Highly fluorescent 1,2,4,5-tetrazine derivatives containing 1,3,4-oxadiazole ring conjugated via a 1,4-phenylene linker

Article abstract of DOI:10.1016/j.dyepig.2020.108715

Symmetrical and unsymmetrical 1,2,4,5-tetrazine derivatives containing 1,3,4-oxadiazole ring were obtained in high yields using commercially-available 4-cyanobenzoic acid, hydrazine hydrate and carboxylic acid chlorides. The few-step transformation involved the Pinner reaction and the subsequent mild oxidation of 1,4-dihydro-1,2,4,5-tetrazines using hydrogen peroxide at room temperature. The obtained compounds exhibited luminescent properties and large quantum yields.

Full text of DOI:10.1016/j.dyepig.2020.108715

Journal Pre-proof
Highly fluorescent 1,2,4,5-tetrazine derivatives containing 1,3,4-oxadiazole ring
conjugated via a 1,4-phenylene linker
Anna Kędzia, Agnieszka Kudelko, Marcin Świątkowski, Rafał Kruszyński
PII:
S0143-7208(20)31412-1
DOI:
https://doi.org/10.1016/j.dyepig.2020.108715
DYPI 108715
Reference:
To appear in: Dyes and Pigments
Received Date: 14 May 2020
Revised Date: 7 July 2020
Accepted Date: 13 July 2020
Please cite this article as: Kędzia A, Kudelko A, Świątkowski M, Kruszyński R, Highly fluorescent
1,2,4,5-tetrazine derivatives containing 1,3,4-oxadiazole ring conjugated via a 1,4-phenylene linker,
Dyes and Pigments, https://doi.org/10.1016/j.dyepig.2020.108715.
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Author Contributions
Anna Kędzia – methodology, investigation, formal analysis, writing;
Agnieszka Kudelko – conceptualization, methodology, supervision, writing, review and editing;
Marcin Świątkowski - methodology, formal analysis, writing;
Rafał Kruszyński - conceptualization, methodology, writing, review and editing.

Highly fluorescent 1,2,4,5-tetrazine derivatives containing
1,3,4-oxadiazole ring conjugated via a 1,4-phenylene linker
Anna Kędziaa, Agnieszka Kudelko*a, Marcin Świątkowskib,
Rafał Kruszyńskib
a Department of Chemical Organic Technology and Petrochemistry, The Silesian University of
Technology, Krzywoustego 4, PL-44100 Gliwice, Poland; E-mail: Agnieszka.Kudelko@polsl.pl
b Institute of General and Ecological Chemistry, Lodz University of Technology, Zeromskiego 116, PL-
90924 Lodz, Poland
CN
R1
R2
HO
10 x mpl s
H2N NH2
POCl3
O
N
N
N
N
O
N
O
N
N
N
O
Cl
Qu tum yi lds i solutio up to 60%
R1, R2 = H, OCH3, C(CH3)3, NO2
R
Keywords: s-tetrazine; 1,3,4-oxadiazole; luminescent properties; Pinner reaction; cyclization
Abstract: Symmetrical and unsymmetrical 1,2,4,5-tetrazine derivatives containing 1,3,4-
oxadiazole ring were obtained in high yields using commercially-available 4-cyanobenzoic
acid, hydrazine hydrate and carboxylic acid chlorides. The few-step transformation involved
the Pinner reaction and the subsequent mild oxidation of 1,4-dihydro-1,2,4,5-tetrazines using
hydrogen peroxide at room temperature. The obtained compounds exhibited luminescent
properties and large quantum yields.
1. Introduction
For decades, researchers have pursued extended π-conjugated scaffolds that exhibit
excellent absorption and emission, along with high thermal and chemical stabilities.
The large family of potential luminophores includes many aromatic compounds such as
heterocyclic arrangements with highly electronegative atoms such as oxygen and nitrogen.
Their presence considerably affects the electron distribution within the molecule, and also
improves intramolecular electron transport, which is important in optoelectronics
applications.[1]
One group of compounds that perfectly fits these requirements are 1,2,4,5-tetrazines (s-
tetrazines), six-membered heterocycles that contain four nitrogen atoms. The center ring is
strongly electron-deficient, which combined with its aromaticity, makes it an interesting
material for optoelectronics and perovskite solar cells. Literature reports show that
derivatives of this compound can be used to produce organic light-emitting diodes (OLEDs),
organic field-effect transistors (OFETs), laser dyes,[2] and perovskite solar cells.[3] In addition,
in the case of charge-transfer chromophoric compounds, their use as D-π-A-π-D dyes leads
to an increase in the absorption cross-section of two photons.[4] s-Tetrazine derivatives are
also popular high-energy-density materials (HEDM) that can be used as propellants or
explosives.[5] In addition, derivatives of this ring have anti-tuberculosis,[6] anti-cancer,[7] anti-
malarial[8] or antibacterial[9] activity, which makes it possible to use them in medicine. In
addition to therapeutic effects, s-tetrazine derivatives also show promise for diagnostic
applications, such as RNA visualization[10] or rapid radioactive labeling.[11]
Another interesting heterocyclic arrangement is the five-membered 1,3,4-oxadiazole that
contains two nitrogen atoms and one oxygen atom. Many small molecules and polymeric
materials based on this ring have been investigated and have been used to produce efficient

and long-lasting light-emitting devices. The improved properties are associated with the
introduction of various moieties and additional 1,3,4-oxadiazole rings.[12-16] This scaffold can
transfer electrons and block holes, which is useful for the production of single-layer organic
semiconductor devices with improved optoelectronic properties. In addition, the presence of
one or more 1,3,4-oxadiazole rings significantly increases the electron affinity of the material.
Compounds containing this system also have a wide energy gap between their highest
occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), which
results in high redox stability and blue light emission.[17] These types of systems also show
a wide range of biological activity, allowing them to be used in medicine[18-24] and
agriculture.[25-26]
In our previous research, we produced several derivatives in which s-tetrazine was
directly conjugated with 1,3,4-oxadiazole.[27] Due to the excellent absorption and emission of
these compounds, we decided to synthesize systems based on the same heterocyclic rings,
but connected through a 1,4-phenylene linker. This approach extended the π-conjugated
electron system and resulted in the formation of both symmetrical and unsymmetrical
derivatives.
2. Result and discussion
2.1. Synthesis
One of the most popular methods for the synthesis of 1,2,4,5-tetrazine derivatives is the
Pinner reaction, which uses nitriles. Therefore, our research began with the synthesis of
carbonitriles that contained 1,3,4-oxadiazole. For this purpose, commercially-available 4-
cyanobenzoic acid (1) was used. This compound contains both a carbonitrile group
necessary for the Pinner reaction and a carboxyl group, which allows the formation of a five-
membered heterocycle. In the first stage, the acid 1 was esterified with methanol in the
presence of hydrochloric acid, giving product 2 in high yield (74%). Ester 2 was then
converted to hydrazide 3 in the presence of hydrazine hydrate with 70% yield. This product
then reacted with several acid chlorides (4a-d), which enabled the introduction of an
additional benzene ring, together with electron-donating groups, such as methoxy or t-butyl,
and electron-withdrawing nitro group. Depending on the chloride used, the products were
obtained in 60-83% yield. The resulting compounds 5a-d were then treated with phosphorus
oxychloride (POCl3) in toluene under reflux, leading to the formation of the desired
derivatives containing a 1,3,4-oxadiazole ring (6a-d) in 79-96% yield (Scheme 1). The
substituents adjacent to the benzene ring affected the yield of products, and the best yields
were obtained with electron-donating groups, while the nitro group caused decreased the
yield and required a longer reaction time (Table 1).
Scheme 1. Synthesis of nitriles containing a 1,3,4-oxadiazole ring (R= H, OCH3, C(CH3)3, NO2).

Table 1. Synthesis of 4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzonitrile derivatives (6a-d).
Product 5
Product 6
Reaction time
[h]
Entry
R
Yield
Yield
[%]
Product
Product
[%]
75
83
80
60
1
2
3
4
H
5a
5b
5c
5d
6a
6b
6c
6d
6
4
96
98
87
79
OCH3
C(CH3)3
NO2
5,5
9
The next step was the Pinner reaction, which involved the formation of dihydro
derivatives of 1,2,4,5-tetrazine from the previously-obtained carbonitriles and hydrazine
hydrate in the presence of sulphur. The first attempt involved the synthesis of a symmetrical
system using 4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzonitrile (6a). The dihydro derivative 7a
was then oxidized with sodium nitrate(III) in an acidic environment; however, this approach
resulted in a relatively low yield of 20%. Therefore, the reaction was repeated using
hydrogen peroxide, which significantly increased the yield to 65%. The reaction was also
tested using a hydrogen peroxide complex with urea in the form of pellets that were soluble
in the reaction medium, but only trace amounts of the product were obtained. The results
revealed that the method using hydrogen peroxide as the oxidizing agent was the best
option, so it was used in further experiments to synthesize four symmetrical products
containing 1,3,4-oxadiazole (8a-d) (Scheme 2). Similarly to the carbonitrile synthesis,
electron-donating substituents increased the reaction yield, while the electron-withdrawing
nitro substituents decreased the yield (Table 2, entry 1-4). In the same way, the synthesis of
unsymmetrical systems was conducted. This time, the Pinner reaction was carried out using
two carbonitriles that differed in their R substituent at the terminal positions, introduced in
a 1:1 molar ratio. This way six new products 8e-j were obtained (Scheme 2). The influence of
individual groups on the reaction yield was observed, similar to the effect noted in previous
experiments (Table 2, entry 5-10).
Scheme 2. Synthesis of target products (R1, R2= H, OCH3, C(CH3)3, NO2).

Table 2. Synthesis of symmetrical and unsymmetrical derivatives of s-tetrazine conjugated via a 1,4-
phenylene linker with a 1,3,4-oxadiazole ring (8a-j).
Yield*
[%]
Yield
[%]
Entry
R1
R2
Product
Product
1
2
H
OCH3
C(CH3)3
NO2
H
7a
7b
7c
7d
7e
7f
63
85
70
51
73
68
64
82
66
67
8a
8b
8c
8d
8e
8f
65
72
67
43
58
56
51
70
47
44
OCH3
C(CH3)3
NO2
3
4
5
H
OCH3
C(CH3)3
NO2
6
H
7
H
7g
7h
7i
8g
8h
8i
8
OCH3
OCH3
C(CH3)3
C(CH3)3
NO2
9
10
NO2
7j
8j
* Yields of instable crude intermediates.
According to the research presented by the Audebert group,[28] the presence of sulphur
increases the reactivity of the hydrazine molecule and promotes the reaction (Scheme 3). In
the case of substrates 6a-d, lowering the electron density at the carbonitrile carbon atom
should give the highest yield.[29] Therefore, the presence of the highly electron-withdrawing
1,3,4-oxadiazole ring improved the reactivity of the entire system, which resulted in high
product yields. However, the literature data show that excessively reducing the electron
density of the 1,2,4,5-tetrazine ring destabilizes it.[30] This may be the reason for the
decrease in yield in the case of derivatives containing an electron withdrawing nitro group.
Scheme 3. Proposed mechanism for the formation of 1,2,4,5-tetrazine ring.[28]
1
Product structures were confirmed by H and 13C NMR spectroscopy. In all cases, the
carbon atoms of the heterocyclic rings provided characteristic and diagnostic signals. The

highest shifts (downfield) corresponded to carbon atoms of the 1,3,4-oxadiazole and 1,2,4,5-
tetrazine rings (over 160 ppm). Signals due to benzene carbon with an attached methoxy
group (~162 ppm), tert-butyl (~155 ppm), and nitro group (~150 ppm) were also observed in
this range. Chemical shifts further upfield were typical for aliphatic carbons from methoxy
(OCH3, ~55 ppm) and tert-butyl (C(CH3)3, ~35 ppm and ~30 ppm) groups adjacent to the
terminal benzene ring.
2.2. Luminescent properties
Three-dimensional fluorescence spectra (Figure 1) and UV-Vis absorption spectra
(Figure 2) were obtained for all products. The fluorescence spectra of compounds 8a, 8c, 8f,
and 8g showed one fluorescence maximum, while compound 8e possessed two maxima.
For compounds 8b, 8d, 8h, 8i, and 8j only one fluorescence maximum was visible; however,
there was a second, weaker local maximum that was partially covered by the global
maximum. In all these cases, the global maximum possessed spherical or ellipsoidal
symmetricity for larger emission intensities, while for smaller intensities an additional
asymmetric shoulder appeared. Due to large differences between the intensities of global
and local maxima and their significant overlap, it was not possible to unambiguously
determine the λex and λem of local maxima, even based on the devaluation of the three-
dimensional function (because both maxima are ellipsoidal, and λex and λem depend on
selecting the foci of the ellipsoids). All synthesized compounds emit fluorescent UV or visible
radiation upon UV irradiation. The first group (emitting UV light) includes compounds 8a, 8c,
8d, 8f, 8g, and 8j, and the second group (emitting visible light) consists of compounds 8b, 8i,
8h. Additionally, compound 8e emitted both UV and visible light. The quantum yields (Φ)
were correlated with fluorescence intensities (lager Φ is associated with larger fluorescence,
whereas there was no relationship between the absorption wavelength and
Φ
(supplementary material). This implies that a similar electronic transition occurred in all
compounds and that the amount of absorbed electromagnetic energy (photons) transformed
into internal energy significantly differed among the studied compounds. This is also why the
wavelengths at radiation absorption and excitation maxima also differed.

Figure 1. Three-dimensional fluorescence spectra of compounds 8a-j. The colour scale represents
flux of emitted photons. The number above colour scales indicates the maximum relative value of
emission intensity represented by colour scale (and indicated in respective figure). The unit of
measurement in each spectrum represents the same number of emitted photons per second, i.e.
fluorescence intensity values in all spectra can be directly compared. The green area (upper left

triangles in each spectrum) indicates the non-fluorescent region in which λex is close to or larger than
λem
.
Figure 2. UV-Vis spectra of 1,2,4,5-tetrazine derivatives 8a-j in methanol at a concentration of 5.0 x
10-6 mol/L at room temperature.
The above-described presence and lack of correlation do not exist for di(1,3,4-oxadiazol-
2-yl)-1,2,4,5-tetrazine and 3,6-di(1,3,4-thiadiazol-2-yl)-1,2,4,5-tetrazine and their derivatives
that were symmetrically substituted at both ends by methyl, ethyl, or phenyl group.[27] In all
studied compounds, the n→π* absorption transitions were the main source of excited states
during fluorescence. The substituent order leading to the smallest to the largest fluorescence
is: NO2/NO2 < NO2/C(CH3)3 < NO2/H < OCH3/H < NO2/OCH3 < C(CH3)3/H < H/H <
OCH3/C(CH3)3 < C(CH3)3/C(CH3)3 < OCH3/OCH3. This sequence generally follows the
electron-withdrawing and electron-donating properties of the substituents. The strong
electron-withdrawing substituent NO2 diminished the fluorescence compared with the

unsubstituted system (8a) because it decreased the electron density in the conjugated
system and reduced the population of excited electrons (e.g., manifested as a decreased
absorption of 8d, Figure 2). The presence of two NO2 groups largely decreased the
fluorescence emission. This effect was slightly compensated in compounds with one NO2
group and other electron-donating groups. The substituents such as OCH3 and C(CH3)3
substituents are mildly electron-donating, but OCH3 possesses a slightly stronger donating
ability than C(CH3)3. Thus, the fluorescence of the compound containing NO2/C(CH3)3
substituents was smaller than that containing NO2/OCH3 substituents. Due to ERG
differences, different fluorescence properties were observed for compounds containing OCH3
and/or C(CH3)3 substituents compared with the unsubstituted system. Compound 8c
possesses two weaker ERGs (C(CH3)3), and precedes compound 8b, which possesses two
stronger ERGs (OCH3). This slightly unintuitive result might be due to the order of
compounds possessing one ERG, as these compounds (8e, 8f) precede the unsubstituted
system (8a). However, these substituents are mildly electron-donating, and 8e (stronger
ERG) possesses two fluorescence maxima, and the second one fits with the above-
described trend. The differences between emission and excitation wavelength maxima fall in
two ranges: 54-81 nm, for compounds without an OCH3 substituent; and 110-120 nm, for
compounds with an OCH3 substituent. The second maximum of compound 8e (C(CH3)3/H
terminal groups) fell within the first range, indicating that this compound possesses a
different energy gap between the orbitals that participated in the fluorescence transitions. It
should be noted that compounds with an OCH3 substituent are not typical fluorescent
compounds that possess λem-λex smaller than 100 nm. With one exception, λex was
correlated with λem, i.e. a larger λex produced emission at larger λem (Figure S5). Compound
8d did not follow this trend due to the presence of two strongly electron-withdrawing NO2
substituents. Noteworthy is the fact that the irradiation of 8b by UV radiation led to deep-blue
fluorescence that was visible to the naked eye.
Table 3. Luminescence properties of s-tetrazine-1,3,4-oxadiazole symmetrical (8a-d) and
unsymmetrical derivatives (8e-j). The quantum yields Φ [31] were determined by comparison with a
2-
quinine sulphate (qn-SO4 ) [32] and trans,trans-1,4-diphenylbuta-1,3-diene (dpb) [33] standards – the
mean value is presented. Stokes shifts were calculated from the equation Δ = λem – λabs
.
Absorption
maximum
Emission
wavelength
λem [nm] at
global emission
maximum
Excitation
wavelength λex [nm]
at global emission
maximum
Stokes
shift
Δ [nm]
Quantum
yield*
Φ
Entry Product
λ
abs [nm]
directly
preceding λem
1
2
3
4
8a
8b
8c
8d
284
309
294
338
294
318
304
338
297
318
296
305
317
348
438
374
407
359
432
359
370
427
64
129
80
0.46
0.60
0.58
0.14
0.30
0.44
0.40
0.26
0.53
69
64
5
8e
295
137
70
6
7
8
8f
8g
8h
289
298
302
72
125

9
8i
8j
306
300
316
303
435
384
129
84
0.38
0.26
10
* Quantum yields Φ were determined according to the method described by Brouwer. [31]
3. Conclusions
We have established an effective methodology for the preparation of extended 1,2,4,5-
tetrazine derivatives conjugated via a 1,4-phenylene linker with a 1,3,4-oxadiazole ring. The
key reagents in the synthesis of the central six-membered ring were commercially-available
4-cyanobenzoic acid and hydrazine hydrate. Five-membered oxadiazole scaffolds were
obtained using aroyl chlorides and oxidative cyclization under the influence of phosphorus
oxychloride. This method permitted the introduction of an additional benzene ring substituted
with various groups. The elaborated approach makes it possible to obtain both symmetrical
and unsymmetrical arrangements, regardless of the nature of the moiety attached to the
external benzene ring. An additional advantage of this methodology is the mild oxidation
conditions of the central tetrazine core and high yields of individual stages. All synthesized
final products emitted fluorescent light upon irradiation by UV light. Compound 8b, with two
terminal ERG OCH3 substituents, showed the largest quantum yield and λem-λex, making it a
potentially useful building block for optoelectronics. The current study also shows interesting
additional prospects. The fluorescence intensity, quantum yield, and λem-λex increased in
compounds with two identical terminal ERG substituents. Consequently, introducing two
identical substituents with stronger electron-donating properties than OCH3 (such as amino,
alkyl/aryl amino) should further increase the fluorescence.
4. Experimental section
4.1. General information
Melting points were measured on a Stuart SMP3 melting point apparatus. NMR spectra
1
were recorded at 25 °C on an Agilent 400-NMR spectrometer at 400 MHz for H and 100
MHz for 13C, using CDCl3 or DMSO as solvent and TMS as the internal standard. UV-Vis
absorption and 3D fluorescence spectra were registered in methanol solutions (c = 5‧10-6
mol/dm3) with Jasco V-660 and Jasco F-6300 spectrometers, respectively. Quantum yields Φ
were calculated according to equation 1 presented in reference [30], with use of emission
[31]
intensity registered for two standard substances: quinine sulphate (qn-SO42-)
and
trans,trans-1,4-diphenyl-1,3-butadiene (dpb) [32]. FT-IR spectra were measured between
4000 and 650 cm-1 on an FT-IR Nicolet 6700 apparatus with a Smart iTR accessory.
Elemental analyses were performed with a VarioEL analyser. High-resolution mass spectra
were obtained using a Waters ACQUITY UPLC/Xevo G2QT instrument. Thin-layer
chromatography was performed on silica gel 60 F254 (Merck) thin-layer chromatography
plates using chloroform/ethyl acetate mixture (5:1, v/v) as the mobile phases.
4.1. Synthesis of compounds
4.2.1 Synthesis of 4-cyanobenzohydrazide (3): prepared according literature
procedures[33-34] in two-step reaction from commercially available 4-cyanobenzoic acid
(1).
4.2.2 General procedure for the synthesis of compounds 5a-d: Aroyl chlorides (4a-d)
were prepared according to a literature procedure[35] from commercially-available aroyl
carboxylic acids. The crude chlorides 4a-d (31 mmol) were dissolved in dry toluene (20
mL) and added dropwise to a mixture of 4-cyanobenzohydrazide (3) (5.00 g, 31 mmol),

sodium bicarbonate (3.60 g, 31 mmol), and water (100 mL). The resulting slurry was
mixed for 24 h at room temperature. The plastic mass was cooled in an ice bath and
filtered. The product was treated with diethyl ether (50 mL), triturated, and dried, followed
by recrystallization from acetonitrile.
4.2.2.1N'-benzoyl-4-cyanobenzohydrazide (5a): According to general procedure: white
solid (6.16 g, 75 % yield), mp. 224-226 °C, 1H NMR (400 MHz, [D6]DMSO): δ = 10.61
(s, 1H; NH), 10.55 (s, 1H; NH), 8.01-7.95 (m, 4H; Ar), 7.95 (d, 2H, JH,H=4 Hz; Ar),
7.60 (t, 1H, JH,H=6 Hz; Ar), 7.53 ppm (t, 2H, JH,H=6 Hz; Ar); 13C NMR (100MHz,
[D6]DMSO) δ = 166.8 (CO), 165.2 (CO), 136.4, 132.9, 132.5, 132.0, 128.5, 128.3,
127.4, 118.3, 114.3 ppm; IR (ATR): ν= 3184, 2230, 1597, 1574, 1559, 1504, 1461,
1439, 1267, 1176, 1114, 1073, 1025, 1015, 961, 841, 792, 756, 713, 698, 681 cm−1;
UV/Vis (CH3OH): λmax(ε·10-3)=204 (27.6), 236 nm (31.0 mol−1dm3cm−1); HRMS (ESI):
m/z calcd for C15H11N3O2+H+: 266.0924 [M+H]+; found: 266.0922; elemental analysis
calcd (%) for C15H11N3O2: C 67.92, H 4.18, N 15.84; found: C 67.90, H 4.19, N 15.81.
4.2.2.24-cyano-N'-(4-methoxybenzoyl)benzohydrazide (5b): According to general
1
procedure: white solid (7.59 g, 83% yield), mp. 176-178°C, H NMR (400 MHz,
[D6]DMSO): δ = 10.61 (s, 1H; NH), 10.96 (s, 1H; NH), 7.99-7.93 (m, 4H; Ar), 7.90 (d,
2H, JH,H=8 Hz; Ar), 7.02 (d, 2H, JH,H=12 Hz; Ar), 3.83 ppm (s, 3H; CH3); 13C NMR
(100MHz, [D6]DMSO) δ = 167.0 (CO), 164.1 (CO), 162.7, 137.3, 132.6, 132.4, 131.3,
127.8, 118.3, 113.7, 113.5, 55.4 ppm (CH3); IR (ATR): ν= 3183, 3015, 2231, 1660,
1599, 1557, 1502, 1464, 1346, 1299, 1287, 1257, 1178, 1128, 1026, 1001, 926, 890,
850, 792, 770, 753, 717, 679 cm−1; UV/Vis (CH3OH): λmax(ε·10-3)=204 (32.8), 239.5
nm (27.9 mol−1dm3cm−1); HRMS (ESI): m/z calcd for C16H13N3O3+H+: 296.1030
[M+H]+; found: 296.1033; elemental analysis calcd (%) for C16H13N3O3: C 65.08, H
4.44, N 14.23; found: C 65.05, H 4.42, N 14.25.
4.2.2.34-(tert-butyl)-N'-(4-cyanobenzoyl)benzohydrazide (5c): According to general
1
procedure: white solid (7.96 g, 80% yield), mp. 212-214 °C, H NMR (400 MHz,
[D6]DMSO): δ = 10.78 (s, 1H; NH), 10.54 (s, 1H; NH), 8.08 (d, 2H, JH,H=8 Hz; Ar),
8.02 (d, 2H, JH,H=8 Hz; Ar), 7.87 (d, 2H, JH,H=8 Hz; Ar), 7.54 (d, 2H, JH,H=8 Hz; Ar),
1.31 ppm (s, 9H; CH3); 13C NMR (100MHz, [D6]DMSO) δ = 165.7, 164.5, 154.8,
136.6, 132.7, 129.6, 128.3, 127.4, 125.3, 118.2, 114.2, 34.7 (C), 30.9 ppm (CH3); IR
(ATR): ν= 3183, 2968, 2230, 1687, 1643, 1607, 1572, 1502, 1462, 1400, 1368, 1303,
1291, 1272, 1189, 1122, 1014, 928, 853, 812, 795, 770, 737, 701 cm−1; UV/Vis
(CH3OH): λmax(ε·10-3)=203.5 (29.7), 240.5 nm (28.4 mol−1dm3cm−1); HRMS (ESI): m/z
calcd for C19H19N3O2+H+: 322.1550 [M+H]+; found: 322.1553; elemental analysis
calcd (%) for C19H19N3O2: C 71.01, H 5.96, N 13.08; found: C 71.00, H 5.98, N 13.04.
4.2.2.44-cyano-N'-(4-nitrobenzoyl)benzohydrazide (5d): According to general procedure:
white solid (5.77 g, 60% yield), mp. 217-219 °C, 1H NMR (400 MHz, [D6]DMSO): δ =
11.00 (s, 1H; NH), 10.94 (s, 1H; NH), 8.38 (d, 2H, JH,H=8 Hz; Ar), 8.16 (d, 2H,
JH,H=8 Hz; Ar), 8.09 (d, 2H, JH,H=12 Hz; Ar), 8.03 ppm (d, 2H, JH,H=8 Hz; Ar); 13C NMR
(100MHz, [D6]DMSO) δ = 164.4 (CO), 164.4 (CO), 149.5, 136.4, 132.7, 130.7, 129.0,
128.3, 123.8, 118.3, 114.4 ppm; ); IR (ATR): ν= 3172, 2967, 2230, 1687, 1641, 1607,
1597, 1573, 1558, 1503, 1461, 1367, 1271, 1122, 1015, 928, 853, 794, 769, 714,
697, 681 cm−1; UV/Vis (CH3OH): λmax(ε·10-3)=203.5 (21.7), 259 nm (17.7
mol−1dm3cm−1); HRMS (ESI): m/z calcd for C15H10N4O4+H+: 311.0775 [M+H]+; found:
311.0774; elemental analysis calcd (%) for C15H10N4O4: C 58.07, H 3.25, N 18.06;
found: C 58.03, H 3.27, N 18.08.
4.2.3 General procedure for the synthesis of derivatives 6a-d: N,N’-diacylhydrazines
5a-d (15.0 mmol) were suspended in dry toluene (40 mL), and then phosphorus
oxychloride (40 mL, 430 mmol) was added. The reaction was heated for 4-9 h, and the

resulting mixture was filtered and the filtrate was evaporated on a rotary evaporator. 50
mL of water was added to the residue, and the precipitate was filtered and washed with
water (20 mL). The crude product was purified by column chromatography using a
chloroform/ethyl acetate mixture (5:1, v/v) as the eluent.
4.2.3.14-(5-phenyl-1,3,4-oxadiazol-2-yl)benzonitrile (6a): According to general procedure:
yellow solid (3.66 g, 96% yield), mp. 174-176 °C, 1H NMR (400 MHz, [D6]DMSO): δ =
8.31 (d, 2H, JH,H=8 Hz; Ar), 8.16 (d, 2H, JH,H=8 Hz; Ar), 8.11 (d, 2H, JH,H=8 Hz; Ar),
13
7.68-7.65 ppm (m, 3H; Ar); C NMR (100MHz, [D6]DMSO) δ = 164.6, 162.9, 133.3,
129.4, 129.4, 127.5, 127.3, 126.8, 123.0, 118.1, 114.1 ppm; IR (ATR): ν= 3171, 2967,
2229, 1687, 1640, 1606, 1575, 1551, 1489, 1463, 1447, 1403, 1271, 1115, 1075,
1014, 854, 774, 738, 707, 686 cm−1; UV/Vis (CH3OH): λmax(ε·10-3)=205 (20.0), 236
(8.5), 291.5 nm (21.3 mol−1dm3cm−1); HRMS (ESI): m/z calcd for C15H9N3O+H+:
248.0818 [M+H]+; found: 248.0815; elemental analysis calcd (%) for C15H9N3O: C
72.87, H 3.67, N 16.99; found: C 72.89, H 3.65, N 16.98.
4.2.3.24-(5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-yl)benzonitrile (6b): According to
1
general procedure: yellow solid (4.07 g, 98% yield), mp. 173-175 °C, H NMR (400
MHz, [D6]DMSO): δ = 8.27 (d, 2H, JH,H=8 Hz; Ar), 8.08 (d, 4H, JH,H=8 Hz; Ar), 7.16 (d,
2H, JH,H=8 Hz; Ar), 3.86 ppm (s, 3H; CH3); 13C NMR (100MHz, [D6]DMSO) δ =164.6,
162.3, 161.9, 132.5, 128.7, 127.4, 127.2, 118.1, 115.3, 114.9, 113.8, 55.5 ppm (CH3);
IR (ATR): ν= 3183, 2962, 2230, 1684, 1606, 1575, 1490, 1460, 1427, 1254, 1172,
1103, 1072, 1015, 852, 835, 797, 772, 745, 703 cm−1; UV/Vis (CH3OH): λmax(ε·10-
3)=204.5 (21.6), 248.5 (15.0), 307 nm (18.1 mol−1dm3cm−1); HRMS (ESI): m/z calcd
for C16H11N3O2+H+: 278.0924 [M+H]+; found: 278.0927; elemental analysis calcd (%)
for C16H11N3O2: C 69.31, H 4.00, N 15.15; found: C 69.33, H 4.03, N 15.12.
4.2.3.34-(5-(4-(tert-butyl)phenyl)-1,3,4-oxadiazol-2-yl)benzonitrile (6c): According to
general procedure: yellow solid (3.95 g, 87% yield), mp. 89-91 °C, 1H NMR (400 MHz,
[D6]DMSO): δ = 8.30 (d, 2H, JH,H=8 Hz; Ar), 8.12 (m, 2H; Ar), 7.67-7.64 (m, 4H; Ar),
1.34 ppm (s, 9H; CH3); 13C NMR (100MHz, [D6]DMSO) δ = 164.7, 162.7, 155.4,
133.4, 127.4, 127.3, 126.3, 126.3, 125.6, 118.1, 114.0, 34.9 (C), 30.8 ppm (CH3); IR
(ATR): ν= 2964, 2230, 1679, 1608, 1492, 1462, 1412, 1364, 1316, 1264, 1173, 1134,
1112, 1069, 1014, 929, 854, 839, 777, 757, 745, 707 cm−1; UV/Vis
(CH3OH): λmax(ε·10-3)=204.5 (35.5), 235.5 (23.9), 279.5 nm (13.7 mol−1dm3cm−1);
HRMS (ESI): m/z calcd for C19H17N3O+H+: 304.1444 [M+H]+; found: 304.1442;
elemental analysis calcd (%) for C19H17N3O: C 75.23, H 5.65, N 13.85; found: C
75.20, H 5.67, N 13.89.
4.2.3.44-(5-(4-nitrophenyl)-1,3,4-oxadiazol-2-yl)benzonitrile (6d): According to general
1
procedure: yellow solid (3.46 g, 79% yield), mp. 180-182 °C, H NMR (400 MHz,
[D6]DMSO): δ = 8.49-8.41 (m, 4H; Ar), 8.33-8.31 (m, 2H; Ar), 8.18-8.16 ppm (m, 2H;
Ar); 13C NMR (100MHz, [D6]DMSO) δ = 165.7, 163.5, 150.0, 132.6, 130.6, 127.6,
127.0, 124.6, 123.7, 118.0, 114.4 ppm; IR (ATR): ν= 3111, 2842, 2555, 2230, 1690,
1605, 1521, 1492, 1427, 1345, 1310, 1292, 1128, 1106, 1071, 1013, 965, 932, 877,
853, 800, 788, 773, 739, 717, 681 cm−1; UV/Vis (CH3OH): λmax(ε·10-3)=204.5 (26.3),
304 nm (22.9 mol−1dm3cm−1); HRMS (ESI): m/z calcd for C15H8N4O3+H+: 293.0669
[M+H]+; found: 293.0666; elemental analysis calcd (%) for C15H8N4O3: C 61.65, H
2.76, N 19.17; found: C 61.67, H 2.73, N 19.15.
4.2.4 General procedure for the synthesis of 1,4-dihydro-1,2,4,5-tetrazine derivatives
(7a-j): One or two of compounds 6a-d (2 mmol of each substrate) and sulfur (0.08 g, 2.5
mmol) were suspended in 60 mL of toluene and cooled to 0 °C. Hydrazine hydrate (0.5
mL, 6 mmol) was added dropwise with stirring. The mixture was allowed to reach room

temperature and then heated under reflux for 2 h. The mixture was then cooled to room
temperature, filtered, and the filtrate was evaporated.
4.2.5 General procedure for the synthesis of derivatives 8a-j: The crude compound 7a-j
(1 mmol) was dissolved in methanol (30 mL), and then 35% hydrogen peroxide (30 mL)
was added. After stirring at room temperature for 24 h, the reaction mixture was filtered
and concentrated by evaporation. The residue was filtered and purified by column
chromatography using a chloroform/ethyl acetate mixture (5:1, v/v) as the eluent.
4.2.5.13,6-bis(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)-1,2,4,5-tetrazine (8a): According
1
to general procedure. Pink solid (0.34 g, 65% yield), mp. 115-117 °C, H NMR (400
MHz, [D6]DMSO): δ = 8.29 (d, JH,H=12 Hz, 4H; Ar), 8.15-8.08 (m, 8H; Ar), 7.67-7.63
ppm (m, 6H; Ar); 13C NMR (100MHz, [D6]DMSO) δ = 164.6, 164.0, 162.8, 132.3,
132.0, 129.4, 129.3, 127.3, 126.8, 126.6, 123.0 ppm; IR (ATR): ν= 3065, 2228, 1608,
1550, 1486, 1446, 1412, 1316, 1270, 1068, 1020, 965, 922, 854, 779, 739, 708, 686
cm−1; UV/Vis (CH3OH): λmax(ε·10-3)=284 nm (59.6 mol−1dm3cm−1); fluorescence
(CH3OH): λex=294 nm; λem=348 nm; HRMS (ESI): m/z calcd for C30H18N8O2+H+:
523.1625 [M+H]+; found: 523.1623; elemental analysis calcd (%) for C30H18N8O2: C
68.96, H 3.47, N 21.44; found: C 68.98, H 3.49, N 21.43.
4.2.5.23,6-bis(4-(5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-yl)phenyl)-1,2,4,5-tetrazine
(8b): According to general procedure. Pink solid (0.42 g, 72% yield), mp. 184-186 °C,
1H NMR (400 MHz, [D6]DMSO): δ = 8.27 (d, JH,H=8 Hz, 4H; Ar), 8.10-8.07 (m, 8H; Ar),
7.17 (d, 4H, JH,H=8 Hz; Ar) 3.87 ppm (s, 6H; CH3); 13C NMR (100MHz, [D6]DMSO) δ =
164.6, 163.4, 162.3, 161.9, 133.3, 128.7, 128.4, 127.4, 127.2, 115.3, 114.9, 55.6 ppm
(CH3); IR (ATR): ν= 2945, 2840, 2229, 1609, 1583, 1549, 1489, 1457, 1439, 1424,
1411, 1367, 13.06, 1253, 1220, 1172, 1118, 1102, 1072, 1028, 963, 834, 799, 773,
745,
704
cm−1;
UV/Vis
(CH3OH): λmax(ε·10-3)=250
(39.5),
309
nm
(69.7 mol−1dm3cm−1); fluorescence (CH3OH): λex=318 nm; λem=438 nm; HRMS (ESI):
m/z calcd for C32H22N8O4+H+: 583.1837 [M+H]+; found: 583.1838; elemental analysis
calcd (%) for C32H22N8O4: C 65.97, H 3.81, N 19.23; found: C 65.95, H 3.80, N 19.20.
4.2.5.33,6-bis(4-(5-(4-(tert-butyl)phenyl)-1,3,4-oxadiazol-2-yl)phenyl)-1,2,4,5-tetrazine
(8c): According to general procedure. Yellow solid (0.43 g, 67% yield), mp. 177-179
1
°C, H NMR (400 MHz, [D6]DMSO): δ = 8.28 (d, JH,H=8 Hz, 4H; Ar), 8.20 (d, JH,H=4
Hz, 4H; Ar), 7.66-7.63 (m, 8H; Ar), 1.33 ppm (s, 18H; CH3); 13C NMR (100MHz,
[D6]DMSO) δ = 164.7, 163.8, 162.7, 154.9, 133.3, 128.5, 127.4, 127.3, 126.3, 126.2,
125.6, 34.8 (C), 30.8 ppm (CH3); IR (ATR): ν= 3389, 3184, 2963, 2870, 2227, 1662,
1615, 1583, 1549, 1492, 1463, 1418, 1393, 1363, 1315, 1270, 1193, 1113, 1097,
1066, 1014, 963, 838, 787, 751, 737, 715 cm−1;UV/Vis (CH3OH): λmax(ε·10-3)=242
(26.4),
294
nm
(63.1 mol−1dm3cm−1);
fluorescence
(CH3OH): λex=304 nm; λem=374 nm; HRMS (ESI): m/z calcd for C38H34N8O2+H+:
635.2877 [M+H]+; found: 635.2875; elemental analysis calcd (%) for C38H34N8O2: C
71.91, H 5.40, N 17.65; found: C 71.90, H 5.44, N 17.92.
4.2.5.43,6-bis(4-(5-(4-nitrophenyl)-1,3,4-oxadiazol-2-yl)phenyl)-1,2,4,5-tetrazine
(8d):
According to general procedure. Yellow solid (0.26 g, 43% yield), mp. 249-251 °C, 1H
NMR (400 MHz, [D6]DMSO): δ = 8.50-8.43 (m, 8H; Ar), 8.39 (d, JH,H=8 Hz, 4H; Ar),
8.16 ppm (d, JH,H=8 Hz, 4H; Ar); 13C NMR (100MHz, [D6]DMSO) δ = 166.8, 164.4,
163.0, 149.3, 130.5, 128.8, 128.5, 128.1, 126.9, 124.6, 123.6 ppm; IR (ATR): ν=
3426, 3340, 3223, 2229, 1604, 1581, 1556, 1490, 1442, 1413, 1311, 1271, 1179,
1071, 1013, 849, 838, 775, 744, 703 cm−1; UV/Vis (CH3OH): λmax(ε·10-3)=258 (32.6),
338 nm (49.0 mol−1dm3cm−1); fluorescence (CH3OH): λex=338 nm; λem=407 nm;
HRMS (ESI): m/z calcd for C30H16N10O6+H+: 613.1327 [M+H]+; found: 613.1328;

elemental analysis calcd (%) for C30H16N10O6: C 58.83, H 2.63, N 22.87; found: C
58.85, H 2.60, N 22.89.
4.2.5.52-(4-methoxyphenyl)-5-(4-(6-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)-1,2,4,5-
tetrazin-3-yl)phenyl)-1,3,4-oxadiazole (8e): According to general procedure. Yellow
1
solid (0.32 g, 58% yield), mp. 142-144 °C, H NMR (400 MHz, [D6]DMSO): δ = 8.29-
8.26 (m, 4H; Ar), 8.15-8.07 (m, 8H; Ar), 7.65-7.64 (m, 3H; Ar), 7.18-7.16 (m, 2H; Ar),
3.87 ppm (s, 3H; CH3); 13C NMR (100MHz, [D6]DMSO) δ = 164.6, 164.6, 164.0,
163.4, 162.9, 162.3, 161.9, 133.3, 133.3, 132.3, 132.0, 129.4, 128.7, 128.3, 127.3,
127.2, 126.8, 126.6, 123.3, 123.0, 115.3, 114.9, 55.5 ppm (CH3); IR (ATR): ν= 3065,
2229, 2162, 2055, 1989, 1609, 1584, 1548, 1489, 1446, 1412, 1307, 1255, 1220,
1172, 1102, 1069, 1028, 964, 926, 835, 799, 776, 745, 738, 708, 687 cm−1; UV/Vis
(CH3OH): λmax(ε·10-3)=253 (31.1), 295 nm (55.8 mol−1dm3cm−1); fluorescence
(CH3OH): λex=297, 318 nm; λem=359, 432 nm; HRMS (ESI): m/z calcd for
C31H20N8O3+H+: 553.1731 [M+H]+; found: 553.1733; elemental analysis calcd (%) for
C31H20N8O3: C 67.39, H 3.65, N 20.28; found: C 67.40, H 3.63, N 20.27.
4.2.5.62-(4-(tert-butyl)phenyl)-5-(4-(6-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)-1,2,4,5-
tetrazin-3-yl)phenyl)-1,3,4-oxadiazole (8f): According to general procedure. Yellow
1
solid (0.32 g, 56% yield), mp. 164-166 °C, H NMR (400 MHz, [D6]DMSO): δ = 8.23-
8.30 (m, 4H; Ar), 8.18-8.03 (m, 6H; Ar), 7.67-7.64 (m, 7H; Ar) 1.34 ppm (s, 9H; CH3);
13C NMR (100MHz, [D6]DMSO) δ = 164.7, 164.6, 164.0, 163.8, 162.9, 162.7, 155.3,
133.3, 132.3, 132.0, 129.4, 129.4, 128.4, 127.4, 127.3, 127.3, 126.9, 126.7, 126.2,
126.2, 125.6, 123.0, 34.8 (C), 30.8 ppm (CH3); IR (ATR): ν= 3395, 3170, 2958, 1663,
1615, 1581, 1548, 1488, 1447, 1421, 1392, 1270, 1179, 1098, 1068, 1015, 964, 924,
939, 782, 750, 739, 710, 687 cm−1; UV/Vis (CH3OH): λmax(ε·10-3)=289 nm
(59.3 mol−1dm3cm−1); fluorescence (CH3OH): λex=296 nm; λem=359 nm; HRMS (ESI):
m/z calcd for C34H26N8O2+H+: 579.2251 [M+H]+; found: 579.2250; elemental analysis
calcd (%) for C34H26N8O2: C 70.58, H 4.53, N 19.37; found: C 70.56, H 4.50, N 19.39.
4.2.5.72-(4-nitrophenyl)-5-(4-(6-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)-1,2,4,5-
tetrazin-3-yl)phenyl)-1,3,4-oxadiazole (8g): According to general procedure. Yellow
1
solid (0.29 g, 51% yield), mp. 164-166 °C, H NMR (400 MHz, [D6]DMSO): δ = 8.44
(d, JH,H=8 Hz, 2H; Ar), 8.39 (d, JH,H=8 Hz, 2H; Ar), 8.33-8.28 (m, 4H; Ar), 8.14-8.09
(m, 6H; Ar), 7.67-7.62 ppm (m, 3H; Ar); 13C NMR (100MHz, [D6]DMSO) δ = 166.5,
164.0, 163.6, 163.3, 162.9, 161.4, 149.3, 132.0, 129.4, 129.4, 128.6, 128.4, 128.2,
127.6, 127.3, 127.0, 126.9, 126.8, 124.6, 123.3, 123.0, 118.0 ppm; IR (ATR): ν=
3367, 2228, 1608, 1576, 1549, 1523, 1489, 1447,1412, 1338, 1311, 1271, 1220,
1179, 1104, 1069, 1015, 964, 852, 774, 745, 738, 709, 689 cm−1;UV/Vis
(CH3OH): λmax(ε·10-3)=298
nm
(53.9 mol−1dm3cm−1);
fluorescence
(CH3OH): λex=305 nm; λem=370 nm; HRMS (ESI): m/z calcd for C30H17N9O4+H+:
568.1476 [M+H]+; found: 568.1478; elemental analysis calcd (%) for C30H17N9O4: C
63.49, H 3.02, N 22.21; found: C 63.47, H 3.05, N 22.19.
4.2.5.82-(4-(tert-butyl)phenyl)-5-(4-(6-(4-(5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-
yl)phenyl)-1,2,4,5-tetrazin-3-yl)phenyl)-1,3,4-oxadiazole (8h): According to general
1
procedure. Yellow solid (0.43 g, 70% yield), mp. 132-134 °C, H NMR (400 MHz,
[D6]DMSO): δ = 8.27-8.25 (m, 4H; Ar); 8.08-8.01 (m, 6H; Ar), 7.65-7.62 (m, 4H; Ar),
7.16 (d, JH,H=8 Hz, 2H; Ar), 3.86 (s, 3H, CH3), 1.32 ppm (s, 9H; CH3); 13C NMR
(100MHz, [D6]DMSO) δ = 164.3, 164.2, 163.8, 163.4, 162.7, 162.2, 162.0, 155.1,
131.3, 130.2, 128.7, 128.5, 128.4, 126.7, 126.6, 126.5, 126.2, 120.7, 120.5, 120.3,
115.5, 114.9, 55.3 (CH3), 34.9 (C), 30.8 ppm (CH3); IR (ATR): ν= 3385, 2958, 2228,
1612, 1549, 1492, 1441, 1416, 1363, 1306, 1263, 1220, 1176, 1109, 1074, 1018,
962, 833, 800, 772, 745, 711, 704 cm−1; UV/Vis (CH3OH): λmax(ε·10-3)=248 (31.4), 302
nm (61.1 mol−1dm3cm−1); fluorescence (CH3OH): λex=317 nm; λem=427 nm; HRMS

(ESI): m/z calcd for C35H28N8O3+H+: 609.2357 [M+H]+; found: 609.2355; elemental
analysis calcd (%) for C35H28N8O3: C 69.07, H 4.64, N 18.41; found: C 69.06, H 4.62,
N 18.40.
4.2.5.92-(4-methoxyphenyl)-5-(4-(6-(4-(5-(4-nitrophenyl)-1,3,4-oxadiazol-2-yl)phenyl)-
1,2,4,5-tetrazin-3-yl)phenyl)-1,3,4-oxadiazole (8i): According to general procedure.
Yellow solid (0.28 g, 47% yield), mp. 179-181 °C, 1H NMR (400 MHz, [D6]DMSO): δ =
8.47-8.40 (m, 4H; Ar), 8.34-8.03 (m, 10H; Ar), 7.18-7.14 (m, 2H; Ar), 3.87 ppm (s, 3H;
CH3); 13C NMR (100MHz, [D6]DMSO) δ = 164.6, 164.2, 163.4, 163.3, 162.3, 162.2,
161.9, 149.3, 133.4, 133.3, 130.0, 128.8, 128.6, 128.5, 127.6, 127.2, 126.4, 125.7,
124.6, 118.1, 115.3, 114.9, 55.6 ppm (CH3); IR (ATR): ν= 3372, 2228, 1680, 1609,
1550, 1522, 1491, 1441, 1422, 1339, 1308, 1255, 1220, 1174, 1102, 1070, 1026,
964, 835, 773, 745, 711 cm−1; UV/Vis (CH3OH): λmax(ε·10-3)=252 (31.0), 306 nm
(56.3 mol−1dm3cm−1); fluorescence (CH3OH): λex=316 nm; λem=435 nm; HRMS (ESI):
m/z calcd for C31H19N9O5+H+: 598.1582 [M+H]+; found: 598.1580; elemental analysis
calcd (%) for C31H19N9O5: C 62.31, H 3.21, N 21.10; found: C 62.34, H 3.20, N 21.12.
4.2.5.10
2-(4-(tert-butyl)phenyl)-5-(4-(6-(4-(5-(4-nitrophenyl)-1,3,4-oxadiazol-2-
yl)phenyl)-1,2,4,5-tetrazin-3-yl)phenyl)-1,3,4-oxadiazole (8j): According to general
1
procedure. Yellow solid (0.27 g, 44% yield), mp. 122-124 °C, H NMR (400 MHz,
[D6]DMSO): δ = 8.31-8.26 (m, 2H; Ar), 8.22 (d, JH,H=8 Hz, 2H; Ar), 8.08-8.06 (m, 6H;
Ar), 7.79 (d, JH,H=8 Hz, 2H; Ar), 7.65-7.62 (m, 4H; Ar), 1.33 ppm (s, 9H; CH3); 13C
NMR (100MHz, [D6]DMSO) δ = 166.5, 164.7, 164.2, 163.8, 162.7, 161.5, 154.9,
152.7, 133.3, 133.3, 128.4, 128.2, 127.3, 126.9, 126.7, 126.5, 126.2, 126.2, 124.6,
120.6, 120.3, 118.2, 34.8 (C), 30.8 ppm (CH3); IR (ATR): ν= 3340, 2966, 2229, 1606,
1581, 1552, 1525, 1490, 1442, 1414, 1363, 1338, 1313, 1271, 1220, 1179, 1104,
1071, 1014, 963, 838, 772, 745, 704 cm−1; UV/Vis (CH3OH): λmax(ε·10-3)=259 (32.3),
300
(46.1),
343
nm
(34.9 mol−1dm3cm−1);
fluorescence
(CH3OH): λex=303 nm; λem=384 nm; HRMS (ESI): m/z calcd for C34H25N9O4+H+:
634.2102 [M+H]+; found: 634.2104; elemental analysis calcd (%) for C34H25N9O4: C
65.48, H 4.04, N 20.21; found: C 65.45, H 4.06, N 20.23.
References
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J. Mol. Liq. 2018, 272, 507
[2] Moral, M., Garzón, A.; Olivier, Y.; Muccioli, L.; Sancho-García, J. C.; Granadino-
Roldán, J. M.; Fernández-Gómez, M.: J. Phys. Chem. C 2015, 119, 18945
[3] Gheno, A.; Trigaud, T.; Bouclé, J.; Audebert, P.; Ratier, B.; Vedraine S.: Opt. Mater.
(Amst) 2018, 75, 781
[4] Quinton, C.; Chi, S.; Dumas-Verdes, C.; Audebert, P.; Clavier, G.; Perry, J. W.; Alain-
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New symmetrical and unsymmetrical s-tetrazine-1,3,4-oxadiazoles were obtained.
Mild oxidation conditions of the tetrazine ring were applied.
Highly luminescent s-tetrazines are good candidates for optoelectronics.

Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests: