2-Aryl-5-amino-1,2,3-triazoles: New effective blue-emitting fluorophores

Article abstract of DOI:10.1016/j.dyepig.2016.08.015

The synthesis of a new series of 2-aryl-5-amino-1,2,3-triazole derivatives is reported. The photochemical properties of these new fluorophores were studied both experimentally and using theoretical models. The compounds were found to be fluorescent, with

Full text of DOI:10.1016/j.dyepig.2016.08.015

Accepted Manuscript
2-Aryl-5-amino-1,2,3-triazoles: New effective blue-emitting fluorophores
Kseniya D. Gavlik, Ekaterina S. Sukhorukova, Yuri M. Shafran, Pavel A. Slepukhin,
Enrico Benassi, Nataliya P. Belskaya
PII:
S0143-7208(16)30398-9
10.1016/j.dyepig.2016.08.015
DYPI 5395
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 16 May 2016
Revised Date: 2 August 2016
Accepted Date: 5 August 2016
Please cite this article as: Gavlik KD, Sukhorukova ES, Shafran YM, Slepukhin PA, Benassi E, Belskaya
NP, 2-Aryl-5-amino-1,2,3-triazoles: New effective blue-emitting fluorophores, Dyes and Pigments (2016),
doi: 10.1016/j.dyepig.2016.08.015.
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Leave this area blank for abstract info.
2-Aryl-5-amino-1,2,3-triazoles: New
Effective Blue-Emitting Ffluorophores
Kseniya D. Gavlik, Ekaterina S. Sukhorukova, Yuri M. Shafran, Pavel A. Slepukhin, Enrico Benassi, Nataliya
P. Belskaya
Ural Federal University, 19 Mira Str., Yekaterinburg 620002, Russia
I. Ya. Postovsky Institute of Organic Synthesis, 20 S. Kovalevskaya Str., Yekaterinburg 620219, Russia
Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
Highlights
•
•
•
•
One-pot synthesis of a series of new 2-aryl-5-amino-1,2,3-triazole derivatives;
Experimental and computational approaches to optical properties correlate well;
High photoluminescence quantum yield (99.6%) was achieved;
Fluorescent properties can be tuned varying the substituents in 1,2,3-triazoles.
1

ACCEPTED MANUSCRIPT
2-Aryl-5-amino-1,2,3-triazoles: New Effective Blue-Emitting Fluorophores
Kseniya D. Gavlik a, Ekaterina S. Sukhorukova a, Yuri M. Shafran a, Pavel A. Slepukhin a,b, Enrico Benassi c, *,
Nataliya P. Belskaya a, *
aUral Federal University, 19 Mira Str., Yekaterinburg 620002, Russia
bI. Ya. Postovsky Institute of Organic Synthesis, S. Kovalevskaya 20, Yekaterinburg 620219, Russia
cScuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
ABSTRACT
The synthesis of a new series of 2-aryl-5-amino-1,2,3-triazole derivatives is reported. The
photochemical properties of these new fluorophores were studied both experimentally and using
theoretical models. The compounds were found to be fluorescent, with Stokes shifts ranging from 40
nm (2494 см-1) to 140 nm (9461 cm-1) and quantum yield values between 0.004 and 0.996. The
fluorescence of the 1,2,3-triazoles was highly structure dependent and could be tuned by variation of
the substituents at the C-4 and C-5 atoms of triazole ring and by the electronic and spatial effect of
substituents within the aromatic cycle. Photophysical studies showed moderate changes in the
fluorescence quantum yields depending on the solvent polarity. The UV-Vis spectra calculations
employing the time-dependent density functional theory (TD-DFT) are in good agreement with the
experimental data. The favourable photophysical properties of the studied compounds and their facile
and high-yielding synthesis make them excellent candidates for commercial application as fluorescent
tags.
Keywords:
2-Aryl-5-amino-1,2,3-triazole
Fluorescence
Stokes shift
Quantum yield
Solvatochromism
1. Introduction
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The design of new fluorescence molecular systems should incorporate synthetic simplicity,
structural variability and excellent photophysical properties. Widespread availability, synthetic
flexibility and the capacity to easily adjust the conjugation system or molecular electronic structure
could facilitate the rapid expansion and straightforward tuning of these fluorophores to promote unique
optical and physical properties and develop them for practical applications [1,2]. 1,2,3-triazoles are
attractive small molecular weight fluorophores because their heterocyclic core is a popular building-
block in medicine, biochemistry and materials chemistry applications [3-7]. Notably, 1,2,3-triazoles
have been disclosed as suitable linkers or spacers in biological systems because they are stable to
metabolic degradation and are capable of hydrogen bonding or covalent attachment to biomolecule
targets [8]. It has been established that the 1,2,3-triazole ring not only functions as a linker between
two or more molecular fragments, but it also contributes to the overall physical and chemical
properties of the entire molecule.
It is well known that 1-aryl-1,2,3-triazoles are easily accessible via copper(I)-catalyzed
cycloaddition between acetylene and azide (CuAAC) [9]. However, the synthesis of isomeric 2-aryl-
1,2,3-triazoles is not as simple and often requires laborious synthetic method development or
separation from the 1-aryl-1,2,3-triazole isomers [10]. While both N(1)-aryl-1,2,3-triazoles and N(2)-
aryl-1,2,3-triazoles absorb under excitation at 330 nm, only the N(2)-analogues exhibit strong
fluorescence emission in the UV/blue range with high efficiency in various solvents [11-18]. Although
many fluorophores have been developed in recent years, effective UV/blue light-emitting small
molecules are rare due to the relatively large energy gap between the interacting orbitals. Meanwhile,
the thriving research areas of OLED display and Forster resonance energy transfer studies have
increased the demand for effective UV/blue light-emitting molecules [16].
Previously, we reported a one-pot synthesis of 2-aryl-1,2,3-triazoles 1 by a sequence of
nucleophilic additions of amines to easily available arylhydrazones bearing nitrile functionality,
followed by oxidative cyclization of the formed arylhydrazonoacetamidines [19]. The wide availability
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of starting compounds, safe synthetic procedures, large yield and simple purification give this method
distinct advantages over other systems [19,20]. Additionally, the method is very versatile, as various
functional groups (e.g., cyano, benzoyl, alkoxycarbonyl and primary, secondary or tertiary amino) and
substituents can be introduced in the triazole and aromatic rings, in contrast to other reported
procedures [10].
Herein, we report the design and synthesis of new 2-aryl-5-amino-1,2,3-triazoles and the study of
their photophysical properties by experimental and theoretical methods. The study also revealed the
structural factors and solvent effects that contribute to the observed fluorescent properties.
2. Experimental
2.1. General information and materials
1
All reactants were obtained from Acros Organics and used without further purification. Н NMR
and 13C NMR spectra were recorded with a Bruker Avance II (Karlsruhe, Germany) (400 MHz for 1H,
13
100 MHz for C) spectrometer. Chemical shifts are reported in parts per million (ppm) relative to
TMS in 1H NMR and to the residual solvent signals in 13C NMR spectra. Coupling constants (J) values
are given in Hertz (Hz). Signal splitting patterns are described as a singlet (s), doublet (d), triplet (t),
quartet (q), sextet (sext), quintet (quin), multiplet (m), broad (br), doublet of doublets (dd), doublet of
triplets (dt) or AA'XX' - spin system of para-substituted benzene with two different substituents. The
13C NMR signal patterns for several compounds were analyzed by APT (attached proton test) and are
described as follows: + for secondary or quaternary carbon atom (positive signal), - for primary or
tertiary carbon atom (negative signal). Mass spectra were recorded with a Shimadzu GCMS-QP 2010
“Ultra” (Kyoto, Japan) mass spectrometer using the electron impact (EI) ionization technique (40-200
°C, 70 eV). The abbreviation [M]+ refers to the molecular ion. The Fourier-transform infrared (FTIR)
spectra were obtained using a Bruker Alpha (NPVO, ZnSe) spectrometer (Ettlingen, Germany).
Elemental analyses were carried out using a CHNS/O analyzer Perkin-Elmer 2400 Series II instrument
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(Shelton, CT USA). Melting points were determined on a Stuart SMP3 apparatus (Staffordshire, ST15
OSA, UK). The reactions were monitored by analytical thin-layer chromatography (TLC) on
aluminium-backed silica-gel plates (Sorbfil UV–254). Visualization of components was accomplished
by short wavelength UV-light (254 nm). Solvents were dried and distilled according to the common
procedures. All solvents were of spectroscopic grade.
The title products were purified by column chromatography on silica gel (0.035–0.070, 60 Å) and
recrystallized from ethanol.
2.2.Synthesis
2-Aryl-1,2,3-triazoles 4 were prepared by the one-port procedure reported in previous article [19].
General procedure for the synthesis of triazoles 4a-v. A solution of arylhydrazonoyl cyanide 1a-o
(1.0 mmol) and amine 2a-i (1.5 mmol) in MeCN (10 mL) was heated under reflux for 10 min. Then
Cu(AcO)2ꢀH2O (100 mg, 0.5 mmol) was added and the reaction mixture was refluxed for 2-17 h at
open air atmosphere, until TLC indicated total consumption of starting hydrazone. The solution was
cooled to room temperature and poured into a mixture of water and crushed ice. The resulting
precipitate was filtered off and crystallized from ethanol.
2.2.1. 2-(3,4-Dimethoxyphenyl)-5-(pyrrolidin-1-yl)-2H-1,2,3-triazole-4-carbonitrile (4a). Colorless
powder, yield: 260 mg (87%), mp 157-158 °С. FTIR νmax (cm-1) 2984, 2960, 2910, 2840 (CH), 2220
1
(CN). H NMR (CDCl3, 400 MHz): δ 1.93-2.15 (m, 4H, СН2), 3.51-3.70 (m, 4Н, СН2), 3.94 (s, 3H,
13
СН3O), 3.98 (s, 3H, СН3O), 6.91 and 7.54 (AA'XX', J = 8.4 Hz, 4H, CHAr). C NMR (CDCl3, 100
MHz): δ 25.5 (2CH2), 48.5 (2CH2), 56.2 (2СН3O), 96.1, 102.8, 105.5, 111.0, 111.1, 114.2 (CN), 133.0,
149.0, 149.4, 156.1. Found: C, 60.4; H, 5.6; N 23.5%; C15H17N5O2 requires C, 60.2; H 5.7; N 23.4%.
MS-EI m/z: 299 [M]+.
2.2.2. 2-(4-Methoxyphenyl)-5-(pyrrolidin-1-yl)-2H-1,2,3-triazole-4-carbonitrile (4b). Colorless
powder, yield: 247 mg (92%), mp 126-127 °С. FTIR, νmax, cm-1: 2980, 2940, 2883, 2840 (C-H), 2221
(CN). 1H NMR (DMSO-d6, 400 MHz): δ 1.94-1.99 (m, 4H, СН2), 3.47-3.52 (m, 4Н, СН2), 3.81 (s, 3H,
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OСН3), 7.11 and 7.85 (AA'XX', J = 9.3 Hz, 4H, CHAr). 13C NMR APT (DMSO-d6, 100 MHz): δ 25.5
(+) (2CH2), 48.7 (+) (2CH2), 56.0 (-) (СН3O), 105.3 (+), 114.4 (+) (CN), 115.2 (-) (2CHAr), 120.1 (-)
(2CHAr), 132.5 (+), 158.2 (+), 159.7 (+). Found: C, 62.2; H, 5.5; N 26.2%; C14H15N5O requires C,
62.4; H 5.6; N 26.0%. MS-EI m/z: 269 [M]+.
2.2.3. 2-Phenyl-5-(pyrrolidin-1-yl)-2H-1,2,3-triazole-4-carbonitrile (4c). Colorless powder, yield: 191
1
mg (80%), mp 102-103 °С. FTIR, νmax, cm-1: 2980, 2940, 2875 (C-H), 2230 (CN). H NMR (DMSO-
d6, 400 MHz): δ 1.83-2.02 (m, 4H, СН2), 3.37-3.53 (m, 4H, СН2), 7.44 (t, J = 7.8 Hz, 1Н, CHAr), 7.55
13
(t, J = 7.8 Hz, 2Н, CHAr), 7.90 (d, J = 7.8 Hz, 2Н, CHAr). C NMR APT (DMSO-d6, 100 MHz): δ
25.4 (+) (2CH2), 48.6 (+) (2CH2), 106.1 (+), 114.2 (+) (CN), 118.8 (-) (2CHAr), 128.8 (-) (CHAr), 130.1
(-) (2CHAr), 138.7 (+), 156.0 (+). Found: C, 65.1; H, 5.6; N 29.4%; C13H13N5 requires C, 65.3; H 5.5;
N 29.3%. MS-EI m/z: 239 [M]+.
2.2.4. 2-(4-Fluorophenyl)-5-(pyrrolidin-1-yl)-2H-1,2,3-triazole-4-carbonitrile (4d). Colorless powder,
1
yield: 216 mg (84%), mp 90-91 °С. FTIR, νmax, cm-1: 2984, 2967, 2871, 2840 (C-H), 2220 (CN). H
NMR (CDCl3, 400 MHz): δ 1.95-2.15 (m, 4H, СН2), 3.61 (t, J = 6.6 Hz, 4Н, СН2), 7.16 (t, J = 8.6 Hz,
13
2Н, CHAr), 7.98 (dd, J = 4.7, 8.6 Hz, 2Н, CHAr). C NMR (CDCl3, 100 MHz): δ 25.5 (2CH2), 48.7
(2CH2), 106.3, 113.9 (CN), 116.1 (d, 2J = 23.1 Hz, 2CHAr), 120.5 (d, 3J = 8.5 Hz, 2CHAr), 135.4 (d, 4J
1
= 2.9 Hz, CAr), 156.1, 162.0 (d, J = 246.7 Hz, CAr). Found: C, 60.6; H, 4.7; N 27.3%; C13H12FN5
requires C, 60.7; H 4.7; N 27.2%. MS-EI m/z: 257 [M]+.
2.2.5. 2-(4-Chlorophenyl)-5-(pyrrolidin-1-yl)-2H-1,2,3-triazole-4-carbonitrile (4e). Colorless powder,
1
yield: 229 mg (84%), mp 81-82 °С. FTIR, νmax, cm-1: 2992, 2964, 2870 (C-H), 2221 (CN). H NMR
(CDCl3, 400 MHz): δ 2.06 (4H, t, J = 6.6 Hz, CH2), 3.61 (4H, t, J = 6.6 Hz, CH2), 7.44 and 7.94 (4H,
13
AA′XX′, J = 8.8 Hz, CHAr). C NMR APT (CDCl3, 100 MHz): δ 25.5 (+) (2CH2), 48.5 (+) (2CH2),
106.6 (+), 113.8 (+) (CN), 119.9 (-) (2CHAr), 129.4 (-) (2CHAr), 133.6 (+), 137.6 (+), 156.0 (+). Found:
C, 56.8; H, 4.6; N 25.5%; C13H12ClN5 requires C, 57.0; H 4.4; N 25.6%. MS-EI m/z: 273 [M]+.
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2.2.6. 2-(3,5-Difluorophenyl)-5-(pyrrolidin-1-yl)-2H-1,2,3-triazole-4-carbonitrile (4f). Colorless
powder, yield: 248 mg (90%), mp 124-125 °С. FTIR, νmax, cm-1: 2984, 2980, 2876, 2840 (C-H), 2221
(CN). 1H NMR (DMSO-d6, 400 MHz): δ 1.88-2.06 (m, 4H, СН2), 3.37-3.56 (m, 4H, СН2), 7.34 (t, J =
13
9.2 Hz, 1Н, CHAr), 7.50 (d, J = 6.8 Hz, 2Н, CHAr). C NMR APT (DMSO-d6, 100 MHz): δ 25.4 (+)
2
2
(2CH2), 48.6 (+) (2CH2), 102.6 (-) (d, J = 30.1 Hz, 2CHAr), 104.0 (-) (t, J = 25.8 Hz, CHAr), 107.8
(+), 113.5 (+) (CN), 140.4 (+) (t, 3J = 13.1 Hz, CAr), 156.0 (+), 163.2 (+) (dd, 1J = 231.4, 3J = 14.5 Hz,
2CAr). Found: C, 57.0; H, 4.2; N 25.2%; C13H11F2N5 requires C, 56.7; H 4.0; N 25.4%. MS-EI m/z:
275 [M]+.
2.2.7.
5-(Pyrrolidin-1-yl)-2-(3-(trifluoromethyl)phenyl)-2H-1,2,3-triazole-4-carbonitrile
(4g).
Colorless powder, yield: 240 mg (78%), mp 115-116 °С. FTIR, νmax, cm-1: 2980, 2964, 2888, 2870 (C-
1
H), 2228 (CN). H NMR (DMSO-d6, 400 MHz): δ 1.86-2.15 (m, 4H, СН2), 3.40-3.74 (m, 4H, СН2),
13
7.69-7.95 (m, 2H, CHAr), 8.00-8.14 (m, 1H, CHAr), 8.14-8.37 (m, 1H, CHAr). C NMR (DMSO-d6,
100 MHz): δ 24.8 (+) (2CH2), 48.0 (+) (2CH2), 106.7 (+), 113.1 (+), 114.5 (-) (q, 3J = 4.1 Hz, CHAr),
122.0 (-) (CHAr), 124.5 (-) (q, 3J = 3.6 Hz, CHAr), 130.3 (+) (q, 2J = 32.3 Hz), 131.1 (-) (CHAr), 138.4
(+), 155.5 (+). Found: C, 54.9; H, 3.8; N 22.9%; C14H12F3N5 requires C, 54.7; H 3.9; N 22.8%. MS-EI
m/z: 307 [M]+.
2.2.8. 2-(4-Cyanophenyl)-5-(pyrrolidin-1-yl)-2H-1,2,3-triazole-4-carbonitrile (4h). Colorless powder,
yield: 193 mg (73%), mp 167-168 °С. FTIR, νmax, cm-1: 2980, 2956, 2934, 2864 (C-H), 2226 (CN). 1H
NMR (CDCl3, 400 MHz): δ 2.00-2.15 (m, 4H, CH2), 3.56-3.71 (m, 4H, CH2), 7.77 and 811 (AA′XX′,
J = 7.1 Hz, 4H, CHAr). 13C NMR (CDCl3, 100 MHz): δ 25.5 (2CH2), 48.5 (2CH2), 108.4, 111.2, 113.3
(CN), 118.1, 119.0 (2CHAr), 133.5 (2CHAr), 141.5, 155.9. Found: C, 63.8; H, 4.7; N 31.6%; C14H12N6
requires C, 63.6; H 4.6; N 31.8%. MS-EI m/z: 264 [M]+.
2.2.9. 2-(2-Methoxyphenyl)-5-(pyrrolidin-1-yl)-2H-1,2,3-triazole-4-carbonitrile (4i). Colorless
powder, yield: 210 mg (78%), mp 107-108 °С. FTIR, νmax, cm-1: 2970, 2860, 2855 (C-H), 2224 (CN).
1H NMR (CDCl3, 400 MHz): δ 1.97-2.08 (m, 4H, СН2), 3.61 (dd, J = 7.8, 5.5 Hz, 4Н, СН2), 3.89 (s,
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3H, OСН3), 7.03-7.12 (m, 2H, CHAr), 7.40-7.47 (m, 1H, CHAr), 7.51 (dd, J = 7.8, 1.6 Hz, 1H, CHAr).
13C NMR (CDCl3, 100 MHz): δ 25.5 (2CH2), 48.5 (2CH2), 56.3 (СН3O), 106.3, 112.9, 114.1, 120.7,
126.9, 129.2, 130.9, 153.6, 155.9. Found: C, 62.2; H, 5.7; N 26.1%; C14H15N5O requires C, 62.4; H
5.6; N 26.0%. MS-EI m/z: 269 [M]+.
2.2.10. 2-(2-Chlorophenyl)-5-(pyrrolidin-1-yl)-2H-1,2,3-triazole-4-carbonitrile (4j). Colorless powder,
1
yield: 210 mg (77%), mp 78-79 °С. FTIR, νmax, cm-1: 2982, 2946, 2880, 2840 (C-H), 2220 (CN). H
NMR (CDCl3, 400 MHz): δ 1.97-2.16 (m, 4H, СН2), 3.62 (t, J = 6.7 Hz, 4Н, СН2), 7.38-7.49 (m, 2H,
13
CHAr), 7.51-7.67 (m, 2H, CHAr). C NMR (CDCl3, 100 MHz): δ 25.5 (2CH2), 48.5 (2CH2), 107.0,
113.7, 127.4 (CHAr), 127.5 (CHAr), 129.3, 130.5 (CHAr), 131.2 (CHAr), 137.4, 155.9. Found: C, 57.2;
H, 4.5; N 25.8%; C13H12ClN5 requires C, 57.0; H 4.4; N 25.6%. MS-EI m/z: 273 [M]+.
2.2.11. 2-(2,6-Dichlorophenyl)-5-(pyrrolidin-1-yl)-2H-1,2,3-triazole-4-carbonitrile (4k). Colorless
powder, yield: 240 mg (78%), mp 103-104 °С. FTIR, νmax, cm-1: 2982, 2960, 2890 (C-H), 2221 (CN).
1H NMR (CDCl3, 400 MHz) δ 1.99-2.16 (m, 4H, СН2), 3.62 (t, J = 6.7 Hz, 4Н, СН2), 7.40-7.54 (m,
13
4H, CHAr). C NMR (CDCl3, 100 MHz): δ 25.5 (2CH2), 48.5 (2CH2), 106.3, 112.9, 114.1, 120.7,
126.9, 129.2, 130.9, 153.6, 155.9. Found: C, 50.4; H, 3.8; N 22.9%; C13H11Cl2N5 requires C, 50.7; H
3.6; N 22.7%. MS-EI m/z: 307 [M]+.
2.2.12.
5-(Pyrrolidin-1-yl)-2-(2-(trifluoromethyl)phenyl)-2H-1,2,3-triazole-4-carbonitrile
(4l).
Colorless powder, yield: 246 mg (80%), mp 93-94 °С. FTIR, νmax, cm-1: 2980, 2946, 2882, 2840 (C-
H), 2222 (CN). 1H NMR (CDCl3, 400 MHz): δ 1.98-2.17 (m, 4H, СН2), 3.61 (t, J = 6.7 Hz, 4Н, СН2),
7.58-7.68 (m, 1H, CHAr), 7.68-7.75 (m, 2H, CHAr), 7.85 (d, J = 7.8 Hz, 1H, CHAr). 13C NMR (CDCl3,
100 MHz): δ 25.5 (2CH2), 48.4 (2CH2), 107.5, 113.5, 122.6 (q, 1J = 271.2 Hz), 125.4 (q, 2J = 33.6 Hz),
127.4, 127.8 (q, 3J = 5.2 Hz), 129.7, 132.8, 137.4, 156.0. Found: C, 54.9; H, 4.0; N 22.6%; C14H12F3N5
requires C, 54.7; H 3.9; N 22.8%. MS-EI m/z: 307 [M]+.
2.2.13.
(2-(4-Methoxyphenyl)-5-(pyrrolidin-1-yl)-2H-1,2,3-triazol-4-yl)(pyrrolidin-1-yl)methanone
(4m). Colorless powder, yield: 297 mg (87%), mp 57-58 °C. FTIR, νmax, cm-1: 2970, 2865, 2836 (C-
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H), 1613 (C=O). 1H NMR (DMSO-d6, 400 MHz): δ 1.87-2.05 (m, 8H, CH2), 3.30-3.44 (m, 4H, CH2),
3.48-3.60 (m, 2H, CH2), 3.62-3.72 (m, 2H, CH2), 3.83 (s, 3H, CH3O), 6.98 and 7.81 (AA'XX', J = 8.8
13
Hz, 4H, CHAr). C NMR (DMSO-d6,100 MHz): δ 24.3 (CH2), 25.4 (2CH2), 26.3 (CH2), 46.4 (CH2),
48.4 (CH2), 50.6 (2CH2), 55.6 (CH3O), 114.2 (2CHAr), 119.5 (2CHAr), 130.8, 133.6, 156.0, 158.5,
161.7 (C=O). Found: C, 63.5; H, 6.9; N 20.7%; C18H23N5O2 requires C, 63.3; H 6.8; N 20.5%. MS-EI
m/z: 307. MS-EI m/z: 341 [M]+.
2.2.14. Ethyl 2-(4-methoxyphenyl)-5-(pyrrolidin-1-yl)-2H-1,2,3-triazole-4-carboxylate (4n). Colorless
powder, yield: 243 mg (77%), mp 85-86 °C. FTIR, νmax, cm-1: 2959, 2902, 2855 (C-H), 1703 (C=O).
1H NMR (CDCl3, 400 MHz): δ 1.45 (t, J = 7.1 Hz, 3Н, CH3CH2O), 1.94-1.99 (m, 4H, СН2), 3.47-3.52
(m, 4Н, СН2), 3.81 (s, 3H, СН3O), 4.44 (q, J = 7.1 Hz, 2Н, CH3CH2O) 7.11 and 7.85 (AA'XX', J = 9.3
13
Hz, 4H, CHAr). C NMR (CDCl3, 100 MHz): δ 14.4 (CH3CH2O), 25.6 (2CH2), 50.4 (2CH2), 55.6
(СН3O), 61.0 (CH3CH2O), 114.2 (2CHAr), 120.3 (2CHAr), 128.2, 133.3, 155.6, 159.0, 161.7. Found: C,
61.0; H, 6.5; N 17.6%; C16H20N4O3 requires C, 60.8; H 6.4; N 17.7%. MS-EI m/z: 316 [M]+.
2.2.15.
(4-Chlorophenyl)(2-(4-methoxyphenyl)-5-(pyrrolidin-1-yl)-2H-1,2,3-triazol-4-yl)methanone
(4o). Yellow powder, yield: 172 mg (45%), mp 89-90 °C. FTIR, νmax, cm-1: 2948, 2873, 2833 (C-H),
1650 (C=O). 1H NMR (DMSO-d6, 400 MHz): δ 1.91-2.08 (m, 4H, CH2), 3.37-3.53 (m, 4H, CH2), 3.85
(s, 3H, CH3O), 7.02 and 7.88 (AA'XX', J = 9.0 Hz, 4H, CHAr), 7.55 and 8.08 (AA'XX', J = 8.5 Hz, 4H,
13
CHAr). C NMR (DMSO-d6, 100 MHz): δ 25.1 (2CH2), 49.8 (2CH2), 55.5 (CH3O), 114.7 (2CHAr),
119.9 (2CHAr), 128.4 (2CHAr), 131.8, 131.8 (2CHAr), 132.3, 136.4, 137.7, 155.2, 158.8, 184.0 (C=O).
Found: C, 62.6; H, 5.1; N 14.5%; C20H19ClN4O2 requires C, 62.8; H 5.0; N 14.6%. MS-EI m/z: 382
[M]+.
2.2.16. 2-(4-Methoxyphenyl)-5-(piperidin-1-yl)-2H-1,2,3-triazole-4-carbonitrile (4p). Colorless
powder, yield: 243 mg (86%), mp 96-97 °С. FTIR, νmax, cm-1: 2990, 2978, 2940 (C-H), 2220 (CN). 1H
NMR (CDCl3, 400 MHz): δ 1.62-1.89 (m, 6H, СН2), 3.46-3.66 (m, 4Н, СН2), 3.88 (s, 3H, OСН3), 6.98
and 7.91 (AA'XX', J = 9.1 Hz, 4H, CHAr). 13C NMR (DMSO-d6, 100 MHz): δ 24.0 (CH2), 25.0
9

ACCEPTED MANUSCRIPT
(2CH2), 48.7 (2CH2), 55.6 (СН3O), 107.0, 114.4 (2CHAr), 120.3 (2CHAr), 132.9, 158.4, 159.5. Found:
C, 63.8; H, 6.0; N 24.5%; C15H17N5O requires C, 63.6; H 6.1; N 24.7%. MS-EI m/z: 283 [M]+.
2.2.17. 2-(4-Methoxyphenyl)-5-morpholino-2H-1,2,3-triazole-4-carbonitrile (4q). Colorless powder,
yield: 234 mg (82%), mp 128-129 °С. FTIR, νmax, cm-1: 2980, 2968, 2890, 2846 (C-H), 2221 (CN). 1H
NMR (CDCl3, 400 MHz): δ 3.48-3.61 (m, 4H, СН2), 3.80-3.93 (m, 7H, OСН3 + СН2), 6.99 and 7.91
13
(AA'XX', J = 9.1 Hz, 4H, CHAr). C NMR (CDCl3, 100 MHz): δ 47.7 (2CH2), 55.6 (СН3O), 66.1
(2CH2), 107.1, 113.5 (CN), 114.4 (2CHAr), 120.3 (2CHAr), 132.7, 158.2, 159.7. Found: C, 59.1; H, 5.4;
N 24.8%; C14H15N5O2 requires C, 58.9; H 5.3; N 24.6%. MS-EI m/z: 285 [M]+.
2.2.18. 5-(Azepan-1-yl)-2-(4-methoxyphenyl)-2H-1,2,3-triazole-4-carbonitrile (4r). Colorless powder,
1
yield: 255 mg (86%), mp 96-97 °С. FTIR, νmax, cm-1: 2976, 2952, 2890 (C-H), 2218 (CN). H NMR
(CDCl3, 400 MHz): δ 1.55-1.68 (m, 4H, СН2), 1.80-1.96 (m, 4H, СН2), 3.62-3.72 (m, 4H, СН2), 3.87
13
(s, 3H, CH3O), 6.98 and 7.91 (AA'XX', J = 9.1 Hz, 4H, CHAr). C NMR (CDCl3, 100 MHz): δ 27.3
(2CH2), 28.2 (2CH2), 49.5 (2CH2), 55.6 (СН3O), 104.7, 114.3 (2CHAr), 114.5 (CN), 120.2 (2CHAr),
132.9, 157.0, 159.3. Found: C, 64.9; H, 6.3; N 23.7%; C16H19N5O requires C, 64.6; H 6.4; N 23.6%.
MS-EI m/z: 297 [M]+.
2.2.19. 2-(4-Methoxyphenyl)-5-(4-(pyridin-2-yl)piperazin-1-yl)-2H-1,2,3-triazole-4-carbonitrile (4s).
Colorless powder, yield: 202 mg (56%), mp 193-194 °С. FTIR, νmax, cm-1: 2982, 2946, 2880, 2840 (C-
H), 2220 (CN). 1H NMR (CDCl3, 400 MHz): δ 3.62-3.78 (m, 8H, СН2), 3.88 (s, 3H, CH3O), 6.68-6.78
(m, 2H, СНPyr), 6.99 and 7.92 (AA'XX', J = 9.1 Hz, 4H, CHAr), 7.51-7.62 (m, 1H, СНPyr), 8.16-8.34
(m, 1H, СНPyr). 13C NMR (CDCl3, 100 MHz): δ 44.6 (2CH2), 47.3 (2CH2), 55.6 (СН3O), 107.3, 107.4,
113.6, 114.0, 114.4 (2CHAr), 120.3 (2CHAr), 132.7, 137.7, 148.0, 158.1, 159.2, 159.7. Found: C, 62.8;
H, 5.2; N 27.3%; C19H19N7O requires C, 63.1; H 5.3; N 27.1%. MS-EI m/z: 361 [M]+.
2.2.20.
5-([1,4'-Bipiperidin]-1'-yl)-2-(4-methoxyphenyl)-2H-1,2,3-triazole-4-carbonitrile
(4t).
Colorless powder, yield: 260 mg (71%), mp 249-250 °С. FTIR, νmax, cm-1: 2967, 2945, 2938, 2880 (C-
H), 2220 (CN). 1H NMR (CDCl3, 400 MHz): δ 1.27-1.52 (m, 1H, СН2), 1.81-2.03 (m, 5H, СН2), 2.31-
10

ACCEPTED MANUSCRIPT
2.59 (m, 4H, СН2), 2.68-2.94 (m, 2H, СН2), 3.06 (d, J = 12.4 Hz, 2H, СН2), 3.15-3.68 (m, 3H, СН2),
3.86 (s, 3H, CH3O), 4.29 (d, J = 13.1 Hz, 2H, СН2), 6.97 and 7.87 (AA'XX', J = 9.1 Hz, 4H, CHAr).
13C NMR (CDCl3, 100 MHz): δ 22.5, 22.7 (2CH2), 25.2 (CH2), 46.8 (2CH2), 49.8 (2CH2), 55.6
(СН3O), 63.6, 107.3, 113.3, 114.5 (2CHAr), 120.3 (2CHAr), 132.5, 157.2, 159.8. Found: C, 65.4; H,
7.1; N 22.7%; C20H26N6O requires C, 65.6; H 7.2; N 22.9%. MS-EI m/z: 366 [M]+.
2.2.21. 5-(n-Butylamino)-2-(4-methoxyphenyl)-2H-1,2,3-triazole-4-carbonitrile (4u). Colorless
powder, yield: 163 mg (60%), mp 121-122 °С. FTIR, νmax, cm-1: 2992, 2938, 2880, 2858 (C-H), 2221
(CN). 1H NMR (CDCl3, 400 MHz): δ 1.00 (t, J = 7.4 Hz, 3H, СН3), 1.46 (sext, J = 7.4 Hz, 2H, СН2),
1.66 (quin, J = 7.4 Hz, 2H, СН2), 3.42 (q, J = 7.4 Hz, 2H, СН2), 3.87 (s, 3H, CH3O), 4.17-4.29 (m,1H,
NH), 6.98 and 7.90 (AA'XX', J = 8.8 Hz, 4H, CHAr). 13C NMR (CDCl3, 100 MHz): δ 13.8 (СН3), 20.0
(CH2), 31.7 (CH2), 44.0 (CH2), 55.6 (СН3O), 106.4, 112.7, 114.4 (2CHAr), 120.2 (2CHAr), 132.9,
157.1, 159.4. Found: C, 62.3; H, 6.2; N 25.9%; C14H17N5O requires C, 62.0; H 6.3; N 25.8%. MS-EI
m/z: 271 [M]+.
2.2.22. 5-(Cyclohexylamino)-2-(4-methoxyphenyl)-2H-1,2,3-triazole-4-carbonitrile (4v). Colorless
1
powder, yield: 180 mg (61%), mp 153-154 °С. FTIR, νmax, cm-1: 2930, 2850 (C-H), 2226 (CN). H
NMR (CDCl3, 400 MHz): δ 1.20-1.34 (m, 3H, СН2), 1.38-1.52 (m, 2H, СН2), 1.61-1.75 (m, 1H, СН2),
1.76-1.88 (m, 2H, СН2), 2.08-2.18 (m, 2H, СН2), 3.53-3.67 (m, 1H, СН), 4.10 (d, J = 7.7 Hz, 1H,
13
NH), 6.99 and 7.90 (AA'XX', J = 9.1 Hz, 4H, CHAr). C NMR (CDCl3, 100 MHz): δ 24.7 (2CH2),
25.6 (CH2), 33.3 (2CH2), 52.9 (CH), 55.6 (СН3O), 106.9, 112.7, 114.4 (2CHAr), 120.2 (2CHAr), 132.9,
156.2, 159.4. Found: C, 64.9; H, 6.5; N 23.4%; C16H19N5O requires C, 64.6; H 6.4; N 23.6%. MS-EI
m/z: 297 [M]+.
2.3. Electronic absorption and emission spectroscopy
UV-Vis absorption spectra were recorded on a Perkin-Elmer Lambda 35 UV-Vis
spectrophotometer (Shelton, CT USA). Fluorescence of the sample solutions was measured using a
11

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Hitachi F-7000 spectrophotometer (Tokyo, Japan). The absorption and emission spectra were recorded
in MeCN, THF, CHCl3, DMF, MeOH, EtOH and n-hexane using 10.00 mm quartz cells. The
excitation wavelength was at the absorption maxima. Atmospheric oxygen contained in solutions was
not removed. Concentration of the compounds in the solution was 1.0 х 10-5 M and 1.0 х 10-6 M for
absorption and fluorescence measurements, respectively. The relative fluorescence quantum yields
(ΦF) were determined using quinine sulfate (1 х 10-5 M) in 0.1 M H2SO4 as a standard (ΦF = 0.546)
[21].
2.4. X-ray crystallography
XRD data were obtained on an “Xcalibur S” diffractometer using a standard procedure (MoK-
irradiation, graphite monochromator, ω-scanning with step 1o, T= 295(2) K). The structure was solved
with the ShelXS structure solution program using Direct Methods and refined with the ShelXL
refinement package using Least Squares minimization [22-24]. All non-hydrogen atoms were refined
in anisotropic approximation, H-atoms were refined in isotropic approximation in the “riding” model.
Suitable single crystals of 1,2,3-triazoles 4d and 4i for X-ray structural analysis were obtained by
slow evaporation of a solution of the compounds in chloroform at room temperature.
For 4d, on the angles 3.00 < Θ < 28.30o 6542 reflections were measured, including 3233 unique
(Rint = 0.0300) which were used in all calculations. Crystal data: C14H14FN5, M = 271.30, monoclinic,
a = 19.5131(15) Å, b = 16.2073(13) Å, c = 8.7864(8) Å, β = 99.370(7), V = 2741.7(4) Å3, space group
C2/c, Z = 8, ꢁ(MoKα) = 0.093 mm-1. The final R1 = 0.0991, wR2 = 0.0742 (all data) and R1 = 0.0360,
wR2 = 0.0684 (I>2σ(I)), GooF= 1.007. Largest diff. peak and hole 0.133 and -0.106 ēÅ-3.
For 4i, on the angles 2.79 < Θ < 26.37o 5990 reflections were measured, including 2745 unique
(Rint = 0.0453) which were used in all calculations. Crystal data: C14H15N5O, M = 269.31, monoclinic,
a = 11.680(3) Å, b = 8.7080(14) Å, c = 13.742(3) Å, β = 101.45(2), V = 1370.0(5) Å3, space group
P21/c, Z = 4, ꢁ(MoKα) = 0.088 mm-1. The final R1 = 0.1304, wR2 = 0.1242 (all data) and R1 =
12

ACCEPTED MANUSCRIPT
0.04940.0360, wR2 = 0.1146 (I>2σ(I)), GooF= 1.002. Largest diff. peak and hole 0.237 and -0.188 ēÅ-
3
.
A summary of the crystallographic data and structure refinement details are given in Supporting
Information. The crystal structures of 4d and 4i are shown in Fig. 1. and Fig. 2.
CCDC 1472551 for compound 4d and CCDC 1472552 for compound 4i can be obtained free of
charge
from
the
Cambridge
Crystallographic
Data
Centre
via
link
www.ccdc.cam.ac.uk/data_request/cif.
2.5. Quantum Mechanical Calculations
The ground state molecular geometry of the compounds under investigation was fully optimized at
Density Functional Theory (DFT) level, both in vacuo and in solvents (CH2Cl2 and MeCN). The
harmonic vibrational frequencies and the thermochemicals were computed. We have compared the
results obtained employing different functionals and different basis sets. In particular, we have chosen
hybrid (viz. B3LYP [25], and M06−2X [26]) and long−range corrected (viz. CAM−B3LYP [27] and
ωB97X [28]), coupled with the 6−31+G*, 6−311+G**, aug−cc−pVDZ and aug−cc−pVTZ [27-33]
basis sets. Solvent effects were taken into account by means of the implicit Polarizable Continuum
Model in its Integral Equation Formalism (IEF−PCM) [34]. The PCM molecular cavity was built
according to the Universal Force Field (UFF) [35] radii, within the value used in the last
implementation of the PCM (based on a continuum surface charge formalism). The standard values for
the dielectric constants and refractive indexes were assumed. Both in vacuo and in solvents, the UV-
Vis spectra were also simulated, accounting for S0 → Sn (n = 1 to 5) transitions. The first S(π,π*) state
geometry was subsequently optimized, using analytical gradients, and the first transitions S1 → S0 of
the emission transition. The Mulliken’s charge population analysis and the electric dipole moment
were also computed for the both ground and S1 excited (vertical and relaxed) states. The calculations
were performed using GAUSSIAN 09 [36].
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3.
Results and discussion
3.1. Synthesis and characterization of 2-aryl-1,2,3-triazoles
The most important structural factors that influence fluorophore absorption and emission are the
system conjugation, the direction and modulus of the electronic effects of the substituents and spatial
effects, which may vary the conjugation on opposite parts of the molecule. To explore the relationship
between these factors and the observed photophysical properties of 2-aryl-5-amino-1,2,3-triazoles,
compounds 4a-v, bearing various substituents within the aromatic ring and at positions 4 and 5 of the
heterocycle (Scheme 1, Table 1) were synthesized. Compounds 4a-v were produced using a recently
reported one-pot reaction with the tandem addition of amines 2a-i to arylhydrazononitriles 1a-o and
subsequent oxidative cyclization of intermediates 3 in the presence of copper(II) acetate (Scheme 1)
[19]. This transformation typically proceeds in 1.5-7 h with moderate to good yields (60-92%). The
longest conversion times were observed for the substrates 1n and 1o, where one of the CN-groups in
the structure of hydrazone 1 was replaced with either an ethoxycarbonyl or aroyl group (Table 1,
entries 14-15) and 4i-l which bear one or two substituents in the ortho-position of the aryl moiety
(Table 1, entries 9-12).
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Scheme 1. One-pot synthesis of 2-aryl-1,2,3-triazoles 4a-v.
Table 1
The time of conversion and yields for the one-pot synthesis of 2-aryl-1,2,3-triazoles 4a-v
Triazole
Entry
1
Ar
NR2R3
Time (h) Yielda (%)
4
R1
4a CN
6
87
3,4-(MeO)2C6H3
4-MeOC6H4
C6H4
Pyrrolidin-1-yl
2
3
4
5
6
7
4b CN
4c CN
4d CN
4e CN
2
7
2
3
7
3
92
80
84
84
90
78
Pyrrolidin-1-yl
Pyrrolidin-1-yl
Pyrrolidin-1-yl
Pyrrolidin-1-yl
Pyrrolidin-1-yl
Pyrrolidin-1-yl
4-FC6H4
4-ClC6H4
4f
CN
3,5-F2C6H3
3-CF3C6H4
4g CN
15

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8
4h CN
4-CNC6H4
15
11
40
28
50
4
73
78
77
88
80
87
77
45
86
82
86
Pyrrolidin-1-yl
9
4i
2-MeOC6H4
2-ClC6H4
CN
Pyrrolidin-1-yl
Pyrrolidin-1-yl
Pyrrolidin-1-yl
Pyrrolidin-1-yl
Pyrrolidin-1-yl
Pyrrolidin-1-yl
10
11
12
13
14
15
16
17
18
4j
CN
4k
2,6-Cl2C6H3
2-CF3C6H4
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
CN
4l
CN
4m
C(=O)Pyrrolidin-
4n CO2Et
20
24
3
4o C(=O)C6H4Cl-4
Pyrrolidin-1-yl
Pyperidin-1-yl
4p
CN
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
4q
3
CN
Morpholin-4-yl
Azepane-1-yl
4r
4
CN
1-(2-Pyridyl)
piperazine
19
4s
5
56
CN
4-MeOC6H4
20
21
22
4t
4
5
6
71
60
61
CN
CN
CN
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
1,4'-Bipiperidine
4u
4v
NH-n-C4H9
NHC6H11-cyclo
aIsolated yield (after the separation and purification).
The newly obtained 2H-1,2,3-triazoles 4a-v were colorless solids. Their structure was confirmed by
1H and 13C spectroscopy, mass spectrometry and X-ray diffraction data for 4d,i (Figs. 1 and 2).
3.2. X-ray crystallography analysis
The spatial structures of compounds 4d and 4i were determined by X-ray diffraction analysis
(Figs. 1 and 2). According to the XRD data for triazole 4d, atoms of CN- and Ph-groups are placed in
the plane of the triazole ring (in limits of 0.025 Å). The piperidine group adopts a chair conformation
with the heterocycle in the equatorial position. There are two hydrogen bonds between the C(10) and
16

ACCEPTED MANUSCRIPT
C(14) hydrogen atoms in the ortho-positions of the aromatic ring and the N(3) and N(1) triazole atoms,
respectively. In contrast, the aryl substituent in triazole 4i is turned to the plane of triazole cycle at an
angle of 53.7o.
a
b
Fig. 1. ORTEP view of 1,2,3-triazole 4d in thermal ellipsoids at 50% probability level: (a) front view
and (b) side view. (RWDW = 2.7Å).
a
b
Fig. 2. ORTEP view of 1,2,3-triazole 4i in thermal ellipsoids at 50% probability level: (a) front view
and (b) side view.
Table 2.
Selected bond lengths for compounds 4d,i according to XRD and the literature [37] data.
Entry Literature data [37]
Compound 4d
Compound 4i
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Bond length, Å
1.366
Bond
Bond length, Å
1.3143(14)
1.3517(12)
1.3399(16)
1.3405(15)
1.4237(16)
1.3638(15)
1.1400(18)
1.422(2)
Bond
Bond length, Å
1.311(2)
1.338(2)
1.337(3)
1.329(3)
1.423(3)
1.336(3)
1.131(3)
1.408(4)
1
2
3
4
5
6
7
8
N(1)-N(2)
N(2)-N(3)
N(1)=C(5)
N(3)=C(4)
N(2)-C(9)
C(4)-N(5)
N(4)≡C(8)
C(5)-C(8)
N(2)-N(1)
N(2)-N(3)
C(2)=N(1)
N(3)=C(1)
N(2)-C(8)
N(4)-C(1)
C(7)≡N(5)
C(2)-C(7)
1.366
1.329
1.329
1.431
1.416
1.136
1.444
Analysis of the bond lengths for the compounds 4d and 4i (Table 2) reveals the shortening of the
single bond lengths and elongation of the double and triple bonds caused by conjugation within the
molecule core.
3.3. Optical properties of 2-aryl-1,2,3-triazoles
2-Aryl-5-amino-1,2,3-triazoles 4a-v dissolve in most common organic solvents including MeCN,
THF, CHCl3, DMF and DMSO. The photophysical properties of compounds 4a-v were examined by
UV-Vis and fluorescence spectroscopy in acetonitrile at room temperature and the results are
summarized in Table 3. All of the investigated compounds exhibited similar absorption and emission
contours (Figs 4, 6, 8-10). The absorption spectra for compounds 4 showed two strong maxima at
approximately 229-259 nm and 317-381 nm. The emission spectra of solutions of 2-aryl-1,2,3-
triazoles 4a-v were measured at an excitation wavelength corresponding to the long-wavelength
maximum in the absorption spectra. Typical emission maxima obtained upon irradiation of the
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solutions were in the blue region. Interestingly, many of the compounds exhibited a significant Stokes
shift up to 140 nm (9461 cm-1), although the extent of the shift varied significantly between structures.
Spectral characteristics such as absorption (λabs), emission (λem), molar absorption coefficient (ε) and
quantum yield (ФF) for the compounds 4a-v were measured in acetonitrile and are presented in Table
3.
As follows from the spectral characteristics (Stokes shift and quantum yield), most of compounds
4a-v have exhibited a strong fluorescence.
Table 3
Photophysical data for 2-aryl-1,2,3-triazoles 4 (solution in acetonitrile).
Triazole
UV-Vis
λabs
Fluorescence
Stokes
shift,
(nm/cm-1)
Entry
Structure
lgεmax
λem (nm) ΦF
4
(nm)
240
344
4.22
4.08
1
2
4a
4b
417
418
0.996
73/6115
78/5488
247
340
4.43
4.13
0.936
243
340
4.50
4.05
3
4
5
423
422
429
0.886
0.683
0.829
83/5771
82/5715
83/5592
4c
4d
4e
243
340
4.28
3.85
251
346
4.37
3.86
245
350
4.27
4.11
6
7
435
430
0.837
0.801
85/5583
83/5563
4f
247
347
4.27
4.04
4g
19

ACCEPTED MANUSCRIPT
259
362
4.41
4.19
8
9
446
418
0.579
0.456
84/5202
4h
4i
240
318
3.89
3.81
100/7523
229
324
4.11
3.73
10
11
12
426
418
433
0.607
0.113
0.710
102/7309
101/7622
107/7580
4j
4k
4l
238
317
3.08
3.69
227
326
4.17
3.79
250
328
3.98
3.99
13
412
0.555
84/6216
4m
256
336
4.26
4.06
14
15
16
17
18
19
20
21
22
423
421
415
410
413
461
403
401
402
0.731
0.004
0.929
0.856
0.980
0.064
0.156
0.918
0.956
87/6121
40/2494
84/6115
86/6474
69/4857
140/9461
78/5955
73/5550
72/5427
4n
4o
4p
4q
4r
4s
266
381
4.33
4.01
239
340
4.16
4.08
245
324
4.14
4.14
250
344
4.29
4.13
250
321
4.48
4.14
247
325
3.97
4.12
4t
240
328
4.11
4.19
4u
4v
241
330
4.16
4.20
20

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aUV-Vis absorption wavelengths at room temperature and concentration 10-5 M.
bFluorescence wavelengths at room temperature and concentration 10-6 M.
cFluorescence quantum yields measured using a 0.1 M H2SO4 solution of quinine sulfate (ΦF = 0.55) as a
reference.
3.3.1 Structure and optical properties
The spectral properties of compounds 4a-v depend on their electronic structure. These properties
are influenced by the conjugation of the aromatic and triazole rings, the nature of substituents within
aromatic cycle, the type of amino group at C(5) position of triazole and the type of electron-
withdrawing group (R1 = CN, CONR2R3 or C(=O)C6H4Cl-4) at C(4) of triazole ring. To rationalize the
relationship between the structure of investigated compounds and their photophysical properties, we
have divided them into several groups in accordance with the above-mentioned structural features.
The XRD (Fig. 1) and computational data (Table 4, Supporting Information, Table S2) for
triazoles 4a-h shows the planar molecular construction of these compounds, which provides good
conjugation between opposite fragments of the molecule. Thus, triazoles 4a-h were considered a
suitable model to establish the relationship between the electronic effects of substitutions on the aryl
moiety and the emission and absorption properties.
Analysis of absorption and emission spectral data for triazoles 4a-h revealed that the presence of
strong electron-withdrawing groups within aromatic ring (compound 4h) leads to a red-shift (up to 22
nm/1787 cm-1) in its absorption spectrum and a 29 nm/1559 cm-1 red-shift in the emission spectrum
(Table 3, Fig. 4). Thus, the most effective conjugation is observed when a CN group in the aryl and
triazole C(5)-amino group are both present (as in triazole 4h). In contrast, the quantum yield is highly
dependent on the degree of conjugation, and it decreases from 0.996 for compound 4a (Ar = 3,4-
(MeO)2C6H3) to 0.579 for compound 4h (R1 = CN) (Table 3). Therefore, the strong fluorescence of 4a
21

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and 4b is likely caused by better internal charge transfer (ICT) from the electron-donating OMe to the
electron-withdrawing C(4)triazole-CN upon light excitation.
b
a
Fig. 3 (a) Photographs of the solutions of 4a-h under irradiation with hand-held UV lamp at
emission wavelength of 380 nm. (b) Photographs of the same solutions taken under daylight.
a
b
Fig. 4. Absorption (a) and emission (b) spectra of 2-aryl-1,2,3-triazoles 4a-h in MeCN at room
temperature.
Triazoles 4i-l contain either one or two substituents at the ortho-position of aromatic ring and can
be used to establish the influence of steric hindrance on the photophysical properties of the compounds
(Table 3, entries 9-12, Figs. 5, 6). The XRD results and the data calculated for the ground states (Fig.
2, Table 6 and Supporting Information, Table S2) for these molecules indicates that the conjugation
between the aromatic and heterocyclic ring systems is disrupted. The strongest intramolecular
repulsion occurs in 4i-l and leads to a significantly twisted molecular conformation. Triazoles 4i-l
showed blue shifts up to 33 nm/2974 cm-1 in the absorption spectra coupled with a decrease in the
molar adsorption coefficient (Table 3, entries 9-12), but the emission parameters were nearly identical
to the compounds with para-located substituents. These spectral features of compounds 4i-l afforded
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an increase in the Stokes shifts (up to 107 nm/7580 cm-1 for 4l) and a decrease in the quantum yields
(0.113-0.71). These results suggest a twisted intramolecular charge transfer (TICT) is realized for
triazoles 4i-l as opposed to planar compounds 4a-h.
a
b
Fig. 5. (a) Photographs of the solutions in MeCN of 4i-l under irradiation with hand-held UV lamp
at emission wavelength of 380 nm. (b) Photographs of the same solutions taken under daylight.
a
b
Fig. 6. Absorption (a) and emission (b) spectra of 2-aryl-1,2,3-triazoles 4i-l in MeCN at room
temperature.
The experimental data for triazoles 4b and 4p-v confirm that the type of alkylamino group at C(5)
of the heterocycle has a dramatic effect on both the Stokes shift and the quantum yield (Table 3,
entries 2, 16-22, Figs. 7, 8). For example, the replacement of the azepane moiety (compound 4r) by 4-
(pyridin-2-yl)piperazine fragment (compound 4s) caused an apparent blue-shift of the absorption
maximum from 344 to 321 nm, an increase in the Stokes shift from 69 nm (4857 cm-1) to 140 nm
(9461 cm-1) and a substantial decrease in the quantum yield (to 0.064). The relatively low quantum
yields observed for compounds 4s and 4t imply a strong non-radiative deactivation pathway for their
excited states.
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a
b
Fig. 7. (a) Photographs of the MeCN solutions of 4b, p-v under irradiation with hand-held UV
lamp at emission wavelength of 380 nm. (b) Photographs of the same solutions taken under daylight at
room temperature.
a
b
Fig. 8. Absorption (a) and emission (b) spectra of 2-aryl-1,2,3-triazoles 4b,p-v in MeCN at room
temperature.
The last group of investigated compounds, 4b and 4m-o, differ in substitution only at the triazole
C(4) position. Absorption spectra of these triazoles exhibited increasing red-shifts in the order 4m < 4n
< 4b < 4o (Table 3, Figs. 9, 10). Further, replacement of the CN-moiety in the molecule of triazole 4b
by any other function led to unfavourable emission parameters. While compound 4b exhibited
extremely high fluorescent emission with a quantum yield >0.90, compound 4o showed very weak
blue emission with a fluorescence quantum yield of 0.004 and a maximum emission wavelength of 421
nm when excited at 381 nm (Table 3, entry 15).
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a
b
Fig. 9. (a) Photographs of the solutions in MeCN of 4b,m,n,o under irradiation with hand-held UV
lamp at emission wavelength of 380 nm. (b) Photographs of the same solutions under daylight.
a
b
Fig. 10. Absorption (a) and emission (b) spectra of 2-aryl-1,2,3-triazoles 4b,m,n,o in MeCN at room
temperature.
The observed photophysical phenomena reveal that the optical properties of the investigated
triazoles 4a-v are very sensitive to structural factors, which allows one to readily tune the
photophysical properties of the fluorophores by appropriate design of the molecule. Among all of the
products studied, compound 4a showed the highest quantum yield (0.996) and a moderate Stokes shift
(73 nm/6115 cm-1), whereas triazole 4s exhibited the largest Stokes shift and one of the lowest
quantum yield (0.064) (Table. 3, entry 19). It is worth nothing that quantum yields of most of the
triazoles investigated were better than for previously investigated 1H-triazoles and even for known
examples of 2H-triazole derivatives [11-18].
3.3.2 Solvatochromism
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Among the major environmental factors influencing electronic spectra, solvent effects are of
particular importance. Solvatochromism involves a change in the absorption and emission spectra
and/or quantum yields when the fluorophore is dissolved in solvents of different polarity. The
solvatochromic effect of compounds 4 was investigated to estimate the difference between the dipole
moment for the ground states and excited states of these molecules. The absorption and emission
spectra of compounds 4b, 4m and 4v were recorded at a standard concentration in different solvents
with varying polarity, including acetonitrile, chloroform, DMF, ethanol, methanol and n-hexane (Table
4, Figs. 12-14).
a
b
Fig. 11. (a) Photographs of the solutions of 4b under irradiation with hand-held UV lamp at
emission wavelength of 380 nm. (b) Photographs of the same solutions under daylight.
a
b
Fig. 12. Absorption (a) and emission (b) spectra of 1,2,3-triazoles 4b in different solvents at 25 °C.
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a
b
Fig. 13. Absorption (a) and emission (b) spectra of 1,2,3-triazole 4m in different solvents at 25 °C.
a
b
Fig. 14. Absorption (a) and emission (b) spectra of 2-aryl-1,2,3-triazoles 4v in different solvents at 25
°C.
Table 4
Fluorescence characteristics of 2-aryl-1,2,3-triazoles 4b,m,v in organic solvents
Stokes
shift
f
λabs,
λem
(nm)
Entry Compound
Solvent
lgε
ΦF
(ε,n2)[a] (nm)
(nm/cm-1)
54/4143
64/4609
75/5520
76/5402
76/5373
75/5488
73/5429
80/5880
62/4687
82/6097
73/5429
66/5193
72/5427
[b]
n-Hexane -0.001
CHCl3
335
342
343
339
340
340
332
331
334
328
332
325
330
4.21 389(
4.17 406
4.14 418
4.18 415
4.17 416
4.13 418
4.13 405
4.17 411
4.18 396
3.99 410
4.13 405
4.23 391
4.21 402
-
1
4b
[b]
0.149
0.275
0.290
0.309
0.305
-
2
3
4
5
[b]
DMF
-
[b]
EtOH
MeOH
MeCN
-
0.98
0.94
0.64
0.77
0.90
0.55
0.11
6
n-Hexane -0.001
CHCl3
DMF
EtOH
MeCN
n-Hexane -0.001
CHCl3 0.149
7
8
9
10
11
12
13
4m
4v
0.275
0.290
0.305
0.149
[b]
-
[b]
-
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[b]
[b]
DMF
EtOH
MeCN
0.275
0.290
0.305
336
333
330
4.17 408
4.20 408
4.20 402
72/5252
75/5520
72/5427
-
-
14
15
16
0.95
[a] The polarity scale chosen is the orientation polarizability employed in the Lippert-Mataga equation
f (ε,n2)= [(ε-1)/(2ε-1)]-[(n2-1)(2n2+1)], taking into account both the solvent dielectric constant and
refractive index [1].
[b] Not detected.
The UV spectra of 4b, 4m and 4v were essentially unchanged in all of the solvents examined,
implying a weak positive solvent-dependence (Table 4, Figs. 12-14). In contrast, the maximum
emission wavelength for these compounds showed a slight bathochromic shift in more polar solvents,
as illustrated in Figs. 12-14. As shown in Table 4, compound 4m is most affected by the solvent
polarity, exhibiting a bathochromically shifted emission maximum in polar solvents (ethanol, methanol
and DMF) compared to non-polar n-hexane. The Stokes shift for compounds 4b and 4m vary widely
in different solvent (1193 and 1259 cm-1), while the Stokes shift for compound 4v shows very little
solvent influence (327 cm-1). These effects are explained by a slight increase in the dipole moment of
the excited states (see Table 5), leading to increased sensitivity toward the surrounding environment.
The intensity of absorption and emission for triazole 4m is also highly dependent on solvent polarity.
In particular, the quantum yield of triazole 4m decreases drastically with decreasing polarity of the
solvents (EtOH [0.90] > DMF [0.77] > n-hexane [0.64] > MeCN [0.55] > CHCl3 [0.11]). The highest
fluorescence quantum yield was observed in ethanol, a polar, protic solvent. It is possible that the
triazole 4m with the carboxamide group at C(4) atom of heterocyclic ring is more readily able to form
hydrogen bonds with the alcoholic solvent than the other proton-donor compounds. This is a very
important interaction (along with the dipole-dipole interactions) that significantly affects the quantum
yield. It should be mentioned that the quantum yield of all of the investigated compounds increased
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substantially in alcoholic solvents. Even triazole 4b, which had an excellent quantum yield in
acetonitrile (0.93), was further improved in methanol (0.98).
It is known that specific solvent–fluorophore interactions could occur either in the ground or in the
excited states [1,2]. As for the investigated triazoles 4, the influence of the solvents appears to have a
larger effect on the emission spectrum than on the absorption spectrum, which suggests that dipolar
moment of the excited states is higher than that in ground state. This statement is supported by the
results from theoretical calculations (Table 5).
3.3. Quantum Mechanical Calculations
The absorption (λabs) and emission (λem) wavelength and oscillator strength (f01, f10), Stokes shifts
(ꢂν), the modulus of the electric dipole moments of the ground state (ꢀ0), of the vertical FC excited
(ꢀ1v) and of the relaxed excited states (ꢀ1r) and the angles formed by the dipole moment vectors (θ0,1v
and θ0,1r) were computed at the DFT CAM-B3LYP/cc-pVTZ level of theory, in the implicit solvated
phase (MeCN). The data provided in Table 5 are in excellent agreement with the experimental
spectroscopic measurements (Table 3), and the calculated oscillator strength for the absorption
transition changes is in accordance with experimental absorption and emission characteristics.
Table 5
Computed absorption wavelength (λa) and oscillator strength (f01), emission wavelength (λe) and
oscillator strength (f10), Stokes shift (ꢂν), the modulus of the electric dipole moment of the ground
state (ꢀ0), of the vertical FC excited (ꢀ1v) and of the relaxed excited states (ꢀ1r) and the angles formed
by the dipole moment vectors (θ0,1v and θ0,1r) for triazoles 4a-v.
Compound λabs
(nm)
f01
λem
(nm)
f10
ꢂν / kK ꢀ0 (D) ꢀ1v (D) ꢀ1r (D) θ0,1v (°) θ0,1r (°)
345
339
340
341
347
0.4084 416
0.3778 417
0.2705 421
0.2680 420
0.3095 427
0.7881 4.952
0.7431 5.523
0.5817 5.664
0.5692 5.521
0.6484 5.404
6.79
8.54
6.43
6.19
6.21
10.79
12.41
12.04
13.02
13.51
6.56
8.23
6.10
6.20
6.28
23
25
39
26
27
4
3
8
7
8
4a
4b
4c
4d
4e
29