-3
3FP-3
410
319
271
252
274
366
474
471
477
399
468
458
410
319
304
247
273
367
467
466
463
393
460
426
56
651
38
726
185
457
64
657
48
675
187
541
57
147
159
146
187
59
a
b
c
Excitation wavelength for emission.
Emission wavelength for excitation.
Maximum emission wavelength.
Maximum excitation wavelength.
Maximum excitation intensity.
Maximum emission intensity.
Stoke’s shift.
DMF.
Dichloromethane.
Acetonitrile.
d
e
f
g
1
2
3
Fig. 6. The changes of the emission intensities of the synthesized compounds related to different concentrations. Conditions: slit: kEx 5 nm, kEm 5 nm; kEx 410 nm and kEm
474 nm for FM-1, kEx 316 nm and kEm 469 nm for FP-1, kEx 271 nm and kEm 477 nm for FM-2, kEx 314 nm and kEm 468 nm for FP-2, kEx 255 nm and kEm 467 nm for FM-3, and
kEx 378 nm and kEm 475 nm for FP-3. Solvents employed: acetonitrile for FM-3 and FP-1, and DMF for the others.

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I. Kaya et al. / Reactive & Functional Polymers 70 (2010) 815–826
825
Table 6
Thermal degradation values of the synthesized compounds.
Compounds
aTon
bWmaxꢂT
20% Weight losses
50% Weight losses
% Carbine residue at 1000 °C
DTA
Exo
DSC
Endo
cTg (ꢀC)
dDCp (J/gꢀC)
FM-1
FP-1
FM-2
FP-2
FM-3
FP-3
379
302
398
250
253
226
408,525
345
408
331
474
419
389
350
561
388
–
918
–
42.28
25.48
51.33
38.02
58.27
47.95
–
–
–
–
–
–
229
–
253
–
–
–
–
210
–
164
–
200
–
0.713
–
0.048
–
529
394,496
318,489
330,447
958
0.212
a
b
c
The onset temperature.
Maximum weight temperature.
Glass transition temperature.
d
Change of specific heat during glass transition.
Fig. 7. TGA curves of the synthesized compounds.
FM-1 and FP-1 are interesting. These materials have o-substituted
hydroxyl groups of azomethine bond. This structure could have
keto-amine M phenol-imine tautomerism [46] which may cause
different solvent effects on the fluorescence spectra.
Fluorescence data are also summarized in Table 5. As seen in
Table 5 with exception of FM-1 and FP-3 the other synthesized
degradation temperatures (Ton) of the polymers are lower than
those of their Schiff base models. This is because of the forma-
tion of CAO etheric bond during the OP reaction (CAOAC cou-
pling). This weak bond is easily broken at moderate
temperatures and makes the polymer thermally unstable. More-
over, carbine residue values also indicate that the synthesized
fluorene monomers are more thermally stable than the co-poly-
phenol derivatives. For example, the initial degradation tempera-
ture (°C) and carbine residue (%) are 379 and 42 for FM-1; 302
and 25 for FP-1; 398 and 51 for FM-2; 250 and 38 for FP-2; 253
and 58 for FM-3; and 226 and 48 for FP-3, respectively. With excep-
tion of FM-1 and FM-2 the DTA curves of the other materials show
no clear endothermic or exothermic peaks. However, the endother-
mic peaks at 229 and 253 °C for FM-1 and FM-2 are recorded,
respectively, indicating their melting points. According to the DSC
analyses glass transition temperatures (Tg) of the polymers are also
calculated and given in Table 6. The synthesized FPs have quite high
Tg values between 164 and 200 °C, agreed with the previously pub-
lished Schiff base substituted oligophenol derivatives [23,25]. Also
materials have quite high Stoke’s shift values (DkST). Stoke’s shift
is an important value for a fluorescence sensor. The higher Stoke’s
shift value supplies very low background signals and resultantly al-
lows the usage of the material in construction of a fluorescence
sensor [47]. A series of Schiff bases and some chelate-structured
polymer models have been presented as possible ion-selective
sensors depending on quenching of the fluorescence intensity val-
ues when exposed to corresponding ion like Fe(II), Cu(II) etc.
[48,49]. FP-1 and FP-3 have chelating groups as well as high fluo-
rescence intensities and they can give a selective-sensitive re-
sponse against some heavy metal ions.
The optimization of the concentrations to obtain maximal emis-
sion intensity is also investigated in different solvents (Fig. 6). The
obtained results show that the synthesized materials have the
maximum fluorescence intensity in the concentration range of
0.5–4 mg/100 ml (except FM-1). However, the optimum fluores-
cence concentration of FM-1 is quite higher than the others (32
times higher than FP-1 and FP-3; 64, 128, and 256 times higher
than FP-2, FM-3, and FM-2, respectively).
the changes of the specific heats (DCp) during the glass transitions
are calculated and the biggest change is recorded for FP-1 which fol-
lowed by FP-3 and FP-2, respectively.
4. Conclusions
Novel fluorene Schiff bases and Schiff base substituted olig-
ophenol derivatives containing fluorene moiety in the side chain
were synthesized by condensation reaction of FDA with aromatic
hydroxyaldehydes and graft copolymerization of FDA with oligo-
hydroxyaldehydes (OSA, O-4-HBA, and O-3,4-HBA), respectively.
Solubility tests showed that the synthesized compounds are fine
3.5. Thermal analysis
Thermal degradation data (TGA, DTG, DTA and DSC) are sum-
marized in Table 6. TGA curves of the synthesized compounds
are also shown in Fig. 7. According to the TGA results, the initial

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quite higher fluorescence intensities than their monomer models.
Especially FP-1 can be a promising spectrofluorometric ion sensor
because of the highly fluorescence intensity and Stoke’s shift with
a suitable chemical structure for complexation with metal ions.
The new fluorene polymers are blue emitting materials with a
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Acknowledgement
_
The authors thank TUBITAK Grants Commission for a research
grant (Project No: TBAG-107T414).
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