Synthesis, photophysical and iron-sensing properties of terpyridyl-based triphenylamine derivatives

Article abstract of DOI:10.1016/j.dyepig.2012.05.004

A series of new terpyridyl phenyl/styryl triphenylamine chromophores were designed and synthesized. The branching number and the rigid/flexible bridge structures had a remarkable effect on the photophysical, selectivity and sensitivity for Fe(II) ion properties of these chromophores. The fluorescence lifetimes of the rigid terpyridyl phenyl triphenylamine chromophores are longer than that of the flexible terpyridyl styryl triphenylamine derivatives. The terpyridyl phenyl/styryl triphenylamine chromophores present an increasing fluorescence lifetime with the increase in the number of branches from 1 to 3. The terpyridyl flexible styryl triphenylamine derivatives have a higher sensitivity than that of the terpyridyl rigid phenyl triphenylamine derivatives for Fe(II) ion in neutral aqueous solution amongst other divalent metal ions such as Cu²⁺, Co²⁺, Ni²⁺, Hg²⁺, Mg²⁺, Pb²⁺, Zn²⁺.

Full text of DOI:10.1016/j.dyepig.2012.05.004

Dyes and Pigments 95 (2012) 757e767
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis, photophysical and iron-sensing properties of terpyridyl-based
triphenylamine derivatives
,
,
a
a
a
Congbin Fan a b, Xiaomei Wang a , Ping Ding , Jingjing Wang , Zuoqin Liang ,
*
Xutang Tao c
a Jiangsu Key Laboratory for Environment Functional Materials, The School of Chemistry and Biological Engineering, Suzhou University of Science and Technology,
Suzhou 215009, PR China
b Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science & Technology Normal University, Nanchang 330013, PR China
c State Key Laboratory of Crystal Materials, Institute of Crystal Materials, Shandong University, Jinan 250100, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new terpyridyl phenyl/styryl triphenylamine chromophores were designed and synthesized.
The branching number and the rigid/flexible bridge structures had a remarkable effect on the photo-
physical, selectivity and sensitivity for Fe(II) ion properties of these chromophores. The fluorescence
lifetimes of the rigid terpyridyl phenyl triphenylamine chromophores are longer than that of the flexible
terpyridyl styryl triphenylamine derivatives. The terpyridyl phenyl/styryl triphenylamine chromophores
present an increasing fluorescence lifetime with the increase in the number of branches from 1 to 3. The
terpyridyl flexible styryl triphenylamine derivatives have a higher sensitivity than that of the terpyridyl
rigid phenyl triphenylamine derivatives for Fe(II) ion in neutral aqueous solution amongst other divalent
Received 13 December 2011
Received in revised form
7 May 2012
Accepted 9 May 2012
Available online 5 June 2012
Keywords:
Triphenylamine
Terpyridine
metal ions such as Cu2þ, Co2þ, Ni2þ, Hg2þ, Mg2þ, Pb2þ, Zn2þ
.
Ó 2012 Elsevier Ltd. All rights reserved.
Rigid/flexible
Multibranches
Photophysical properties
Iron-sensing
1. Introduction
Ir(III) dyad that exhibits high charge-separation efficiency [15]. Lin
et al., reported a series of p-conjugated bis-terpyridyl ligands
having donor-acceptor units and their corresponding Ru(II)-
containing main-chain metallo-polymers for solar cell applica-
tions [16]. The properties were significantly influenced by the
position of the 40-terpyridyl substituent which affected the pho-
tophysics of the terpyridyl-Pt(II) complexes [17]. In particular,
a large aryl substituent (such as pyrenyl) in the 40-position of the
terpyridyl ligand led to alteration of the lowest excited state [18].
Terpyridine ligands have generally not been used for sensors
and the reason is attributed to their strong ability to coordinate
with metal ions (i.e., the binding constant is extremely high).
The terpyridyl derivatives self-assembled with ferrous ions
showing a band in the visible region of the absorption spectrum.
In preliminary studies, we found that the properties of terpyr-
idyl derivatives self-assembled withe Fe(II) ion could be
controlled by using the rigid phenyl triphenylamine and flexible
styryl striphenylamine groups. This feature is crucial to the
binding of ferrous ions because iron plays crucial roles in the
transport and storage of oxygen and also in electron transport in
diverse metalloenzymes [19e22]. Obviously, because iron is
Triphenylamine derivatives have been widely used as two-
photon absorption (TPA) materials [1,2], in memory devices [3]
and hole transporting materials [4e10]; these applications make
use of the fact that triphenylamine derivatives exhibit multifunc-
tional properties. On the other hand, the multifunctional 40-ter-
pyridyl unit, which is capable of chelation, can be assembled with
metal ions to furnish materials that possess useful properties, as
exemplified by the bis-terpyridyl-stilbene derivatives of Ru(II) and
Ir(III), which have been examined for two-photon luminescence
[11].
A
terpyridyl-Pt(II) complex is used for label- and
immobilization-free detection of the lysozyme, thrombin [12] and
generation of hydrogen from water [13]. To date, research has been
devoted to the synthesis of terpyridyl-type of ligands in order to
understand fundamental chemical properties [14]. For example,
Flamigni et al., have reported a triphenylamine/bis(terpyridine)
* Corresponding author. Tel./fax: þ86 512 68326615.
E-mail address: wangxiaomei@mail.usts.edu.cn (X. Wang).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.05.004

758
C. Fan et al. / Dyes and Pigments 95 (2012) 757e767
present is living systems, the tracking of its homeostasis is of
significance [23,24].
TMS):
d
1.32 (s, 12H, -CH3), 7.04 (t, 4 H, J ¼ 8.0 Hz, benzene-H), 7.11
(d, 4 H, J ¼ 8.0 Hz, benzene-H), 7.26 (t, 4 H, J ¼ 8.0 Hz, benzene-H),
7.66 (d, 2 H, J ¼ 8.0 Hz, benzene-H).
2. Experimental section
2.1.1.5. Synthesis of 4,40-bis(4,4,5,5-tertramethyl-[1,3,2]dioxabor-
olane)phenyl-N-phenylamine (compd 5). n-Butyl lithium in hexane
(1.6 M, 2.50 mL, 4.0 mmol) was added to a stirred solution of
4,40-bisbromotriphenylamine (0.81 g, 2.0 mmol) in dry THF
(50 mL) at ꢁ78 ꢀC under nitrogen atmosphere. After stirring
for 30 min, 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
(0.74 g, 4.0 mmol) was added to the reaction mixture. The
ensuing mixture was warmed to room temperature and then
quenched with water (10 mL). The mixture was extracted with
chloroform. Next, the organic phases were dried with magne-
sium sulfate and the solution was concentrated in vacuo. The
crude product was purified by column chromatography on SiO2
using hexane as the eluent and 0.52 g product obtained as white
2.1. Synthesis
2.1.1. Synthesis of components
2.1.1.1. Synthesis of 1-[3-oxo-3-(2-pyridyl)propen-1-yl]-4-bromo-
benzene (compd 1). To a methanol (100 mL) solution of 4-
bromobenzaldehyde (2.0 g, 10.8 mmol) was added 2-
acetylpridine (1.30 g, 10.8 mmol) and 2% aqueous NaOH (0.44 g,
22 mL), and the mixture was stirred for 2 h at room temperature
(Scheme 1). The white precipitate formed was collected by filtra-
tion, and washed sequentially with H2O, methanol for three times,
respectively. The off-white solid was dried in vacuo to give product
1.75 g, 56.3%. m.p. 118e119 ꢀC. 1H NMR (CDCl3, 400 MHz, TMS):
d
7.44 (t, 1H, J ¼ 6.0 Hz, pyridyl-H), 7.48 (d, 2H, J ¼ 8.0 Hz, benzene
solid in 52.7% yield. 1H NMR (400 MHz, CDCl3, TMS):
d 1.32 (s,
eH), 7.53 (d, 2H, J ¼ 8.0 Hz, benzene eH), 7.78e7.84 (m, 2H, pyridyl-
H), 8.13 (d, 1H, J ¼ 8.0 Hz, CHeH), 8.24 (d, 1H, J ¼ 12.0 Hz, CHeH),
8.68 (d, 1H, J ¼ 4.0 Hz, pyridyl-H).
24H, -CH3), 6.96e7.08 (m, 9H, benzene-H), 7.61e7.68 (m, 4H,
benzene-H).
2.1.1.6. Synthesis of 4,40,40’-tri(4,4,5,5-tertramethyl-[1,3,2]dioxabor-
olane)phenylamine (compd 6). To a
solution of 4,40,40’-tri(4-
2.1.1.2. Synthesis of pyridinium iodide salt (compd 2). Under the
anhydrous and oxygen-free conditions, I2 (5.06 g, 20 mmol) was
dissolved in pyridine (30 mL) and the mixture was stirred and
heated to 70 ꢀC for 0.5 h. Then 2-acetylpridine (2.42 g, 20.0 mmol)
was added to the solution and the mixture was stirred and heated
to 80 ꢀC for 4 h. After the mixture cooled, the solution was filtered
and washed with ethanol for five times. The yellow-green solid was
then dried in vacuo to give product 4.38 g, 67.2%. m.p. 227e228 ꢀC.
bromophenyl)amine (2.41 g, 5.0 mmol) in dry THF (50 mL)
at ꢁ78 ꢀC was added n-butyllithium (1.6 M in hexane, 8.85 mL,
15 mmol). After stirring at ꢁ78 ꢀC for 30 min, 2-isopropoxy-4,4,5,5-
tetramethethyl-dioxaborolane (3.07 g,16.5 mmol) was added to the
resulting suspension and stirring was continued for another 2 h at
this temperature. The solution was allowed to warm up to room
temperature and quenched by the addition of water. The solid
product was purified by column chromatography on silica using
petroleum ether as the eluant to give light green solid 1.10 g, in
1H NMR(CDCl3, 400 MHz, TMS):
d 6.89 (s, 2H, CH2eH), 7.58 (t, 1H,
J ¼ 6.0 Hz, pyridyl-H), 7.88 (t, 1H, J ¼ 8.0 Hz, pyridyl-H), 8.02 (d, 1H,
J ¼ 8.0 Hz, pyridyl-H), 8.08 (t, 2H, J ¼ 8.0 Hz, pyridyl-H), 8.49 (t, 1H,
J ¼ 8.0 Hz, pyridyl-H), 8.72 (d, 1H, J ¼ 8.0 Hz, pyridyl-H), 9.12 (d, 2H,
J ¼ 4.0 Hz, pyridyl-H).
34.8% yeild. m.p > 300 ꢀC. 1H NMR (400 MHz, CDCl3, TMS):
d 1.34 (s,
36H, -CH3), 7.07 (d, 6H, J ¼ 8.0 Hz, benzene-H), 7.68 (d, 6H,
J ¼ 8.0 Hz, benzene-H).
2.1.1.3. Synthesis
of
40-(4-bromophenyl)-2,20:60,200-terpyridine
2.1.1.7. Synthesis of 4- vinylphenyl-N,N-diphenylamine (compd 7). 4-
(Diphenylamino) benzaldehyde (3.05 g, 11.16 mmol) and methyl
triphenylphosphonium iodide [25] (10.64 g, 26.30 mmol) were
dissolved in dry 1,4-dioxane (50 mL). To this solution was added
sodium ethoxide (2.0 g, 29.40 mmol) as strong base at room
temperature. The mixture was refluxed for 6 h under the nitrogen
atmosphere and then poured into excess distilled water. The
precipitate was purified by column chromatography on silica using
petroleum ether as the eluant to give white solid 1.72 g, 6.35 mmol,
(compd 3). A methanol (100 mL) solution of 1-[3-oxo-3-(2-pyridyl)
propen-1-yl]-4-bromobenzene (1.75 g, 6.07 mmol) was added
pyridinium iodide salt (1.98 g, 6.07 mmol) and ammonium acetate
(11.01 g, 142.8 mmol) at room temperature, and the mixture was
stirred and refluxed (70 ꢀC) for overnight. The white precipitate
formed was collected by filtration, and washed sequentially with
H2O and methanol for three times, respectively. The white solid was
then dried in vacuo to give product 0.84 g, yielding 35.6%. m.p
134e136 ꢀC. 1H NMR (CDCl3, 400 MHz, TMS):
d
7.29e7.32 (m, 2H,
in 56.9% yield. m.p 75e76 ꢀC. 1H NMR (400 MHz, CDCl3, TMS):
d 5.16
pyridyl-H), 7.58 (d, 2H, J ¼ 8.0 Hz, benzene-H), 7.72 (d, 2H,
J ¼ 8.0 Hz, benzene-H), 7.81e7.85 (m, 2H, pyridyl-H), 8.61 (d, 2H,
J ¼ 4.0 Hz, pyridyl-H), 8.64 (s, 2H, pyridyl-H), 8.67 (d, 2H, J ¼ 8.0 Hz,
pyridyl-H).
(d, 1H, J ¼ 10.8 Hz, ¼CH), 5.64 (d, 1H, J ¼ 17.6 Hz, ¼CH), 6.62e6.70
(m, 1H, -CH ¼ ), 7.01 (d, 2H, J ¼ 8.0 Hz, benzene-H), 7.168e7.362 (m,
10H, benzene-H), 7.68 (d, 2H, J ¼ 8.0 Hz, benzene-H).
2.1.1.8. Synthesis of 4,40-bisvinylphenyl-N-phenylamine (compd 8).
4,40-Bisformylphenyl-N-phenylamine (1.0 g, 3.3 mmol) and methyl
triphenylphosphonium iodide (5.92 g, 14.65 mmol) were dissolved
in 50 mL of dry1,4-dioxane. To this solution was added sodium
ethoxide (1.2 g, 17.6 mmol) as strong base at room temperature. The
mixture was refluxed for 6 h under the nitrogen atmosphere and
then poured into excess distilled water. The precipitate was purified
by column chromatography on silica using petroleum ether as the
eluant to give yellow liquid 0.49 g, in 49.9% yield. 1H NMR
2.1.1.4. Synthesis of 4-(4,4,5,5-tertramethyl-[1,3,2]dioxaborolane)
phenyl-N,N-diphenylamine (compd 4). n-Butyl lithium in hexane
(1.6 M, 1.25 mL, 2.0 mmol) was added to a stirred solution of 4-
bromotriphenylamine (0.64 g, 2.0 mmol) in dry tetrahydrofuran
(THF) (50 mL) at ꢁ78 ꢀC under nitrogen atmosphere. After stirring
for 30 min, 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
(0.37 g, 2.0 mmol) was added to the reaction mixture. The
ensuing mixture was warmed to room temperature and then
quenched with water (10 mL). The mixture was extracted with
chloroform. Next, the organic phases were dried with magnesium
sulfate and the solution was concentrated in vacuo. The crude
product was purified by column chromatography on SiO2 using
hexane as the eluent and 0.50 g product was obtained as white
solid in 68. 1% yield. m.p 103e104 ꢀC. 1H NMR (400 MHz, CDCl3,
(400 MHz, CDCl3, TMS):
6.61e6.68 (m, 2H, -CH ¼ ), 7.02 (d, 5H, benzene-H), 7.08 (d, 2H,
J ¼ 8.0 Hz, benzene-H), 7.21e7.28 (m, 6H, benzene-H).
d
5.15 (d, 2H, ¼CH2), 5.63 (d, 2H, ¼CH2),
2.1.1.9. Synthesis of 4,40,40’-trivinylphenylamine (compd 9). 4,4’40’-
Triformylphenylamine (0.6 g, 1.8 mmol) and methyl

C. Fan et al. / Dyes and Pigments 95 (2012) 757e767
759
Br
O
NaOH/CH3OH/H2O
CH2Cl2
O
N
Br
O
CHO
+
N
N
N
NH4OCOCH3
CH3OH
1
N
Br
Reflux
O
+
Reflux
N
I-
+
I2
+
N
3
N
N
2
Br
O
O
O
O
O
B
O
B
B
3
n-BuLi
N
Br
N
Br
Chromophores I, II, III
Pd(PPh3)4/Na2CO3
N
Br
,
,
N
N
N
O
O
B
Br
,
Br
O
O
B
O
,
B
O
O
O
B
4
5
6
O
I-
OHC
CHO
P+
3
IV, V, VI
Chromophores
N
CHO
,
N
N
CHO
N
N
N
Triethylamine,
Acetonitrile
O
Reflux
O
,
,
Pd(OCOCH3)2,PPh3
,
Reflux
OHC
OHC
7
8
9
N
N
N
N
N
N
N
1
n=0 or 1
r
o
0
=
n
Chromophores I or IV
N
N
n=0 or 1
N
N
N
n=0 or 1
Chromophores III or VI
N
N
N
N
n=0 or1
n
=
0
N
N
o
N
r
1
N
N
Chromophores II or V
N
Scheme 1. The synthetic routes for chromophores IeVI.
triphenylphosphonium iodide (6.25 g, 18.3 mmol) were dissolved
in dry 1,4-dioxane (50 mL). To this solution was added sodium
ethoxide (0.3 g, 4.4 mmol) as strong base at room temperature. The
mixture was refluxed for 6 h under the nitrogen atmosphere and
then poured into excess distilled water. The precipitate was purified
by column chromatography on silica using petroleum ether as the
eluant to give yellow liquid 0.27 g, in 46.4% yield. 1H NMR
(400 MHz, CDCl3, TMS):
J ¼ 16.0 Hz, ¼CH), 5.84e5.88 (m, 3H, -CH ¼ ), 6.62, 6.69 (m, 6H,
d
4.99 (d, 3H, J ¼ 8.0 Hz, ¼CH), 5.64 (d, 3H,
benzene-H), 7.47e7.60 (m, 6H, benzene-H).

760
C. Fan et al. / Dyes and Pigments 95 (2012) 757e767
2.1.2. Synthesis of chromophores
under an argon atmosphere (Scheme 1). The crude product solvent
was removed by evaporation, and the slurry was purified through
a chromographic column on silica gel by using pure chloroform and
THF as the eluent. Yellow powders (0.93 g) were obtained in 53.7%
yield. MS m/e: 578.47; m.p 135e136 ꢀC; Anal. Calcd for C41H30N4
(%): C, 85.09; H, 5.23; N, 9.68. Found C, 85.04; H, 5.28; N, 9.62; 1H
2.1.2.1. 4-[4-(2,20:60,20’-terpyridinyl)]phenyltriphenylamine (chromo-
phore
I). Using
4-(4,4,5,5-tertramethyl-[1,3,2]dioxaborolane)
phenyl-N,N-diphenylamine (compd 4) (0.37 g, 1.0 mmol) with 40-
(4-bromophenyl)-2, 20:60, 200-terpyridine (compd 3) (0.39 g,
1.0 mmol), tetrakis (triphenylphosphine)palladium (0) [Pd(PPh3)4
ed. Note: caution: irritant; air sensitive; light sensitive; incompat-
ible with oxidants] (0.10 g) and Na2CO3 (6.40 g, 60 mmol) in
tetrahydrofuran (THF) (80 mL containing 10% water) were heated at
70 ꢀC for 15 h (Scheme 1). The crude product was distillated in
vacuo and purified by column chromatography on SiO2 using
hexane and THF as the eluent. Then, 0.40 g of chromophore I was
obtained as a white solid in 72.5% yield. MS (m/e): 552.45; m.p
251e252 ꢀC; Anal. Calcd for C39H28N4 (%): C, 84.76; H, 5.11; N, 10.14.
Found C, 84.80; H, 5.08; N, 10.12; 1H NMR (400 MHz, CDCl3, TMS):
NMR (400 MHz, CDCl3, TMS):
d
7.36 (t, 4H, J ¼ 8.0 Hz, benzene-H),
7.63 (d, 4H, J ¼ 8.0 Hz, benzene-H), 7.77 (d, 4H, J ¼ 8.0 Hz, benzene-
H), 7.89 (t, 4H, J ¼ 8.0 Hz, pyridyl-H), 8.66e8.75 (m,14H, benzene-H,
pyridyl-H, -CH ¼ ); 13C NMR (100 MHz, CDCl3, TMS):
d 118.57,
121.40, 123.96, 128.91, 132.12, 136.94, 149.15, 156.09.
2.1.2.5. 4,40-bis[4-(2,20:60,20’-terpyridinyl)] styryl triphenylamine
(chromophore V). Chromophore V was synthesized by an analo-
gous method to that used for chromophore IV by using compd. 8
(0.50 g, 1.68 mmol), compd 3 (1.31 g, 3.36 mmol), triphenylphos-
phine (0.08 g), palladium acetate (0.023 g) and obtained yellow
solid 1.08 g, in 70.4% yield. MS m/e: 912.17; m.p 128e129 ꢀC; Anal.
Calcd for C64H45N7 (%): C, 84.28; H, 4.97; N,10.75. Found C, 84.30; H,
d
7.17 (t, 4H, J ¼ 6.0 Hz, benzene-H), 7.23e7.30 (m, 4H, benzene-H),
7.36 (t, 2H, J ¼ 8.0 Hz, benzene-H), 7.56 (d, 2H, J ¼ 8.0 Hz, benzene-
H), 7.65 (t, 2H, J ¼ 8.0 Hz, benzene-H), 7.72 (d, 2H, J ¼ 8.0 Hz,
benzene-H), 7.89 (t, 2H, J ¼ 8.0 Hz, pyridyl-H), 7.99 (d, 2H, J ¼ 8.0 Hz,
benzene-H), 8.68 (t, 4H, J ¼ 8.0 Hz, pyridyl-H), 8.73 (t, 2H, J ¼ 8.0 Hz,
pyridyl-H), 8.79 (s, 2H, pyridyl-H); 13C NMR (100 MHz, CDCl3, TMS):
5.01; N, 10.72; 1H NMR (400 MHz, CDCl3, TMS):
d 7.37 (t, 6H,
J ¼ 8.0 Hz, benzene-H), 7.64 (d, 6H, J ¼ 8.0 Hz, benzene-H), 7.78 (d,
6H, J ¼ 8.0 Hz, benzene-H), 7.89 (t, 6H, J ¼ 8.0 Hz, pyridyl-H),
8.66e8.74 (m, 21H, benzene-H, pyridyl-H, -CH ¼ ); 13C NMR
d
118.64, 121.40, 121.79, 123.07, 123.37, 123.81, 123.96, 124.54,
124.99, 127.04, 127.71, 127.77, 128.92, 129.33, 132.12, 135.85, 136.90,
149.16, 149.82, 156.32.
(100 MHz, CDCl3, TMS):
d 118.59, 121.41, 123.50, 123.98, 127.15,
127.60, 128.58, 128.92, 132.12, 136.96, 137.43, 149.15, 156.05, 156.10.
2.1.2.2. 4,4’-bis[4-(2,20:60,20’-terpyridinyl)]phenyltriphenylamine
(chromophore II). Chromophore II was synthesized by an analo-
gous method to that used for chromophore I by using compd 3
(0.79 g, 2.0 mmol), compd 5 (0.50 g, 1.0 mmol), tetrakis (triphe-
nylphosphine) palladium (0) (0.10 g), Na2CO3 (6.40 g, 60 mmol) in
tetrahydrofuran (THF) (80 mL containing 10% water) and obtained
yellow solid 0.45 g, in 28.9% yield. MS m/e: 860.17; m.p 181e182 ꢀC;
Anal. Calcd for C60H41N7 (%): C, 83.79; H, 4.81; N, 11.40. Found C,
83.80; H, 4.78; N, 11.42; 1H NMR (400 MHz, CDCl3, TMS):
2.1.2.6. 4,40,40’-tri[4-(2,20:60,20’-terpyridinyl)] styryl triphenylamine
(chromophore VI). Chromophore VIwas synthesized byananalogous
method to that used for chromophore IV by using compd. 9 (0.25 g,
0.77 mmol), compd 3 (0.90 g, 2.31 mmol), a small amount of triphe-
nylphosphine (0.08 g) and palladium acetate (0.023 g) and obtained
yellow solid 0.55 g, in 57.4% yield. m.p 158e159 ꢀC; Anal. Calcd for
C87H60N10 (%): C, 83.90; H, 4.86; N, 11.25. Found C, 83.91; H, 4.88; N,
11.22; 1H NMR (400 MHz, CDCl3, TMS):7.36e7.42 (m, 9H, benzene-H),
7.63 (d, 8H, J ¼ 8.0 Hz, benzene-H), 7.78 (d, 8H, J ¼ 8.0 Hz, benzene-H),
7.86e7.90 (m, 9H, pyridyl-H), 8.66e8.75 (m, 26 H, benzene-H, pyr-
d
7.22e7.26 (m, 9H, benzene-H, pyridyl-H), 7.35e7.38 (m, 4H,
benzene-H), 7.50e7.55 (m, 4H, benzene-H), 7.58e7.61 (m, 4H,
benzene-H), 7.67e7.50 (m, 4H, benzene-H), 8.00 (d, 4H, J ¼ 8.0 Hz,
pyridyl-H), 8.69 (d, 4H, J ¼ 8.0 Hz, pyridyl-H), 8.74e8.75 (m, 4H,
pyridyl-H), 8.79 (s, 4H, pyridyl-H); 13C NMR (100 MHz, CDCl3, TMS):
idyl-H, -CH ¼ ); 13C NMR (100 MHz, CDCl3, TMS):
d 118.56, 121.34,
123.43, 123.87, 127.50, 128.86, 132.07, 137.43, 149.10, 156.08.
d
118.66, 121.39, 123.77, 124.21, 125.49, 127.71, 128.42, 129.15, 131.41,
2.2. Measurements
136.85, 149.14, 155.98, 156.36.
All chemicals were purchased from Aldrich or Acros Chemical
Co. and were used without any further purification. Electron impact
(mode laser) mass spectra and EI mass spectra were obtained on
a 4700 Proteome Analyzer (MALDI-TOF-TOF, ABI Company) and HP
5989 mass spectra instrument, respectively. Melting points (m.p.)
were recorded on an X-5 melting point measurement instrument
(Gongyi City Yuhua Instrument Co., Ltd). Elemental analyses were
determined with a PE CHN 2400 analyzer. 1H NMR of the chro-
mophores was performed on a INOVA-400 spectrometer with
CDCl3 as the solvent and tetramethylsilane as an internal standard.
X-ray diffraction data crystals were collected on a Bruker SMART
APEX diffractometer.
UVevis absorption spectra were measured on a Hitachi U-3500
recording spectro-photometer from quartz curettes of 1 cm path.
Fluorescence measurements were carried out with a PTI (Photo
Technology International) fluorescence spectrometer. All the fluo-
rescence spectra were recorded on a FluoroMaxÒ 3 Fluorometer
2.1.2.3. 4,40,40’-tri[4-(2,20:60,20’-terpyridinyl)]phenyltriphenylamine
(chromophore III). Chromophore III was synthesized by an analo-
gous method to that used for chromophore I by using compd 3
(0.58 g, 1.5 mmol), compd 6 (0.31 g, 0.5 mmol), tetrakis (triphe-
nylphosphine)palladium (0) (0.10 g), Na2CO3 (6.40 g, 60 mmol) in
tetrahydrofuran (THF) (80 mL containing 10% water) and obtained
yellow solid 0.44 g, in 75.6% yield. MS m/e: 1165; m.p 274e275 ꢀC;
Anal. Calcd for C81H54N10 (%): C, 83.34; H, 4.66; N, 12.00. Found C,
83.40; H, 4.65; N, 11.98; 1H NMR (400 MHz, CDCl3, TMS):
d 7.31 (d,
6H, J ¼ 6.0 Hz, benzene-H), 7.36 (t, 6H, benzene-H), 7.54e7.63 (m,
6H, benzene-H), 7.75 (t, 6H, pyridyl-H), 7.89 (t, 6H, J ¼ 8.0 Hz,
benzene-H), 8.00 (t, 6H, J ¼ 6.0 Hz, pyridyl-H), 8.67 (d, 6H,
J ¼ 8.0 Hz, pyridyl-H), 8.75 (d, 6H, J ¼ 4.0 Hz, pyridyl-H), 8.80 (d, 6H,
J ¼ 4.0 Hz, pyridyl-H); 13C NMR (100 MHz, CDCl3, TMS):
d 118.67,
121.41, 123.83, 124.21, 124.87, 127.76, 127.88, 127.99, 128.46, 129.44,
132.16, 134.94, 136.88, 141.26, 149.16, 149.80, 155.99, 156.34.
(HORIBA). The fluorescence quantum yields (
using a standard method under the same experimental conditions
for all compounds. Fluorescein dissolved in methanol (
[26], at the same concentration as the other sample, was used as the
standard. Fluorescence lifetimes were measured with a Laser
Strobe Fluorescence Lifetime Spectrometer (Photo Technology
International) with 375 nm laser pulses from a nitrogen laser fiber-
F) were measured by
2.1.2.4. 4-[4-(2,20:60,20’-terpyridinyl)] styryl triphenylamine (chro-
mophore IV). Under anhydrous and oxygen-free conditions compd.
7 (0.81 g, 3.0 mmol), compd 3 (1.16 g, 3.0 mmol), a small amount of
triphenylphosphine (0.16 g) and palladium acetate (0.045 g) in
refined acetonitrile (20 mL) and refined triethylamine (30 mL)
mixture solvent were stirred and refluxed in a flask at 85 ꢀC for 48 h
F
¼ 0.93)

C. Fan et al. / Dyes and Pigments 95 (2012) 757e767
761
Table 1
The band gaps were obtained from the absorption spectra
(absorption edge) of the chromophores, and the LUMO level was
calculated from the values of band gap and the HOMO [27].
Crystal data collection and structure refinement of chromophore I.
Formula
C39H28N4
Formula weight
Temperature
Crystal system
Space group
a (Å)
552.65
296 (2)
3. Results and discussion
Orthorhombic
P2 (1) 2 (1) 2 (1)
11.2141 (8)
14.8037 (11)
35.007 (3)
90.00
90.00
90.00
5811.4 (7)
1.263
8
3.1. Crystal structure of chromophore I
b (Å)
c (Å)
The crystal of chromophore I, suitable for X-ray analysis, was
obtained from the slow evaporation CH2Cl2/ethanol at room
temperature (Table 1). The ORTEP drawing is shown in Fig. 1 and its
packing diagram is shown in Fig. 2. As shown in Fig. 1, there are two
independent molecules (molecules I and II) in the unit cell.
a
b
g
(o)
(o)
(o)
Volume (Å3)
Density (calcd.) (g/cm3)
Z
In both molecules, the biphenyl ring system is twisted about the
biphenyl bond, the dihedral angle being 41.8 (2)ꢀ in one molecule,
and 37.6 (2)ꢀ in the other. For the 40-terpyridyl substituent, the N-
atoms of the flanking pyridine rings are oriented away from the N-
atom of the central pyridine ring. If these had pointed towards
inwards, the substituent would have been planar owing to less
crowding. In fact, only one of the two flanking rings is severely
twisted, as noted by the dihedral angles of 1.5 (3) and 32.2 (2)ꢀ in
the first molecule, and 7.7 (3) and 28.3 (2)ꢀ in the second. This non-
planar feature differs from other reported examples [28]. At the
diphenylamino end, the central nitrogen exists in a trigonal plane,
with the sum of the three CeNeC angles being almost 360ꢀ. The
three benzene rings connected to this atom are arranged in
Goodness-of-fit on F2
1.013
0.0691
0.1365
0.1825
Final R indices [I/2
wR2
R indices (all data) R1
wR2
s
(I)] R1
0.2259
coupled to a lens-based T-formal sample compartment equipped
with a stroboscopic detector. Details of the Laser Strobe systems are
described on the manufactures web site, http://www.pti-nj.com.
The fitting results were judged by their values of ‘‘reduced chi-
squared’’. All measurements were carried out in air at room
temperature.
Fig. 1. ORTEP drawings of chromophore I, showing 35% probability displacement ellipsoids: (A) molecule I and (B) molecule II.

762
C. Fan et al. / Dyes and Pigments 95 (2012) 757e767
ring and adjacent benzene rings for chromophores IeIII or between
triphenylamine benzene ring and adjacent vinylbenzene rings for
chromophores IVeVI. The results show that the molar extinction
coefficient ratios of the second/first absorption bands of chromo-
phore IeIII are larger than that of chromophores IVeVI. This clearly
suggests that the
pep* intra-molecular transition energy level in
the triphenylamine benzene ring and adjacent rigid benzene rings
for chromophores IeIII are higher than that of the flexible styryl
system for chromophores IVeVI
For the similar containing phenyl or styryl chromophores, the
molar extinction coefficient of chromophores in the first band at
around 290e302 nm increase with a corresponding increasing the
number of terpyridine multibranches from 1 to 3. For chromo-
phores IeVI, the molar extinction coefficient is in the order of
chromophore III ＞ II ＞ I and chromophore VI ＞ V ＞ IV. On the
other hand, the absorption peak is shifted to the red with the cor-
responding branching increased in the second band around
352e410 nm. Compared with chromophore I, the chromophores II
and III have red shifted maxima by about 20 nm and the absorption
peaks of chromophores V and VI have a red shift of about 15 nm in
comparison with chromophore IV.
In order to investigate the UVevis properties in the solid state
the chromophores were processed as a film in quartz glass [31],
which show similar absorption properties as compared to that in
THF solution. In the second absorption band the chromophores II,
III have a red shift compared to chromophore I and chromophores
V, VI have a red shift compared to chromophore IV, respectively.
Fig. 2. A packing diagram of chromophore I along the a direction.
a propeller-like fashion. Further details of the crystal structure
investigation have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication number
CCDC834975 for this paper. These data can be obtained free of
charge via www.ccdc.can.ac.uk/conts/retrieving.html(or from the
Cambridge Crystallographic Centre, 12 Union Road, Cambridge
CB21EZ, UK [fax: þ44 1223 336033; e-mail:deposit@ccdc.cam.ac.
uk]).
The second maximum absorption peaks of
pep* intra-molecular
charge transfer (ICT) in triphenylamine adjacent vinylbenzene
rings for chromophores IV, V, VI films increases with the branch
numbers (see Fig. 3 inset). This property is different from that in
THF solution due to the fact that in the solid film there is restricted
torsion of the flexible molecular structure [30].
It is obvious that in the second absorption band, maximum
absorption intensities for chromophores IeIII are higher than that
of chromophores IVeVI whether in THF solution or in a solid film
due to the effect of the rigid phenyl versus flexible styryl ring
structure. On the other hand, the absorption peaks of multi-
branches (chromophores II, III, VI, V) are red shifted, relative to
those of monobranched chromophores (chromophores I, IV) due to
the monobranching effect.
3.2. UVevis absorption spectroscopy
The UVevis absorption spectra of chromophores IeVI in tetra-
hydrofuran (THF) (C ¼ 1.0 ꢂ 10ꢁ5 mol/L) exhibit two absorption
bands at around 290e302 nm and 352e410 nm (Fig. 3). The first
absorption band at around 290e302 nm contributes to the tri-
phenylamine [29,30] and the conjugated terpyridine. The second
In order to further investigate the optical properties of chromo-
phores IeVI by means of molecular orbital calculations at the B3LYP/
6e31G level of density functional theory (DFT) were used [32]. Seen
absorption band at around 352e410 nm contributes to pep* intra-
molecular charge transfer (CT) between triphenylamine benzene
the HOMO is a
moiety; LUMO is of
p
orbital concentrated on the central triphenylamine
* character distributed on the terpyridyl ring
0.7
p
chromophore I
(Fig. 4) for chromophores I, II and V, VI. The LUMO mainly accu-
mulates in the two arms of terpyridyl ring moiety which is similar to
other multi-branched systems [32]. The DFT results indicate that the
features of the frontier molecular orbital do not change significantly
with phenyl or styryl groups. The calculated HOMO-LUMO gaps for
chromophores IeVI follow the order: chromophore I (339.34 kJ/
mol) > chromophore II (336.24 kJ/mol) > chromophore III
(333.87 kJ/mol) > chromophore IV (305.10 kJ/mol) > chromophore
V (290.60 kJ/mol) > chromophore VI (284.27 kJ/mol). It was shown
that the phenyl/stryryl groups effectively determine the properties
of the HOMOs. The trend is expected because the terpyridyl phenyl
triphenylamine chromophores tend to stabilize the HOMO signifi-
cantly, giving the energy gap larger than that of terpyridyl styryl
triphenylamine chromophores.
chromophore II
0.6
chromophore III
chromophore IV
0.5
chromophore V
chromophore VI
0.4
0.3
0.2
0.1
0.0
250
300
350
400
450
500
550
600
Wavelength / nm
3.3. Luminescence spectroscopy
Fig. 3. Absorption spectrum of chromophores IeVI inTHF solution (C ¼ 1.0 ꢂ 10ꢁ5 mol/L).
The inset presents the normalized UVevis spectra of chromophores VI, V, VI in
films.
On excitation at the respective maximum absorption wave-
length, the chromophores IeVI emit strong fluorescence, as shown

C. Fan et al. / Dyes and Pigments 95 (2012) 757e767
763
Fig. 4. Calculated spatial distributions of the HOMO and LUMO levels of chromophores IeVI.

764
C. Fan et al. / Dyes and Pigments 95 (2012) 757e767
Table 2
A
The absorption spectra and fluorescence spectra of chromophores IeVI in different
Actone
solvents at 1 ꢂ 10ꢁ5 M.
400
300
200
100
0
Dichloromethane
Ethyl acetate
Methanol
Chromophore I
Solvent
Hexane Ethyl Tetrahydro- Dichloro- Actone Methanol
Chromophores
acetate
furan
methane
I
Absa
Em
Abs
Em
Abs
Em
Abs
Em
Abs
Em
Abs
Em
352
408
367
418
375
422
382
430
383
485
390
440
353
464
370
469
373
467
386
495
390
495
393
495
356
358
486
372
487
376
471
389
516
394
520
396
514
354
507
374
509
373
502
387
529
389
537
395
543
356
540
369
536
376
489
387
563
391
558
392
556
Tetrahydrofuran
Hexane
469
373
476
375
470
389
496
393
498
393
506
II
III
IV
V
VI
a
Abs and Em are absorption and fluorescence emission maxima of chromophores
400
500
600
700
in different solvent, respectively.
Wavelength/ nm
B
Actone
where, me and mg are the dipole moments in the excited and ground
states, respectively. (yabseyem) is Stokes shift. The symbols a and c
are the molecular size and the speed of light in a vacuum, respec-
Dichloromethane
Ethyl acetate
Methanol
Chromophore IV
300
200
100
0
tively. The symbol h is Plank constant. Orientation polarizability of
D
solvent ( f) is defined by Eq. (2), wherein ε is the dielectric constant
Tetrahydrofuran
Hexane
and n is the optical refractive index. One can see that the slopes are
all larger than zero. As a result, the fluorescence spectra of the
chromophores are red shifted with the increase of dielectric
constant (k). The slope (k) is proportional to the value of me
Since the molecular dimension ( ) becomes larger with the branch
/mge/ .
a3
a
number, the fact that slopes (k) in the order of chromophore
I > chromophores II/III and chromorphore IV > chromophores
V/VI implies the same sequence of dipole moment change
(
Dmge
¼
meemg), that is, the excited state (me) is larger than that in the
ground state (mg). The fluorescence emission spectra maximum
value of the chromophores increased with the polarity of the
solvent, and is consistent with the other triphenylamine derived
chromophores [37].
400
500
600
700
Wavelength/ nm
Fig. 5. The fluorescence emission spectral of chromophores in different solvents at
C ¼ 1.0 ꢂ 10ꢁ5 mol/L: (A) for chromophore I and (B) for chromophore IV.
Time-resolved decay curves for all chromophores in dichloro-
methane are shown in Fig. 7 and the corresponding lifetime (s) data
are presented in Table 3. It is obvious that the fluorescence lifetime
of triphenylamine in the rigid benzyl unit chromophores IeIII
(lifetime 2.94e3.16 ns) are longer than that of flexible styryl unit
chromophores IVeVI (lifetime 2.11e2.48 ns). As can be seen for
in the Fig. 5. It is found that the fluorescence intensities of the
multibranching chromophores are stronger than those of the
monobranched chromophores in dichloromethane (1 ꢂ 10ꢁ5 M).
The six fluorescence spectra incline to red shift as the solvent
dielectric constant increase (see Table 2), as for chromophore I,
from 408 nm (hexane, k, 1.89) to 464 nm (ethyl acetate, k, 6.02), to
469 nm (tetrahydrofuran, k, 7.58), to 486 nm (dichloromethane, k,
9.1), to 507 nm (actone, k, 20.7), to 540 nm (methanol, k, 31.2) [33].
The fluorescence intensity decreased with the increased solvent
dielectric constant for chromophore I, this can be explained by the
“twisted intra-molecular charge transfer” (TICT) model in which
the solvent with the larger dielectric constant solvates the TICT
state more efficiently so that the chromophore gives very low
fluorescence intensity in such solvent [34]. A similar trend was
observed for the other chromophores.
Here, the dipole moment of dye in the excited state is also
greater than that in the ground state, which can be certified by the
Lipperte-Mataga equation [35,36][Fig. 6].
À
Á
À
Á
1
2
Zc yabs
ꢁ
yem
¼
me me
ꢁ
mg
D
f þ const
(1)
(2)
o a3
4
p
ε
À
Á
n2 ꢁ 1
ε ꢁ 1
D
f ¼
ꢁ
2n2 þ 1
2ε þ 1
Fig. 6. The Lippert-Mataga plots for chromophores IeVI.

C. Fan et al. / Dyes and Pigments 95 (2012) 757e767
765
1.0
A
Decay curve
Fitted curve
Chromo IV
2+
2+
2+
3
2
1
0
Cd
Co
Cu
0.8
2+
Fe
Life time:2.942 ns
0.6
0.4
0.2
0.0
2+
2+
Hg
Wavelength/ nm
Mg
2+
Ni
2+
Pb
2+
Zn
300
400
500
600
700
1.7
1.8
1.9
2.0
2.1
Wavelength/ nm
Log(Time)
Fig. 8. The normalized UVevis absorption spectra of chromophore IV in water ob-
tained upon addition of different divalent metal ions (1 equivalent). The inset presents
the changes in absorption spectral of (10ꢁ5 M in water) on the addition of Fe2þ in
aqueous solution.
B
Decay curve
Fitted curve
0.9
(C ¼ 1.0 ꢂ 10ꢁ5 mol/L). As shown in Fig. 8 inset, it is of interest to
note that following addition of Fe2þ ion to chromophore IV a strong
metal-to-ligand-charge transfer (MLCT) [38,39] band originates
centered at 567 nm with the evolution of a bright violet color. With
the increasing of Fe2þ ion, the sharp new peak gradually intensified
until the mole ratio (chromophore IV/Fe2þ) of 1:1 was reached. It
was of interest to assess the colorimetric sensing ability of the
chromophores towards different cationic guests. In order to do so,
a series of coloring experiments were performed in water. The
0.6
0.3
0.0
Life time:2.108 ns
addition of other metal ions, such as Cd2þ, Co2þ, Cu2þ, Hg2þ, Mg2þ
,
Ni2þ, Pb2þ, Zn2þ, did not show significant changes in absorption
between 450 and 700 nm for aqueous solution, compared with the
addition of Fe2þ ion [see Fig. 8]. The observed distinct changes in
absorption suggest that chromophore IV has strong binding affinity
for Fe2þ with high selectivity for identifying the colour changes by
eye [see Fig. 8]. The new MLCT band centered at 567 nm in the case
of Fe2þ ion over the other metal ions suggests that the chromo-
phore IV can act as an effective chemosensor towards the detection
of Fe2þ ion in solution.
1.7
1.8
1.9
2.0
2.1
Log (Time)
Fig. 7. The fluorescence lifetime of chromophores in CH2Cl2 (C ¼ 1.0 ꢂ 10ꢁ5 mol/L):
(A) for chromophore I and (B) for chromophore IV.
structurally similar chromophores (containing phenyl or styryl
unit), the fluorescence lifetime (s) values in dichloromethane are
increasing with the increase of molecular branch from 1 to 3, in the
order of chromophore III > II > I and chromophore VI > V > IV.
0.24
3.4. Colorimetric sensor for detecting ions (II)
The chromophore IV was based on a donor-p-acceptor system
Chrom I
0.18
that could display a strong color development as well as intense
absorbance; such properties are useful for the development of
colorimetric sensors. The selective and sensitive signal response
ability of the chormohore IV for Fe2þ ion was studied
through UVevis spectra in aqueous solution around pH 7.0
Chrom II
Chrom III
Chrom IV
Chrom V
0.12
Chrom VI
Table 3
0.06
Fluorescence, electrochemical and thermogravimetric analysis properties of chro-
mophores IeVI.
Chromophores
F
s
(ns)
HOMO/LUMO (ev)
Eg
Td (ꢀC)
0.00
I
II
III
IV
V
0.54
0.42
0.80
0.88
0.81
0.74
2.94
2.99
3.16
2.11
2.29
2.48
ꢁ5.79/ꢁ2.93
ꢁ5.77/ꢁ3.11
ꢁ5.78/ꢁ3.03
ꢁ5.78/ꢁ2.90
ꢁ5.77/ꢁ3.15
ꢁ5.69/ꢁ3.06
2.86
2.66
2.75
2.88
2.62
2.63
481
487
549
334
344
340
400
600
Wavelength/ nm
Fig. 9. Comparison of UVevis absorption spectra of different chromophores in water
VI
(C ¼ 1.0 ꢂ 10ꢁ5 mol/L) with addition of 1 equivalent of Fe2þ
.

766
C. Fan et al. / Dyes and Pigments 95 (2012) 757e767
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absorbance band centered at 567 nm increased with the addition of
Fe2þ ion until the [Fe2þ]/[terpyridyl] of chromophores V and VI
reaches 1:1, the aqueous solution showing a magenta color which
can be seen by eye. No color change was observed by eye for
chromophers I, II, III (see Fig. 9 and inset) when the same amount
of Fe2þ ion was added under the same conditions. From the above,
the conclusion can be drawn that the chromophers with flexible
styryl unit have high selectivity and sensitivity for Fe2þ ion in
neutral aqueous solution among the divalent metal ions such as
Cd2þ, Co2þ, Cu2þ, Hg2þ, Fe2þ, Mg2þ, Ni2þ, Pb2þ, Zn2þ, while the
chromophores with a rigid phenyl terpyridyl unit do not display
these colour development properties due to the rigid phenyl unit
influencing the activity characteristics of the linked terpyridyl unit.
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Acknowledgments
The authors are grateful to the National Natural Science Foun-
dation of China (50973077), the Natural Science Foundation of
Jiangsu Province Education Committee (11KJA430003), the Natural
Science Foundation of Jiangxi Province (2010GZH0040), Project of
Person with Ability of Jiangsu Province (2010-xcl-015) and the
Priority Academic Program Development of Jiangsu Higher
Education Institutions (PAPD) for financial supports. We are
grateful to Prof. Seik Weng Ng in Department of Chemistry,
University of Malaya at Kuala Lumpur in Malaysia for crystal
assistance.
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