Synthesis, spectroscopic and structural elucidation of 1-butyl-4-[2-(3,5- dimethoxy-4-hydroxyphenyl)ethenyl)]pyridinium chloride tetrahydrate

Article abstract of DOI:10.1016/j.saa.2009.09.020

The novel chloride salt of 1-butyl-4-[2-(4-hydroxyphenyl)ethenyl)]pyridine (1), has been synthesized as the tetrahydrate and its structure and properties elucidated in detail spectroscopically, thermally and structurally, using single crystal X-ray diffra

Full text of DOI:10.1016/j.saa.2009.09.020

Spectrochimica Acta Part A 74 (2009) 1120–1126
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectroscopic and structural elucidation of
1-butyl-4-[2-(3,5-dimethoxy-4-hydroxyphenyl)ethenyl)]pyridinium
chloride tetrahydrate
B.B. Kolevaa,b, T. Koleva,∗, M. Lamshöfta, H. Mayer-Figgeb, W.S. Sheldrickb, M. Spitellera
a Institut für Umweltforschung, Universität Dortmund, Otto-Hahn-Strasse 6, 44221 Dortmund, Germany
b Lehrstuhl für Analytische Chemie, Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The novel chloride salt of 1-butyl-4-[2-(4-hydroxyphenyl)ethenyl)]pyridine (1), has been synthesized
as the tetrahydrate and its structure and properties elucidated in detail spectroscopically, thermally
and structurally, using single crystal X-ray diffraction, linear-polarized solid-state IR-spectroscopy, UV-
spectroscopy and mass spectrometry. Quantum chemical calculations were performed with a view
to supporting and explaining the experimental structural and spectroscopic data. The compound (1)
Received 5 December 2008
Received in revised form 21 August 2009
Accepted 12 September 2009
Keywords:
1-Butyl-4-[2-(4-
¯
crystallizes in triclinic P1 space group and its unit cell contains two independent 1-butyl-4-[2-(3,5-
dimethoxy4-hydroxyphenyl)ethenyl)]pyridinium] cations, differing with respect to the butyl chain
torsion angle for which values of 80.0(9)◦ and 173.6(3)◦ are observed. The cations and anions are
joined into infinite layers, formed by two different dimers and including solvent molecules. Hydrogen
bonds OH· · ·OH2 (2.814 Å), HOH· · ·O(CH3) (2.960 Å), OH· · ·Cl (2.967 Å), HOH· · ·Cl− (3.034, 3.188, 3.161 and
3.062 Å) and HOH· · ·OH2 (2.772 Å) are observed. For first time in the literature, we are reporting the crystal
structure of the dye with the syring-fragment in the molecule. The spectroscopic properties of the novel
compound are compared and with those of the corresponding quinoide form (2). Both the forms (1) and
(2) are characterized by 21 and 140 nm solvatochromic effects depending of the type of the solvent. The
UV-spectroscopic data in solution confirm the formation of classical H-aggregates in polar protic solvent
mixture.
hydroxyphenyl)ethenyl)]pyridinium]
chloride tetrahydrate
Single crystal, X-ray data, Solid-state
linear-polarized IR-spectroscopy, UV–vis,
MS, TGA and DTA
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
pyridinium] chloride tetrahydrate and its quinoide form, obtained
after deprotonation of the 4-OH group (Scheme 1, Table 1). The rela-
Pyridinium salts have received considerable attention during
the past 30 years, due to many of their derivatives possessing large
second order molecular hyperpolarisability. Studies of the second
harmonic generation (SHG) from powders and Langmuir–Blodgett
films of these merocyanine dyes have been performed due to their
application in various areas of non-linear optics. Second order non-
linear optical properties of these materials are very sensitive to the
symmetry of the structure [1–4]. It has been found that the variation
of the counterion in organic salts is a simple and highly successful
approach to creating materials with larger ꢀ values. This method-
ology has been also supported by the obtained crystal structure and
properties of DAST [1].
tionship between the structure and the spectroscopic properties
has been elucidated using the single crystal X-ray diffrac-
tion, UV–vis and fluorescence methods, polarized linear-dichroic
infrared (IR-LD) spectroscopy of oriented colloid suspensions in
a nematic liquid crystal, mass spectrometry, and TGV and DSC
methods.
2. Experimental
2.1. Materials and methods
X-ray diffraction intensities were measured in the ␻ scan mode
on a Siemens P4 diffractometer equipped with MoK␣ radiation
(ꢁ = 0.71073 Å, ꢂmax = 25◦). The structure was solved by direct
methods and refined against F2 [30,31]. An ORTEP plot illustrates
the anion and cation structures at the 50% probability level.
Relevant crystallographic structure data and refinement details
are presented in Table 2, selected bond distances and angles in
Table 3. The hydrogen atoms were constrained to calculated posi-
As a part of our systematic study of organic dyes [5–9], we now
present a spectroscopic and structural elucidation of the newly syn-
thesized 1-butyl-4-[2-(3,5-dimethoxy4-hydroxyphenyl)ethenyl)]
∗
Corresponding author. Tel.: +44 0 231 755 7069.
E-mail address: kolev@orgchm.bas.bg (T. Kolev).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.09.020

B.B. Koleva et al. / Spectrochimica Acta Part A 74 (2009) 1120–1126
1121
for accuracy, precision and the influence of the liquid crystal
medium on peak positions and integral absorbances of the guest
molecule bands have been presented [32–35]. The nature and
balance of the forces in the nematic liquid crystal suspension
system, the mathematical model for their clearance, the mor-
phology of the suspended particles and the influence of the
space system types on the degree of orientation (i.e. ordering
parameter) have been demonstrated [35] using five liquid crystals
and fifteen compounds. The applicability of the latter approach
to experimental IR-spectroscopic band assignment as well as in
obtaining stereo-structural information has been demonstrated
for a series of organic systems and coordination complexes of
heterocyclic ligands, Cu(II) complexes, polymorphs, codeine
derivatives, Au(III) peptide complexes and their hydrochlorides
and hydrogensquarates [36–39]. The theory of IR-LD spectroscopy
and the employed polarized IR-spectra interpretation difference-
reduction procedure are given in Refs. [40–43]. FAB mass spectra
were recorded on a Fisons VG Autospec instrument employing 3-
nitrobenzylalcohol (Sigma–Aldrich) as the matrix. Ultraviolet (UV-)
spectra were recorded on Tecan Safire Absorbance/Fluorescence
XFluor 4 V 4.40 spectrophotometer operating between 190 and
Scheme 1. Chemical diagram of stubazolium salts.
tions and refined using riding models in all cases. The IR-spectra
were measured on a Thermo Nicolet OMNIC FTIR-spectrometer
(4000–400 cm−1, 2 cm−1 resolution, 200 scans) equipped with a
Specac wire-grid polarizer. Non-polarized solid-state IR-spectra
were recorded using the KBr disk technique. The oriented samples
were obtained as a suspension in a nematic liquid crystal (MLC
6815, Merck) with the presence of an isolated nitrile stretching
IR-band at about 2245 cm−1 additionally serving as an orientation
indicator. The theoretical approach as well as the experimental
technique for preparing the samples, and procedures for polar-
ized IR-spectra interpretation and the validation of this new
linear-dichroic infrared (IR-LD) orientation solid-state method
Table 1
Crystal structures of stubazolium salts with formulae, given in Scheme 1.
R1
R2
R3
X
CCDC codea [ref.]
CH3
CH3
CH3
CH3
H
H
H
H
H
H
H
H
H
(+)-Camphor-10-sulfonate
Toluene-p-sulfonate
Bromobenzenesulfonate
Triiodide iodide
2,4-dihydroxyacetophenone
Cl−
BOJWAY [10]
JOYBEE [11], JOYBEE10 [12]
LANLAO [13]
LIBZEC [14]
OH
OCH3
H
2-Hydroxyethyl
Butyl
CH3
CH3
NUPFUZb [15]
OMIXAJ [16]
OMIXUD [17], VIJPAF [18]
WAQNOS [19]
QAWMIK [20]
QIGHET [21]
SIFFAOb [22]
SUJKUDb [23]
TAQQEI [24]
TEBLUH, TEBMAO [25]
TETQAK [26]
TOHGIG [27]
YIFPIN [28]
OH
OCH3
OCH3
OCH3
H
H
H
H
H
H
OCH3
H
H
H
P-toluenesulfonate
Chlorobenzenesulfonate
I−
CH3
2-Hydroxyethyl
CH3
2-Hydroxyethy
CH3
CH3
2-Hydroxyethy
CH3
CH3
CH3
CH3
Butyl
I−
Tetraphenylborate dimethylsulfoxide solvat
2-Amino-4-nitrophenol
2,4-Dihydroxybenzaldehyde
I−
Bromide iodide
Hydrogensquarate
Hydrogenphosphate
Cl−
[29]
[9]
(1)
H
OCH3
OCH3
a
CCDC: Cambridge Crystallographic Data Centre (http://www.ccdc.cam.ac.uk/).
Quinoide form (2) in Scheme 2, of the dyes obtained after deprotonation of the 4-OH group.
b
Table 2
Crystal and refinement data for (1).
Empirical formula
Formula weight
C38H48Cl2N2O6
699.68
Temperature
294(2) K
Wavelength
Crystal system, space group
Unit cell dimensions
0.71073 Å
Triclinic, P1
a = 12.587(8) Å
¯
˛ = 97.01(2)◦
ˇ = 115.64(5)◦
ꢃ = 90.61(3)◦
b = 12.753(6) Å
c = 14.269(8) Å
2044(2) Å3
Volume
Z
2
Calculated density
Absorption coefficient
F(0 0 0)
1.137 mg/m3
0.201 mm−1
744
Crystal size
0.21 mm × 0.33 mm × 0.12 mm
ꢂ Range for data collection
Limiting indices
Reflections collected/unique
Refinement method
Goodness-of-fit on F2
Final R indices [I > 2ꢄ (I)]
R indices (all data)
1.81–25.00◦
−1< = h< = 14, −15< = k< = 15, −16< = l< = 15
8131/7086 [R(int) = 0.0248]
Full-matrix least-squares on F2
1.509
R1 = 0.1035, wR2 = 0.2559
R1 = 0.1794, wR2 = 0.2961

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B.B. Koleva et al. / Spectrochimica Acta Part A 74 (2009) 1120–1126
Table 3
Selected bond lengths (Å) and angles (◦) for (1).
N1 C11 1.316(7)
O3 C12 1.341(6)
C12 C18 1.377(8)
C27 C35 1.395(7)
N1 C9 1.345(7)
O4 C39 1.361(6)
C13 C17 1.376(7)
C28 C29 1.374(8)
N1 C7 1.476(6)
O4 C24 1.431(7)
C14 C17 1.397(8)
C28 C35 1.380(7)
O1 C18 1.379(7)
C4 C7 1.492(9)
C40 C18 1.360(7)
C30 C33 1.301(7)
O1 C5 1.431(8)
O5 C37 1.373(6)
C40 C20 1.394(8)
C30 C34 1.474(7)
N2 C32 1.324(6)
O6 C36 1.365(6)
C16 C19 1.309(7)
C31 C39 1.383(7)
N2 C29 1.326(7)
O6 C25 1.437(6)
C16 C20 1.447(7)
C31 C34 1.391(8)
N2 C26 1.470(6)
C8 C10 1.391(7)
C17 C19 1.445(7)
C33 C35 1.459(7)
O2 C10 1.382(7)
O2 C6 1.415(7)
C2 C3 1.323(14)
C2 C4 1.651(12)
C8 C20 1.393(8)
C9 C14 1.359(7)
C21 C22 1.647(12)
C22 C23 1.403(11)
C23 C26 1.505(11)
C27 C32 1.375(7)
C34 C38 1.372(8)
C36 C38 1.392(7)
C36 C37 1.395(7)
C37 C39 1.380(7)
C10 C12 1.372(8)
C11 C13 1.344(7)
C12 C10 C8 120.9(6)
O2 C10 C8 124.3(6)
N1 C11 C13 122.7(6)
O3 C12 C10 119.5(6)
O3 C12 C18 121.4(6)
C10 C12 C18 119.1(5)
C11 C13 C17 121.4(6)
C9 C14 C17 120.7(5)
C18 C40 C20 119.8(6)
C19 C16 C20 128.6(6)
C13 C17 C14 115.4(5)
C13 C17 C19 121.0(5)
C14 C17 C19 123.6(5)
C40 C18 C12 121.5(6)
C40 C18 O1 125.1(6)
C12 C18 O1 113.4(5)
C11 N1 C9 118.4(5)
C11 N1 C7 121.7(5)
C9 N1 C7 119.9(5)
C18 O1 C5 118.4(5)
C32 N2 C29 120.3(5)
C32 N2 C26 119.6(5)
C29 N2 C26 120.1(5)
C10 O2 C6 116.8(5)
C3 C2 C4 111.7(11)
C39 O4 C24 118.0(4)
C7 C4 C2 107.8(7)
C36 O6 C25 117.5(4)
N1 C7 C4 110.3(5)
C10 C8 C20 119.1(6)
N1 C9 C14 121.4(5)
C12 C10 O2 114.7(5)
C16 C19 C17 126.3(6)
C8 C20 C40 119.5(5)
C8 C20 C16 121.2(6)
C40 C20 C16 119.4(6)
C23 C22 C21 109.5(9)
C22 C23 C26 111.2(8)
N2 C26 C23 111.3(5)
C32 C27 C35 120.7(5)
C29 C28 C35 121.0(5)
N2 C29 C28 121.1(5)
C33 C30 C34 128.7(6)
C39 C31 C34 120.8(5)
N2 C32 C27 120.9(5)
C30 C33 C35 124.9(6)
C38 C34 C31 120.2(5)
C38 C34 C30 123.8(5)
C31 C34 C30 116.0(5)
C28 C35 C27 116.0(5)
C28 C35 C33 120.1(5)
C27 C35 C33 123.9(5)
O6 C36 C38 126.3(5)
O6 C36 C37 113.6(4)
C38 C36 C37 120.1(5)
O5 C37 C39 117.6(5)
O5 C37 C36 122.1(5)
C39 C37 C36 120.3(5)
C34 C38 C36 119.5(5)
O4 C39 C37 115.4(4)
O4 C39 C31 125.4(5)
C37 C39 C31 119.2(5)
900 nm, using water, methanol, dichloromethane, tetrahydrofu-
ran, acetonitrile, acetone, 2-propanol and ethyl acetal as solvents
(all Uvasol, Merck products) at concentrations of 2.5 × 10−5 M,
in 0.921 cm quarz cells. Quantum chemical calculations were per-
formed using the GAUSSIAN 98 and Dalton 2.0 program packages
[44,45] with visualization being done by the ChemCraft program
[46]. The geometries of the cationic and quinoide forms of the
dye were optimized at two different levels of theory: Restricted
Hartree-Fock (RHF) and density functional theory (DFT) using the
6-311++G** basis set. In the second case the B3LYP method, which
combines Becke’s three-parameter non-local exchange functional
with the correlation function of Lee, Yang and Parr was applied.
Molecular geometries of the studied species were fully optimized
by the force gradient method using Bernys’ algorithm. For every
structure the stationary points found on the molecule potential
energy hypersurfaces were characterized using standard analytical
harmonic vibrational analysis. Absence of imaginary frequencies
and negative eigenvalues of the second-derivative matrix con-
firmed that the stationary points correspond to minima of the
potential energy hypersurfaces. The calculations of vibrational fre-
quencies and infrared intensities were checked to establish which
kind of performed calculations agreed best with the experimental
data. A modification of the results using the empirical scaling factor
0.9614 was performed with a scaling factor of 0.8929 being used
in the case of HF calculations. The solvent effects on the absorption
bands were studied at the TD [47] DFT level of theory combined
with the polarized continuum model (PCM) [48–50]. The thermal
analyses were carried out in the 25–300 ◦C range with a Differ-
ential Scanning Calorimeter PerkinElmer DSC-7 and a Differential
Thermal Analyzer DTA/TG (Seiko Instrument, model TG/DTA 300).
The experiments were performed at a scanning rate of 10 K/min
under an argon atmosphere. The elemental analysis was carried out
according to the standard procedures for C and H (as CO2, and H2O)
and N (by the Dumas method).
2.2. Synthesis
The
starting
compounds,
1-methyl-4-butylpyridinum
chloride and 4-syringaldehyde, for the synthesis of 1-butyl-
4-[2-(3,5-dimethoxy-4-hydroxyphenyl)ethenyl)]piridinium]
chloride tetrahydrate were Merck (Germany) products. 2.3500 g
(10.0 mmol) of the first compound is mixed with 1.2200 g
(10.0 mmol) of the aldehyde in 50.0 ml toluene. 5.00 ml acetic acid
and 0.77 g (10.00 mmol) ammonium acetate are then added to
the reaction mixture and the resulting suspension is stirring for
24 h at room temperature. Then 0.50 ml c. HI acid and 10.00 ml
ethanol are added and the reaction mixture is left to stand
for 16 h at room temperature. The resulting orange crystalline
precipitate is filtered off, washed with C2H5OH and dried on
P2O5 at 298 K. Yields 61%. Found: C, 54.10; H, 7.66; N, 3.31;
[C19H32NO7Cl] calcd.: C, 54.09; H, 7.64; N, 3.31%. TGV and DSC
analysis in the range 300–500 K showed that (1) contains four
water molecules, on the basis of the observed weight loss of
17.01%. The obtained enthalpy effect of 28.01 kcal/mol, proved
Scheme 2. Scheme for obtaining of quinoide form (2), using the novel compounds (1).

B.B. Koleva et al. / Spectrochimica Acta Part A 74 (2009) 1120–1126
1123
TGA data additionally. The most intensive signal in the mass
spectrum of the title compound is that of the peak at m/z 314.71,
corresponding to the singly charged cation [C19H24NO3]+ with
a molecular weight of 314.40. 1-Methyl-4-[2-(3,5-dimethoxy-
4-oxocyclohexadienylidene)ethylidene]-1,4-dihydropyridine (2)
(Scheme 2) can be prepared in the following way: 10.0 mg of the
salt (1) are dissolved in 10.00 mmol ethanol and then 5 ml 1.0 M
KOH are added. The resulting violet solution is heated for 2 h at
a temperature of 70 ◦C and then is left to stand at 4 ◦C for 16 h.
The resulting violet precipitate is filtered off and dried on P2O3 at
298 K. Yield 88%. Found: C, 72.80; H, 7.38; N, 4.47; [C19H23NO3]
calcd.: C, 72.82; H, 7.40; N, 4.47%. TGV and DSC analysis in the
range 300–500 K showed that no solvent molecules were included
in compound 2. The most intensive signal in the mass spectrum of
(2) is that of the peak at m/z 314.27, corresponding to the singly
charged cation [C19H24NO3]+ with a molecular weight of 314.40.
4-hydroxyphenyl)ethenyl)]pyridinium] cations, which exhibit
torsion angles of 80.0(9)◦ and 173.6(3)◦, respectively, in their
butyl chains (H3CCH2CH2CH2) (Fig. 1). The molecules are joined
into infinite layers, formed by two different dimers of the cations,
anions and included solvent molecules (Fig. 2). The observed
hydrogen bonds are OH· · ·OH2 (2.814 Å), HOH· · ·O(CH3) (2.960 Å),
OH· · ·Cl (2.967 Å), HOH· · ·Cl− (3.034, 3.188, 3.161 and 3.062 Å)
and HOH· · ·OH2 (2.772 Å), respectively (Fig. 2). The 4-[2-(3,5-
dimethoxy-4-hydroxyphenyl)ethenyl)]pyridinium] fragment of
the cation is effectively flat with a deviation from total planarity
of only 0.2◦. The bond lengths and angles of the benzene ring
and the pyridine fragment are all in accordance with aromatic
character, similar to those of previously reported structures of
this class of compounds (Table 1). The corresponding values of
the geometrical parameters (Table 3) correlate well with those of
other merocyanine dyes given in Table 1. The typically observed
crystallographic disorder of the double bond in these dyes is due
to the presence of tautomers with either a formally single central
bond or a formally double central bond. In our case only disorder
of the anions is observed. Like other dyes [51,52], this disorder led
to the relatively high observed R factor (Table 2).
3. Results and discussion
1-Butyl-4-[2-(3,5-dimethoxy-4-hydroxyphenyl)ethenyl)]pyri-
dinium] chloride tetrahydrate crystallizes in the tri-
¯
The theoretical conformational analysis of the cationic form
of compound (1) and its neutral form (2) (Scheme 3) shows that
clinic space group P1 (Fig. 1). The unit cell contains two
crystallographically independent 1-butyl-4-[2-(3,5-dimethoxy-
Fig. 1. The molecular structure of 1-butyl-4-[2-(3,5-dimethoxy4-hydroxyphenyl)ethenyl)]pyridinium] chloride tetrahydrate, showing the atom-labeling scheme. Displace-
ment ellipsoids are drawn at the 50% probability level.
Fig. 2. Linkage of the molecules of 1-butyl-4-[2-(3,5-dimethoxy-4-hydroxyphenyl)ethenyl)]pyridinium] chloride tetrahydrate.

1124
B.B. Koleva et al. / Spectrochimica Acta Part A 74 (2009) 1120–1126
Scheme 3. 3D graph of the Phi and Psi values vs energy (kJ/mol) for the cationic (1) and quinoide (2) forms of the dye 1-butyl-4-[2-(3,5-dimethoxy4-
hydroxyphenyl)ethenyl)]pyridine.
in both cases the conformer with torsion angles of 178.9(1)◦ and
179.9(0)◦, respectively (Scheme) in the butyl chain is energeti-
cally favourable. The corresponding energies are 0.1 and 0.0 kJ/mol.
These data suggest that the presence of a conformer in solid state
with a torsion angle for the discussed chain of 80.0(9)◦ is the result
of the steric effects in the condensed phase.
The observed significant degree of macro-orientation in the
polarized IR-spectrum of the sample facilitates an adequate inter-
pretation of the polarized IR-data and results from the presence
of a pseudo layer structure, which adopts a macro-orientation in
the solid phase toward the orientation director (n) of the liquid
crystal. The detailed IR-LD spectroscopic analysis is supported by
the theoretical vibrational analysis at the B3LYP/6-311++G** level.
The non-polarized IR-spectrum shows a relatively intensive band
at 3383 cm−1 corresponding to the stretching ꢅOH vibration of the
hydrogen bonded OH-group in the merocyanine dye, thus corre-
lating with the experimental crystallographic data. The band at
3515 cm−1 is caused by the same vibration but belongs to the water
molecules of crystallisation. In the 1700–1600 cm−1 range aromatic
i.p. modes of the benzene and pyridine rings were observed at
1614 cm−1 (8a(py)) and 1584 cm−1 (8a(Ph)). The absorbtion maxima
the ground and exited state, i.e. determines their signifi-
cant solvatochromism, or NLO properties in solution. Depend-
ing of the solvent polarity, the CT band in 1-butyl-4-[2-
(3,5-dimethoxy-4-hydroxyphenyl)ethenyl)]pyridinium] chloride
exhibits a bathochromic shift of 21 nm for ꢁmax (Fig. 4) on going
from 1,2-dichloromethane to acetonitrile. The obtained negative
solvatochromic effect in these compounds has been explained by
both intra and intermolecular charge transfer. In contrast to (1), the
quinoide form of the compound (2) is characterized by an observed
solvatochromic effect of 140 nm (Fig. 4). In acetone and acetonitrile
two bands at about 600 and 640 nm as well as a shoulder at about
560 nm are observed. These maxima as well as the spectral changes
and the well-defined isosbestic points provide good evidence for an
equilibrium between monomeric and dimeric species [9,53,54]. It
is noteworthy that in addition to the very intense hypsochromically
shifted absorption band for the H-dimer, a weak band appears at
longer wavelength, which can be ascribed to the forbidden tran-
sition to the lower energy exciton state. It is interesting to note
that these dimers are strongly affected by solvent mixtures like
acetonitrile/H2O with a band at 547 nm.
belonging to the out-of-plane (o.p.) bending vibrations ꢃC
and
C,
11-ꢃCH of the benzene ring and the o.p. mode of the pyridine ring
are observed at 996, 849 and 734 cm−1, respectively. Spectroscopic
support of the experimental crystal structure is obtained by appli-
cation of the reducing difference procedure to polarized IR-spectra,
where the elimination of the bands at 1614 and 1584 cm−1 at the
same dichroic ratio occurs because the corresponding transition
moments are orientated in a co-linear manner. On the other hand,
the disappearance of the maxima at 996, 849 and 734 cm−1 at same
dichroic ratio (Fig. 3) indicates a mutually co-planar disposition of
the aromatic rings and the double bond, also in good agreement
with the X-ray crystal structure. This result is in accordance with
other derivatives with small R1-substituents (Table 1).
In the corresponding Raman spectrum of (1) (supplementary
material Fig. S1), the series of in-plane vibrations of the benzene
and pyridine rings are observed at 1616, 1584, 1561 and 1516 cm−1
.
The out-of-plane modes at 996 and 739 cm−1 are characterized by
relatively low intensity, while the band at 849 cm−1 is absent.
The possible redistribution of the electronic density in
these compounds as typical push–pull systems depends on
the solvent polarity. As far as the electron transition is con-
nected with intramolecular charge transfer (CT) this leads
Fig. 3. Non-polarized IR-(1) and reduced IR-LD (2) spectrum of the 1-butyl-4-[2-
(3,5-dimethoxy4-hydroxyphenyl)ethenyl)]pyridinium] chloride tetrahydrate after
to
a significant difference between the dipole moment in
the elimination of the band at 849 cm−1
.

B.B. Koleva et al. / Spectrochimica Acta Part A 74 (2009) 1120–1126
1125
Scheme 4. Molecular orbital surface of the HOMO and LUMO for the ground state of cationic (1) and quinoide form (2) of the dye 1-butyl-4-[2-(3,5-dimethoxy-4-
hydroxyphenyl)ethenyl)]pyridine.
The distribution of the highest occupied (HOMO) and lowest
unoccupied (LUMO) molecular orbitals for the ground state is illus-
trated in Scheme 4. Nearly all of the MOs are substantially localized
on the conjugated plane, with only small contributions to the group
out of the plane in the case of (1). In contrast, the underlying CT is
observed in compound (2).
For the precise investigation of the geometry changes associ-
ated with the electronic excitation, to the lowest singlet excited
state, the geometry of the studied compounds was optimized at
the CIS/6-31++G** level of theory for comparison with the data for
the ground state optimized at HF/6-31++G**. The data indicate that
the structural shift is predominantly localized on the conjugated
plane in (1) and that the groups out of the discussed plane are not
changed significantly. The distributions for the HOMO and LUMO
of the lowest single exited state show a strong optical emission in
case of (2).
S2A), using the atom numbering Scheme 2. The OCH3 signals are
observed within the 3.75–3.85 ppm range as singlets with intensity
6H. The signals between 0.90 and 2.00 ppm belong to the aliphatic
CH3CH2CH2CH2 protons. The H-2 and H-6 signals are observed at
about 7.00 in (1) and 6.80 ppm in (2), respectively. The AB signals
of H-7 and H-8 are at 7.35 and 7.95 ppm (1). The analogous signals
in (2) are observed at 6.51 and 7.55 ppm. The AAꢀBBꢀ chemical shift
signals are within the 8.70–8.00 ppm (1) and 7.55–8.00 ppm (2)
ranges. In the case of (1), the peak at 9.20 ppm can be attributed to
the OH proton (supplementary material Fig. S2B). The correspond-
ing 13C NMR spectra of both the compounds, exhibit OCH3 signals
at about 5.6 ppm. The peaks at about 106.00, 120.00, 122.25, 122.70,
125.60, 138.00, 140.00, 145.00, 149.00 and 152.00 ppm correspond
to C-2ꢀ/C-6ꢀ, C-7, C3/C5, C1ꢀ, C-4ꢀ, C-8, C-2/C-6, C-3ꢀ/C-5ꢀ and C-4
carbon chemical shifts, respectively.
The proton chemical shifts of both the compounds (1) and (2)
are assigned in the following way (supplementary material Fig.
4. Conclusion
We are reported the new chloride salt of 1-butyl-4-[2-
¯
(4-hydroxyphenyl)ethenyl)]pyridine, crystallizing in triclinic P1
space group. Its unit cell contains two independent 1-butyl-4-
[2-(3,5-dimethoxy4-hydroxyphenyl)ethenyl)]pyridinium] cations,
differing with respect to the butyl chain torsion angle for which
values of 80.0(9)◦ and 173.6(3)◦. The cations and anions are
joined into infinite layers, formed by two different dimers and
including solvent molecules. Hydrogen bonds OH· · ·OH2 (2.814 Å),
HOH· · ·O(CH3) (2.960 Å), OH· · ·Cl (2.967 Å), HOH· · ·Cl− (3.034,
3.188, 3.161 and 3.062 Å) and HOH· · ·OH2 (2.772 Å) are observed.
For first time in the literature, we are reporting the crystal
structure of the dye with the syringaldehyde-fragment in the
molecule.
Supporting information
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre,
CCDC 705628 Copies of this information may be obtained from
the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(Fax: +44 1223 336 033; e-mail: deposit@ccdc.cam.ac.uk or
http://www.ccdc.cam.ac.uk). Raman (supplementary material Fig.
S1) as well as 1H and 13C NMR spectra (supplementary material
Figs. S2A and S2B), respectively.
Fig. 4. UV–vis spectra of 1-butyl-4-[2-(3,5-dimethoxy-4-hydroxyphenyl)-
ethenyl)]piridinium] chloride tetrahydrate in different media at a concentration of
2.5 × 10−5 M.

1126
B.B. Koleva et al. / Spectrochimica Acta Part A 74 (2009) 1120–1126
Acknowledgements
[25] F. Pan, M. Wong, G. Gramlich, C. Bosshard, P. Günter, Chem. Commun. 1996
1557.
[26] F. Pan, M. Wong, V. Gramlich, C. Bosshard, P. Günter, J. Am. Chem. Soc. 118
(1996) 6315.
T.K. and M.S. wish to thank the DAAD for a grant within the
priority program “Stability Pact South-Eastern Europe” and DFG
under the grant number SP 255/21-1. B.K. thanks the Alexander
von Humboldt Foundation for the Fellowship.
[27] D. Zhang, T. Zhang, Y. Zhang, Z. Fei, K. Yu, Acta Crystallogr. 53C (1997) 364.
[28] S. Chantrapromma, H. Fun, Acta Crystallogr. 63E (2007) o2882.
[29] B. Koleva, T. Kolev, H. Mayer-Figge, W. Sheldrick, Anal. Sci., in press.
[30] G.M. Sheldrick, SHELXTL, Release 5.03 for Siemens R3 Crystallographic
Research System, Siemens Analytical X-Ray Instruments, Inc., Madison, USA,
1995.
Appendix A. Supplementary data
[31] G.M. Sheldrick, SHELXS97 and SHELXL97, University of Goettingen, Germany,
1997.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2009.09.020.
[32] B. Ivanova, M. Arnaudov, P. Bontchev, Spectrochim. Acta 60A (2004) 855.
[33] B. Ivanova, D. Tsalev, M. Arnaudov, Talanta 69 (2006) 822.
[34] B. Ivanova, V. Simeonov, M. Arnaudov, D. Tsalev, Spectrochim. Acta 67A (2006)
66.
[35] B. Koleva, T. Kolev, V. Simeonov, T. Spassov, M. Spiteller, J. Inclus. Prenome.
(2009), doi:10.1007/s10847-008-9425-5.
References
[36] B. Ivanova, J. Mol. Struct. 782 (2006) 122.
[37] B. Ivanova, Spectrochim. Acta 64A (2006) 931.
[38] B.B. Ivanova, T. Kolev, S. Zareva, Biopolymers 82 (2006) 587.
[39] T. Kolev, Biopolymers 83 (2006) 39.
[1] S. Marder, J. Perry, W. Schaefer, Science 245 (1989) 626.
[2] S. Marder, J. Perry, B. Tiemann, R. Warsh, W. Schaefer, Chem. Matter 2 (1990)
685.
[3] G. Ashwell, R. Hargreaves, C. Baldwin, G. Bahra, C. Brown, Nature 357 (1992)
393.
[4] D. Lupo, W. Prass, U. Scheunemann, A. Laschewsky, R. Ringsdorf, I. Ledoux, J.
Opt. Soc. Am. B 5 (1988) 300.
[5] T. Kolev, D. Yancheva, S. Stoyanov, Adv. Funct. Mater. 14 (2004) 799.
[6] T. Kolev, R. Wortmann, M. Spiteller, W. Sheldrick, M. Heller, Acta Crystallogr.
E60 (2004) o1449.
[7] T. Kolev, R. Wortmann, M. Spiteller, W. Sheldrick, H. Mayer-Figge, Acta Crys-
tallogr. E61 (2005) o1090.
[8] T. Kolev, B. Stamboliyska, D. Yancheva, Chem. Phys. 324 (2006) 489.
[9] T. Kolev, B. Koleva, M. Spiteller, H. Mayer-Figge, W.S. Sheldrick, Dyes Pigments
79 (2008) 7.
[10] R. Ziolo, W. Günther, G. Meredith, D. Williams, J. Troup, Acta Crystallogr. 38B
(1982) 341.
[11] S. Marder, J. Perry, W. Schaefer, J. Mater. Chem. 2 (1992) 985.
[12] S. Marder, J. Perry, C. Yakymyshyn, Chem. Mater. 6 (1994) 1137.
[13] B. Jindawong, S. Chantrapromma, H. Fun, X. Yu, C. Karalai, Acta Crystallogr. 61E
(2005) o1340.
[40] B. Jordanov, B. Schrader, J. Mol. Struct. 347 (1995) 389.
[41] B. Jordanov, R. Nentchovska, B. Schrader, J. Mol. Struct. 297 (1993) 401.
[42] J. Michl, E.W. Thulstrup, Spectroscopy with Polarized Light. Solute Alignment by
Photoselection, in Liquid Crystals, Polymers, and Membranes, VCH Publishers,
NY, 1986.
[43] E.W. Thulstrup, J. Eggers, Chem. Phys. Lett. 1 (1996) 690.
[44] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
V.G. Zakrzewski, J.A. Montgomery Jr., R.E. Stratmann, J.C. Burant, S. Dapprich,
J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, Ö. Farkas, J. Tomasi, V. Barone,
M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski,
G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, P. Salvador, J.J. Dannenberg,
D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz,
A.G. Baboul, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komáromi, R. Gom-
perts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara,
M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C.
Gonzalez, M. Head-Gordon, E.S. Replogle, J.A. Pople, Gaussian 98, Gaussian, Inc.,
Pittsburgh, PA, 1998.
[45] “DALTON”,
a
molecular electronic structure program, Release 2.0,
[14] S. Chantrapromma, K. Chanawanno, H. Fun, Acta Crystallogr. 63E (2007) o1554.
[15] C. Bosshard, M. Wong, F. Pan, V. Gramlich, P. Günter, Adv. Mater. 9 (1997) 554.
[16] T. Kolev, T. Berends, D. Kleb, H. Preut, M. Spiteller, Acta Crystallogr. 59E (2003)
o1788.
http://www.kjemi.uio.no/software/dalton/dalton.html, 2005.
[46] G.A. Zhurko, D.A. Zhurko, ChemCraft: Tool for treatment of chemical data, Lite
version build 08, 2005.
[47] D. Tozer, N. Handy, Phys. Chem. Chem. Phys. 2 (2000) 2117.
[48] J. Tomasi, M. Persico, Chem. Rev. 94 (1994) 2027.
[49] R. Cammi, M. Cossi, J. Tomasi, J. Chem. Phys. 104 (1996) 4611.
[50] R. Cammi, C. Rossi, B. Bennucci, J. Tomasi, J. Chem. Phys. 105 (1996)
10556.
[51] S. Benard, P. Yu, J. Audiere, E. Riviere, R. Clement, J. Guilhem, L. Tchertanov, K.
Nakatani, J. Am. Chem. Soc. 122 (2000) 9444.
[52] Y. Ren, F. Qi, W. Yu, H. Lei, Y. Tian, M. Jiang, Q. Yang, T. Mak, J. Mater. Chem. 10
(2005) 2025.
[17] A. Rahman, I. Razak, H. Fun, P. Saenee, B. Jindawong, S. Chantrapromma, C.
Karalai, Acta Crystallogr. 59E (2003) o1798.
[18] S. Okada, A. Masaki, H. Matsuda, H. Nakanishi, M. Kato, R. Muramatsu, M.
Otsuka, Japan. J. Appl. Phys. 29 (1990) 1112.
[19] S. Chantrapromma, B. Jindawong, H. Fun, S. Anjum, C. Karalai, Acta Crystallogr.
61E (2005) o2096.
[20] T. Zhang, L. Ge, G. Zhang, Y. Zhang, K. Yu, Chin. J. Struct. Chem. 19 (2000) 6.
[21] P. Lacroix, C. Lepetit, J. Daran, New J. Chem. 25 (2001) 451.
[22] D. De, D. Ridder, H. Heijdenrijk, H. Schenk, R. Dommisse, R. Lemiere, J. Lepoivre,
F. Alderweireldt, Acta Crystallogr. 46C (1990) 2197.
[53] T. Kimura, X. Duan, M. Kato, H. Matsuda, T. Fukuda, S. Yamada, S. Okad, H.
Nakanishi, Macromolec. Chem. Phys. 199 (1998) 1193.
[54] P. Acebal, S. Blaya, L. Carretero, J. Phys. 36 (2003) 2445.
[23] P. Lacroix, J. Daran, P. Cassoux, New J. Chem. 22 (1998) 1085.
[24] W. Yang, S. Li, D. Zhang, Acta Crystallogr. 61E (2005) o2461.