Optical and nonlinear optical properties of new Schiff's bases: Experimental versus theoretical study of inclusion interactions

Article abstract of DOI:10.1007/s10847-012-0163-3

Experimentally and theoretically were studied the physical properties of 19 new Schiff's bases and their different protonated forms, depending on reaction conditions. It was elucidated the correlation between the type of molecular architecture, substituen

Full text of DOI:10.1007/s10847-012-0163-3

J Incl Phenom Macrocycl Chem (2013) 75:211–221
DOI 10.1007/s10847-012-0163-3
ORIGINAL ARTICLE
Optical and nonlinear optical properties of new Schiff’s bases:
experimental versus theoretical study of inclusion interactions
•
Bojidarka B. Ivanova Michael Spiteller
Received: 24 June 2011 / Accepted: 27 April 2012 / Published online: 10 June 2012
Ó Springer Science+Business Media B.V. 2012
Abstract Experimentally and theoretically were studied
the physical properties of 19 new Schiff’s bases and their
different protonated forms, depending on reaction condi-
tions. It was elucidated the correlation between the type of
molecular architecture, substituents and pH of the medium
on first hyperpolarizability (b) with regard to the potential
application of these compounds as organic nonlinear opti-
cal materials. The structure and optical properties were also
studied, comparing quantum chemical data and experi-
mental results from the mass spectrometry, electronic
absorption, diffuse reflectance, and fluorescence spectros-
copy, vibrational spectroscopy in condense phase, nuclear
magnetic resonance, as well as thermal methods.
architecture for organic, the coordination ability and no
covalently interactions [44–59]. In this context it was
presented new derivatives (Scheme 1), designed towards
the large first hyperpolarizability b that translates into v(2)
in the crystals, where the noncentrosymmetric structures
were essential. Advanced have been investigated both
experimentally and theoretically the effect of the substit-
uents in the molecular skeleton, and the pH of the medium
in view of subsequent receipt of organic salts. The last
objects have been shown great potential, by analogy with
(E)-40-(dimethylamino)-N-methyl-4-stilbazolium tosylate
(DAST) [1–31]. The important role of the organic salts is
that depending of the counter ion was used to modify
crystal packing, solubility, stability and higher chromo-
phore number densities. Based on our previous studies on
organic dyes [60–63] have been selected 19 new com-
pounds (Scheme 1) in which it studied the relationship
between structure, spectroscopic and NLO properties.
Keywords Schiff’s bases ꢀ Optical and NLO properties ꢀ
Quantum chemistry ꢀ Spectroscopy
Introduction
Great potential relevance of the organic materials in the
electro-optical (EO), nonlinear optical (NLO) and THz-
technologies, doing the research in this area innovative and
dynamic [1–31]. The possibilities of THz-spectroscopy
opens up new areas of interdisciplinary application such as
security, environmental inspection, biomedical analysis
[32–43]. The Schiff’s bases are among the most exploited
in the design of organic and the metal–organic NLO
materials, enabling the design and tuning of the molecular
Experimental
Physical measurements
The UV–VIS–NIR spectra between 190 and 1,190 nm,
using solvent acetonitrile (Uvasol, Merck product) at a
concentration of 2.5 9 10-5 M in 0.921 cm quartz cells
were recorded on Tecan Safire Absorbance/Fluorescence
XFluor 4 V 4.40 spectrophotometer. The thermogravi-
metric study was carried out using a Perkin-Elmer TGS2
instrument. The calorimetric measurements were per-
formed on a DSC-2C Perkin Elmer apparatus under argon.
Diffuse reflectance (Ds) spectra were measured on a
PerkinElmer Lambda 750 in reflectance mode. The
reflection spectra were automatically converted to
B. B. Ivanova (&) ꢀ M. Spiteller
Institute of Environmental Research (INFU) of the Faculty of
Chemistry, Dortmund University of Technology,
Otto-Hahn-Str. 6, 44227 Dortmund, Germany
e-mail: B.Ivanova@infu.uni-dortmund.de; B.Ivanova@web.de
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J Incl Phenom Macrocycl Chem (2013) 75:211–221
H
N
points found on the molecule potential energy hypersur-
faces were characterized using standard analytical har-
monic vibrational analysis. The absence of the imaginary
frequencies, as well as of negative eigenvalues of the
second-derivative matrix, confirmed that the stationary
points correspond to minima of the potential energy
hypersurfaces. The molecular properties of the studied
species in acetonitrile solution were obtained at CAM-
B3PW91 and M06-2X level of theory, using the
6-31 ? G(d) basis set. The protonation ability of the
molecules was evaluated by the NBO analysis. The theo-
retical calculations of the molecular hyperpolarizability
were performed, using the diffuse and polarization func-
tions. As far as it has been shown that the B3LYP method
give unreliable results for these calculations in some con-
jugated organic NLO materials, the CAM-B3PW91 and
M06-2X functionals were used also for calculation of the
hyperpolarizability, providing better agreement with
experiments, as well as close results in the property to
predict the molecular properties of organic, metal–organic
and no covalently interaction systems [71–81]. The NBO
analysis were preformed at the same theoretical levels.
The b total values are calculated according the Eq. 1,
where are bx, by and bz are described with the Eqs. 2–4,
respectively.
NH2
CN
N
N
R1
NH2
NH
n
CN
CN
R1 = SH, H
R2 = H, R
3 = R or Ar
N
N
+
R
H
N
O
NH2
CN
+
N
N
R1
O
or
R2
R3
n
R1
R2 R3
Scheme 1 Synthetic pathway of the heterocyclic fragments in (13)–
(19)
absorbance spectra using Kubelka–Munk theory. The mass
spectrometric measurements were made, using TSQ
Quantum AM ULTRA (Thermo Electron Corporation)
instrument. Two eluents were used A—H2O with 0.1 %
HCOOH and B—CH3CN with 0.1 % HCOOH. ESI mass
spectrometry: a triple quadruple mass spectrometer (TSQ
7000 Thermo Electron, Dreieich, Germany) equipped with
an ESI 2 source was used for detection and operated under
the following conditions: capillary temperature 120 °C;
sheath gas 60 psi and spray voltage 4.5 kV. The samples
were injected into the ion source by an auto sampler
(Surveyor) with a flow rate of 0.2 ml/min pure acetonitrile.
1 mg/ml of the sample will be dissolved in acetonitrile.
The data obtained were processed using Xcalibur 1.3
1=2
jjbtotjj ¼ ðb2x þ by2 þ bz2Þ
bx ¼ bxxx þ bxyy þ bxzz
by ¼ byyy þ bxxy þ byzz
ð1Þ
ð2Þ
ð3Þ
software. H- and 13C-NMR measurements, referenced to
1
and
sodium 3-(trimethylsylyl)-tetradeuteriopropionate, were
made at 298 K with a Bruker DRX-400 spectrometer using
5 mm tubes and D2O as solvent. The thermal analyses were
performing in the 300–500 K range on a Differential
Scanning Calorimeter Perkin-Elmer DSC-7, and a Differ-
ential Thermal Analyzer DTA/TG (Seiko Instrument,
model TG/DTA 300). The experiments were carried out
with a scanning rate of 10 K min-1 under an argon
atmosphere.
bz ¼ bzzz þ byyz þ bxxz
ð4Þ
The experimental and theoretical spectroscopic patterns
were processed by R4Cal OpenOffice STATISTICs for
Windows 7 program package [82]. Baseline corrections
and curve-fitting procedures were applied. For the
interpretation of the CD and fluorescence spectra [83–
96], the Gaussian function best fits to the experimental data
set, thus giving in our cases the r2 values within the range
0.97933–0.99083, respectively. The statistical significance
of each regression coefficient was checked by the use of
t test (calculation of the number of significance using data
from the experimental error, usually higher than 0.100).
The model fit was determined by F test (comparison of
calculated by the model and experimentally obtained signal
values).
Computational details
Quantum chemical calculations are performed with
GAUSSIAN 98, 09 and Dalton 2.0 program packages [64–
66]. The result files are visualized by means of the Gaus-
View03 [67]. The geometries of the studied species were
optimized at density functional theory (DFT) using the
6-31 ? G(d,p) basis set. The DFT method employed is
B3LYP [68–70]. Molecular geometries of the studied
species were fully optimized by the force gradient method
using Bernys’ algorithm. For every structure the stationary
Synthesis
Equimolar amounts of the aldehydes and aromatic amines
were mixed in 50 ml toluene under stirring at heating
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J Incl Phenom Macrocycl Chem (2013) 75:211–221
213
(40–100 °C) for 1–6 h, according the classical synthetic
scheme [97–99]. To the reaction mixtures were added
10 ml CH3COOH. The obtained dark colored powders
were filtered off and recrystallized from methanol. Yields
of (1)–(19) are within 90–95 %. The modeled heterocyclic
structural fragments in (13)–(19) structural fragment was
obtained according [100, 101], by mixing of the equimolar
amounts of the starting compounds in 50 ml methanol,
under stirring at heating reflux (50 °C) for 2 h.
methyl]-2,6-dimethoxy-phenol (7): Found, C, 69.50, H,
7.35, N, 8.55; Calc. [C19H24N2O3], C, 69.49, H, 7.37, N,
1
8.53 %; H-NMR: 3.33 (3H, –NCH2, t), 3.31 (3H, –NCH2,
t), 4.11, 4.15 (29 OCH3, s), 5.04 (1H, s), 7.12–7.55 ppm
(6H, m), 11.3 (OH, s, broad), 13C-NMR: 27.8, 28.5 (NCH2),
32.5, 32.4 (29 CH3) 75.1 (NCH), 86.4, 86.7 (–OCH3),
130.0–144.0 ppm (CHAr); 4-methyl-2-[(4-morpholin-4-yl-
benzylidene)-amino]-benzoic acid (8): Found, C, 70.33; H,
6.20; N, 8.66; Calc. [C19H20N2O3], C, 70.35, H, 6.21, N,
1
(4-Dimethylamine-benzylidene)-pyridin-4-yl-amine (1):
Found, C, 74.58; H, 6.70; N, 18.66; Calc. [C14H15N3], C,
74.64; H, 6.71; N, 18.65 %; 1H-NMR: 3.24 (3H, –NCH3, s),
3.27 (3H, –NCH3, s), 5.00 (1H, s), 7.26–7.88 ppm (8H, m),
8.64; H-NMR: 2.25 (3H, –CH3, s), 3.30 (2H, –NCH2, t),
3.32 (2H, –NCH2, t), 4.12 (2H, –NCH2CH2, t), 4.12 (2H,
–NCH2CH2, t), 5.11 (1H, s), 7.22–7.76 (7H, m), 8.45 ppm
(OH, s, broad), 13C-NMR: 27.3, 28.1, 29.30, 29.45
(NCH2CH2), 77.0 (NCH), 126.0–135.5 (CHAr), 177.7 ppm
13C-NMR:
27.8,
28.8
(NCH3),
77.6
(NCH),
127.8–135.8 ppm (CHAr); (4-diethylamine-benzylidene)-
pyridin-4-yl-amine (2): Found, C, 75.88, H; 7.52; N,
16.59 %; Calc. [C16H19N3], C, 75.86; H, 7.56; N, 16.59 %;
1H-NMR: 3.22 (3H, –NCH2, t), 3.29 (3H, –NCH2, t), 3.33,
3.41 (29 CH2, q, J = 7.0 Hz), 5.02 (1H, s), 7.22–7.90 ppm
(8H, m), 13C-NMR: 27.7, 28.2 (NCH3), 32.7, 32.2 (29
CH2) 77.0 (NCH), 128.1–136.6 ppm (CHAr); N,N-diethyl-
N0-(4-pyrrolidin-1-yl-benzylidene)-benzene-1,4-diamine
(3): Found, C, 78.55; H, 8.47; N, 13.07 %; Calc.
(COOH);
amino]-benzoic acid (9): Found, C, 74.10; H, 6.55; N, 9.10;
4-methyl-2-[(4-pyrrolidin-4-yl-benzylidene)-
1
Calc. [C19H20N2O2], C, 74.00, H, 6.54, N, 9.08; H-NMR:
2.26 (3H, –CH3, s), 3.32 (2H, –NCH2, t), 3.34 (2H, –NCH2,
t), 3.21 (2H, –NCH2CH2, t), 3.12 (2H, –NCH2CH2, t), 5.06
(1H, s), 7.20–7.88 (7H, m), 8.59 ppm (OH, s, broad), 13C-
NMR: 28.1, 29.5, 29.7, 29.9 (NCH2CH2), 79.0 (NCH),
125.1–133.7 (CHAr), 180.1 ppm (COOH); 4-[(4-hydroxy-
benzylidene)-amino]-benzene-1,3-diol (10): Found, C,
68.10; H, 4.85; N, 6.15; Calc. [C13H11O3N], C, 68.11; H,
4.84; N, 6.11 %; 4-[(3,4-dihydroxy-benzylidene)-amino]-
benzene-1,3-diol (11): Found, C, 59.75; H, 5.00; N, 6.34 %;
Calc. [C13H11O4N], C, 59.73; H, 5.01; N, 6.33 %; 1H-NMR:
5.30 (1H, s), 7.80–7.95 (6H, m), 10.4, 8.59, 8.20, 8.18 ppm
(49 OH, s, broads), 13C-NMR: 81.5 (NCH), 136.8–
140.5 ppm (CHAr), 4-[(3,5-dimethoxy-4-hydroxy-benzyli-
dene)-amino]-benzene-1,3-diol (12): Found, C, 62.30, H,
5.23, N, 4.84; Calc. [C15H15O5N], C, 62.28, H, 5.23, N,
4.84 %; 1H-NMR: 4.46, 4.50 (3H, –OCH3, s), 5.22 (1H, s),
7.56–7.90 (5H, m), 10.4, 8.59, 8.18 ppm (39 OH, s,
broads), 13C-NMR: 33.3, 34.2 (OCH3), 80.0 (NCH),
135.7–139.2 ppm (CHAr). The quinoide forms of (10)–(12),
were obtained by mixing of corresponding compounds
(10)–(12), by mixing of the preliminary dissolved sub-
stances in 25 ml methanol and adding the the equimolar
amount of KOH dissolved in same solvent. 3-Hydroxy-4-
(4-oxo-cyclohexa-2,5-dienylidenemethylimino)-cyclohexa-
2,5-dienone (10a): Found, C, 68.77, H, 3.99, N, 6.15 %,;
Calc. [C13H10O3N], C, 68.10; H, 4.82; N, 6.10 %; 4-[(2-
hydroxy-4-oxo-cyclohexa-2,5-dienylideneamino)-methy-
lene]-2-hydroxy-cyclohexa-2,5-dienone (11a): Found, C,
64.20; H, 3.75, N, 5.77; Calc. [C13H10O4N], C, 59.72; H,
5.00; N, 6.32 %; 4-[(2-hydroxy-4-oxo-cyclohexa-2,5-di-
enylideneamino)-methylene]-2,6-dimethoxy-cyclohexa-
2,5-dienone (12a): Found, C, 62.75, H; 4.55; N, 4.90 %,
Calc. [C15H14O5N], C, 62.22, H, 5.22, N, 4.83 %; 3-amino-
5-phenyl-7-[(4-pyrrolidin-1-yl-benzylidene)-amino]-5,8-
dihydro-[1, 2, 4]triazolo[4,3-a]pyrimidine-6-carbonitrile
(13): Found, C, 67.22, H, 5.66, N, 27.25 %; Calc.
1
[C21H27N3], C, 78.46, H, 8.47; N, 13.07 %; H-NMR: 3.21
(3H, –NCH3, t), 3.30 (3H, –NCH3, t), 3.21, 3.40 (29 CH2,
q, J = 7.1 Hz), 3.12, 3.16 (8H, t, m, J = 6.2 Hz), 5.01
(1H, s), 7.20–7.85 ppm (8H, m), 13C-NMR: 27.2, 28.0
(NCH3), 32.5, 32.1 (29 CH2), 29.7, 28.9, 30.1, 34.4 (49
CH2), 77.2 (NCH), 128.0–135.0 ppm (CHAr); N,N-Die-
thyl-N0-(4-morpholin-1-yl-benzylidene)-benzene-1,4-dia-
mine (4): Found, C, 74.77; H, 8.10; N, 12.55; Calc.
[C21H27N3O], C, 74.74; H, 8.06; N, 12.45 %; 1H-NMR:
3.20 (3H, –NCH3, t), 3.28 (3H, –NCH3, t), 3.20, 3.42 (29
CH2, q, J = 7.1 Hz), 4.22, 4.19 (8H, t, m, J = 7.7 Hz),
5.00 (1H, s), 7.25–7.66 ppm (8H, m), 13C-NMR: 27.3, 28.2
(NCH3), 32.2, 32.0 (29 CH2), 30.2, 30.8, 38.3, 39.1 (49
CH2), 77.0 (NCH), 128.0–136.2 ppm (CHAr); N,N-diethyl-
N0-(4-piperidin-1-yl-benzylidene)-benzene-1,4-diamine
(5): Found, C, 57.11; H, 6.50; N, 9.10; Calc. [C22H30N3I],
1
C, 57.02; H, 6.52; N, 9.07 %; H-NMR: 3.22 (3H, –NCH3,
t), 3.30 (3H, –NCH3, t), 3.29, 3.40 (29 CH2, q,
J = 7.0 Hz), 4.30, 4.20, 4.88 (10H, t, m, m, J = 7.2-
8.3 Hz), 4.77 (1H, m), 5.02 (1H, s), 7.30–7.70 ppm (8H,
m), 13C-NMR: 27.2, 28.1 (NCH3), 30.6 (CH), 32.0, 32.2
(29 CH2), 29.7, 30.2, 30.2, 33.1, 34.1 (59 CH2), 77.3
(NCH), 128.2–135.7 ppm (CHAr); 2-[(4-dimethylamino-
benzylidene)-amino]-4-methyl-benzoic acid (6): Found, C,
72.11, H, 6.62, N, 9.90 %; Calc. [C17H18N2O2], C, 72.33; H,
1
6.44; N, 9.92 %; %; H-NMR: 2.23 (3H, –CH3, s), 3.25
(3H, –NCH3, s), 3.30 (3H, –NCH3, s), 5.11 (1H, s),
7.30–7.90 (7H, m), 9.88 ppm (OH, s, broad), 13C-NMR:
27.0, 28.2 (NCH3), 77.1 (NCH), 125.5–134.4 (CHAr),
178.2 ppm (COOH); 4-[(4-diethylamino-phenylimino)-
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[C23H23N8], C, 67.14, H, 5.63, N, 27.23 %; 3-amino-5-(4-
dimethylamino-phenyl)-7-[(4-pyrrolidin-1-yl-benzylidene)-
amino]-5,8-dihydro-[1, 2, 4]triazolo[4,3-a]pyrimidine-6-
carbonitrile (14): Found, C, 66.10; H, 6.20, N, 27.75; Calc.
[C25H28N9], C, 66.06, H, 6.21, N, 27.73 %; 3-amino-7-[(4-
pyrrolidin-1-yl-benzylidene)-amino]-5-(4-pyrrolidin-1-yl-
phenyl)-5,8-dihydro-[1, 2, 4]triazolo[4,3-a]pyrimidine-6-
carbonitrile (15): Found, C, 67.50; H, 6.30, N, 26.25; Calc.
[C27H30N9], C, 67.48, H, 6.29, N, 26.23; 3-amino-5-(4-
morpholin-4-yl-phenyl)-7-[(4-pyrrolidin-1-yl-benzylidene)-
amino]-5,8-dihydro-[1, 2, 4]triazolo[4,3-a]pyrimidine-6-
carbonitrile (16): Found, C, 65.32, H, 6.10, N, 25.40; Calc.
[C27H30N9O], C, 65.30, H, 6.09, N, 25.38 %; 3-amino-5-
cyclohexyl-7-[(4-pyrrolidin-1-yl-benzylidene)-amino]-5,8-
dihydro-[1, 2, 4]triazolo[4,3-a]pyrimidine-6-carbonitrile
(17): Found, C, 65.66, H, 6.50, 27.85 %; Calc. [C22H26N8],
C, 65.65, H, 6.51, N, 27.84; 3-amino-5-cyclooctyl-7-[(4-
pyrrolidin-1-yl-benzylidene)-amino]-5,8-dihydro-[1, 2, 4]triaz-
olo[4,3-a]pyrimidine-6-carbonitrile (18): Found, C, 66.98, H,
7.01, N, 26.05 %; Calc. [C24H30N8], C, 66.95, H, 7.02, N, 26.03;
3-amino-7-[(4-morpholin-4-yl-benzylidene)-amino]-5-(4-mor-
pholin-4-yl-phenyl)-5,8-dihydro-[1, 2, 4]triazolo[4,3-a]pyr-
imidine-6-carbonitrile (19): Found, C, 63.30, H, 5.92, N, 24.60;
Calc. [C27H30N9O2], C, 63.27, H, 5.90, N, 24.59 %,
respectively.
most derivatives.It provided, excellent opportunities of (6),
(8) and (9) for application in the coordination chemistry as
ligands for the design of metal–organic NLO materials.
In many cases it was preferred to become a classical
scheme for 5- or 6-member chelating between the –OH and
N(=C) centres. In (3), (4), (5) and (7), was preferred
–N(CH2CH3)2 nitrogen as a proton accepting center. In the
series (13)–(19) as preferred protonated centre appeared
NH2, followed by NH group in the heterocyclic fragment.
The protonated forms of compounds (5) and (6) are char-
acterized by significant b-values, 2.5–3 times higher,
exceeding this of DAST core (Figs. 1, 2), which makes
them particularly attractive as new materials. The dyes of
similar type have been shown excellent experimental NLO
properties and applicability in THz-technologies [32–43].
Protonated N(=C) imine nitrogen in the Schiff’s bases
affected to some extent b-values. Much more significant
effect, has the protonation at Npy- or nitrogen atoms in the
aliphatic bulk substituents. The inclusion of competitive
substitutes with the stronger basic properties, such as
morpholin, pyrrolidine or diethylamine ones, changed the
basic properties in the first degree of protonation, which
was preferable according the obtained b-values. This was a
key stage in the design of these derivatives to the desired
application areas. The fact that the already established in
practice derivatives such as DAST, DAT2, or PyT1 have
substituents of types –N(CH2CH3)2 or pyrrolidine as con-
firms in addition the correctness of these conclusions about
the search of new materials, among derivatives of this class
[20, 23, 43, 105, 106]. The neutral forms of of (1) and (2)
showed the comparable b-values with this of DAST core,
moreover the (2) crystalized in the noncentrosymmetric
Pca21 space group [105]. The obtained btot values for the
isolated molecule as well as the crystals of (2) show 4 times
higher values in the crystal (Fig. 3). These data announced
to be taken into account considering the values obtained for
isolated molecules. The data for (10a)–(12a), obtained by
electronic absorption spectroscopy suggested the stabil-
ization of the quinoide forms, significantly shifted bato-
chromically the kmax more than 270 nm (Figs. 1, 3). A
hyperchromic effect was found. For (13)–(19), the obtained
b-values of the protonated forms were comparable with the
DAST ones. Comparing theoretical and experimental data
for the kmax, difference 3–9 nm was observed. The new
dyes showed intense absorption CT bands in the visible
region, within 380–440 nm. The calculated properties in
excited state (ES) show that the HOMO–LUMO gaps were
mostly located on the electron-rich functionals, with a
limited contributions to rest molecular fragments.
Regarding the obtained diffuse reflectance (Ds) and fluo-
rescence spectra (Fs) in solid-state, announced to note that
CT bands was shifted and splitted, similar to the ES
(Fig. 3) [107, 108]. The performed vibrational analysis
Results and discussion
Theoretical dipole moments (ltot), static polarizabilities
(aij) and first hyperpolarizability (btot) were shown in
Fig. 1. The protonated forms were elucidated, using theo-
retical data for NBO analysis. According the qN(NBO) val-
ues obtained, conclusions about the protonation ability
were presented. The corresponding forms were labeled on
Scheme 2. Theoretical data were obtained using two con-
sidered the most successful theoretical approaches, i.e.
CAM-B3PW91 and M06-2X functionals, showing good
correlation between predicted and experimental observed
physical properties [71–81]. The performed regression
analysis resulted to 99.4–97.9 % level of confidence
between the data of aij, obtained at both methods. As seen
from the data, the correlation, refers to Dirac d(X) and
Sinc(X) the aij data in various forms. The theoretical data
predicted the greatest sensitivity of btot, axx and Am1 in the
process of protonation. Interestingly were the obtained for
the preferred protonated centers in various derivatives in
accordance to the NBO analysis. In compounds (1), (2),
(6), (8) and (9) preferred protonation position was found
imine N(=C) nitrogen. Moreover, the spectral data for
compounds (6), (8) and (9) showed zwitterion structure
[99–101]. The protonation resulted to recovery of the
COOH group. Such a structure was generally valid for
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J Incl Phenom Macrocycl Chem (2013) 75:211–221
215
Fig. 1 Regression and correlation dependences of the theoretically obtained optical and NLO properties of the studied compounds
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J Incl Phenom Macrocycl Chem (2013) 75:211–221
Scheme 2 Chemical diagrams of the studied bases; theoretical qN(NBO) charges, protonation positions i (i = 1–5) optimized molecular
geometries, crystal structure of (2) as well as photograph of corresponding crystals
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J Incl Phenom Macrocycl Chem (2013) 75:211–221
217
Fig. 2 Mathematically non- and procedured (baseline corrected) absorption (A), diffuse reflectance (D) and fluorescence (F) spectra in condense
phases. Photographs of the crystals. Theoretical electronic absorption spectra and b values of isolated molecule and the crystal of (2), respectively
showed that common to all Schiff’s bases was the disap-
pearance in the IR- and Raman spectra of the mC=O
stretching vibration of the starting aldehyde group and the
observation of the series of vibrational bands at
associated with the bulk substituents in the aromatic sys-
tems. The effect of the –OH and –N substituents is eval-
uated in a range of 0.5–2.1 ppm, respectively. The shifting
of the values up to 2.0 ppm are mainly related to the proton
signals of the generated N?H groups in salts. Interest are
also data obtained from the high resolution mass spectra for
the structures of the studied dyes (Fig. 3). As for waiting
for all the compounds are characterized by peaks of the
cations of the bases. For compounds with morpholine
fragment however the chromatographic data show number
of peaks corresponding to the derivatives with the cleavage
morpholine cycle. It is interesting that the derivatives with
pyrrol-fragment or compounds of type (17) and (18) are not
observed similar processes related to cyclic fragments.
Therefore, the data would be connected with the influence
of O– in the morpholine during the ionization processes.
1,664 cm-1
. The corresponding mN=C vibration was
observed about 1,625 cm-1. Significant changes were
observed in vibrations associated with different types of
substitution in benzene nuclei. The observed results were
connected with the fact that the overall geometry of the
molecules remains at a significant degree. For all com-
pounds, the observed planar geometry of the aromatic
skeleton with a deviation in the range within 2–7°,
respectively. In the protonated forms, significantly has
influenced the molecular geometry in the bulky substitu-
ents to benzene nuclei areas, because of conjugation of the
electron-pair of nitrogen with the aromatic system was
impaired. This significantly effected the regions of
stretching and bending vibrations related to the N?H-group
about within 3,100–2,800 and 1,645 cm-1, respectively
[13–17]. The nuclear magnetic resonance characteristics,
also vary within narrow limits in these compounds, such
significant differences are observed only at derivatives
Conclusions
Unlike the general accepted view of applicability of
the Schiff’s bases as ligands in the design of new metal–
123

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J Incl Phenom Macrocycl Chem (2013) 75:211–221
Fig. 3 Chromatographic, electronic absorption and high resolution mass spectrometric data. Photograph of the thin 2D film
organic NLO materials, in this work has been provided
new derivatives, characterising with marked optical and
nonlinear optical properties, thus assuming their potential
usage as novel organic materials, themselves. Certainly,
the molecular architecture of some of the compounds
displayed suggesting chelating-effect, made them also
suitable as ligands in coordination chemistry. Much more
significant, have been received properties for the deriva-
tives with more than one proton accepting center, practi-
cally giving greater opportunities for further modeling
design of organic salts, depending on the ratio of Schiff’s
base: acid, functionality of the acids [102–104] as well as
its properties, i.e. tuning the hydrogen bonding and Cou-
lomb interactions in the crystals. It could be noted that:
(a) the classic conception for the protonation ability of the
Schiff’s bases, i.e. imine N(=C) nitrogen was confirmed
only in the case of derivatives with a substituents –NH2,
–OH, and/or –OCH3; (b) for derivatives containing
heterocyclic fragments with –NH2 or cyclic NH groups
or substituents such as –N(CH2CH3)2, morpholine or
pyrrolidine types, has been found as most preferred for
protonation. These data highlighted the novelty of the
presented study towards the further molecular design of
organic salts and corresponding metal–organic complexes
with tunable NLO properties, and underlined the impact of
the theoretical analysis of the protonation ability; (c) the
optical properties both in ground and excited state show
the CT band within 380–400 nm, shifted about 5–10 nm
in solid-state and spitted in the diffuse reflectance and
fluorescence spectra; (d) the obtained btot values of the
protonated forms were 2.5–7.0 times higher than those of
neutral ones. All novel derivative were characterized with
btot 4.0–5.5 times higher than the of DAST value, using as
standard; (e) for compound (4-diethylamine-benzylidene)-
pyridin-4-yl-amine, crystallizing in the non centrosym-
metric space group Pca21, the obtained btot values of the
crystal are 4 times higher than the corresponding one of
isolated molecule.
Acknowledgments The authors thank the DAAD (Deutscher
Dienst),
Akademischer Austausch
Forschungsgemeinschaft).
and
DFG
(Deutsche
123

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