Synthesis of a novel class of chromophoric cross-linkers

Article abstract of DOI:10.1007/s13738-016-0811-4

Considering the special place of aromatic diazo compounds in photo-responsive materials and growing demand for materials with interesting optical properties, a new class of chromophoric cross-linkers was synthesized by acrylation of diazo derivatives of m-diaminobenzene. The cross-linkers are soluble in a wide variety of organic solvents as well as in mixtures of water and water miscible solvents. The chromophores of the cross-linkers are stable in protic and some certain aprotic solvents and remain stable after cross-linking. The chemical structure of this class allows one to have a cross-linker with tuned chemical reactivity and solubility with post-linking applicability. The cross-linkers are obtained from reactions with simple chemistry in high yields and are able to participate in radical and ionic polymerization as well as in nucleophilic addition reactions. Successful participation of these substances in acrylamide polymerization and sol-gel preparation is demonstrated.

Full text of DOI:10.1007/s13738-016-0811-4

J IRAN CHEM SOC
DOI 10.1007/s13738-016-0811-4
ORIGINAL PAPER
Synthesis of a novel class of chromophoric cross‑linkers
Kamahldin Haghbeen1 · Raymond L. Legge2
Received: 14 June 2015 / Accepted: 11 January 2016
© Iranian Chemical Society 2016
Abstract Considering the special place of aromatic diazo
compounds in photo-responsive materials and growing
demand for materials with interesting optical properties, a
new class of chromophoric cross-linkers was synthesized
by acrylation of diazo derivatives of m-diaminobenzene.
The cross-linkers are soluble in a wide variety of organic
solvents as well as in mixtures of water and water misci-
ble solvents. The chromophores of the cross-linkers are sta-
ble in protic and some certain aprotic solvents and remain
stable after cross-linking. The chemical structure of this
class allows one to have a cross-linker with tuned chemi-
cal reactivity and solubility with post-linking applicability.
The cross-linkers are obtained from reactions with sim-
ple chemistry in high yields and are able to participate in
radical and ionic polymerization as well as in nucleophilic
addition reactions. Successful participation of these sub-
stances in acrylamide polymerization and sol–gel prepara-
tion is demonstrated.
that could create new materials with modified physical and
mechanical properties [1]. Advances in different branches
of science and technology expanded the concept and appli-
cation of cross-linkers. In addition to the synthetic poly-
mers [2], cross-linkers play key roles in interfacial and
separation technologies [3], photo responding materials
[4], protein science [5], genetic research [6], ligand and
receptor interactions [7], immobilization techniques [8],
cell biology [9], label transfer agents [10], sensor technol-
ogy [4, 11], pharmaceutical and drug delivery [12]. There
is also a growing demand for post-linking roles of cross-
linkers such as responding to electromagnetic radiation
[13], exhibiting fluorescence or luminescence activity [14],
degradability [9, 15], and performing structural changes.
Such expectations have led research for making versatile
cross-linkers.
Photo aligning phenomenon was first described for the
reversible cis–trans isomerization of azobenzene units
attached to a substrate. It was also shown that the opti-
cal nonlinearity of nematic liquid crystals could be fur-
ther enhanced by adding a small amount of dye impuri-
ties. Therefore, polymers with azobenzene side groups
and materials containing pure photochemically stable
azo dye layers were investigated [16, 17]. Research has
demonstrated that aromatic diazo dyes can be inserted
into different polymeric matrix and make them applica-
ble in production of optical responsive materials such as
liquid crystals [18]. These materials are employed in mak-
ing electro-optical displays, optical storage devices, and
muscle-like actuators [2, 4, 16]. Considering this impor-
tant potential of aromatic diazo structure, a new class of
chromophoric cross-linkers with general structure of II
(illustrated in Scheme 1) was developed through a facile
method which is described in this paper. These cross-link-
ers are anticipated to facilitate the association of various
Keywords Cross-linker · Diazo · Acrylation ·
m-Diaminobenzene · Hydrogel
Introduction
Cross-linkers are designed to bind covalently to at least two
growing molecular chains during polymerization, a process
* Kamahldin Haghbeen
kamahl@nigeb.ac.ir
1
National Institute for Genetic Engineering
and Biotechnology, P.O.Box: 14965/161, Tehran, Iran
2
Department of Chemical Engineering, University
of Waterloo, Waterloo, ON N2L 3G1, Canada
1 3

J IRAN CHEM SOC
N2+A-
NH2
Z
NH2
NO+
X
Y
X
Y
NH2
Z
Ha
B
A
2
1
H2N
NH2
3
a
5
6
X15
Hf
16'
Hf'
16
4
Hc
N
Hg'
17'
17
O
Hg
8
O
Cl
Hb
N
Y14
18
7
O
18'
Ha
9
IH
HI'
2
b
11
12
He
1
HN
NH
2
10
B
Z13
3
A
a
5
6
Hc
N
N
X15
Hd
4
Hb
Y 14
8
7
(I)
9
b
11
12
He
10
Z
13
Hd
(II)
Scheme 1 Synthetic scheme for making diazo dyes of meta-diaminobenzene with general structure of I and their corresponding homofunc-
tional cross-linkers (II)
Table 1 Yields of the reactions introduced in Scheme 1
diazo moieties into the polymer matrices with photo-
responsive properties.
Compound
X
Y
Z
%Yield of I %Yield of II
1
2
3
4
5
6
7
–H
–H –H
100
100
85
95
76
76
83
68
79
–H
–H –OCH3
Results and discussion
–H
–H –SO2NH2 100
–CH3
–H
–H –I
–I –CH3
100
100
92
Preparation of diazo derivatives
of meta‑diaminobenzene
–OCH3 –H –NO2
–NO2 –H –OCH3
100
To prepare the cross-linkers with the general structure of
II, diazo dyes of meta-diaminobenzene were prepared
first (Scheme 1). To make dyes with the general structure
of I, diazonium salts of the desired amines had to be syn-
thesized. The coupling reaction between diazonium salts
and meta-diaminobenzene resulted in compounds of I. The
chemistry of both reactions, diazotization and coupling,
is well known [19]. The latter reaction is usually carried
out in aqueous media, but the right medium for the for-
mer reaction, diazotization, is based on the solubility and
susceptibility to oxidation of the selected amine. The effi-
ciency of a diazotization reaction is heavily dependent on
the chosen reaction medium and the nature of the substit-
uents presents on the aromatic ring of the selected amine.
Electron-withdrawing substituents usually decrease yield
of the reaction [2].
meta-diaminobenzene participates in coupling reactions
with different diazonium salts and produces the corre-
sponding dye. Amino substituents not only are activator
of the aromatic ring in electrophilic substitution reactions,
they are also ortho/para directing groups. As a result, the
coupling reaction is highly regioselective and substitu-
tion happens mostly at position 4 shown in Scheme 1. The
final yield of the diazo dyes hardly falls below 70 % and
it is first merit of these cross-linkers as they are prepared
through facile and high yield reactions. Data in Table 1
show the efficiency of this preparation method.
Preparation of the cross‑linkers
Similar to ortho and para-dihydroxy benzenes, ortho
and para-diaminobenzenes fall in oxidation during cou-
pling reaction with diazonium salts [20]. In contrast,
All the cross-linkers described in this paper were obtained
in excellent yield (Table 1). These results indicate that the
1 3

J IRAN CHEM SOC
reaction of acryloyl chloride with the dyes carrying elec-
tron donating group(s) is better. It also appears that THF
works as a proper reaction medium for the dyes with the
general structure of I. However, solubility of some certain
dye molecules might be problematic which necessitates a
change of the reaction medium. Dimethylformamide is
suggested for more hydrophilic precursors [21]. It is impor-
tant to note that carrying a double bond in the vicinity of a
conjugated carbonyl functional group renders these cross-
linkers very reactive. This high reactivity is another advan-
tage of these compounds as it facilitates their participation
in various reactions; however, it also affects their suscep-
tibility. NMR experiments confirmed high sensitivity of
these compounds to light at room temperature especially in
some certain solvents such as chloroform.
Physical phenomena such as light, pressure and temper-
ature can cause structural changes in dye molecules which
result in color changes. One example of this type phenome-
non is the reversible response of certain dyes to pH changes
[24]. Figure 2a shows the change in the color solution of I2
upon a shift in pH. Comparing the λmax(s) of compounds I
with those of compounds II (Table 2) reveals a blue shift
in the λmax(s) of the dyes after acrylation (Fig. 1). None-
theless, compounds II are still sensitive to pH changes
(Fig. 2a). This feature is faded upon cross-linking (Fig. 2b).
Therefore, if the cross-linkers II are expected to respond to
pH changes, appropriate substituent/s have to be placed on
the aromatic ring (b).
Second, conjugation makes it possible to control the
reactivity of the double bond at the “C” terminals of the
acrylamido groups. For instance, the reactivity of the cross-
linker toward nucleophiles can be enhanced by adding an
electron-withdrawing group to the second aromatic ring
(b). This feature is important when the cross-linker is to be
used to bind molecules containing moderate nucleophilic
functional groups such as proteins.
The structural features of the second aromatic ring (b)
in I and II not only influence the visible spectrum and
chemical reactivity of the cross-linker but also affect the
solubility. For example, adding a sulfonamide or sulfonic
substitute to the second aromatic ring promotes both the
chemical activity of the cross-linker toward nucleophiles
and its solubility in aqueous media. The more soluble is
the cross-linker, the higher amount of that can be used in
reactions which are run in water. For instance, II3 was suc-
cessfully used as cross-linker in acrylamide polymerization
(Fig. 3a).
Polyacrylamide is obtained by radical polymerization
of acrylamide in the presence of a cross-linker in aqueous
medium [25]. In contrast, sol–gels do not need a cross-linker
as they are produced by hydrolysis of orthosilanes followed
by polymerization of the hydrolysis products through a
nucleophilic condensation mechanism [26]. In comparison
with hydrogels, sol–gels are robust materials which can be
used for immobilization purposes where hydrogels may not
Structure and properties
Structure II consists of three distinct components: acryla-
mido moiety which is expected to give the whole molecule
homofunctional cross-linking ability. Second, a benzene
ring (a) conjugated to the acrylamido substituents. The
benzene ring also functions as a docking terminal for the
third part of the molecule, an aromatic diazo moiety. With
acrylamido groups as the binding arms, it is assumed that
the cross-linker will show the chemical activity of α-β-
unsaturated carbonyl compounds. Therefore, it is antici-
pated that the cross-linker can take part in both radical and
ionic reactions. However, there are two significant differ-
ences between the chemical structures of II and acryla-
mides. First, the “N” terminals of the acrylamido groups
are conjugated to the benzene ring (a) and the conjugation
has been extended to another aromatic moiety (b) through
the double bond of a diazo functional group. As a result,
the electronic transitions in the whole conjugated system
shift toward visible region and make the molecule color-
ful (Fig. 1). This additional feature increases post-link-
ing applications of the cross-linker especially where the
chromophoric behavior of the material is important [22,
23].
Fig. 1 The overlaid UV–visible
(a)
(b)
1.5
1.2
0.9
0.6
0.3
0
1
5
1.4
1.2
1
spectra of compounds with gen-
eral structure of a I including
(1) I2, (2) I7, (3) I5, (4) I3, (5) I1,
(6) I4, (7) I6 and b II including
(1) II1, (2) II7, (3) II3, (4) II6,
(5) II2, (6) II5, (7) II4 in ethanol
at 20 °C
1
2
3
4
2
3
0.8
0.6
0.4
0.2
0
6
4
5
6
7
7
280
360
440
520
600
280
360
440
520
600
Wavelength nm
Wavelength nm
1 3

J IRAN CHEM SOC
Fig. 2 a Cross-linker II2 in phosphate buffer solution at two different
pH (left 2.2 and right 10.5). b Poly acrylamide hydrogel obtained by
polymerization of acrylamide in the presence of bis-acrylamide and
II2 as cross-linkers in phosphate buffer solution at two different pH
(left 2.2 and right 10.5)
Table 2 UV-visible data of compounds I and II in ethanol at 20 °C
Dye λmax(EtOH), nm ε, M−1 cm−1 Cross-linker λmax (EtOH), nm
Proton and carbon chemical shifts are relative to TMS. Mul-
tiplicity determinations and 2D NMR (COSY and HMQC)
were conducted using standard pulse programs. CH3OD
was used for proton exchange experiments. Infrared spec-
tra were recorded by a Brucker (Tensor 27) FTIR. Electron
impact mass spectra were acquired with a JEOL HX110
double focusing mass spectrometer operated at a mass res-
olution of ~1000. Typical source conditions were: source
temp = 200 °C and electron energy of 70 eV. All samples
were introduced by direct insertion. Molecules with the gen-
eral structure of II were made through a three-step process
illustrated in Scheme 1; diazonium salt preparation, diazo
coupling reaction, and acrylation of the diazo dye.
I1
I2
I3
I4
I5
I6
I7
418
430
450
441
449
503
462
20,920
19,770
30,700
26,180
30,800
38,880
25,590
II1
II2
II3
II4
II5
II6
II7
384
399
390
395
445
440
410
be applicable [27]. In addition; combining dyes with sol–
gels through various methods is a hot topic in the on-going
research on the sol–gels applications [28]. Figure 3c shows
successful application of II2, II3, and II7 in xerogel prepa-
ration. The color stability of the obtained materials was
confirmed by placing them in pure organic solvents such as
acetone, ethanol and THF (Fig. 3b, d).
Procedure for preparation of diazonium chloride
solutions of aromatic amines
The desired aromatic amine (0.01 M) was dissolved in a
mixture of concentrated HCl (5 ml) and distilled water
(20 ml). A solution of sodium nitrite (0.83 g, 0.012 M) in
distilled water (5 ml) was prepared in a test tube and added
to the acidic solution of amine dropwise over 5 min at 0 °C.
To complete the reaction, the overall mixture was stirred at
the same temperature for 40 min.
Experimental
Aniline, 1,3-diaminobenzene, p-nitroaniline, 2-methoxy-
4-nitro-aniline, 4-methoxyaniline, 4-methoxy-2-nitro-
aniline, 4-sulfonamidoaniline, 4-iodo-2-methyl-aniline,
3-iodo-4-methyl-aniline, acryloyl chloride and tetraethoxy
orthosilicate (TEOS) were purchased from the Sigma-
Aldrich (Oakville, ON, Canada). The organic solvents and
the other chemicals were reagent grade. NMR spectra were
recorded by a Brucker (Ultrashield, 300 MHz) spectrometer.
Modified procedure for preparation of diazonium
chloride solution of p‑nitroaniline
Some aromatic amines, such as p-nitroaniline, are less
soluble in water. As a result, a modified procedure was
employed for preparation of the corresponding diazonium
1 3

J IRAN CHEM SOC
Fig. 3 Polyacrylamide hydro-
gel obtained by polymerization
of acrylamide in the presence
of bis-acrylamide and II3 as
cross-linkers in a water and b
acetone; c xerogels obtained
by drying the sol–gels resulted
from polymerization of TEOS
sol in the presence of c1 II2, c2
II3, c3 II7. d Samples c1 and c3
in ethanol and in acetone. See
the “Experimental” section for
the details of preparation
salts. p-Nitroaniline (1.38 g, 0.01 M) was dissolved in a
mixture of methanol (20 ml) and concentrated HCl (5 ml).
The isoamyl nitrite (1.34 ml, 0.01 M) was then added to
this solution at 0 °C. A yellow precipitate gradually formed.
The reaction mixture was kept stirring at the same tempera-
ture for 45 min to get completed.
to stir at <5 °C for an extra hour. The product appeared as
a precipitate which was collected and recrystallized either
from water or ethanol. The product can be increased com-
pletely, if the pH is raised to 7. Chemical structures for the
compounds I1 to I7 were assigned by the following spectro-
scopic data. The star sign on some protons indicates over-
lapped ones.
General procedure for making diazo derivatives
of 1,3‑diaminobenzene with general structure of I
in Scheme 1
I1: (E)‑4‑(2‑phenyldiazenyl)benzene‑1,3‑diamine
Light orange powder, IR in KBr: [(–NH2 = 3473, 3379,
1619 cm−1), (–CHAr = 3056 cm−1), (–C=CAr = 1568 cm−1),
The desired aryl diazonium chloride solution was added
dropwise to a mixture of 1,3-diaminobenzene (0.01 M) in
15 ml of double-distilled water containing 1 ml of con-
centrated HCl at 0 °C. The reaction mixture was continu-
ously stirred at 0 °C for 30 min. The pH was raised to 5
by adding sodium acetate and the resulting mixture was left
1
(–N=N– 1450 cm−1), (–C–N– = 1331 cm−1)]; HNMR
in CDCl3: δ [Ha(5.87, 1H, d, j–j = 2.4 Hz), Hb(7.63,
1H, d, j–j = 8.7 Hz), Hc*(6.12, 3H, q), Hd&Y(7.41, 2H,
t), He&X(7.72, 2H, d, j–j = 7.8 Hz), Z(7.30, 1H, q),
NH2A(3.90, 2H, br), NH2B*(overlapped by Hc)]; 13CNMR
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J IRAN CHEM SOC
in CDCl3: δ [C1(150.3), C2(99.4), C3(144.7), C4(131.4),
C5(131.4), C6(106.1), C7(153.2), C8(121.4), C9(128.8),
C10(128.4), C11(128.8), C12(121.4)].
(–CH = 1370 cm−1), (–C=CAr = 1575 cm−1), (–N=N–
1
1469 cm−1), (–C–N– = 1324 cm−1)]; HNMR in CDCl3:
δ [Ha(5.87, 1H, s), Hb&He(7.59, 2H, t), Hc*(6.12, 3H,
d, j–j = 8.4), Hd(7.25, 1H, d, j–j = 8.4), X(8.17, 1H, s),
Z(2.44, 3H, s), NH2A(3.99, 2H, br), NH2B*(overlapped
by Hc)], 13CNMR in CDCl3: δ [C1(150.6), C2(99.2),
C3(144.8), C4(131.2), C5(131.6), C6(106.2), C7(152.0),
I2: (E)‑4‑(2‑(4‑methoxyphenyl)diazenyl)
benzene‑1,3‑diamine
Yellow powder, IR in KBr: [(–NH2 = 3473, 3432,
C8(131.0),
C12(121.9), C13(27.8)].
C9(101.20),
C10(141.2),
C11(129.7),
3375,3348, 1637 cm−1), (–CHAr
=
=
3000 cm−1),
(–CH
=
2837, cm−1), (–C=CAr
1571 cm−1),
(–N=N– 1450 cm−1), (–C–N– = 1330 cm−1)]; HNMR
in CDCl3: δ [Ha(5.91, 1H, d, j–j = 2.4 Hz), Hb(7.59, 1H,
d, j–j = 8.7 Hz), Hc(6.11, 1H, q), Hd&Y(6.93, 2H, q),
He&X(7.70, 2H, q), Z(3.84, 3H, s), NH2A(3.90, 2H, br),
NH2B(5.95, 2H, br)], 13CNMR in CDCl3: δ [C1(149.9),
C2(99.8), C3(144.6), C4(131.5), C5(130.1), C6(106.0),
C7(147.5), C8(123.0), C9(114.1), C10(160.2), C11(114.1),
C12(123.0), C13(55.5)].
I6: (E)‑4‑(2‑(2‑methoxy‑4‑nitrophenyl)diazenyl)
benzene‑1,3‑diamine
1
Dark metallic brown powder, IR in KBr: [(–NH2 = 3462,
3370, 3335, 3212, 1621 cm−1), (–CHAr = 3099 cm−1),
(–CH = 2997, 1370 cm−1), (–C=CAr = 1579 cm−1),
(–N=N– 1416 cm−1), (–C–N–
=
1304 cm−1),
1
(–C–NO2 = overlapped)]; HNMR in CDCl3: δ [Ha(5.85,
1H, d, j–j = 1.8 Hz), Hb(7.62, 1H, d, j–j = 8.7 Hz),
Hc(6.16, 1H, q), Hd*(7.86, 2H, d, j–j = 9.9 Hz), He(7.75,
1H, d, j–j = 8.7 Hz), X(4.02, 3H, s), Y(overlapped by
Hd), NH2A(4.14, 2H, br), NH2B(6.85, 2H, br)], 13CNMR
in CDCl3: δ [C1(147.2), C2(98.4), C3(144.8), C4(132.9),
C5(135.1), C6(106.9), C7(146.4), C8(154.6), C9(107.2),
C10(151.3), C11(116.7), C12(115.7), C15(56.3)].
I3: (E)‑4‑(2‑(4‑sulfonamido)diazenyl)benzene‑1,3‑diamine
Dark orange powder, IR in KBr: [(–NH2 = 3481,
3418, 3387,3350, 1622 cm−1), (–CHAr = 3043 cm−1),
(–C=CAr
=
1559 cm−1), (–N=N– 1464 cm−1),
(–C–N– = 1301 cm−1)]; 1HNMR in CDCl3: δ [Ha(5.89, 1H,
d, j–j = 1.8 Hz), Hb(7.59, 1H, d, j–j = 8.7 Hz), Hc*(6.10,
3H, q), Hd&Y(7.37, 2H, d, j–j = 7.8 Hz), He&X(7.68, 2H,
d, j–j = 8.1 Hz), Z(7.27, 2H, d, j–j = 7.2 Hz), NH2A(4.0,
2H, br), NH2B*(overlapped by Hc)], 13CNMR in CDCl3:
δ [C1(150.4), C2(99.3), C3(144.7), C4(131.3), C5(128.3),
C6(106.0), C7(153.2), C8(121.4), C9(128.7), C10(131.4),
C11(128.7), C12(121.4)].
I7: (E)‑4‑(2‑(4‑methoxy‑2‑nitrophenyl)diazenyl)
benzene‑1,3‑diamine
Shiny brown powder, IR in KBr: [(–NH2 = 3481,
3427, 3385, 3226, 1633 cm−1), (–CHAr = 3009 cm−1),
(–CH = 2924, 1370 cm−1), (–C=CAr = 1566 cm−1),
(–N=N– 1421 cm−1), (–C–N–
=
1308 cm−1),
1
I4: (E)‑4‑(2‑(4‑iodo‑2‑methylphenyl)diazenyl)
benzene‑1,3‑diamine
(–C–NO2 = overlapped)]; HNMR in CDCl3: δ [Ha(5.83,
1H, d, j–j = 2.1 Hz), Hb(7.54, 1H, d, j–j = 8.7 Hz), Hc(6.12,
1H, q), Hd(7.10, 1H, q), He(7.85, 1H, d, j–j = 9.3 Hz),
Y(7.33, 1H, d, j–j = 2.4 Hz), Z(3.87, 1H, s), NH2A(4.13,
2H, br), NH2B(6.65, 2H, br)], 13CNMR in CDCl3: δ
[C1(151.1), C2(98.6), C3(144.4), C4(131.9), C5(135.7),
C6(106.4), C7(139.9), C8(146.2), C9(108.1), C10(158.8),
C11(120.0), C12(118.6), C13(55.9)].
Orange to dark red powder, IR in KBr: [(–NH2 = 3430,
3373, 3199, 1620 cm−1), (–CHAr
=
3048 cm−1),
(–CH = 2903, 1364 cm−1), (–C=CAr = 1570 cm−1),
(–N=N– 1465 cm−1), (–C–N– = 1327 cm−1)]; HNMR
1
in CDCl3: δ [Ha(5.89, 1H, d, j–j = 3 Hz), Hb(7.33, 1H, d,
j–j = 8.4 Hz), Hc(6.14, 1H, q), Hd(7.52, 1H, q), He*(7.62,
2H, d, j–j = 8.7 Hz), X(2.50, 3H, s), Y(overlapped by
He), NH2A(3.99, 2H, br), NH2B(6.24, 2H, br)], 13CNMR
in CDCl3: δ [C1(150.9), C2(99.2), C3(144.3), C4(132.0),
C5(116.9), C6(106.3), C7(150.5), C8(137.2), C9(139.5),
C10(93.9), C11(135.6), C12(133.0), C15(17.8)].
General procedure for acrylation of diazo derivatives
of 1,3‑diaminobenzene
The desired diazo derivative of 1,3-diaminobenzene
(0.01 M) was dissolved in dried THF (25 ml) in a round-bot-
tom flask equipped with a separatory funnel. The flask was
put on ice with mixing. An excess amount of acryloyl chlo-
ride (0.04 M) in dry THF (15 ml) was prepared and poured
into the separatory funnel. The content of the funnel was
slowly added to the flask while the mixture was mixed until
the ice melted and the temperature of the resulting water
I5: (E)‑4‑(2‑(3‑iodo‑4‑methylphenyl)diazenyl)
benzene‑1,3‑diamine
Orange to brown powder, IR in KBr: [(–NH2 = 3432,
3356, 3206, 1617 cm−1), (–CHAr
=
3048 cm−1),
1 3

J IRAN CHEM SOC
reached the room temperature. The content of the reaction
flask was then added to a saturated solution of ammonium
bicarbonate (50 ml) and the resulting mixture left under a
fume hood overnight. THF evaporation resulted in precipita-
tion. The product was washed with hot water and reprecipi-
tated from acetone. Chemical structures for the compounds
II1 to II7 were assigned by the following spectroscopic data.
(–C=O = 1673 cm−1), (–C=CAr = 1519 cm−1), (–N=N–
1
1464 cm−1), (–C–N– = 1326 cm−1)]; HNMR in DMSO-
d6: δ [Ha(8.73, 1H, s), Hb(7.78, 1H, d, j–j = 9 Hz), Hc(7.73,
1H, d, j–j = 9 Hz), Hd&Y(7.98, 2H, d, j–j = 8.4 Hz),
He&X(8.12, 2H, d, j–j = 8.4 Hz), Z(7.51, 2H, s),
NHA(10.38, 1H, s), NHB(10.62, 1H, s), Hf(6.46, 1H, q),
Hf′(6.71, 1H, q), Hg&Hg′(5.80, 2H, m), HI&HI′(6.28,
2H, q)], 13CNMR in DMSO-d6: [C1(143.7), C2(112.0),
C3(137.0), C4(138.2), C5(117.9), C6(115.1), C7(153.7),
C8&12(123.3), C9&C11(126.8), C10(145.5), C16(163.5),
C16′(163.6), C17(131.5), C17′(132.1), C18(127.7),
C18′(127.9)]. Mass spectrum (Mw) ion m/z 399. Elemental
analysis (%) calcd for C18N5O4SH17 (399.43): C 54.13, H
4.29, N 17.53, S 8.03; found: C 54.00, H 4.28, N 17.47, S
7.99.
II1: N,N′‑{4‑[(E)‑phenyldiazenyl]benzene‑1,3‑diyl}
bisprop‑2‑enamide
Dark orange powder, melting point (120 °C). IR in KBr:
[(–NH = 3279, 1603 cm−1), (–CHAr = 3055 cm−1),
(–C=O=1666 cm−1), (–C=CAr = 1527 cm−1), (–N=N–
overlapped cm−1), (–C–N– = 1331 cm−1)]; 1HNMR
in DMSO-d6: δ [Ha(8.68, 1H, s), Hb&Hc*(7.75, 2H, d,
j–j = 4.5 Hz), Hd&Y*(7.56, 3H, m), He&X(7.97, 2H, d,
j–j = 7.8 Hz), Z*(7.50, 1H, m, overlapped by Hd), NHA(10.34,
1H, s), NHB(10.52, 1H, s), Hf(6.45, 1H, q), Hf′(6.7, 1H,
q), Hg&Hg′(5.79, 2H, q), HI&HI′(6.27, 2H, q)]; 13CNMR
[C1(142.8), C2(112.1), C3(137.0), C4(137.5), C5(117.8),
C6(115.1), C7(152.2), C8&C12(122.9), C9&C11(129.3),
C10(131.1), C16(163.4), C16′(163.5), C17(131.6), C17′(132.1),
C18(127.5), C18′(127.7)]. Mass spectrum (Mw) ion m/z 320.
Elemental analysis (%) calcd for C18N4O2H16 (320.35): C
67.49, H 5.03, N 17.49; found: C 67.32, H 5.05, N 17.43.
II4: N,N′‑{4‑[(E)‑(4‑iodo‑2‑methylphenyl)diazenyl]
benzene‑1,3‑diyl}bisprop‑2‑enamide
Orange-brown powder, melting point (290 °C). IR in KBr:
[(–NH = 3272, 3199, 1600 cm−1), (–CHAr = 3055 cm−1),
(–CH
=
2946 cm−1), (–C=O
=
16,666 cm−1),
(–C = CAr = 1520 cm−1), (–N=N– 1466 cm−1),
(–C–N– = 1329 cm−1)]; 1HNMR in DMSO-d6: δ
[Ha(8.54, 1H, d, j–j = 1.5 Hz), Hb(7.59, 1H, d, j–j = 9 Hz),
Hc&Hd(7.53, 2H, t), He(7.41, 1H, d, j–j = 8.4 Hz), X(2.6,
3H, s), Y(7.69, 1H, s), NHA(10.15, 1H, s), NHB(10.42,
1H, s), Hf(6.30, 1H, q), Hf′(6.53, 1H, q), Hg(5.64, 1H, q),
Hg′(5.67, 1H, q), HI(6.12, 1H, q), HI′(6.18, 1H, q)]; 13CNMR
in DMSO-d6: [C1(137.6), C2(112.2), C3(137.6), C4(142.9),
C5(117.9), C6(115.2), C7(149.7), C8(139.7), C9(139.8),
C10(98.5), C11(135.4), C12(117.8), C15(16.7), C16(163.4),
C16′(163.5), C17(131.6), C17′(132.0), C18(127.5),
C18′(127.7)]. Mass spectrum (Mw) ion m/z 460. Elemen-
tal analysis (%) calcd for C19N4O2IH17 (460.27): C 49.58,
H 3.72, N 12.17, I 27.57; found: C 49.47, H 3.71, N 12.13.
II2: N,N′‑{4‑[(E)‑(4‑methoxyphenyl)diazenyl]
benzene‑1,3‑diyl}bisprop‑2‑enamide
Orange powder, melting point (159 °C). IR in KBr:
[(–NH = 3432, 3297, 1597 cm−1), (–CHAr = 3093 cm−1),
(–CH = 2940, 2838 cm−1), (–C=O = 1675 cm−1),
(–C=CAr = 1527 cm−1), (–N=N– = 1465 cm−1),
(–C–N– = 1339 cm−1)]; 1HNMR in DMSO-d6: δ [Ha(8.64,
1H, d, j–j = 1.8 Hz), Hb(7.68, 1H, d, j–j = 8.7 Hz), Hc(7.61,
1H, q), Hd&Y(7.07, 2H, d, j–j = 8.7 Hz), He&X(7.93,
2H, d, j–j = 8.7 Hz), Z(3.84, 3H, s), NHA(10.25, 1H, s),
NHB(10.46, 1H, s), Hf(6.40, 1H, q), Hf′(6.64, 1H, q),
Hg&Hg′(5.75, 2H, m), HI&HI′(6.24, 2H, oct)]; 13CNMR in
DMSO-d6: [C1(142.4), C2(112.5), C3(137.3), C4(137.4),
C5(117.8), C6(115.5), C7(146.9), C8&C12(125.3),
C9&C11(114.9), C10(162.2), C13(56.0), C16(163.7),
C16′(163.8), C17(131.0), C17′(132.6), C18(127.7),
C18′(127.9)]. Mass spectrum (Mw) ion m/z 350. Elemen-
tal analysis (%) calcd for C19N4O3H18 (350.38): C 65.13, H
5.18, N 15.99; found: C 64.93, H 5.16, N 15.93.
II5: N,N′‑{4‑[(E)‑(3‑iodo‑4‑methylphenyl)diazenyl]
benzene‑1,3‑diyl}bisprop‑2‑enamide
Orange powder, melting point (117 °C). IR in KBr:
[(–NH = 3270, 3199, 1601 cm−1), (–CHAr = 3048 cm−1),
(–CH = 2910 cm−1), (–C = O = 1664 cm−1),
(–C=CAr = 1523 cm−1), (–N=N– = 1471 cm−1),
(–C–N– = 1328 cm−1)]; 1HNMR in DMSO-d6: δ [Ha(8.66,
1H, d, j–j = 1.8 Hz), Hb&Hc (7.72, 2H, m), He(7.92, 1H, q),
Hd(7.52, 1H, d, j–j = 8.4 Hz), X(8.40, 1H, d, j–j = 1.8 Hz),
Z(3.32, 3H, s), NHA(10.35, 1H, s), NHB(10.52, 1H, s),
Hf(6.45, 1H, q), Hf′(6.70, 1H, q), Hg&Hg′(5.78, 2H, q),
HI(6.27, 1H, q), HI′(6.32, 1H, q)]; 13CNMR in DMSO-d6:
[C1(143.0), C2(112.3), C3(137.0), C4(137.6), C5(117.7),
C6(115.1), C7(151.0), C8(131.6), C9(101.8), C10(143.9),
II3: N,N′‑{4‑[(E)‑(4‑sulfamoylphenyl)diazenyl]
benzene‑1,3‑diyl}bisprop‑2‑enamide
Orange-reddish powder, melting point (225 °C). IR in KBr:
[(–NH = 3305, 3231, 1598 cm−1), (–CHAr = 3077 cm−1),
C11(130.3),
C12(123.9)
C13(27.5),
C16(163.5),
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J IRAN CHEM SOC
C16′(163.5), C17(127.7), C17′(132.1), C18&C18′(127.5)].
Mass spectrum (Mw) ion m/z 460. Elemental analysis (%)
calcd for C19N4O2IH17 (460.27): C 49.58, H 3.72, N 12.17,
I 27.57; found: C 49.43, H 3.71, N 12.12.
pH 7) containing the desired cross-linker II (10 mM, pre-
pared in ethanol) was added and mixed. The final mixture
was cast in a disposable aluminum cap at room temperature.
Cross-linked poly acrylamide polymers were prepared
as previously described [25] except that half of the cross-
linker (bis-acrylamide) concentration was replaced by the
desired cross-linker II. The reaction mixture contained
acrylamide (1.69 M), bis-acryl amide (10 mM), the desired
cross-linker II (10 mM). Polymerization was carried out in
the presence of constant amounts of TEMED (6.6 mM) and
ammonium persulfate (2.2 mM) in 10 ml phosphate buffer
(0.01 M) at pH 6.8 and room temperature.
II6: N,N′‑{4‑[(E)‑(2‑methoxy‑4‑nitrophenyl)diazenyl]
benzene‑1,3‑diyl}bisprop‑2‑enamide
Dark red brownish powder, melting point (225 °C).
IR in KBr: [(–NH
=
3428, 3245, 1608 cm−1),
(–CHAr
=
3017 cm−1), (–CH
=
2940 cm−1),
1517 cm−1),
(–C=O
=
1667 cm−1), (–C=CAr
=
(–N=N– = 1466 cm−1), (–C–N– = 1336 cm−1), (–C–
NO2 = overlapped)]; HNMR in DMSO-d6: δ [Ha(8.78,
1
1H, s), Hb&Hc(7.89, 2H, s), Hd&He(7.77, 2H, d,
j–j = 3.9 Hz), X(4.08, 3H, s), Y(7.99, 1H, s), NHA(10.67,
1H, s), NHB(11.05, 1H, s), Hf(6.44, 1H, q), Hf′(6.54, 1H,
q), Hg&Hg′(5.78, 2H, q), HI&HI′(6.26, 2H, q)]; 13CNMR
[C1(144.4), C2(111.4), C3(136.6), C4(136.9), C5(117.5),
C6(116.1), C7(overlapped by C10), C8(156.3), C9(108.4),
Conclusions
The cross-linkers introduced in this paper are prepared in
high yields using facile procedures. The chemical structure
of these cross-linkers allows to tune solubility and chemical
reactivity of the cross-linker through choosing the desired
starting materials. The cross-linkers are anticipated to par-
ticipate in various types of ionic and radical polymerization
as well as nucleophilic addition reactions. The photochro-
mic properties and trans–cis isomerization of the diazo
motif of these cross-linkers can be used for post-linking
purposes.
C10(149.4),
C11(115.2),
C12(124.2),
C15(56.8),
C16&C16′(163.8), C17(131.5), C17′(132.1), C18&C18′
(128.1)]. Mass spectrum (Mw) ion m/z 395. Elemental
analysis (%) calcd for C19N5O5H17 (395.37): C 57.72, H
4.33, N 17.71; found: C 57.56, H 4.30, N 17.07.
II7: N,N′‑{4‑[(E)‑(4‑methoxy‑2‑nitrophenyl)diazenyl]
benzene‑1,3‑diyl}bisprop‑2‑enamide
Acknowledgments This work was supported by the Natural Sci-
ences and Engineering Research Council (NSERC) in the form of
a Discovery Grant to RLL. Sincere collaboration of Dr Richard W.
Smith manager of Mass Spectrometry Facility of University of Water-
loo is appreciated.
Shiny metallic red brownish powder, melting point
(192 °C). IR in KBr: [(–NH = 3415, 3262, 1606 cm−1),
(–CHAr = 3027 cm−1), (–CH = 2836 cm−1), (–C=C–
C=O = 1697, 1677 cm−1), (–C=CAr = 1526 cm−1),
(–N=N– = 1467 cm−1), (–C–N– = 1340 cm−1), (–C–
NO2 = overlapped)]; 1HNMR in DMSO-d6: δ [Ha(8.73, 1H,
s), Hb*(7.63, 2H, t), Hc(7.56, 1H, d, j–j = 9 Hz), Hd(7.34,
1H, q), He(8.03, 1H, d, j–j = 9.3 Hz), Y*(overlapped by
Hb), Z(3.91, 3H, s), NHA(10.23, 1H, s), NHB(11.62, 1H,
s), Hf(6.43, 1H, q), Hf′(6.64, 1H, q), Hg&Hg′ (5.79, 2H, t),
HI&HI′(6.27, 2H, q)]; 13CNMR in DMSO-d6: [C1(143.8),
C2(112.4), C3(137.4), C4(137.6), C5(118.6), C6(115.6),
C7(138.1), C8(149.8), C9(108.5), C10(161.7), C11(119.3),
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