Optical poling effect and optical absorption of cyan, ethylcarboxyl and tert-buthyl derivatives of 1H-pyrazolo[3,4-b]quinoline: Experiment and quantum-chemical simulations

Article abstract of DOI:10.1016/j.saa.2004.07.025

We present here results of experimental studies and quantum-chemical simulations of optical absorption and optical poling effects performed on a new synthesized cyan, ethylcarboxyl and tert -buthyl derivatives of 1H-pyrazolo[3,4-b]quinoline incorporated into polymer matrix or dissolved in organic solutions. The efficiency of second-order optical susceptibility d vs photoinduced power density Ip clearly saturates to certain magnitude deff at sufficient power densities (Ip≥ 1.3 GW cm^-2). Comparing experimental data and results of semiempirical quantum-chemical simulations one can conclude that there exists generally a good correlation between the magnitude of saturated susceptibilities deff and macroscopic hyperpolarizabilities for all compounds except the chromophore 1,3-dimethyl-6-cyano-[PQ] only. The discrepancy for this compound may reflect a specific contribution of surrounding polymer matrix. According to the quantum chemical analysis the methyl-containing cyan and ethylocarcoxyl derivatives reveal four/five strong absorption bands in the spectral range 200-500 nm. A substitution of the methyl groups by the phenyl group causes the substantial changes of the absorption spectra mainly in the spectral range 240-370 nm. Measured and calculated absorption spectra manifest rather good agreement mainly in the part regarding the spectral positions of the first oscillator (absorption threshold). The quantum-chemical PM3 method shows the best agreement with experiment. At the same time a considerable broadening almost of all absorption bands appears as a characteristic feature of all measured spectra. The discrepancies between the calculated and the measured spectra are attributed to electron-vibronic coupling as well as to a specific rotational dynamics of phenyl rings.

Full text of DOI:10.1016/j.saa.2004.07.025

Spectrochimica Acta Part A 61 (2005) 1933–1938
Optical poling effect and optical absorption of cyan, ethylcarboxyl and
tert-buthyl derivatives of 1H-pyrazolo[3,4-b]quinoline: experiment and
quantum–chemical simulations
a
b
b
c
d
e
a,∗
´
´
E. Koscien , J. Sanetra , E. Gondek , B. Jarosz , I.V. Kityk , J. Ebothe , A.V. Kityk
a
Institute for Computer Science, Technical University of Czestochowa, Armii Krajowej 17, 42-200 Czestochowa, Poland
b
Institute of Physics, Technical University of Krakow, Podhorazych 1, 30-084 Krakow, Poland
Department of Chemistry, Hugon Kołłotaj Agricultural University, Al. Mickiewicza 24/28, 30-059 Krakow, Poland
c
d
Institute of Biology and Biophysics, Technical University of Czestochowa, PL-42200 Czestochowa, Poland
c
Universite de Reims, UTAP-LMET, EA No 2061, UFR Sciences, Boite Postale 138, 21 Rue Clement Ader, Reims, France
Received 2 July 2004; accepted 28 July 2004
Abstract
We present here results of experimental studies and quantum–chemical simulations of optical absorption and optical poling effects performed
on a new synthesized cyan, ethylcarboxyl and tert-buthyl derivatives of 1H-pyrazolo[3,4-b]quinoline incorporated into polymer matrix or
dissolved in organic solutions. The efficiency of second-order optical susceptibility d vs photoinduced power density Ip clearly saturates to
certain magnitude deff at sufficient power densities (Ip ≥ 1.3 GW cm−2). Comparing experimental data and results of semiempirical quantum–
chemical simulations one can conclude that there exists generally a good correlation between the magnitude of saturated susceptibilities
deff and macroscopic hyperpolarizabilities for all compounds except the chromophore 1,3-dimethyl-6-cyano-[PQ] only. The discrepancy for
this compound may reflect a specific contribution of surrounding polymer matrix. According to the quantum chemical analysis the methyl-
containing cyan and ethylocarcoxyl derivatives reveal four/five strong absorption bands in the spectral range 200–500 nm. A substitution of the
methyl groups by the phenyl group causes the substantial changes of the absorption spectra mainly in the spectral range 240–370 nm. Measured
and calculated absorption spectra manifest rather good agreement mainly in the part regarding the spectral positions of the first oscillator
(absorption threshold). The quantum–chemical PM3 method shows the best agreement with experiment. At the same time a considerable
broadening almost of all absorption bands appears as a characteristic feature of all measured spectra. The discrepancies between the calculated
and the measured spectra are attributed to electron–vibronic coupling as well as to a specific rotational dynamics of phenyl rings.
© 2004 Elsevier B.V. All rights reserved.
PACS: 33.20.Lg; 33.20.Kf; 33.70.-w; 42.70.Ky
Keywords: Organic materials; Visible and ultraviolet spectra; Optical poling; Optical second harmonic generation (SHG)
1. Introduction
by the formation of a spatially periodic electrostatic field.
Due to the loss of the center of symmetry there appear
the properties of a non-centrosymmetric uniaxial medium
with a photoinduced optical axes determined by the light
polarization of the pumping beam. As a result, the optically
induced second harmonic generation (SHG) and parametric
amplification become possible in such perturbed medium.
Optical poling is thereby a relatively new and quite effec-
tive technique providing an important information about
second-order optical properties of disordered materials.
Long illumination of an isotropic medium, such as glasses
or polymers, by two mutually coherent sources with different
frequencies (ω and 2ω) results in the accumulation of the
reversible long-lived static polarization inside the medium
[1–3]. The magnitude of the polarization is determined
∗
Corresponding author. Tel.: +48 34 3250 838; fax: +48 34 3250 823.
E-mail address: kityk@ap.univie.ac.at (A.V. Kityk).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.07.025

1934
E. Kos´cien´ / Spectrochimica Acta Part A 61 (2005) 1933–1938
The main purpose of the present work is the experimental
studies of the optical absorption and optical poling effects of
new synthesized cyan, ethylcarboxyl and tert-buthyl deriva-
tives of 1H-pyrazolo[3,4-b]quinoline (hereafter referred
as [PQ]) incorporated into polymer matrix or dissolved
in organic solutions. The paper deals with the follow-
ing organic semiconductors: 1,3-dimethyl-6-COOEt-1H-
pyrazolo[3,4-b]quinoline (1,3-dimethyl-6-COOEt-[PQ]),
Scheme 1. Synthesis of the 1-H-pyrazolo[3,4-b]quinoline ([PQ]-) deriva-
tives. Conditions: at the temperature of 140–190 ◦C within 30–60 min. The
radicals R1, R2 and R3 are mentioned in the Table 1.
1,3-dimethyl-6-cyano-1H-pyrazolo[3,4-b]quinoline
dimethyl-6-cyano-[PQ]), 1-phenyl-3-methyl-6-COOEt-1H-
pyrazolo[3,4-b]quinoline (1-phenyl-3-methyl-6-COOEt-
(1,3-
gel 60 (230–400 mesh) using toluene/ethyl acetate (3:1) as
eluent. All the [PQ]-derivatives 3 were prepared accord-
ing to procedures described in Ref. [9–12] by condensa-
tion of substituted aromatic amines 2 with 5-chloro-1,3-
dimethyl- and 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-
carbaldehydes 1 (see Scheme 1 and Table 1). As the result,
the following compounds were synthesized for further op-
tical studies: 1,3-dimethyl-6-COOEt-[PQ], 1,3-dimethyl-6-
cyano-[PQ], 1-phenyl-3-methyl-6-COOEt-[PQ], 1-phenyl-
3-methyl-6-cyano-[PQ] and 1-phenyl-3-methyl-6-t-buthyl-
[PQ]. The purity of these compounds was checked by TLC
(Merck). The optical absorption spectra were recorded in
tetrahydrofuran solution (mass concentration of about 0.1%)
using Shimadzu UV–vis 2101 scanning spectrophotometer in
range 200–500 nm. The measurements were performed us-
ing standard 1 cm path length quartz cuvette for absorption
spectrometry.
The measurements of the optical second-order suscepti-
bility have been performed in standard optical poling exper-
iments. The experimental setup is shown in Fig. 1). As a
fundamental laser source we have used Gd:YAG-laser gen-
erating at λ = 1.7 ␮m with pulse power P=21 MW and pulse
duration about 30 ps. The laser beam is consequently split
into two coherent beams by the beamsplitter BS. The sec-
ond beam is converted by ␤-BBO crystal to a doubled-
frequency signal (λ = 0.88 ␮m). Using two-channel scheme,
[PQ]), 1-phenyl-3-methyl-6-cyano-1H-pyrazolo[3,4-b]qui-
noline (1-phenyl-3-methyl-6-cyano-[PQ]), 1-phenyl-3-
methyl-6-t-buthyl-1H-pyrazolo[3,4-b]quinoline (1-phenyl-
3-methyl-6-t-buthyl-[PQ]). The optical absorption and
optical poling can be considered as the most appropriate
methods to study the basic electronic properties of these
materials. The absorption spectra in UV and visible regions
give an important information about interacting conjugated
␲-electrons which obviously are also the basis of the relevant
luminescent and electroluminescent properties of the organic
materials. It is amazing that [PQ]-derivatives are known as a
class of highly fluorescent materials in the blue spectral range
[4] as well as promising materials for electroluminescent
applications [5,6]. Since the origin of these effects are related
much with molecular electron structure, the experimental
results are supplied by quantum–chemical calculations.
The quantum PM3 and AM1 method have been found as
the most appropriate for simulations of the experimental
data.
The optical properties of the [PQ]-derivative materials sig-
nificantly depend on the pattern of substitution as well as on
the type of substituents, as documented in several our re-
cent publications [7,8]. In particular, a substitution of the
methyl groups by at least one phenyl group causes the drastic
changes of the absorption spectra mainly in the spectral range
240–370 nm. These differences are attributed to additional
molecular double bounded conjugated segments C=C of the
substituted phenyl groups i.e. to ␲→␲∗ transitions. The mea-
sured spectra demonstrate usually a considerable broadening
almost of all absorption bands. The experiments performed
with highly and weakly polar organic solvents [8] show that
the solvatochromic effect on the absorption spectra is indeed
small. For this reason the discrepancies between the calcu-
lated and the measured spectra have been attributed mainly to
electron–vibronic coupling as well as to rotational dynamics
of phenyl rings.
Table 1
Supplement to the Scheme 1: Chemical radicals R1, R2 and R3
Compound
R1
R2
R3
1,3-Dimethyl-6-COOEt-[PQ]
1,3-Dimethyl-6-cyano-[PQ]
1-Phenyl-3-methyl-6-COOEt-[PQ]
1-Phenyl-3-methyl-6-cyano-[PQ]
1-Phenyl-3-methyl-6-t-buthyl-[PQ]
Me
Me
Ph
Ph
Ph
Me
Me
Me
Me
Me
6-COOC2H5
6-CN
6-COOC2H5
6-CN
6-C3H9
[PQ], 1H-pyrazolo[3,4-b]quinoline.
2. Synthesis and experimental
Depending on lateral substituants, several chemical com-
pounds mentioned below were used for the synthesis of
a particular [PQ]-derivative. All reagents were used as re-
ceived from Aldrich or Fluka without further purification.
Column chromatography was performed on Merck silica
Fig. 1. The setup in optical poling experiment. BS is the beamsplitter; P1,
P2 and P3 are the polarizers; S is the sample; F is the filter; PM is the
photomultiplier; BC is the electronic boxcar.

E. Kos´cien´ / Spectrochimica Acta Part A 61 (2005) 1933–1938
1935
we achieved the interaction of two coherent waves. We have
found that coherence length is equal to about 28–36 ␮m.
The observed output signal is detected by photomultiplier
PM. Evaluation of the effective second-order susceptibility
was done using a simple procedure described in the [13].
The investigated organic compounds were incorporated into
the PMMA polymer matrices with weight concentration of
about 5.5%.
The molecular nonlinear hyperpolarizabilities βijk have
been calculated using the model with so-called multilevel
excitation [14]:
ꢁ
ꢀ
1
8ꢀ2
βijk
=
(µgjnꢀ Mni ꢀnµkng + µgknꢀ Mni ꢀnµnjg)
nꢀ,n,nꢀ=n=g
ꢂ
ꢃ
1
1
×
+
ꢀ
ꢀ
(ωn g − ω)(ωng + ω) (ωn g + ω)(ωng − ω)
+ (µgi nꢀ Mnjꢀnµkng + µignꢀ Mnkꢀnµjng)
3. Calculation procedure
ꢂ
ꢃ
1
1
×
+
The calculation of optical absorption spectra, static dipole
moments and molecular second-order optical constants have
been performed using the molecular dynamics quantum–
chemical package Hyperchem 7.5. The geometrical opti-
mization has been carried out by (MM+) force field method.
Together with semi-empirical AM1 and PM3 methods this
model is known to be as the most general and frequently used
for molecular mechanics calculations developed principally
for organic molecules. The calculations of optical absorp-
tion spectra and nonlinear susceptibility were consequently
performed within several semi-empirical quantum–chemical
models available in this software. However, the results will be
presented for AM1 and parameterized PM3 methods, only.
These methods indeed give the best agreement withthe exper-
iment. The optical spectra were calculated considering only
the singly excited configuration interactions (CI); the excita-
tion energies has been limited in both methods by the orbital
criterion, i.e. to 12 occupied and 12 unoccupied orbitals.
The intensity of spectral optical absorption I(ω) is deter-
mined by the following expression (for details see e.g. [7,8]):
ꢀ
ꢀ
(ωn g +2ω)(ωng +ω) (ωn g − 2ω)(ωng − ω)
+ (µgjnꢀ Mnkꢀnµing + µkgnꢀ Mnjꢀnµing)
ꢂ
ꢃꢄ
1
1
×
+
ꢀ
ꢀ
(ωn g −ω)(ωng +2ω) (ωn g +ω)(ωng −2ω)
(3)
where index gn(gnꢀ) means the transitions from the ground
state g to excited state n(nꢀ), ωn g and ωng are the correspond-
ꢀ
(x,y,z)
(x,y,z)
gnꢀ
ing transition frequencies; M
= (M
− Mg(xn,y,z)),
nꢀn
(x,y,z)
(x,y,z)
M
and M
are the excited state dipole compo-
nꢀn
nꢀn
nents. Since the molecules in the polymer matrix are ran-
domly oriented, the calculated second-order susceptibili-
ties will be presented by its average (effective) magnitude
ꢅ
βav
=
(βx2xx + βy2yy + βz2zz)/3.
4. Experimental results and discussion
n
| < Ψ∗|iꢀ∇r|Ψk > |
2
ꢀ ꢀ
We start immediately with the analysis of optical absorp-
tion data. Measured spectra of 1,3-dimethyl-6-COOEt-[PQ],
1,3-dimethyl-6-cyano-[PQ], 1-phenyl-3-methyl-6-COOEt-
[PQ], 1-phenyl-3-methyl-6-cyano-[PQ] and 1-phenyl-3-
methyl-6-t-buthyl-[PQ] are presented in Figs. 2(a)–6(a),
respectively, whereas the calculated absorption spectra
(Γ = 0.12 eV) are shown in Figs. 2(b)–6(b). First two
compounds of this list contain only methyl groups and
their measured and calculated spectra are rather similar.
The calculated spectra are characterized mainly by five
or six relatively strong absorption bands. In particular
one obtains for 1,3-dimethyl-6-COOEt-[PQ]: 394.5(370),
361(356), 292.5(282), 251(257), 239.5(233.5), 224(221) nm
and for 1,3-dimethyl-6-cyano-[PQ]: 399(374.5), 365(358.5),
295(284.5), (258)251, 243(237.5), 226.5(222.5) nm as calcu-
lated by quantum–chemical PM3(AM1) methods. The corre-
sponding experimental spectra (see Figs. 2(a) and 3(a)) have
an absorption threshold at about 396 and 401 nm, respec-
tively, which appears to be in fairly good agreement with
quantum–chemical simulations, namely for absorption spec-
tra calculated by PM3 method. The spectral positions of the
strongest broad absorption band at about 268 and 252 nm (as
for 1,3-dimethyl-6-COOEt-[PQ] and 1,3-dimethyl-6-cyano-
i
ji
I(ω) ≈ ω
(1)
ꢀ2(ω − ωjk)2 + (Γ/2)2
i=x,y,z
k=1
where Ψj and Ψk∗ are wave functions of j-th and k-th energy
levels and iꢀ∇r is a transition dipole momentum operator
of molecule, ꢀωjk = (Ej − Ek) is the energy difference be-
tween the ground and excited state, ω is the frequency of
incident electromagnetic wave. Taking into account that the
integration is performed over the space volume the intensity
of spectral absorption then reads:
|(µ)ijk|
n
2
ꢀ ꢀ
I(ω) ≈ ω
,
(2)
(ω − ωjk)2 + (Γ/2ꢀ)2
i=x,y,z
k=1
where (µ)ijk = | < Ψ∗|∇r|Ψk > | are the transition dipole
i
ji
moments. It is necessary to emphasize that the resonance
frequencies ωjk and transition dipole momentum (µ)ijk have
been obtained directly within PM3 and AM1 procedures, as
described above. The empirical parameter Γ was chosen at
magnitude of 0.12 eV, what gives the best agreement in line-
shape of calculated optical absorption spectra compared to
experimental data.

1936
E. Kos´cien´ / Spectrochimica Acta Part A 61 (2005) 1933–1938
[PQ], respectively)inthemeasuredspectrawellcoincidewith
the calculated spectra; PM3 method gives here again a bit bet-
ter agreement. In addition, this absorption band of measured
spectra is clearly asymmetric what let us to conclude that it
appears as results of superposition of several overlapping un-
resolved broad spectral bands. Note, that quantum chemical
calculations indeed shows in the same spectral region three
relatively strong absorption bands for each compound.
Other three compounds, which represent the group of
phenyl containing [PQ]-derivatives (see Figs. 4–6), show
substantially different calculated spectra. The quantum–
chemical simulations reveal here series of additional rela-
tively strong absorption bands (from five up to seven ones)
in the spectral range of 240–370 nm. Such feature is com-
mon for all [PQ]-derivatives containing phenyl groups as has
been already shown (see e.g. [7,8]). An appropriate inter-
pretation obviously refers to additional molecular doubled
bonding segments C=C of the substituted phenyl groups. The
absorption bands may be attributed in this case to π → π∗
electronic transition from the bonding to anti-bonding molec-
ular configuration. Total spectra of these organic compounds
contain 8–11 relatively intense bands as one can realize
from Figs. 4(b)–6(b). The measured absorption thresholds
for all phenyl containing [PQ]-derivatives (λg ≈ 399 nm) dif-
fer here slightly from those calculated by AM1(PM3) meth-
ods which give 406.5(373), 410(379) and 405(377.5) nm as
calculated for 1-phenyl-3-methyl-6-COOEt-[PQ], 1-phenyl-
Fig. 2. (a) Measured absorption spectra of 1,3-dimethyl-6-COOEt-[PQ] and
(b) calculated spectra within the semi-empirical quantum–chemical PM3
and AM1 models. Insert shows the chemical structure of 1,3-dimethyl-6-
COOEt-[PQ] obtained within the geometrical optimization procedure.
Fig. 4. (a) Measured absorption spectra of 1-phenyl-3-methyl-6-COOEt-
[PQ]and(b)calculatedspectrawithinthesemi-empiricalquantum–chemical
PM3 and AM1 models. Insert shows the chemical structure of 1-phenyl-3-
methyl-6-COOEt-[PQ] obtained within the geometrical optimization proce-
dure.
Fig. 3. (a) Measured absorption spectra of 1,3-dimethyl-6-cyano-[PQ] and
(b) calculated spectra within the semi-empirical quantum–chemical PM3
and AM1 models. Insert shows the chemical structure of 1,3-dimethyl-6-
cyano-[PQ] obtained within the geometrical optimization procedure.

E. Kos´cien´ / Spectrochimica Acta Part A 61 (2005) 1933–1938
1937
3-methyl-6-cyano-[PQ] and 1-phenyl-3-methyl-6-t-buthyl-
[PQ], respectively. In addition, the experimental spectra in
UV region is characterized by only two/three broad absorp-
tion bands. The most strongest bands appear at about 276–
280 nm, i.e. are clearly shifted for all compounds to the red
region with respect to the position of the series of most in-
tense absorption bands obtained by the quantum–chemical
simulations.
The reasons for the discrepancies observed between the
measured and calculated spectra of the [PQ]-derivatives have
been attributed initially [7] to the solvatochromic effect [15].
Later on, the experiment with strongly and weakly polar sol-
vents (see [8]) have indicated indeed rather small its influ-
ence on the absorption spectra. All the solutions clearly have
shown only a weak blue shift of λg as the solvent polarity
increased. A substantial broadening of spectral bands as well
as their spectral shifts are, therefore, rather a result of two
other eventual mechanisms which are not considered in our
quantum–chemical calculations. The first one is the electron–
vibronic coupling. Indeed, the lowest energy absorption band
reveals features very similar to vibronic replica [see e.g. Figs.
2(a) and 3(a)]. The second mechanism is actual for the [PQ]-
derivatives containing methyl, phenyl or t-buthyl groups. One
should be emphasized that our quantum–chemical calcula-
tions have been performed for isolated molecules in vacuum.
The optimization procedure gives here a planar molecular
configuration for all the [PQ]-derivatives. This is likely not
quite correct for solutions where the methyl, phenyl or t-
buthyl groups are presumably to rotate dynamically affecting
the symmetry selection rules for different electronic transi-
tions.
Fig. 5. (a) Measured absorption spectra of 1-phenyl-3-methyl-6-cyano-[PQ]
and(b)calculatedspectrawithinthesemi-empiricalquantum–chemicalPM3
and AM1 models. Insert shows the chemical structure of 1-phenyl-3-methyl-
6-cyano-[PQ] obtained within the geometrical optimization procedure.
The experimental efficiency of second-order optical sus-
ceptibility d versus photoinduced power density Ip for is
shown for each chromophore in the Fig. 7. One can see that
the efficiency d clearly saturates to certain magnitude deff
Fig. 6. (a) Measured absorption spectra of 1-phenyl-3-methyl-6-t-buthyl-
[PQ]and(b)calculatedspectrawithinthesemi-empiricalquantum–chemical
PM3 and AM1 models. Insert shows the chemical structure of 1-phenyl-3-
methyl-6-t-buthyl-[PQ] obtained within the geometrical optimization pro-
cedure.
Fig. 7. Efficiency of second-order optical susceptibility d vs photoin-
duced power density. Comp.1: 1,3-dimethyl-6-COOEt-[PQ]; Comp.2:
1,3-dimethyl-6-cyano-[PQ]; Comp.3: 1-phenyl-3-methyl-6-COOEt-[PQ];
Comp.4: 1-phenyl-3-methyl-6-cyano-[PQ]; Comp.5: 1-phenyl-3-methyl-6-
t-buthyl-[PQ].

1938
E. Kos´cien´ / Spectrochimica Acta Part A 61 (2005) 1933–1938
Table 2
Saturated second-order optical susceptibility deff , calculated dipole moment |p| and calculated effective (averaged) molecular optical nonlinear constant βav
Compound
deff [pm V−1] (exp.)
|p| [D] (AM1)
|p| [D] (PM3)
βav [au] (AM1)
βav [au] (PM3)
Mg [D] (AM1)
Mg [D] (PM3)
Comp.1
Comp.2
Comp.3
Comp.4
Comp.5
0.62
3.49
2.59
1.98
1.14
0.652
2.610
3.072
2.14
1.13
56.4
53.1
400.0
330.7
295.8
211.9
343.3
681.5
455.3
452.9
3.26
4.875
6.776
4.920
7.358
1.635
2.751
2.463
2.319
2.511
4.761
3.507
5.133
0.673
2.961
Comp.1: 1,3-dimethyl-6-COOEt-[PQ]; Comp.2: 1,3-dimethyl-6-cyano-[PQ]; Comp.3: 1-phenyl-3-methyl-6-COOEt-[PQ]; Comp.4: 1-phenyl-3-methyl-6-
cyano-[PQ]; Comp.5: 1-phenyl-3-methyl-6-t-buthyl-[PQ].
at sufficient power densities (Ip ≥ 1.3 GW/cm2). Table 2
lar double bonding segments C=C of the substituted phenyl
groups, thereby the electronic ␲→␲∗ transitions appear to be
lists the saturated second-order optical susceptibility deff
involved into the absorption process. The comparison of mea-
sured and calculated absorption spectra manifests rather good
agreement, namely in the part regarding the spectral positions
of the first oscillator (absorption threshold). At the same time,
the measured spectra reveal the considerable broadening al-
most of all absorption bands and even complete damping
some of them in the case of phenyl derivatives. The discrep-
ancies between the calculated and the measured spectra are
attributed to electron–vibronic coupling as well as to specific
rotational dynamics of phenyl rings.
(as obtained from the data presented in the Fig. 7) as well
as the dipole moments |p|, effective (averaged) molecu-
lar optical nonlinear constant βav and excited state dipole
ꢅ
(y)2
(x)2
g1
(z)2
g1
moments Mg =
M
+ Mg1 + M
corresponding to
the first active oscillator (as calculated within semiempir-
ical AM1 i PM3 methods). From the data presented one
can clearly see that there exists a good correlation between
the magnitude of saturated susceptibilities deff and macro-
scopic hyperpolarizabilities for all compounds except the
chromophore 1,3-dimethyl-6-cyano-[PQ] (Comp.2). It may
reflect a specyfic contribution of surrounding polymer ma-
trix for the two methyl-cyano compounds. A substitution a
methyl group by the aromatic group probably scatter the cor-
responding charge transfer thus reducing deff. In this case
the maximally achieved deff for Comp.2 likely indicates on
polarizable effects of guest molecules.
Acknoledgements
This work was supported by KBN grant no. 3-T11-B-
074-26.
5. Conclusion
References
In conclusion, we present here results of experimental
studies and quantum chemical simulations of optical poling
effect and optical absorption performed on a new synthe-
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pyrazolo[3,4-b]quinoline incorporated into polymer matrix
or dissolved in organic solutions. The efficiency of second-
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power densities (Ip ≥ 1.3 GW cm−2). Comparing experi-
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simulations one can conclude that there exists generally a
good correlation between the magnitude of saturated suscep-
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compounds except the chromophore 1,3-dimethyl-6-cyano-
[PQ] only. The discrepancy for this compound may reflect a
specific contribution of surrounding polymer matrix.
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absorption spectra of methyl-containing derivatives which
are characterized by four or five strong absorption bands in
the spectral range 200–500 nm. A substitution of the methyl
groups by the phenyl group causes the substantial changes
of the absorption spectra mainly in the spectral range 240–
370 nm. We attribute these differences to additional molecu-
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