Full text of DOI:10.1134/S1070363218040369

ISSN 1070-3632, Russian Journal of General Chemistry, 2018, Vol. 88, No. 4, pp. 846–848. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © I.E. Mikhailov, L.D. Popov, G.A. Dushenko, Yu.V. Revinskii, V.I. Minkin, 2018, published in Zhurnal Obshchei Khimii, 2018,
Vol. 88, No. 4, pp. 700–702.
LETTERS
TO THE EDITOR
Spectral Luminescent Properties
of 3-[5-(4-Methoxyphenyl)-1,3,4-oxadiazol-2-yl]acrylic Acid
and Its Complex with Zn(II)
I. E. Mikhailova,b*, L. D. Popovc, G. A. Dushenkoa,
Yu. V. Revinskiib, and V. I. Minkina
a Research Institute of Physical and Organic Chemistry, Southern Federal University,
pr. Stachki 194/2, Rostov-on-Don, 344090 Russia
*e-mail: mikhail@ipoc.sfedu.ru
b Federal Research Center, Southern Science Center, Russian Academy of Sciences, Rostov-on-Don, Russia
c Southern Federal University, Rostov-on-Don, Russia
Received December 14, 2017
Abstract—Zinc complex of (E)-3-[5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-yl]acrylic acid has been prepared;
1
its structure and composition have been elucidated by means of IR and Н as well as 13С NMR spectroscopy.
Spectral luminescent properties of the ligand and the complex have been studied. Both compounds exhibit blue-
fl
max
violet luminescence (λ 402‒467 nm, φ 0.06–0.82) with low self-absorbance of the emitted light.
Keywords: 3-(5-aryl-1,3,4-oxadiazol-2-yl)acrylic acids, metal complexes, luminescence, quantum yield
DOI: 10.1134/S1070363218040369
1,3,4-Oxadiazoles and their derivatives exhibit
strong and diverse biological activity [1] as well as
spectral luminescent properties enabling the prepara-
tion of fluorescent and phosphorescent luminophors
[2–5], organic semiconductors, and other materials for
modern optoelectronics [6] on their basis. Chelate
complexes with oxadiazol ligands are widely used as
metal complex luminophors [7, 8] as well as emission
and electron-transport materials for organic and light
emitting diodes (OLED) [9].
plex has been prepared [13]. Therefore, we prepared
(E)-3-[5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-yl]-
acrylic acid 1 (L) [12], refluxing of methanolic
solution of which with 0.5 eq. of zinc acetate dihydrate
in the presence of KOH gave the corresponding metal
complex L2Zn 2 (Scheme 1).
Composition and structure of the zinc complex 2
were elucidated using the data of elemental analysis,
1
and IR as well as Н and 13С NMR spectroscopy. The
complex formation resulted in the disappearance of the
bands of the О–Н group (2617 and 2524 cm–1) [12] of
the ligand 1 due to the substitution of the proton with
Starting from oxadiazolylpropionic [10] and oxadi-
azolylacrylic [10–12] acids, only a single metal com-
Scheme 1.
H
O
O
O
O
O
O
O
NHNH
NHNH2
AcOH
MeO
MeO
N N
O
N N
O
(1) KOH
(2) Zn(OCOCH3)2 2H2O
POCl3
DMF
O
OH
_
Zn2+/2
MeO
MeO
O
O
1
2
846

SPECTRAL LUMINESCENT PROPERTIES
847
the metal ion, and the band of the С=O group
(1715 cm–1) was shifted to longer wavelength
(1612 cm–1) due to the formation of the chelate structure.
acylation of hydrazide of o-methoxybenzoic acid with
maleic anhydride, followed by cyclization of the
formed aroylhydrazinyloxobutenoic acid under the
action of POCl3 in DMF. Yield 56%, colorless crystals,
mp 238–240°С (toluene) (mp 237–239°C [12]). Data
The signal of the OH group (observed in the spec-
trum of the ligand 1 at 13.18 ppm [12]) in the 1Н NMR
spectrum of complex 2 (DMSO-d6) disappeared, the
signals of the olefinic protons were shifted upfield (the
weaker-field signal was shifted by 0.26 ppm, and the
stronger-field signal was shifted by 0.19 ppm),
allowing their assignment to the proton in position 2 of
the acrylate fragment, located closer to the coordina-
tion site. The constants of the spin-spin interaction of
the protons at the double bond –СН=СН– in the ligand
1 and its complex 2 (3J = 16.2 and 17.0 Hz) evidenced
the E-configuration of the compounds. As far as the
13С NMR spectra are concerned, the complex forma-
tion resulted in the downfield shift of the signals of the
С=О group (by 3.07 ppm) and the С2 atom of the
unsaturated fragment (by 6.35 ppm), whereas the
signal of the С3 atom was shifted upfield by 3.83 ppm.
1
of IR and H NMR spectroscopy coincided with the
reference data [12]. Electronic spectrum, λmax, nm
[ε×10–4 L mol–1 cm–1, λex 300 nm]: toluene, 316 [2.01],
fl
fl
λmax (φ) 402 (0.45); dioxane, 311 [2.83], λmax (φ) 408
(0.67); acetonitrile, 266 [2.94], 284 [2.79], 292 [2.84],
fl
fl
312 [2.87], λmax (φ) 463 (0.81); DMSO, 304 [2.78], λmax
(φ) 467 (0.12). 13C NMR spectrum (DMSO-d6), δC,
ppm: 56.00 (OCH3), 115.34 (2CAr3,5), 115.55 (Cipso,1),
124.63 (=С3), 129.33 (=С2), 129.35 (2CAr2,6), 162.21
(Cipso,4), 162.91 (CHet), 164.86 (CHet), 166.40 (С=O).
Zinc(II) bis{(E)-3-[5-(4-methoxyphenyl)-1,3,4-oxa-
diazol-2-yl]acrylate} (2). A mixture of 0.002 mol of
compound 1 and 0.002 mol of KOH in 20 mL of
methanol was refluxed during 15 min, then 0.001 mol
of Zn(OCOCH3)2·2H2O in 10 mL of methanol was
added, and the mixture was refluxed during 5 h. The
precipitate formed after cooling down to ambient was
filtered off, washed with hot methanol (2×15 mL), and
dried in air. Yield 75%, colorless crystals, mp > 300°С.
IR spectrum, ν, cm–1: 3407 (Н2О), 1651 (С=С), 1614
(СOO‒), 1574 (С=СAr), 1510, 1505 (С=N), 1277,
1196, 1126 (С–О–С), 972 [δ(trans-CH=CH)], 822
The electronic absorption spectra of compounds 1
and 2 contained the long-wave bands (assigned to the
π→π* transitions in the conjugated 1,3,4-oxadiazol
and aryl fragments) with maximum at 301–318 nm.
Whereas the effect of the polarity of the solvent in the
position of the absorption bands in the electronic
absorption spectra of compounds 1 and 2 was not
revealed, their luminescence spectra were affected by
the medium polarity. Compounds 1 and 2 exhibited
strong luminescence in the short-wave part of the
visible spectral range (λmflax 402–467 nm, φ 0.06–0.82),
showing the bathochromic shift by 30–65 nm and
1
[δ(С–HAr)]. Н NMR spectrum (DMSO-d6), δ, ppm:
3.38 s (4H, 2H2O), 3.82 s (3H, OCH3), 6.97 d (1Н,
=CH3, J 17.0 Hz), 7.09 d (2НAr3,5, J 8.3 Hz), 7.18 d
(1Н, =CH2, 3J 17.0 Hz), 7.96 d (2НAr2,6, 3J 8.3 Hz). 13C
NMR spectrum (DMSO-d6), δC, ppm: 55.97 (OCH3),
115.30 (2CAr3,5), 115.81 (Cipso,1), 120.80 (=С3), 129.12
(2CAr2,6), 135.68 (=С2), 162.70 (Cipso,4), 163.01 (CHet),
164.36 (CHet), 169.47 (С=O). Electronic spectrum,
3
3
significant decrease in the quantum yield of lumine-
fl
scence in strongly polar solvent (DMSO) (1, λ
max
fl
467 nm, φ 0.12; 2, λ
434 nm, φ 0.06). In polar
max
λ
max, nm [ε×10–4 L mol–1 cm–1, λex 300 nm]: dioxane,
313 [2.77], λmax (φ) 408 (0.82); acetonitrile, 276 [2.89],
318 [2.92], λmax (φ) 438 (0.16); DMSO, 301 [3.34],
λmax (φ) 444 (0.06). Found, %: C 48.39; H 3.82; N
solvents, the acid 1 emitted longer-wave light with
fl
fl
higher quantum yield (acetonitrile, λ
463 nm,
max
fl
fl
φ 0.81) as compared to the zinc complex 2 (λ
4
max
fl
38 nm, φ 0.16). Since the luminescence bands of
compounds 1 and 2 exhibited strong Stokes shift in
nonpolar solvents (6770–7644 cm–1) and anomalously
strong Stokes shift in polar solvents (8616–11487 cm–1),
their self-absorption of the emitted light was low.
9.53. C24H18N4O8Zn·2H2O. Calculated, %: C 48.71; H
3.75; N 9.47.
IR spectra were recorded in Vaseline oil using a Varian
1
Excalibur 3100 FT-IR spectrometer. Н (250.13 MHz)
and 13С (62.90 MHz) NMR spectra were recorded
using a Bruker DPX-250 instrument. Absorption and
fluorescence spectra were recorded using a Cary Scan
100 spectrophotometer and a Cary Eclipse spectro-
fluorimeter, respectively. Quantum yield of fluore-
scence was determined with respect to a solution of
anthracene in acetonitrile as the reference [14].
The described features showed that (E)-3-[5-(4-meth-
oxyphenyl)-1,3,4-oxadiazol-2-yl]acrylic acid 1 and its
zinc complex 2 belonged to the group of demanded
luminophors with low self-absorbance of the emitted light.
(E)-3-[5-(4-Methoxyphenyl)-1,3,4-oxadiazol-2-yl]-
acrylic acid (1) was prepared as described in [12], via
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 88 No. 4 2018

848
MIKHAILOV et al.
Chem., 2014, vol. 20, no. 4, p. 1198. doi 10.1016/
ACKNOWLEDGMENTS
j.jiec.2013.09.036
7. Beldovskaya, A.D., Dushenko, G.A., Vikrishchuk, N.I.,
Popov, L.D., Revinskii, Yu.V., Mikhailov, I.E., and
Minkin, V.I., Russ. J. Gen. Chem., 2014, vol. 84, no. 1,
p. 171. doi 10.1134/S1070363214010290
This study was financially supported by the Russian
Foundation for Basic Research (project no. 16-03-
00095a).
8. Mikhailov, I.E., Vikrishchuk, N.I., Popov, L.D.,
Dushenko, G.A., Beldovskaya, A.D., Revinskii, Yu.V.,
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no. 5, p. 1054. doi 10.1134/S1070363216050121
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