Derivatives of Δ2-pyrazoline-products of 1,5-diaminotetrazole interaction with chalcone: Molecular structure and spectral properties

Article abstract of DOI:10.1016/j.molstruc.2005.10.004

1,5-diaminotetrazole at conditions of its interaction with chalcones (1,3-diphenylpropenones) in hot DMF undergoes Dimroth rearrangement to 5-tetrazolylhydrazine, which results in formation of 1-(5-tetrazolyl)-3,5- diaryl-Δ²-pyrazolines (I). St

Full text of DOI:10.1016/j.molstruc.2005.10.004

Journal of Molecular Structure 785 (2006) 114–122
www.elsevier.com/locate/molstruc
Derivatives of D2-pyrazoline-products of 1,5-diaminotetrazole interaction
with chalcone: Molecular structure and spectral properties
a
a
a,
b
N.N. Kolos a, B.V.Paponov a, ,V.D. Orlov ,M.I. Lvovskaya ,A.O. Doroshenko ,O.V. Shishkin
*
*
a Kharkov V.N.Karazin National University, 4 Svobody square, 61077 Kharkov, Ukraine
b Ukrainian Academy of Science Institute for Single Crystals, 60 Lenin avenue, 61001 Kharkov, Ukraine
Received 10 August 2005; received in revised form 30 September 2005; accepted 3 October 2005
Available online 14 November 2005
Abstract
1,5-diaminotetrazole at conditions of its interaction with chalcones (1,3-diphenylpropenones) in hot DMF undergoes Dimroth rearrangement to
5-tetrazolylhydrazine, which results in formation of 1-(5-tetrazolyl)-3,5-diaryl-D2-pyrazolines (I). Structure of the obtained products was
confirmed by their parallel synthesis and X-ray structural analysis. Unusual fluorescence behavior of the tetrazolopyrazolynes in polar solvents
was attributed to the dissociation of their highly acidic tetrazole N–H group. The last hypothesis was confirmed at the investigation of the
protolytic interactions of I with tertiary amine.
q 2005 Elsevier B.V. All rights reserved.
Keywords: 1,5-diaminotetrazole; Dimroth rearrangement; D2-Pyrazolines; X-ray structural analysis; High stokes shift fluorescence; Excited state photodissociation
1. Introduction
molecular structure of tetrazolo[1,5-b] triazepines was
proposed earlier to the products of the discussed reaction [5],
however such a conclusion was not supported later by the data
for chalcone reactions with several N-amino group containing
vicinal diaminoimidazoles and diaminotriazoles [6–9]. Gener-
ally, 1,3,5-triaryl derivatives of D2-pyrazoline belong to a class
of highly effective organic luminophores with the intensive
blue–green emission in the solid state and in the liquid
solutions [10], while as we did not expected pronounced
fluorescence ability of tetrazolo[1,5-b]triazepines. Taking into
account the fact, that structural and spectral features of triaryl-
D2-pyrazolines with the electronodeficite heterocyclic moieties
in position 1 were not described properly, in this paper we
decided to focus our attention on the synthesized 1-(5-
tetrazolyl)-3,5-diaryl-D2-pyrazolines (I) [4].
Condensation of nitrogen-containing binucleophilic agents
with a,b-unsaturated ketones is one of the most suitable
synthetic pathways to five-, six- and seven-membered partially
hydrogenated heterocyclic compounds-potential pharmaceuti-
cally active analogs of natural compounds. High regio-
selectivity of the discussed reaction owing to the pronounced
difference in electrophilic parameters of carbonyl and b-carbon
reaction centers is the most important advantage of this
reaction, which allows to synthesize several hardly accessible
compounds, over the widely known analogous reactions of
b-diketones. Our interest to 1,5-diaminotetrazole as binucleo-
philic agent in the above mentioned condensation was
stipulated by its possible tetrazolo-azido tautomerism and its
structural transformation owing to the Dimroth rearrangement
[1–3].
2. Experimental
In our preliminary publication [4], we reported formation of
fluorescent products in reaction of 1,5-diaminotetrazole with
chalcones and made a hypothesis about the possible presence
of D2-pyrazoline ring in their molecules. The alternative
The investigated 1-(5-tetrazolyl)-3,5-diaryl-D2-pyrazolines
Ia–i were synthesized by two general schemes: at heating of
equimolar amounts of 1,5-diaminotetrazole (II) with chalcones
(1,3-diarylpropenones, IIIa–d) in DMF at 150 8C [1,5] or by
the classical method for obtaining pyrazolines-at interaction of
corresponding chalcones with 5-tetrazolohydrazine (Scheme 2,
Table 1).
*
Corresponding authors. Tel.: C380 577075335; fax: C380 577075130.
E-mail addresses: andrey.o.doroshenko@univer.kharkov.ua (A.O. Dor-
oshenko), boris.v.paponov@univer.kharkov.ua (B.V. Paponov).
1,5-Diaminotetrazole (II) was synthesized at interaction of
semicarbazide with NaN3 and access amounts of NH4Cl and
yellow modification of PbO in DMF [11]. Thermal
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.10.004

N.N. Kolos et al. / Journal of Molecular Structure 785 (2006) 114–122
115
Table 1
Experimental physico-chemical parameters of the synthesized tertazolopyrazolines Ia–i
Compound
R1
R2
Molecular
Element analysis (found/calc., %)
M.P. 8Ca
Yield %
composition
C
H
N
Ia
Ib
Ic
Id
Ie
If
H
H
C16H14N6
66.19
66.04
67.06
66.94
63.74
63.93
51.87
52.05
51.89
52.05
51.14
50.91
42.88
42.69
59.17
58.95
64.66
64.41
4.78
4.86
5.19
5.30
5.07
5.03
3.46
3.55
3.40
3.55
3.67
3.79
2.78
2.70
4.14
4.03
5.29
5.43
29.01
28.95
27.51
27.61
26.19
26.23
22.58
22.76
22.53
22.76
20.87
21.05
18.49
18.75
25.62
25.88
25.04
25.13
228–229b
211–213e
201–202
236–237
223–224
203–204
232–234
224–225
193–195
60c
39d
61c
H
CH3
OCH3
Br
C17H16N6
H
C17H16N6O
C16H13N6Br
C16H13N6Br
C17H15N6BrO
69c
H
51c
43d
41d
Br
Br
Br
Cl
OCH3
H
OCH3
Br
62d
36d
49d
56d
Ig
Ih
Ii
C
C
16H13N6Br2
16H13N6Cl
H
CH3
C18H18N6O
a
Uncorrected melting points.
b
c
d
e
M.P.Z227 [5].
This compound was synthesized at interaction of 1,5-diaminotetrazole with the corresponding 1,3-diarylpropenone-1.
This compound was synthesized at interaction of 5-tetrazolylhydrazine with the corresponding 1,3-diarylpropenone-1.
M.P.Z211 [5].
isomerization diaminotetrazole4tetrazolohydrazine takes
place at such conditions, this is the classical example of the
Dimroth rearrangement [2].
Compound Ic1—C17H16N6O, MrZ320.35; aZ8.450(3);
˚
bZ14.706(4); cZ13.804(4) A; bZ101.70(2)8; VZ
3
˚
1679.7(9) A ; monoclinic crystals; space group P21/c; ZZ4;
dcalcZ1.338 g/cm3; TZ293 K; F(000)Z712. Elementary cell
parameters and intensities of 4888 independent reflections
(RintZ0.028) were collected on Siemens-P3/PC automatic
diffractometer (m(Mo Ka)Z0.093 mmK1, graphite monochro-
mator, q/2q-scanning, 2qmaxZ608).
5-Tetrazolohydrazine (IV) was obtained at the reaction of
5-aminotetrazole with aqueous NaNO2 in diluted acetic acid,
followed by the reduction of the formed 1,3-di(5-tetrazolyl)-
triazene by SnCl2 dihydrate in concentrated hydrochloric acid
[12]. Then 5-tetrazolohdrazine water solution (contents of IV
was detected by the quantitative precipitation of its benzalhy-
drazone from the small aliquot) was introduced into reaction
with chalcones.
The structure was solved by direct method with the use of
SHELX97 software [13]. Hydrogen atoms positions were
calculated geometrically and were refined within the ‘riding’
model with the fixed isotropic thermal corrections UisoZnUeq,
determined by the neighboring non-hydrogen atom (nZ1.5 for
Interaction of 5-tetrazolylhydrazine with chalcones, general
procedure: aqueous solution of IV (35 mmol) was added to
chalcone (35 mmol) solution in 50 ml of ethanol. Reaction
mixture was heated during 6.5 h, evaporated down to 2/3 of the
initial volume and the residue was poured into the 100 ml of ice
water. Precipitated solid was filtered, dried and recrystallized
from benzene.
methyl group hydrogens and nZ1.2 for all the other ones).
2
)
Structure refinement on (Fhkl
with the full-matrix least
squares method in the anisotropic approximation for non-
hydrogen atoms were performed to wR2Z0.147 (R1Z0.060)
by 2230 reflections with FO2s(F), SZ0.93.
All the synthesized compounds were purified by the
recrystallization from benzene (TLC control with the benze-
ne/diethyl ether 3/2 as eluent).
1 CCDC 181907 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing data_request@ccdc.cam.ac.uk, or by contact-
ing The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, UK; Fax: C44 1223 336033.
Crystals of Ic suitable to X-ray structural analysis were
obtained by the diffusion of diethyl ether vapor into the
saturated benzene solution of Ic.

116
N.N. Kolos et al. / Journal of Molecular Structure 785 (2006) 114–122
Infrared spectra were measured on the Specord 75 IR
spectrometer in the KBr pellets. NMR 1H spectra in DMSO D6
were taken on Varian 200 Mercury VX device.
To determine the reaction pathway and to identify the
structure of the formed products we have made an attempt to
realize the alternative synthetic scheme and to obtain the
required products by direct interaction of 5-tetrazolohydrazine
IV with 1,3-diarylpropenones IIIa,d–i (Scheme 2). The
synthesized compounds were identical to the earlier products
Ia,d–i by all their physico-chemical and spectral parameters.
Thus, formation of 5,7-diaryl-5,6-dihydro-4H-tetrazolo[1,5-b]-
1,2,4-triazepins and results, reported in [5], should be
disclaimed, owing to the irreversibility of transformation of
1,5-diamino-tetrazole into 5-tetrazolo-hydrazine in soft
reactions conditions.
Electronic absorption spectra were recorded on the
HITACHI U3210 spectrophotometer. Fluorescence spectra
and quantum yields were measured on the HITACHI F4010
spectrofluorimeter with quinine sulphate in 0.5 M H2SO4 as the
quantum yield reference standard (ffZ0.546 [14]).
The constants of protolytic equilibrium for compounds Ia,
Ic and Ih in the ground state were calculated from spectro-
photometic titration data by the nonlinear iterative least-
squares method [15] using a specially designed program based
on the Fletcher–Powell algorithm. The excited-state protolytic
equilibrium constants were evaluated by a fluorimetric titration
technique according to the procedure proposed by Melo et al.
[16]. In this case, the data treatment procedure also employed
the nonlinear least squares routine.
Formation of 6,8-diaryl-7,8-dihydro-4(H)-tetrazolo[5,1-c]
triazepines B seems to us less probable, owing to the higher
nucleophilic ability of the exo-hydrazinic group with respect to
the endocyclic tetrazolic NH group, which make five-
membered pyrazoline cycle closing more favorable compared
to the seven-membered triazepine one. Another one: com-
pounds IIIa-i demonstyrate presence of higly acidic group with
Semiempirical quantum-chemical calculations of the
electron spectra and the excited state electron density
redistribution of the studied compounds were made by
INDO/S method [17] basing on the optimized molecular
geometry obtained with semiempirical method AM1 [18].
1
NMR H signal at 15-16 ppm. This fact corresponds better to
the structure A with its tetrazolic NH proton in and not to
structure B, which azepinic NH signal are expected to manifest
itself at much higher field region.
Therefore, final arguments in favor of the formation of
pyrazolyne cycle were obtained by the X-ray structural
analysis on the example of compound Ic. Its molecular
geometry and atoms numbering scheme are shown on Fig. 1,
atom coordinates are presented in the Table 3.
3. Results and discussion
IR and NMR 1H spectra were measured for all the
synthesized compounds (Table 2). Absence of infrared
absorption near 2200 cmK1 confirms out expectations that in
the crystalline phase tetrazol moiety exist in the cyclic form
and its possible transformation into azide does not take place.
Absorption bands at 1630 cmK1 were attributed to C–Carom
and CaN bond stretching, while as the broad diffuse band at
3400 cmK1 corresponds to the H-bonded tetrazolic cycle N–H
vibrations. Signals of aromatic protons at 6.90–7.70 ppm were
˚
Pyrazoline ring of Ic is planar within 0.01 A as well as the
other cycles in this molecule. The most important part of the
main chromophoric moiety of Ic, pyrazoline cycle and phenyl
cycle in its position 3 are almost coplanar: the angle between
their least-squares planes was found near 68(G0.28). Tetrazole
cycle forms an angle of 188(G0.28) with the neighboring
pyrazoline one, however, slight pyramidalization of the
pyrazoline nitrogen atom in position 1 is the main reason of
this (see valence angles C1–N5–N6 117.70(14), C1–N5–C2
123.46(15), N6–N5–C2 114.31(14)). Aryl group in position 5 of
the pyrazoline cycle is almost orthogonal to the rest of this
molecule. As in the case of another triaryl-pyrazolines [19 and
citation wherein], this moiety is not conjugated with the main
chromophoric system of Ic and thus has no effect on its UV–vis
and fluorescence spectra.
1
present in the NMR H spectra. Typical ABX-system signals
were observed: two doublets of methylenic protons at 3.15–
3.35 and 3.80–4.12 ppm (HA, HB) and double doublet at 5.35–
5.57 ppm (HX). Broad low-field singlet deuterium-exchange-
able signals of tetrazolic proton (15.4–15.8 ppm, 1H) is present
as well. Position of the last signal demonstrates high acidity of
tetrazolic NH, comparable to that of intermediately strong
carboxylic acids.
However, the spectral data of Table 2 were not completely
sufficient for unambiguous identification of the nature of the
products formed. Particularly, if we take into account the
possibility of the ring-chain tautomerizm of 1,5-diaminote-
trazole II and participation of any of its isomeric structures in
the reaction with 1,3-diarylpropenones-1, formation of three
alternative isomeric products should be considered: 5,7-diaryl-
5,6-dihydro-4H-tetrazolo[1,5-b]-1,2,4-triazepin (C) (as it was
reported in [5]), i.e. in analogy to aromatic ortho-diamines, and
products A and B, which obtaining requires transformation of
diamine II into its azide form followed by the Dimroth
rearrangement prior the reaction with chalcone. At these
conditions two different heterocyclic systems could be formed:
seven-membered triazepine (B) and five-membered pyrazoline
(A) (Scheme 1).
Generally, 1,3,5-tryarylpyrazolines are known as effective
organic luminophores with blue–green emission in solid state
and in solutions. This fact inspires our interest to the
fluorescence properties of their newly synthesized tetrazole
analogs.
Substitution of phenyl moiety to tetrazole cycle in position 1
of 1,3,5-triphenylpyrazoline molecule leads to hypsochromic
shift in its absorption spectrum from 358 nm [10] down to 308–
314 nm (Table 4, toluene). The analogous behavior was
observed for several other substituted pyrazolines with
electron-accepting groups in one-position [20]. To our under-
standing this is the result of the electron influence of the
introduced electron-withdrawing center onto the excited state
electron density redistribution typical to this class of

Table 2
IR and NMR 1H spectral data for tetrazolo-pyrazolynes Ia–i
Co mpound
IR spectra n (cmK1
)
NMR 1H spectra d (ppm), J (Hz)
CaC CaN
NH
ABX-system, 1H dd
3.90–4.11
J (ABX)
Aromatic protons
NH 1Hs Other
Ia
Ib
Ic
Id
Ie
If
1620
3414
3427
3426
3427
3431
3428
3434
3428
3426
3.19–3.31
3.19–3.29
3.16–3.24
3.22–3.34
3.22–3.34
3.17–3.31
3.21–3.36
3.20–3.36
3.14–3.28
5.43–5.56
5.40–5.51
5.36–5.48
5.39–5.53
5.44–5.56
5.37–5.51
5.42–5.57
5.41–5.57
5.34–5.47
K17.9
7.7
7.5
7.7
7.9
7.9
7.9
7.9
7.6
7.3
11.7
11.1
11.4
11.6
11.9
11.6
11.9
11.2
11.6
7.25–7.39 5H m, 7.43–7.53 3H m, 7.78–7.86 2H d
(JZ8.7)
6.92–7.00 2H d (JZ8.6) 7.11–7.24 4H, m
7.44–7.53 3H, m
15.7
15.4
15.6
15.7
15.5
15.6
15.6
–
1620
1620
1624
1628
1624
1626
1622
1618
3.92–4.12
3.89–4.09
3.92–4.09
3.92–4.10
3.88–4.06
3.89–4.08
4.00–4.19
3.84–4.03
K17.5
K17.9
K18.0
K18.0
K18.0
K18.0
K18.0
K17.7
2.20 3H, s. CH3
6.97–7.04 2H d (JZ8.2), 7.13–7.27 4H m
7.46–7.57 3H m
3.77 3H, s.
OCH3
–
7.26–7.33 2H d (JZ8.9) 7.43–7.50 3H m
7.60–7.69 2H d (JZ8.5) 7.77–7.85 2H d (JZ8.9)
7.32–7.44 4H m 7.54–7.61 3H m 7.77–7.86 2H d
(JZ8.9)
6.99–7.09 2H d (JZ8.9) 7.25–7.34 2H d (JZ8.2)
7.49–7.58 2H d (JZ8.2) 7.70–7.79 2H d (JZ8.9)
7.26–7.33 2H d (JZ8.2) 7.49–7.57 2H d (JZ8.9)
7.65–7.78 4H m
–
3.79 3H s OCH3
Ig
Ih
Ii
–
–
7.35–7.43 2H d (JZ8.5) 7.56–7.63 3H m 7.78–7.85 15.8
2H d (JZ8.9) 8.11–8.20 2H d (JZ8.9)
6.99–7.06 2H d (JZ8.5) 7.09–7.26 4H m 7.71–7.77 15.5
2H d (JZ8.5)
2.25 3H s CH3
3.75 3H s OCH3

118
N.N. Kolos et al. / Journal of Molecular Structure 785 (2006) 114–122
Scheme 1. Alternative structures, which could by considered as products of interaction of II with chalcones.
Scheme 2. Reagents and condition: (i) DMF 150 8C; (ii) NaNO2, HOAc, 10 8C; (iii) SnCl2*2H2O, HCl, r.t.; (iv) C2H5OH, reflux.
luminescent compounds (Scheme 3). Appearance of the strong
electron acceptor in pyrazolinic position 1 prevents removal of
electron density from N-1 atom towards the benzene ring in
position 3 giving rise to changes in optical parameters of the
compounds on study. The analogous, however, less distinct
hypsochromic effect should be observed at introduction of
electron donor groups into phenyl-3.
The lowest singlet excited state electron density redistribu-
tion is shown on the above scheme in comparison to the ground
state for the molecule of 1,3,5-triphenylpyrazoline according to
our INDO/S calculations (thick arrow). Electron accepting
(EA) substituent in phenyl-1 and electron donor (ED) ones in
phenyl-3 prevent this charge transfer making it less effective
and resulting in hypsochromic shifts in the absorption spectra
(their influence onto electron density moving is shown by thin
arrows).
High fluorescence quantum yields (0.6–0.8) are typical to
tetrazolo-pyrazolines in toluene (Table 4). Definite deviations
are observed to compounds with electron donor groups in
phenyl-3. Such behavior could be attributed to the electronic
effect of substituents pushing electron density in direction
Fig. 1. X-ray molecular structure, scheme of atom numbering and thermal
vibrations ellipsoids (at 50% probability) for compound Ic.

N.N. Kolos et al. / Journal of Molecular Structure 785 (2006) 114–122
119
Table 3
2
Atom coordinates (A) and equivalent isotropic displacement parameters (A )
opposite to the main excited state charge redistribution in these
molecules. Fluorescence Stokes shifts in toluene are slightly
˚
˚
for compound Ic
larger than expected ‘normal’ values of 3000–5000 cmK1
.
Atom
X
y
Z
Ueq
However, the observed enlarged DnST in the range of
6000 cmK1 could be explained by the possible excited state
planarization [21–23] of the main chromophoric unit, which
includes tetrazole, pyrazoline and benzene cycles. In particu-
larly, pyramidalized pyrazolinic nitrogen atom in position 1
could change its conformation to more flattened one.
N1
1.02559(18)
1.1251(2)
1.1484(2)
1.0660(2)
0.8967(2)
0.85566(19)
0.43990(17)
0.9932(2)
0.8854(2)
0.8218(3)
0.8108(2)
0.7547(2)
0.7601(2)
0.7054(3)
0.6439(3)
0.6378(3)
0.6936(2)
0.7744(2)
0.6310(2)
0.5237(3)
0.5575(2)
0.6996(2)
0.8073(2)
0.4679(3)
0.9899
0.14148(10)
0.18162(12)
0.26357(12)
0.27997(10)
0.18719(10)
0.09787(10)
0.53693(11)
0.20225(11)
0.24997(13)
0.18387(13)
0.09429(12)
0.00928(12)
K0.07160(13)
K0.15144(14)
K0.15150(15)
K0.07245(15)
0.00831(14)
0.32870(12)
0.31687(14)
0.38726(15)
0.47192(13)
0.48593(13)
0.41390(13)
0.62565(15)
0.0866
0.73191(11)
0.67876(12)
0.71132(13)
0.78522(12)
0.86207(12)
0.87801(12)
0.83150(12)
0.79655(14)
0.94427(14)
1.01485(15)
0.96173(14)
0.99860(13)
0.94761(15)
0.98166(17)
1.06696(17)
1.11806(16)
1.08514(14)
0.91042(13)
0.84160(15)
0.81698(16)
0.86003(15)
0.92710(16)
0.95179(15)
0.8733(2)
0.7250
0.0386(4)
0.0472(4)
0.0494(4)
0.0439(4)
0.0442(4)
0.0390(4)
0.0581(4)
0.0363(4)
0.0417(5)
0.0463(5)
0.0364(4)
0.0362(4)
0.0429(5)
0.0496(5)
0.0520(5)
0.0527(6)
0.0460(5)
0.0373(4)
0.0466(5)
0.0516(5)
0.0430(5)
0.0451(5)
0.0423(5)
0.0618(6)
0.046
N2
N3
N4
N5
N6
O1
Interesting changes in spectral properties were detected in
polar, and, especially, in proton-donating solvents. Having five
potentially nucleophilic nitrogen atoms and one rather acidic
N–H group in their molecules, tetrazolo-pyrazolynes are able
to form multiple hydrogen bonds with solvent molecules.
And indeed, in methanol practically all the compounds on
study demonstrate hypsochromic shifts in their absorption
spectra (Table 4). These changes could be explained by the
formation of H-bonds with tetrazolic nitrogens, which make
the heterocycle more electron accepting, lowering the main
intramolecular excited state charge transfer to the phenyl-3 and
thus, shifts the absorption of tetrazolo-pyrazlines further to the
short wavelengths. Another hydrogen bonding with the
participation of pyrazolinic N-2 atom should be considered
as well, because the spectral effect of such interaction might be
the same.
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
H1N
H2
0.9931
0.2722
0.9753
0.050
In contrast to the absorption spectra, significant red shift was
observed for the emission bands of tetrazolo-pyrazolines in
methanol. This results in the increase of the Stokes shifts up to
8500–9000 cmK1. At the same time, fluorescence intensity
decreases significantly: quantum yields in this solvent did not
exceed 0.1. Moreover, in aprotonic polar acetonitrile we
observed two-banded emission spectra with positions of short-
wavelength bands close to that in toluene, while as the long-
wavelength ones were located in the spectral region typical to
that of methanol solutions. Fig. 2 demonstrates that fluor-
escence spectrum of Ia in acetonitrile (A) could be presented as
practically the superposition of the emission bands in toluene
(T) and in methanol (M): (A–M)wT.
H3A
H3B
H6
0.8961
0.1803
1.0783
0.056
0.7167
0.2029
1.0254
0.056
0.8011
K0.0720
K0.2053
0.8899
0.052
H7
0.7099
0.9471
0.060
H8
0.6065
K0.2054
K0.0728
0.0617
1.0897
0.062
H9
0.5960
1.1754
0.063
H10
H12
H13
H15
H16
H17A
H17B
H17C
0.6901
1.1207
0.055
0.6075
0.2604
0.8118
0.056
0.4279
0.3780
0.7712
0.062
0.7236
0.5429
0.9556
0.054
0.9035
0.4234
0.9971
0.051
0.5650
0.6502
0.8579
0.093
0.4790
0.6220
0.9438
0.093
0.3783
0.6644
0.8464
0.093
Table 4
UV/vis spectral and fluorescent properties of tetrazolo-pyrazolynes Ia–i
Com-pound
Solvent
la, nm (na cmK1
)
3a
lf, nm (nf cmK1
)
DnST, cmK1
ff
Ia
Toluene
methanol
Methanol
Toluene
methanol
Toluene
methanol
Methanol
Toluene
methanol
Methanol
Toluene
methanol
Toluene
methanol
314 (31840)
309 (32360)
309 (32360)
315 (31760)
312 (32050)
314 (31840)
312 (32050)
308 (32470)
315 (31780)
313 (31950)
314 (31840)
314 (31880)
314 (31840)
316 (31660)
312 (32050)
–
388 (25800)
425 (23520)
422 (23700)
390 (25660)
423 (23640)
387 (25860)
431 (23200)
433 (23090)
391 (25560)
435 (22990)
435 (22990)
387 (25840)
429 (23310)
391 (25560)
425 (23530)
6040
8840
8660
6100
8410
5980
8850
9380
6220
8960
8850
6040
8530
6100
8520
0.82
0.07
0.08
0.56
0.08
0.69
0.08
0.06
0.60
0.06
0.08
0.71
0.07
0.79
0.08
18200
18500
–
Ib
Ic
18800
–
Id
18000
18300
–
Ie
If
18800
18200
–
Ig
Ih
18900
–
Ii
18000

120
N.N. Kolos et al. / Journal of Molecular Structure 785 (2006) 114–122
3410–3430 cmK1 and NMR 1H signal positions at 15.5–
15.7 ppm are in line with the above statement. Acidic
properties of tetrazolic cycle in the studied molecules were
checked also at our experiments on titration of tetrazolo-
pyrazolines in acetonitrile by strong organic base-triethylamine
(Fig. 3). As an example we have checked protolytic interaction
of three compounds belonging to the studied series: unsub-
stituted molecule (Ia, pK 4.02G0.03), its Cl–(Ih, pK 4.37G
0.02) and -OCH3 (Ic, pK 3.52G0.04) derivatives.
Scheme 3. The main excited state electron density redistribution in the
molecule of 1,3,5-triarylpyrazolyne and its deterioration by the substituents in
side phenyl moieties.
Thus, we had to check the hypothesis, that the anomalous
fluorescence behavior of tetrazolo-pyrazolines in polar
solvents may be determined with the excited state N–H
photodissociation. The latter could be of two types: inter-
molecular, when proton is transferred to the neighboring
solvent molecule, and intramolecular, when proton moves to
This abnormal spectral behavior needs justification, and first
we made series of quantum-chemical calculations in our
attempt to understand the reasons for the observed abnormal
spectral properties of tetrazolo-pyrazolines in polar solvents.
Tetrazolic N–H group demonstrate rather high proton
mobility in the studied compounds: its IR frequencies at
Fig. 2. Fluorescence spectra of compound Ia in toluene (T), acetonitrile (A) and methanol (M). Difference of the spectra in acetonitrile and methanol (A–M) is close
in shape and in position to the spectrum in toluene.
Fig. 3. Spectrophotometric titration by triethylamine (0, 4.10K6–0.02 Mol/dm3) of the tetrazolo-pyrazoline Ia in acetonitrile.

N.N. Kolos et al. / Journal of Molecular Structure 785 (2006) 114–122
121
Fig. 4. Fluorimetric titration by triethylamine (0, 4.10K6–0.02 Mol/dm3) of the tetrazolo-pyrazoline Ia in acetonitrile.
the closest basic center of the same molecule-nitrogen atom in
position 2 of pyrazoline cycle.
parallel synthesis and X-ray structural analysis (on the example
of Ic). Unusual fluorescence behavior of the tetrazolopyrazo-
lines in polar solvents was attributed to the dissociation of their
highly acidic tetrazole N–H group. The last hypothesis was
confirmed at the investigation of the protolytic interactions of I
with tertiary amine.
Our X-ray structural experiments reported the distance
between the above mentioned acidic (N1–H) and basic (N6)
˚
centers, rH–Nw2.6 A. Thus, we have to consider the
intramolecular H-bond in the studied molecules should not
be strong. According to our INDO/S calculations, in S1 -state
N–H group should increase its acidity (DqNZ0.01 e), while as
pyrazolinic N-2 atom should become more basic (DqNZ
0.06 e), however the above mentioned changes are not very
high. If the intramolecular proton phototransfer would be
realized at the electronic excitation, the energy of the lowest
singlet excited state should decrease down to w1000 nm
(AM1CINDO/S modeling data), which could not be observed
on our spectrometers. Moreover, such a low energy gap
between the ground and the excited states get rise the effective
internal conversion [24,25], which concur with fluorescence
emission and makes the latter nearly impossible.
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