X-ray structures of precursors of styrylpyridine-derivatives used to obtain 4-((E)-2-(pyridin-2-yl)vinyl)benzamido-TEMPO: Synthesis and characterization

Article abstract of DOI:10.3390/molecules20045793

The synthesis and characterization of the precursor isomers trans-4-(2-(pyridin-2-yl)vinylbenzaldehyde (I), trans-4-(2-(pyridin-4-yl)vinylbenzaldehyde (II), trans-4-(2-(pyridin-2-yl)vinylbenzoic acid (III) and (E)-4-(2-(pydridin-4-yl)vinylbenzoic acid (IV

Full text of DOI:10.3390/molecules20045793

Molecules 2015, 20, 5793-5811; doi:10.3390/molecules20045793
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
X-ray Structures of Precursors of Styrylpyridine-Derivatives
Used to Obtain 4-((E)-2-(Pyridin-2-yl)vinyl)benzamido-
TEMPO: Synthesis and Characterization
Guillermo Soriano-Moro *, María Judith Percino, Ana Laura Sánchez, Víctor Manuel Chapela,
Margarita Cerón and María Eugenia Castro
Laboratorio de Polímeros, Centro de Química, Instituto de Ciencias, Benemérita Universidad
Autónoma de Puebla (BUAP), Complejo de Ciencias, ICUAP, Edif. 103H, 22 Sur y San Claudio, C.P.
7
2570 Puebla, Puebla, Mexico
*
Author to whom correspondence should be addressed; E-Mail: jesus.soriano@correo.buap.mx;
Tel. +52-222-2295500 (ext. 7299); Fax: +52-222-2295551.
Academic Editor: Derek J. McPhee
Received: 25 February 2015 / Accepted: 25 March 2015 / Published: 2 April 2015
Abstract: The synthesis and characterization of the precursor isomers trans-4-(2-(pyridin-
2
-yl)vinylbenzaldehyde (I), trans-4-(2-(pyridin-4-yl)vinylbenzaldehyde (II), trans-4-(2-
(
pyridin-2-yl)vinylbenzoic acid (III) and (E)-4-(2-(pydridin-4-yl)vinylbenzoic acid (IV) are
reported. These compounds were prepared in order to obtain trans-4-((E)-2-(pyridin-2-
yl)vinyl)benzamide-TEMPO (V). Compounds I and II were obtained by using a
Knoevenagel reaction in the absence of a condensing agent and solvent. Oxidation of the
aldehyde group using the Jones reagent afforded the corresponding acid forms III and IV.
A condensation reaction with 4-amino-TEMPO using oxalyl chloride/DMF/CH
2
Cl
2
provided the 4-((E)-2-(pyridin-2-yl)vinyl)benzamide-TEMPO. Single crystals of
compounds I, II and III were obtained and characterized by X-ray diffraction. Compound I
belongs to space group P2
β = 97.203(13)° and the asymmetric unit was Z = 4, whereas compound II was in the space
group P2 , with a = 3.85728(9) Å, b = 10.62375(19) Å, c = 12.8625(2) Å, β = 91.722 (2)°
and the asymmetric unit was Z = 2. Compound III crystallized as single colorless needle
crystals, belonging to the monoclinic system with space group P2 , with Z = 2, with
1
/c, a = 12.6674(19) Å, b = 7.2173(11) Å, c = 11.5877(14) Å,
1
1
a = 3.89359(7) Å, b = 17.7014(3) Å, c = 8.04530(12) Å, β = 94.4030 (16)°. All compounds
1
were completely characterized by IR, H-NMR, EI-MS and UV-Vis.

Molecules 2015, 20
5794
Keywords: X-ray structures; single crystal; styrylpyridine derivatives; 4-((E)-2-(pyridin-2-
yl)vinyl)benzamido-TEMPO; methylpyridines; p-terephthaldehyde
1
. Introduction
Since the first stable radical compound was synthesized in 1961 [1] a series of stable radical
structures, such as nitroxyl, phenoxyl, and hydrazyl have been successfully synthesized. These
compounds are stable radical compounds that have an electron spin in spite of being organic materials [2].
Nitrogen heterocyclic nitroxides and their diamagnetic derivatives (sterically hindered amine and
hydroxylamine) are known as low-molecular-weight multifunctional antioxidants that can participate in
one-electron redox processes. Nitroxides have attenuated oxidative damage in various experimental
models, including cultured cells [3], brain injury [4], lipid peroxidation in liver microsomes [5],
post-ischemic reperfusion injury in isolated organs [6], and exhibit ionizing irradiation damage in rats
and mice [7]. Recent investigations have focused on the synthesis of several molecules modified with
nitroxides [8–11]. For example, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and its derivatives have
been successfully used in modification processes to graft polar species such as –OH or ester groups onto
polymers [12]. Also, molecules bearing nitroxides covalently linked to fluorophore have been used as
fluorescence spin-label [13–16] or nuclear-localizing redox probes [17].
In recent years, dyes have been widely used as photoinitiators of free radical polymerization and as
fluorescence probes for spectroscopy studies in monitoring specific chemical properties of the medium
in which they are incorporated. Therefore, these compounds permit measurements of medium polarity
or degree of cure by measuring the changes in the emission intensity or value of the shift in the emission
maximum. Also, these dyes have found applications in the development of organic and molecular-based
magnetic materials [18]. Currently, there is great interest in applying molecular-based magnetic
materials to the development of spin systems with various properties, particularly with respect to photo-
and heat-responsive spin systems. The development of novel spin systems has led to the discovery of
conjugated organic spin systems which respond to outside stimuli, such as light, heat, pressure and
electrons, etc. Attempts have been made to develop spin systems with multiple properties [19].
Distyrylbenzenes and related fluorophores have found widespread applications in optical display
devices [20–25], as nonlinear optical materials [26–28], two-photon absorbers [29–31], and for sensing
purposes [32,33]. The combination of electron-pair donating and electron-pair accepting (EPA)
substituents on a π-system can lead to an efficient internal charge transfer, resulting in bathochromic
shifts of the electronic spectra, dual fluorescence [34–37], and efficient two-photon absorption. These
properties depend on the length and nature of the π-system and the strength and position of donor and
acceptor groups [38]. In addition, the presence of electron withdrawing groups in the π-system, such as
replacing benzene rings with electron deficient heterocycles like pyridine [39–42], has been a successful
route to increase the electron affinity. The introduction of a nitrogen atom into the ring noticeably affects
the photophysical and photochemical behavior of stilbene. Our work has focused on model compounds
with trans conformation distyrylbenzene (DSB) linked with pyridine moieties (styrylpyridines) which
had been obtained without the need for catalyst and solvent [43–51]. We have also conducted studies to

Molecules 2015, 20
5795
understand their effects on the optics and electronic properties from a theoretical perspective [52]. X-
ray studies of model compounds showed that although the molecules were planar, they did not exhibit a
total delocalization of their electrons throughout the whole molecule, i.e., they did not exhibit complete
aromaticity. X-ray results reported that the conformation of the double bond was trans. Therefore, using
conjugated compounds such as styrylpyridine attached to TEMPO could be widely used to prolong the
lifetime of coatings, bulk polymers, thin films, as well applications to label polymers or as a measure of
molecular mass by IR and UV spectroscopy.
In this paper, we report the preparation of precursors to obtain low molecular weight styrylpyridine
derivatives bearing TEMPO, and their structures obtained by X-ray crystallography analysis, together
with their complete characterization. Our goal is to use these compounds as labels of polymers to
measure the polymer molecular mass. The precursors are interesting because of the presence of groups
such as –COH and –COOH, that allow different absorption properties.
2
. Results and Discussion
Several approaches for the preparation for methylpyridines with aromatic aldehydes have recently
been carried out. Solvent-free methods at temperatures of 120–140 °C were successfully used to
synthesize different styrylpyridines and α,β-acrylonitriles as well as intermediates formed in the
condensation reaction of methylpyridines and aromatic aldehyde compounds [53,54]. The procedure to
obtain the compounds I and II allowed us to control the reaction of just one aldehyde group from
terephthalaldehyde during the condensation reaction with the methyl group that formed the double bond.
The behavior of this reaction is attributed to the control of the reaction temperature rather than to the
molar ratios of reactants, because when the reaction was carried out at higher temperature, compounds
such as 1,4-bis(2,2-diphenylethenyl)benzene or 1,4-bis(4,4-diphenylethenyl)benzene were formed
instead of I and II. Our results also showed that the position of the methyl group on the pyridine ring
affected its reactivity. Compounds III and IV were prepared with Jones oxidation conditions allowing
their preparation in a convenient and safe procedure. The modest yield was attributed to the effect of the
nitrogen atom in the ortho position, affording lower solubility to compound IV. In addition, we obtained
3
III as the pure acid by recrystallization with CH OH:DMF (80:20).
2
.1. Characterization
1
Characterization from IR, H-NMR, and EI spectra of I–V showed characteristic features indicating
that the precursors with the isomers structures of trans-(E)-4-(2-(pyridin-2-yl)vinyl- and trans-(E)-4-(2-
pyridin-4-yl)vinyl- contained the functional group –COH, –COOH. The ORTEP structures of I–III
(
including the atomic numbering scheme are shown in Figure 1. Selected crystal data, structure solution
and refinement for isomers I, II and III are listed in Table 1. Table 2 gives selected bond lengths with
estimated standard deviations also for all three compounds.

Molecules 2015, 20
5796
I
II
III
Figure 1. Molecular structures of I, II and III. The displacement ellipsoids are drawn at the
5
0% probability level and H atoms are shown as small spheres of arbitrary radii.
Table 1. Crystallography Data for I, II and III compounds.
I
II
III
Empirical formula
Crystal system
Color, Habit
Formula weight
Space group
T (K)
C
14
H
11NO
C
14
H
11NO
C
14
H
11NO
2
monoclinic
colorless irregular block
209.24
monoclinic
yellow, block
209.24
monoclinic
Needle, colorless
225.24
P 2
1
/c
P2
1
P 2
1
110(2)
12.6674(19)
7.2173(11)
11.5877(14)
90.00
100(2)
3.85728(9)
10.62375(19)
12.8625(2)
90.00
110(2)
3.89359(7)
17.7014(3)
8.04530(12)
90.00
A (Å)
b (Å)
c (Å)
α (°)
β (°)
97.203(13)
90.00
91.722(2)
90.00
94.4030(16)
90.00
γ (°)
3
V (Å )
1051.0(3)
526.852(18)
552.862(16)

Molecules 2015, 20
5797
Table 1. Cont.
I
4
II
2
III
2
Z
−
3
Dc(g cm )
1.322
1.319
1.353
440
F (000)
592
220
−
1
μ (mm )
λ (Å)
0.663
0.662
0.740
1.5418
1.5418
1.5418
3
Crystal size (mm )
0.25 × 0.10 × 0.03
143.8
0.39 × 0.28 × 0.22
143.8
0.24 × 0.09 × 0.06
143.8
2
θmax (°)
No of reflections
6697
6136
7517
N° of unique reflections, I > 2 σ(I)
1933
2037
2165
R
1
(I > 2 σ(I)), R
(I > 2 σ(I)), wR
goodness-of-fit
Largest diff peak and hole (e Å )
1
(all)
6.08, 8.29
17.16, 18.39
1.169
3.03, 3.05
8.63, 8.65
1.085
2.75, 2.79
7.43, 7.48
1.054
wR
2
2
(all)
−
3
0.22 and −0.27
0.21 and −0.21
0.21 and −0.16
Table 2. Bond lengths (Å) for compounds I, II and III.
I
II
III
C(1)-O(1)
C(1)-C(2)
1.212(4)
1.470(4)
1.391(4)
1.398(4)
1.400(4)
1.406(4)
1.462(4)
1.376(4)
1.331(4)
1.469(4)
1.399(4)
1.382(5)
1.395(5)
1.370(5)
1.351(4)
1.330(4)
1.212(2)
1.477(2)
1.392(2)
1.394(2)
1.402(2)
1.403(2)
1.470(2)
1.386(2)
1.331(2)
1.469(2)
1.393(2)
1.391(2)
1.388(2)
1.219(2)
1.493(2)
1.392(2)
1.398(3)
1.399(3)
1.401(2)
1.466(2)
1.383(3)
1.335(3)
1.470(2)
1.397(3)
1.381(3)
1.386(3)
1.386(3)
1.352(2)
1.335(2)
1.317(2)
C(2)-C(3)
C(2)-C(7)
C(4)-C(5)
C(5)-C(6)
C(5)-C(8)
C(6)-C(7)
C(8)-C(9)
C(9)-C(10)
C(10)-C(11)
C(11)-C(12)
C(13)-C(14)
C(12)-C(13)
C(10)-N(1)
C(14)-N(1)
C(1)-O(2)
C(10)-C(14)
C(12)-N(1)
C(13)-N(1)
1.397(2)
1.338(2)
1.343(2)
The molecular structures for compounds I and II were ordered. The 4-phenylcarbaldehyde moiety is
located trans to the pyridine ring in the molecule in relation to the double bond. The bond lengths for
compound I were C(10)-C(9) [1.469(4) Å], C(9)-C(8) [1.331(4) Å], C(8)-C(5) [1.462(4) Å], (Table 2)
while the corresponding bonds lengths for the compound II were 1.469(2) Å 1.331(2) Å, 1.470(2) Å.
These values indicated that the compounds contained a double bond in conjugation with an aromatic
2
2
2
ring, (Csp =Csp ; trans of 1.32 Å conjugation; Csp -Car (C=C-Car conjugated at 1.47 Å) as well as a

Molecules 2015, 20
5798
delocalization of the π electrons Car Car in the phenyl ring of 1.387 Å, in the two six-membered rings
through the C(8)-C(9) bond. Similar distances were observed for the 2-styrylpyridine derivatives and
were slightly different than the reported values [55]. Bond lengths C(1)-O(1) for I and II were of the
2
equal value, 1.212(4) Å for aldehyde (Csp =O in Car-C=O of 1.221 Å) [55]. Also, the results showed
that structures I and II were almost planar molecules, with the pyridyl ring and 4-phenylcarbaldehyde
group being coplanar with the double bond (Tables 3 and 4). For I, the torsion angles between the atoms
C(8)-C(9)-C(10)-N(1) were 0.4(5)°, C(4)-C(5)-C(8)-C(9) of 1.0(5)° and between O(1)-C(1)-C(2)-C(3)
were −172.1(3)°. Compound II showed torsion angles between C(8)-C(9)-C(10)-C(14) of 1.2(3)°, C(4)-
C(5)-C(8)-C(9) of −4.6(2)°, and between O(1)-C(1)-C(2)-C(3) of 179.57(16)°. The partial π character
of the C(9)-C(8), C(10)-C(9) and C(8)-C(5) bonds (Table 2) helps to explain the aromatic planar nature
of the molecules. The difference between both compounds is in the molecular crystal packing (Figure 2).
For I, the molecular packing does not present regular hydrogen bonding between molecules. However,
the packing motif showed a non-classical herringbone packing with a weak π-π overlap between
neighboring molecules. For compound I, the distances between the co-facial π-π overlap interaction
…
…
C/π…C/π was 3.381 Å, between CH(py) C(Ar) (2.843 Å) and C(Ar) CH(py) (2.865 Å). Within each
stack, however, the molecules are translated (slipped) along the short axis, thus minimizing the
…
π-overlapping between them. A similar interaction arises for compound II between CH(COH) N(Py)
…
of 2.683 Å, and C(CO) CH(Py) 2.615 Å, but II did not present short contact interactions such as
CH/π⋅⋅⋅⋅–CH/π.
Table 3. Bond angles (°) for compounds I, II and III.
I
II
III
O(1)-C(1)-C(2)
C(3)-C(2)-C(1)
124.5(3)
119.0(3)
122.1(3)
122.8(3)
119.4(3)
126.4(3)
124.7(3)
119.9(3)
124.0(3)
122.0(3)
118.1(3)
119.4(3)
118.1(3)
117.5(3)
124.68(16)
118.97(15)
121.11(15)
122.25(14)
118.76(13)
126.24(14)
125.54(14)
119.68(14)
124.18(15)
122.50(17)
121.85(17)
119.15(16)
119.27(16)
122.46(16)
125.65(17)
124.62(17)
123.49(16)
122.86(19)
120.93(17)
115.58(16)
119.76(18)
118.04(18)
119.27(16)
C(7)-C(2)-C(1)
C(4)-C(5)-C(8)
C(6)-C(5)-C(8)
C(9)-C(8)-C(5)
C(8)-C(9)-C(10)
C(11)-C(10)-C(9)
N(1)-C(14)-C(13)
N(1)-C(10)-C(11)
N(1)-C(10)-C(9)
C(13)-C(12)-C(11)
C(12)-C(13)-C(14)
C(14)-N(1)-C(10)
C(11)-C(10)-C(14)
C(14)-C(10)-C(9)
N(1)-C(12)-C(11)
C(13)-C(14)-C(10)
C(12)-N(1)-C(13)
C(1)-O(2)-H(2)
O(2)-C(1)-C(2)
116.77(14)
123.54(15)
124.19(16)
119.44(15)
115.91(14)
114.4(18)
113.39(16)
124.11(17)
O(1)-C(1)-O(2)

Molecules 2015, 20
5799
Table 4. Torsion angles (°) for compounds I, II and III.
I
II
III
O(1)-C(1)-C(2)-C(3)
O(1)-C(1)-C(2)-C(7)
C(4)-C(5)-C(8)-C(9)
C(6)-C(5)-C(8)-C(9)
−172.1(3)
7.5(5)
179.57(16)
−1.9(3)
170.38(19)
−8.9(3)
1.0(5)
−4.6(2)
−165.4(2)
15.8(3)
179.5(3)
178.9(3)
−178.5(3)
0.4(5)
175.87(15)
178.74(15)
−178.21(15)
C(5)-C(8)-C(9)-C(10)
C(8)-C(9)-C(10)-C(11)
C(8)-C(9)-C(10)-N(1)
N(1)-C(10)-C(11)-C(12)
C(9)-C(10)-C(11)-C(12)
C(9)-C(10)-N(1)-C(14)
C(10)-C(11)-C(12)-C(13)
C(11)-C(12)-C(13)-C(14)
C(12)-C(13)-C(14)-N(1)
C(13)-C(14)-N(1)-C(10)
C(11)-C(10)-N(1)-C(14)
C(8)-C(9)-C(10)-C(14)
C(14)-C(10)-C(11)-C(12)
C(11)-C(10)-C(14)-C(13)
C(9)-C(10)-C(14)-C(13)
C(11)-C(12)-N(1)-C(13)
C(14)-C(13)-N(1)-C(12)
O(2)-C(1)-C(2)-C(3)
−179.94(17)
19.0(3)
−161.1(2)
1.9(3)
−0.8(5)
178.1(3)
−178.8(3)
0.7(5)
0.0(3)
178.96(14)
−178.31(19)
178.04(16)
0.0(3)
−0.1(5)
−0.6(5)
0.6(5)
−1.6(3)
1.4(3)
0.1(2)
0.5(3)
0.1(4)
−2.1(3)
1.2(3)
−0.5(2)
0.4(2)
−178.99(15)
0.5(2)
−0.6(2)
−9.3(3)
O(2)-C(1)-C(2)-C(7)
171.38(17)
In contrast, for III, the structure was comprised of three groups, phenyl, pyridyl and a double bond;
the –COOH group was not completely coplanar due most likely to the intermolecular H-bonding
between OH group of one molecule N and nitrogen atoms of a symmetry-related pyridine ring
…
…
…
[
O(2)-H(2) N(1), 1.669 Å, O(2)-H(2), 0.97(3) Å, O(1) N(1) 2.642 Å, O(2)-H(2) N(1) 178.29°],
symmetry code: 2−x, −1/2+y, 1−z. Figure 2 illustrates that in the molecular structure, the styryl-moiety
is moved out the plane that contains the pyridine ring. The torsion angle (Table 4), between C(6)-C(5)-
C(8)-C(9) is 15.8(3)° and between C(4)-C(5)-C(8)-C(9) is −165.4(2)°. With respect to the pyridine ring,
the plane was moved out with torsion angles between C(8)-C(9)-C(10)-N(1) of −161.1(2)°, between
C(11)-C(10)-C(9)-C(8) of 19.0(3)°, and between C(15)-C(16)-C(18)-C(19) of −15.7(2)°.
Figures 1 and 2 show that compound III displayed a rotation in the opposite direction to that of
compounds I and II. This was an interesting outcome because even though the double bond exhibited a
trans configuration, its position showed a different arrangement compared to several previously reported
styrylpyridines [43–51]. According to a recently calculated report [52] of the energy for the
conformation of 2-styrylpyridine, the nitrogen atom of the pyridine could rotate around the bond between
the double bond and the pyridine ring to diminish the steric effects of the proton of the ring with the
protons of double bond H(1) or H(2) (Scheme 1). In the calculated results, the energy corresponding to
−1
−1
the syn form (a) is 5.561 KJ mol and for trans form (b) is 4.536 KJ mol , indicating that rotamer (b)
should be more stable than (a), by almost 3 orders of magnitude order at the theory level. In contrast to

Molecules 2015, 20
5800
the X-ray crystallography of III, in its molecular structure, the proton H(1) is located syn to the nitrogen
atom even in the presence of a free pair of electrons that should contribute to destabilization of the
molecule, according to different reports. This configuration is an indication of the possible presence of
different rotamers. However, the molecular structure of III was obtained with proton H(1) located in a
syn configuration. The molecular packing also showed weaker intermolecular interactions in form of
face to face and side by side (π-π) molecular stacking.
I
II
III
Figure 2. Molecular crystal packing of I, II and III short contacts (dashed red lines).

Molecules 2015, 20
5801
H(1)
H(1)
N
N
H(2)
H(2)
a
b
Scheme 1. Rotamers where the pyridine group could be in syn (a) or anti (b) configuration
for 2-styrylpyridine.
2
.2. Characterization of trans-4-((E)-2-(Pyridin-2-yl)vinyl)benzamido-TEMPO (V)
Characterization by IR of trans-4-((E)-2-(pyridin-2-yl)vinyl)benzamido-TEMPO (V) (Figure 3)
−1
−1
showed characteristic bands at 1661 cm and 1587 cm which were assigned to the ν(C=O) and ν(C-N)
corresponding to the amide group (−C(O)NH) present in the compound. Also, the vibration
•
−1
corresponding to ν(N-O ) from nitroxyl group is observed at 1360 cm , which is in agreement with the
−1
−1
−1
experimental and calculations reports [56–58]. In addition, bands at 3545 cm , 3008 cm , 2925 cm
−1
and 977 cm which correspond to ν(N-H), ν(C-H, aromatic), ν(CH
2
) and δ(=C-H, trans) vibration are
−1
observed. Also, at 1259 cm there is a weak band corresponding to the interaction between N-H bending
and C-N stretching of the amide group. This spectral evidence gave information about the formation of
1
V. Currently, investigations to acquire the H-NMR spectrum of the corresponding hydroxylamine
analogue are underway. The outcome of these studies should give more evidence regarding the
conformation of V.
Figure 3. IR spectrum corresponding to trans-4-((E)-2-(pyridin-2-yl)vinyl)benzamido-TEMPO (V).

Molecules 2015, 20
.3. One Photon Absorption Characterization
5802
2
Absorption spectra of the 2-styrylpyridine and 4-styrylpyridine (Figure 4) were recorded in methanol
in allow comparison with the compounds I, II, III and IV and to evaluate the effect of the −CHO and
COOH substituents (Figures 5 and 6). An insignificant red shift in the absorption wavelength occurred
−
due to presence of −COH for both isomers. The 2-styrylpyridine compound exhibited one band at 309
nm corresponding to the π→π* transition characteristic for a double bond in the trans position; this
result agreed well with previous reports [45,50,52]. 4-Styrylpyridine exhibited an absorption band at 303
nm corresponding to the π→π* transition due to the double bond, which is in agreement with theoretical
reports [59,60]. The spectra for both isomers I and II displayed a significant red shift as compared with
the corresponding 2- and 4-styrylpyridine compounds (Figure 5) due to the presence of the −COH in
both isomers. Compound I exhibited a stronger red shift than did II. However, for compounds III and
IV in the acid form, the −COOH group had little effect on the absorption wavelength position (Figure 6).
Compounds III–IV showed an absorption at 232 nm, which could be assigned to the transition of the
n→π* of the electron-withdrawing −COOH. This red shift was related to intermolecular hydrogen
bonding interactions between two adjacent groups. The spectrum of compound V (Figure 7) was
completely different, but the band at λmax 289 nm could attribute to the chromophore N-O present in the
structure [61].
3
03.8 nm
1
0
0
.0
.5
.0
0
0
0
0
.8
.5
.3
.0
4-styrylpyrydine
3
09 nm
2-styrylpyrydyne
2
72 nm
2
50
300
350
400
250
300
350
400
wavelength (nm)
wavelength (nm)
Figure 4. Absorption spectra of 2-styrylpyridine and 4-styrylpyridine in methanol.
0
0
0
0
.6
.4
.2
.0
I
0.6
0.4
II
3
23 nm
3
17.4 nm
2
32 nm
2
26 nm
0
0
.2
.0
2
00
250
300
350
400
450
500
550
2
00
250
300
350
400
450
500
550
wavelength (nm)
wavelength (nm)
Figure 5. Absorption spectra of (I) and (II).

Molecules 2015, 20
5803
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
IV
III
0.4
0.2
0.0
3
12 nm
3
25 nm
2
33 nm
232 nm
2
00
250
300
350
400
450
500
550
200
250
300
350
400
450
500
550
wavelength (nm)
wavelength (nm)
Figure 6. Absorption spectra of the (III) and (IV) respectively.
2
1
1
0
0
.0
.5
.0
.5
.0
2
89 nm
3
40 nm
4
63 nm
3
00
350
400
450
500
550
wavelength (nm)
Figure 7. Absorption spectrum of (V).
3. Experimental Section
3.1. Materials and Instrumentation
Methylpyridines, p-terephthalaldehyde, NH
2
-TEMPO, oxalyl chloride, DMF, and CH
2
Cl
2
, were
acquired from Aldrich Chemical Co. (Toluca, México) and were purified before use. The Jones reagent
was prepared during the oxidation reaction. Melting points were measured with an SEV (0–300 °C)
apparatus and were reported as uncorrected values. IR spectra of the products were recorded on a Vertex
(
model 70, Bruker Optics, Ettlingen, Germany) 750 FT-IR spectrophotometer by attenuated total
1
13
reflectance (ATR). H-NMR and C-NMR spectra were obtained in CDCl
3
and DMSO-d
6
, on a Varian
4
00 MHz NMR spectrometer (Varian NMR, Walnut Creek, CA, USA). The electron ionization (EI)
spectra were acquired on a JeolMStation 700-D mass spectrometer (Jeol USA, Peabody, MA, USA).
UV-Vis spectra were acquired with a Spectrometer SD2000 (Ocean Optics, Dunedin, FL, USA)
equipped with a pulse Xenon light source PX-2 (Ocean Optics). The solvent used for measurements in
solution was methanol of spectroscopic grade and was preliminarily checked for the absence of
absorbing impurities within the scanned spectral ranges.

Molecules 2015, 20
.2. Synthesis and Characterization of Precursors I–IV
The precursors trans-4[-(2-(pydridin-2-yl)vinyl)]benzaldehyde (I) and trans-4[-(2-(pyridin-4-
5804
3
yl)vinyl]-benzaldehyde (II) were prepared as follows. The basic structures of (I) and (II) were modified
by oxidation of the –COH group to a carboxylic acid (III and IV) (Scheme 2). Then, trans-(E)-4-(2-
(
(
pydridin-2-yl)vinylbenzoic acid (III) was condensed with amino-TEMPO to obtain the trans-4-((E)-2-
pyridin-2-yl)vinyl)benzamido-TEMPO (V) (Scheme 3).
COH
X
CH3
+
COH
X
Y
Y
I and II
HOC
COOH
I X=N; Y=CH
II X=CH; Y=N
X
Jones reagent
I and II
Y
III and IV
Scheme 2. Syntheses of trans-4-(2-(pyridin-2-yl)vinylbenzaldehyde (I), trans-4-(2-
pyridin-4-yl)vinylbenzaldehyde (II), trans-4-(2-(pydridin-2-yl)vinylbenzoic acid (III), (E)-
(
4
-(2-(pydridin-4-yl)vinylbenzoic acid (IV).
O
O
N
Oxalyl chloride
DMF, CH Cl2
2
0°C to rt
+
N
NH
2
O
O
N
C
N
H
N
Scheme 3. Synthesis of trans-4-((E)-2-(pyridin-2-yl)vinyl)benzamido-TEMPO (V).
Compounds I and II were obtained by slight modifications of the reported methodology [43].
Terephthaldehyde (2.35 g; 25.3 mmol) with 2-methylpyridine for I and 4-methylpyridine for II (2.5 mL;
5.3 mmol) were refluxed in the absence of a condensing agent at 120 °C for 50–60 h. In both cases the
2
reaction mixtures were oily and had brown or red-brown color. The mixture was treated with a solution
of 2 N NaOH (643 mL) to precipitate a solid. The products were purified by recrystallization with
1
cyclohexane and characterized by IR, H-NMR, EI and single crystal X-ray crystallography. The yields

Molecules 2015, 20
5805
were 18.81% (I) and 20.12% (II). The melting point was 80–81 °C and 109–111 °C for (I) and
(
(
II), respectively.
~
−
1
ν
I) IR(KBr), /cm : 1695 (sharp, νC=O), 1599 (w, νC=N Py), 1600 (broad, νC=C Ar), 974 (s,
1
δC-H CHR
1
=CHR
2
in trans). H-NMR (500 MHz, CD
3
Cl) δ (ppm): 10.03 (s, 1H), 8.67–8.66 (dd, 1H,
J
H-H = 5.5; 4.5; 0.5), 7.93–7.91 (dd, 2H, JH-H = 8; 6.5; 1.5), 7.76–7.72 (m, 4H, JH-H = 8.5; 6; 5.5; 5.0),
7
.46–7.44 (d, 1H, JH-H = 8), 7.35–7.32 (d, 1H, JH-H = 16), 7.25–7.21 (dd, 1H, JH-H = 16). EI (m/z, %):
+
molecular ion 209 [M , 25], 208 (92), 180 (15), 178 (6), 133 (100), 105 (52), 77 (50).
~
−1
ν
(
II) IR (KBr): /cm :1688 (sharp, νC=O), 1567 (w, νC=N, Py), 1598 (broad, νC=C, Ar), 979 (s,
1
δC-H CHR
1
=CHR
2
in trans). H-NMR (500 MHz), (CD
3
Cl): δ (ppm): 10.03 (s, 1H), 8.64–8.63 (d, 2H,
J
H-H = 6), 7.93–7.91 (dd, 2H, JH-H = 8.5), 7.37–7.34 (d, 1H, JH-H = 16), 7.19–7.16 (d, 1H, JH-H = 16),
+
7
.71–7.7 (d, 2H, JH-H = 8.5), 7.42–7.40 (dd, 2H, JH-H = 8; 5). EI (m/z, %): 209 [M , 100], 208 (77), 180
(96), 178 (10), 104 (7), 76 (15).
3
.2.1. Synthesis and Characterization of trans-(E)-4-(2-(Pydridin-2-yl)vinylbenzoic acid and trans-(E)-
-(4-(pydridin-4-yl)vinylbenzoic acid (III and IV)
4
For both compounds, the oxidation reaction used the Jones reagent, which was prepared with 0.66 g
of CrO
3
(6.6 mmol) dissolved in H
2
O. To the solution, an adequate quantity of H
2
SO was added until a
4
red precipitate formed. An acetone solution with 1.38 g (6.6 mmol) I or II was prepared at room
temperature and it was added to the solution of Jones reagent dissolved in small quantity of water. The
reaction mixture was refluxed for about 24 h. After the mixture was treated with NaHCO
pH = 7, a yellow precipitate (III or IV) formed. The solid III was purified by recrystallization with a
solvents mixture of H O/acetone (80:20), whereas IV was recrystallized with DMF:CH OH (20:80).
3
/H
2
O to reach
2
3
Finally, the compounds were treated with heated hexane to eliminate any remains of I and II. The
products III and IV were characterized by IR, H-, 13C-NMR and EI. Compound III was further
characterized by single crystal X-ray crystallography. The yields were 39.40% for III and 11.27% for
IV; the melting point of III was of 217–220 °C while IV did not present a melting point >300 °C.
1
~
−1
ν
(
III) IR (KBr):
/
cm : 1692 (s and broad, νC=O), 1601 (w, νC=C, Ar), 1569 (νC=N, Py), 1281 (s,
1
wide, νC-O), 964 (s, δC-H CHR
1
=CHR
2
in trans). H-NMR (500 MHz), (DMSO-d
6
): δ (ppm): 12.97
(wide signal, 1H) 8.61–8.60 (dd, 1H, JH-H = 5.5, 4.5, 3.5), 7.97–7.95(dd, 2H, JH-H = 8), 7.84–7.58 (m,
4
H, JH-H = 16, 8, 6, 5.5), 7.60–7.58 (dd, 1H, JH-H =8), 7.48–7.45 (dd, 1H, JH-H = 16), 7.31–7.28 (m, 1H,
1
3
J
H-H = 5.5). C (500MHz), (DMSO-d
6
) δ (ppm): 167.73 (COOH), 155.16 (Ar), 150.29 (py), 141.35 (py),
1
1
37.61 (Ar), 131.55 (Ar), 131.15 (CH=CH), 130.8 (Ar), 130.49 (Ar), 127.76 (CH=CH), 123.62 (py),
+
23.52 (py). EI (m/z, %): 225 [M , 22], 224 (100), 178 (7), 87 (15).
~
−1
…
ν
(
IV) IR (KBr): /cm : 2435 (s, wide, COH OC), 1699 (s and broad, νC=O), 1604 (w, νC=C, Ar,),
1
1
567 (w, νC=N, Py), 1286(s, wide, νC-O), 959 (s, δC-H CHR
1
=CHR
2
in trans). H-NMR (500 MHz),
(
CD
3
)
2
SO), δ (ppm): 8.59–8.58 (dd, 2H, JH-H = 5.5), 7.98–7.96 (d, 2H, JH-H = 8.5), 7.79–7.77 (dd, 2H,
1
3
J
H-H = 8), 7.65–7.60 (m, 3H, JH-H = 17.5, 6), 7.43–7.39 (dd, 1H, JH-H = 16.5). C (DMSO-d
6
), δ (ppm):
1
67.49 (COOH), 150.6 (py), 144.31 (py), 140.85 (Ar), 132.42 (Ar), 131.0 (CH=CH), 130.29 (Ar),

Molecules 2015, 20
5806
+
1
1
28.90 (Ar), 127.57 (CH=CH), 121.57 (py). EI (m/z, (%): 225 [M , 18], 206 (90), 180 (60), 178 (20),
52 (41), 102 (7), 76 (10).
3
.2.2. Condensation Reaction to Obtain the trans-4-((E)-2-(Pyridin-2-yl)vinyl)benzamido-TEMPO (V)
To synthesize V, carboxylic acid III was reacted with 4-NH
and CH Cl [62] (Scheme 3). To a three-necked flask was added 0.22 g (1 mmol) of III dissolved in
mL of DMF at 4 °C. The mixture was reacted for 30 min with stirring and then oxalyl chloride
0.22 mL, 2 mmol) was added, and the temperature was increased to room temperature. 4-Amino
TEMPO (NH -TEMPO) (0.170 g, 1 mmol) dissolved in DMF was then added. The mixture was stirred
for 48 h at 90 °C. During this time the mixture changed from light yellow to orange and finally to orange-
pink. After the reaction time, the mixture was treated with acetone/H O (2:1) to precipitate an orange
2
-TEMPO using oxalyl chloride, DMF
2
2
5
(
2
2
solid, which was isolated by vacuum-filtration. The solid was purified by recrystallization with a mixture
of EtOH/ethyl acetate (1:1); yield was 35% with m.p. of 140–142 °C.
3
.3. Crystallization of Compounds I, II and III
Crystals of I were obtained with 55 mg of I dissolved in 3 mL of a mixture of solvents THF/hexane
(
(
80:20) and kept at room temperature. After 24 h, colorless crystals were formed.
Crystals of II were obtained with 55 mg of compound II dissolved in 5 mL of EtOH/cyclohexane
80:20). The solution was kept at room temperature and allowed to slowly evaporate and after 2 days,
crystals were formed.
Crystals of III were obtained with 4 mg of compound III dissolved in 5 mL of MeOH/DMF (80:20)
at high temperature. The solution was kept at 4 °C and allowed to slowly evaporate. After 8 days, crystals
were obtained.
3
.4. X-ray Crystallography
All reflection intensities of I and III were measured at 110(2) K and for II at 100(2) K using a
SuperNova diffractometer (equipped with Atlas detector) with Cu Kα radiation (λ = 1.54178 Å). The
program CrysAlisPro (Version 1.171.36.32 2013, Agilent Technologies, Santa Clara, CA, USA) was
used to refine the cell dimensions and for data reduction. The structures were solved with the program
2
SHELXS-2013 and were refined on F with SHELXL-2013 [63]. Empirical absorption correction using
spherical harmonics implemented in the SCALE3 ABSPACK scaling algorithm was applied using
CrysAlisPro (Version 1.171.36.32). The temperature of the data collection was controlled using the
system Cryojet (manufactured by Oxford Instruments, Abingdon, Oxford, UK). The H atoms were
placed at calculated positions using the instructions AFIX 43 with isotropic displacement parameters
having values 1.2 times Ueq of the attached C atoms. The H atom attached to O was found from the
2
difference Fourier map, and its coordinates were refined freely.
4
. Conclusions
We have synthesized precursors of styrylpyridine in good yield and they were well characterized.
The crystallography data gave evidence that the molecular structure of the double bond was in the trans

Molecules 2015, 20
5807
conformation, as well as that one of the phenyl rings in III was twisted appreciably and featured an
intermolecular hydrogen bond with one of the neighboring complexes to form a one-dimensional or
two-dimensional network. These intermolecular interactions would induce cooperative effects, leading
to good conjugation properties. Finally, this methodology has developed a general method to
functionalize the synthesized precursors III–VI with NH -TEMPO.
2
Supplementary Materials
Crystallographic data (excluding structure factors) reported in this paper have been deposited with
the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC 1054889,
1054890, 1054891. Copies of available material can be obtained, free of charge, on application to
the CCDC, 12 Union Road. Cambridge CB2 IEZ, UK, fax: +44-(0)1223-336033 or e-mail:
deposit@ccdc.cam.ac.uk.
Acknowledgments
The authors wish to express their gratitude to VIEP-BUAP (projects PEZM-NAT15-G, CHCV-NAT15-G
and SOMJ-NAT15-I), PROMEP-SEP (Thematic network of collaboration and CONACyT (projects
1
57552 and 183833), as well as to Maxime A. Siegler (Johns Hopkins University) for his valuable help
with the X-ray crystallography and Vladimir Carranza for assistance with EI mass spectrometry.
Author Contributions
Conceived and designed the experiments: M.C., G.S-M. and M.J.P.; Performed the experiments:
M.C. and A.L.S.; Analyzed the data: M.J.P., G.S-M.; Contributed reagents/materials/analysis tools:
M.J.P., G.S-M., V.M.CH. and M.E.C.; Wrote the paper G.S-M. and M.J.P. All authors read and
approved the final manuscript.
Conflicts of Interest
The authors declare no conflict of interest.
References
1.
2.
3.
Hoffman, A.K.; Henderson, A.T. A new stable free radical: Di-t-butylnitroxide. J. Am. Chem. Soc.
961, 83, 4671–4672.
1
Korshak, Y.V.; Medvedeva, T.V.; Ovchinnikov, A.A.; Spector, V.N. Organic polymer ferromagnet.
Nature 1987, 326, 370–372.
Mitchell, J.B.; Samuni, A.; Krishna, M.C.; DeGraff, W.G.; Ahn, M.S.; Samuni, U.; Russo, A.
Biologically active metal-independent superoxide dismutase mimics. Biochemistry 1990, 29,
2
802–2807.
4
.
Cuzzocrea, S.; McDonald, M.C.; Mazzon, E.; Siriwardena, D.; Costantino, G.; Fulia, F.;
Cucinotta, G.; Gitto, E.; Cordaro, S.; Barberi, I.; et al. Effects of tempol, a membrane-permeable
radical scavenger, in a gerbil model of brain injury. Brain Res. 2000, 875, 96–106.

Molecules 2015, 20
5808
5
6
.
.
Miura, Y.; Utsumi, H.; Hamada, A. Antioxidant activity of nitroxide radicals in lipid peroxidation
of rat liver microsomes. Arch. Biochem. Biophys. 1993, 300, 148–156.
Li, H.; Xu, K.Y.; Zhou, L.; Kálai, T.; Zweier, J.L.; Hideg, K.; Kuppusamy, P. A pyrroline derivative
of mexiletine offers marked protection against ischemia/reperfusion-induced myocardial contractile
dysfunction. J. Pharmacol. Exp. Ther. 2000, 295, 563–571.
7
8
9
1
1
.
.
.
Mitchell, J.B.; DeGraff, W.; Kaufman, D.; Krishna, M.C.; Samuni, A.; Finkelstein, E.; Ahn, M.S.;
Hahn, S.M.; Gamson, J.; Russo, A. Inhibition of oxygen-dependent radiation-induced damage by
the nitroxide superoxide dismutase mimic, Tempol. Arch. Biochem. Biophys. 1991, 289, 62–70.
Fritscher, J.; Beyer, M.; Schiemann, O. Synthesis, crystal structure and magnetic properties of a
novel nitroxide biradical. Theoretical investigation of the exchange mechanism. Chem. Phys. Lett.
2
002, 364, 393–401.
Fujiwara, H.; Fujiwara, E.; Kobayashi, H. Synthesis, structures and properties of new organic
donors connecting to a TEMPO radical through a pyrrolidine ring. Synth. Met. 2003, 133–134,
3
59–360.
0. Tudose, M.; Ionita, P.; Dunitrascu, F.; Draghici, C.; Caproiu, M.T.; Covaci, I.C.; Constantinescu, T.;
Banciu, M.; Balaban, A.T. Synthesis and properties of dinitrobenzamido-TEMPO derivatives.
ARKIVOC 2005, 225–237.
1. Kasumov, V.T.; Ucar, I.; Bulut, A.; Yerli, Y. Synthesis, crystal structure and intermolecular
magnetic interactions of a new N-TEMPO-3,5-di-tert-butylsalicylaldimine radical. Solid State Sci.
2
011, 13, 1852–1857.
1
2. Cicogna, F.; Coiai, S.; Pinzino, C.; Ciardelli, F.; Passaglia, E. Fluorescence polyolefins by free
radical post-reactor modification with functional nitroxides. React. Funct. Polym. 2012, 72, 695–702.
3. Lozinsky, E.; Martin, V.V.; Berezina, T.A.; Shames, A.I.; Weis, A.L.; Likhtenshtein, G.I.
Dual fluorophore–nitroxide probes for analysis of vitamin C in biological liquids. J. Biochem.
Biophys. Methods 1999, 38, 29–42.
1
1
1
1
4. Chen, J.-L.; Zhuo S.-J.; Wu, Y.-Q.; Fang, F.; Li, L.; Zhu, C.-Q. High selective determination iron(II)
by its enhancement effect on the fluorescence of pyrene-tetramethylpiperidinyl (TEMPO) as a spin
fluorescence probe. Spectrochim. Acta Part A 2006, 63, 438–443.
5. Sato, S.; Suzuki, M.; Soma, T.; Tsunoda, M. Synthesis and properties of umbelliferone-nitroxide
radical hybrid compounds as fluorescence and spin-label probes. Spectrochim. Acta Part A 2008,
7
0, 799–804.
6. Sato, S.; Tsunoda, M.; Suzuki, M.; Kutsuna, M.; Takido-uchi, K.; Shindo, M.; Mizuguchi, H.;
Obara, H.; Ohya, H. Synthesis and spectral properties of polymethine-cyanine dye-nitroxide radical
hybrid compounds for use as fluorescence probes to monitor reducing species and radicals.
Spectrochim. Acta Part A 2009, 71, 2030–2039.
1
1
1
7. Ikeda, M.; Nagawa, H.; Suzuki, T.; Miyata, N. Novel bisbenzimide-nitroxides for nuclear redox
imaging in living cells. Bioorg. Med. Chem. Lett. 2012, 22, 1949–1952.
8. π–Electron Magnetism: From Molecule to Magnetic Materials. Structure and Bonding; Rawson, J.M.,
Palacio, F., Veciana, J., Eds.; Springer Verlag: Berlin, Germany, 2001; Volume 100, pp. 93–128.
9. Hata, M.; Akutsu, H.; Yamada, J.-I.; Nakatsuji, S. N-Salicylideneamine derivatives with TEMPO
substituents. Molecules 2004, 9, 746–756.

Molecules 2015, 20
5809
2
2
2
2
0. Burroughes, J.H.; Bradley, D.D.C.; Brown, A.R.; Marks, R.N.; Mackay, K.; Friend, R.H.; Burn, P.L.;
Holmes, A.B. Light-emitting diodes based on conjugated polymers. Nature 1990, 347, 539–541.
1. Goodson, T.; Li, W.; Gharavi, A.; Yu, L. Oligophenylenevinylenes for light-emitting diodes.
Adv. Mater. 1997, 9, 639–643.
2. Müllen, K.; Wegner, G. Electronic Materials: The Oligomer Approach; Wiley-VCH: New York,
NY, USA, 1998.
3. Gierschner, J.; Ehni, M.; Egelhaaf, H.-J.; Millian, B.; Beljonne, D.; Benmansour, H.; Bazan, G.C.
Solid-state optical properties of linear polyconjugated molecules: π-Stack contra herringbone.
J. Chem. Phys. 2005, 123, 144914.
2
2
2
4. Kraft, A.; Grimsdale, A.C.; Holmes, A.B. Elektrolumineszierende konjugierte polymere-polymere
erstrahlen in neuem licht. Angew. Chem. 1998, 110, 416–443.
5. Kraft, A.; Grimsdale, A.C.; Holmes, A.B. Electroluminescent conjugated polymers—Seeing
polymers in a new light. Angew. Chem. Int. Ed. Engl. 1998, 37, 402–428.
6. Mathy, A.; Ueberhofen, K.; Schenk, R.; Gregorius, H.; Garay, R.; Müllen, K.; Bubeck, C.
Third-harmonic-generation spectroscopy of poly(p-phenylenevinylene): A comparison with
oligomers and scaling laws for conjugated polymers. Phys. Rev. B 1996, 53, 4367–4375.
7. Gurge, R.M.; Hickl, M.; Krause, G.; Lahti, P.M.; Hu, B.; Yang, Z.; Karasz, F.E. Synthesis of a
green-emitting alternating block copolymer. Polym. Adv. Technol. 1998, 9, 504–510.
8. Skotheim, T.A.; Reynolds, J.R. Handbook of Conducting Polymers, Part III: Properties and
Characterization of Conducting Polymers; CRC Press: Boca Raton, FL, USA, 2007.
9. Strehmel, B.; Sarker, A.M.; Detert, H. The Influence of σ and π Acceptors on Two-Photon
Absorption and Solvatochromism of Dipolar and Quadrupolar Unsaturated Organic Compounds.
ChemPhysChem 2003, 4, 249–259.
2
2
2
3
0. Collette, J.C.; Harper, A.W. Properties and chemical environment effects of alkylamino styryl
pyrazine two-photon fluorophores. Proc. SPIE 2003, 5212, 184–192.
31. Woo, H.Y.; Liu, B.; Kohler, B.; Korystov, D.; Mikhailovsky, A.; Bazan, G.C. Solvent Effects on
the Two-Photon Absorption of Distyrylbenzene Chromophores. J. Am. Chem. Soc. 2005, 127,
1
4721–14729.
3
3
3
3
2. Czerney, P.; Grummt, U.-W. New near-infrared-absorbing acidochromic dyes and their application
in sensor techniques. Sensor. Actuat. B.-Chem. 1997, 39, 395–400.
3. Schmitt, V.; Glang, S.; Preis, J.; Detert, H. Proton-Induced Multiple Changes of the Absorption and
Fluorescence Spectra of Amino-Aza-Oligo(phenylenevinylene)s. Sens. Lett. 2008, 6, 524–530.
4. Lippert, E.; Lüder, W.; Moll, F.; Nägele, W.; Boos, H. Prigge, H.; Seybold-Blankenstein, I.
Umwandlung von Elektronenanregungsenergie. Angew. Chem. 1961, 73, 695–706.
5. Rettig, W. Ladungstrennung in angeregten Zuständen entkoppelter Systeme—TICT-Verbindungen
und Implikationen für die Entwicklung neuer Laserfarbstoffe sowie für den Primärprozeß von
Sehvorgang und Photosynthese. Angew. Chem. 1986, 98, 969–986.
3
6. Rettig, W. Charge separation in excited states of decoupled systems—Tict compounds and
implications regarding the development of new laser dyes and the primary process of vision and
photosynthesis. Angew. Chem. Int. Ed. Engl. 1986, 25, 971–988.

Molecules 2015, 20
5810
3
7. Dobkowski, J.; Michl, J.; Waluk, J. Electronic spectroscopy and photophysics of 2-(N-methyl-N-
isopropylamino)-5-cyanopyridine and related compounds. Phys. Chem. Chem. Phys. 2003, 5,
027–1031.
1
3
3
4
4
8. Nemkovich, N.A.; Detert, H.; Schmitt, V. Localized excitation effect on dipole moments of
oligophenylenevinylenes in their excited Franck–Condon state. Chem. Phys. 2010, 378, 37–41.
9. Detert, H.; Sadovski, O.; Sugiono, E. Acidochromism of C
2
-symmetrical aza-analogues of
1
,4-distyrylbenzene. J. Phys. Org. Chem. 2004, 17, 1046–1050.
0. Detert, H.; Sugiono, E. Bis(pyridylvinyl)diaminobenzenes: Synthesis, acidochromism and
solvatochromism of the fluorescence. J. Lumin. 2005, 112, 372–376.
1. Hancock, J.M.; Jenekhe, S.A. Unusual protonation-induced continuous tunability of optical
properties and electroluminescence of a π-conjugated heterocyclic oligomer. Macromolecules
2
008, 41, 6864–6867.
4
4
4
2. Yamaguchi, Y.; Kobayashi, S.; Wakamiya, T.; Matsubara, Y.; Yoshida, Z.-I. Banana-shaped
oligo(aryleneethynylene)s: Synthesis and light-emitting characteristics. Angew. Chem. Int. Ed.
2
005, 44, 7040–7044.
3. Percino, M.J.; Chapela, V.M.; Sánchez, A.; Maldonado-Rivera, J.L. Condensation reactions of
methylpyridines and aromatic aldehydesunder catalyst and solvent free conditions. Chem. Indian J.
2
006, 3, 262–267.
4. Percino, M.J.; Chapela, V.M.; Salmón, M.; Toscano, R.A. Unexpected crystallization and X-ray
crystal structure of racemic 1-phenyl-2-(4-pyridyl)ethanol intermediate. J. Chem. Crystallogr. 2000,
30, 385–388.
4
4
4
5. Percino, M.J.; Chapela, V.M.; Salmón, M.; Espinoza-Pérez, G.; Herrera, A.M.; Flores, A. X-ray
crystal structure of 2-styrylpyridine. J. Chem. Crystallogr. 1997, 27, 549–552.
6. Chapela, V.M.; Percino, M.J.; Rodríguez-Barbarín, C. Crystal structure of 2,6-distyrylpyridine.
J. Chem. Crystallogr. 2003, 33, 77–83.
7. Percino, M.J.; Chapela, V.M.; Montiel, L.-F.; Rodríguez-Barabrin, C. X-Ray crystal structures of a
1
-(p-fluorophenyl)-2-(α-pyridyl)ethanol intermediate and the 1-(p-fluorophenyl)-2-(α-
pyridyl)ethane dehydration compound obtained from the condensation reaction of 2-methylpyridine
and p-fluorobenzaldehyde. Open Crystallogr. J. 2008, 1, 37–41.
4
8. Percino, M.J.; Chapela, V.M.; Montiel, L.-F.; Pérez-Gutierrez, E.; Maldonado, J.L. Spectroscopic
characterization of halogen- and cyano-substituted pyridinevinylenes synthesized without catalyst
or solvent. Chem. Pap. 2010, 64, 360–367.
4
9. Percino, M.J.; Chapela, V.M. Unexpected intermediate 1-phenyl-2-(4-pyridyl)ethanol isolated from
benzaldehyde and 4-picoline condensation reaction. Res. Chem. Intermed. 2000, 26, 303–307.
0. Pérez-Gutierrez, E.; Percino, M.J.; Chapela, V.M.; Maldonado, J.L. Optical and morphological
characterization by atomic force microscopy of luminescent 2-styrylpyridine derivative compounds
with poly(N-vinylcarbazole) films. Thin Solid Films 2011, 519, 6015–6020.
5
5
1. Percino, M.J.; Chapela, V.M.; Urzua, O.; Montiel, L.-F.; Rodríguez-Barabrín, C.
1
-(p-Fluorophenyl)-2-(2'-pyridyl)ethanol and 1-(p-Fluorophenyl)-2-(2'-pyridyl)ethene obtained
from the condensation reaction of 2-picoline and p-fluorophenylaldehyde under catalyst- and
solvent-free conditions. Res. Chem. Intermed. 2007, 33, 623–629.

Molecules 2015, 20
5811
5
5
5
5
2. Castro, M.E.; Percino, M.J.; Chapela, V.M.; Cerón, M.; Soriano, G.; Melendez, F. Theoretical
Study of the UV/Vis Absorption Spectra of Styrylpyridine Compounds Using TD-DFT
Calculations. J. Mol. Model. 2013, 19, 2015–2026.
3. Percino, M.J.; Chapela, V.M.; Perez-Gutierrez, E.; Ceron, M.; Soriano, G. Synthesis, optical and
spectroscopic characterization of substituted 3-phenyl-2-arylacrylonitriles. Chem. Pap. 2011, 65,
4
2–51.
4. Percino, M.J.; Chapela, V.M.; Cerón, M.; Soriano-Moro, G.; Castro, M.E. Synthesis and molecular
structure of the 1-phenyl-2-(2-pyridyl)ethanol intermediate obtained from the condensation reaction
of 2-picoline and benzaldehyde. Res. Chem. Intermed. 2013, doi:10.1007/s11164–013–141471-y.
5. Allen, F.H.; Kennard, O.; Watson, D.G.; Brammer, L.; Orpen, A.G.; Taylor, R. Tables of bond
lengths determined by X-ray and neutron diffraction. Part 1. Bond lengths in organic compounds.
J. Chem. Soc. Perkin Trans. 1987, 12, S1–S19.
5
5
5
5
6
6. Rintoul, L.; Micallef, A.S.; Bottle, S.E. The vibrational group frequency of the N-O• stretching
band of nitroxide stable free radicals. Spectrochim. Acta Part A 2008, 70, 713–717.
7. Nakanishi, K.; Solomon P.H. Infrared Absorption Spectroscopy, 2nd ed.; Holden-Day Inc.:
Oakland, CA, USA, 1977.
8. Williams, D.H.; Fleming, I. Spectroscopic Methods in Organic Chemistry, 3rd ed.; McGraw-Hill:
Maidenhead, UK, 1980.
9. Daku, L.M.L.; Linares, J.; Boillot, M.-L. Ab Initio Static and Molecular Dynamics Study of
4
-Styrylpyridine. ChemPhysChem 2007, 8, 1402–1416.
0. Daku, L.M. L.; Linares, J.; Boillot, M.-L. Ab initio static and molecular dynamics study of the
absorption spectra of the 4-styrylpyridine photoswitch in its cis and trans forms. Phys. Chem.
Chem. Phys. 2010, 12, 6107–6123.
6
6
6
1. Zhadanov, R.I.; Golubev, V.A.; Rozantsev, E.G. Synthesis and structure of 1-oxopiperidinium
tribromides. Izv. Akad. Nauk SSSR. Ser. Khim. 1970, 1, 186–187.
2. Dane, E.L.; Maly, T.; Debelouchina, G.T.; Griffin, R.G.; Swager, T.M. Synthesis of a
BDPA-TEMPO biradical. Org. Lett. 2009, 11, 1871–1874.
3. Sheldrick, G.M. SHELXTL/PC User Manual; Siemens Analytical X-ray Instruments Inc.: Madison,
WI, USA, 1990.
Sample Availability: Samples of the compounds are available from the authors.
©
2015 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
http://creativecommons.org/licenses/by/4.0/).
(