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Communication

Polyaromatic Hydrocarbon (PAH)-Based Aza-POPOPs: Synthesis, Photophysical Studies, and Nitroanalyte Sensing Abilities

by
Mohammed S. Mohammed
1,
Igor S. Kovalev
1,
Natalya V. Slovesnova
1,2,
Leila K. Sadieva
1,3,
Vadim A. Platonov
1,
Alexander S. Novikov
4,5,
Sougata Santra
1,
Julia E. Morozova
6,*,
Grigory V. Zyryanov
1,3,
Valery N. Charushin
1,3 and
Brindaban C. Ranu
1,7
1
Department of Organic and Biomolecular Chemistry, Ural Federal University, 19, Mira St., 620002 Yekaterinburg, Russia
2
Department of Pharmacy and Chemistry, Ural Medical University, 3, Repina St., 620028 Yekaterinburg, Russia
3
I. Ya. Postovsky Institute of Organic Synthesis of RAS (Ural Division), 22/20, S. Kovalevskoy/Akademicheskaya St., 620137 Yekaterinburg, Russia
4
Institute of Chemistry, Saint Petersburg State University, Universitetskaya Nab., 7/9, 199034 Saint Petersburg, Russia
5
Research Institute of Chemistry, Peoples’ Friendship University of Russia (RUDN University), Miklukho-Maklaya St., 6, 117198 Moscow, Russia
6
Arbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Center of RAS, Arbuzov Str. 8, 420088 Kazan, Russia
7
School of Chemical Sciences, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2023, 24(12), 10084; https://doi.org/10.3390/ijms241210084
Submission received: 17 April 2023 / Revised: 31 May 2023 / Accepted: 7 June 2023 / Published: 13 June 2023

Abstract

:
1,4-Bis(5-phenyl-2-oxazolyl)benzene (POPOP) is a common scintillation fluorescent laser dye. In this manuscript, the synthesis of 2-Ar-5-(4-(4-Ar’-1H-1,2,3-triazol-1-yl)phenyl)-1,3,4-oxadiazoles (Ar, Ar’ = Ph, naphtalenyl-2, pyrenyl-1, triphenilenyl-2), as PAH-based aza-analogues of POPOP, by means of Cu-catalyzed click reaction between 2-(4-azidophenyl)-5-Ar-1,3,4-oxadiazole and terminal ethynyl-substituted PAHs is reported. An investigation of the photophysical properties of the obtained products was carried out, and their sensory response to nitroanalytes was evaluated. In the case of pyrenyl-1-substituted aza-POPOP, dramatic fluorescence quenching by nitroanalytes was observed.

1. Introduction

One of the most important tasks of modern synthetic organic chemistry is obtaining new compounds that will find wide application in various industrial areas and medicine. One of the most representative examples of a novel type of compounds is azaheterocyclic fluorophores, which can also act as drug candidates and contain cyclic azole or azine core as a common pharmacophore or ligand unit, as well as fused or conjugated (poly)aromatic moieties as fluorogenes and/or receptor units. 1,4-Bis(5-phenyl-2-oxazolyl)benzene (POPOP) is a well-known organic fluorophore (Figure 1), which is commonly used as a spectrum shifter, including in multilayer scintillation screen to visualize radiation that is invisible to the human eye [1,2]. Due to its excellent photophysical properties, especially its high quantum yield (up to 97.5% in cyclohexane or 91% in ethanol [3]), POPOP is successfully utilized in dye vapor lasers [4,5]. On the other hand, aza-analogues of POPOP, such as 1,3,4-oxadiazoles, are of wide interest due to the promising biological activity of oxadizoles [6,7,8] and their intriguing photophysical properties [9,10,11,12].
The term “click chemistry” was introduced for the first time in 1998 by K. Barry Sharpless, the 2001 and 2022 Nobel Prize Laureate in Chemistry, and it was fully described by B.K. Sharpless, H. C. Kolb, and M.G. Finn in 2001 [13]. Since then, this approach has gained worldwide acknowledgment for its simple reaction technique leading to single product formation without by-products. The copper(I)-catalyzed azide/alkyne “click” reaction (also termed Sharpless “click” reaction) occurs through the interaction between a terminal alkyne and an azide in the presence of Cu(I) catalysis, and results in a cycloaddition product—1,4 disubstituted 1,2,3-triazole [14,15,16,17]. This reaction is also known as Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition between alkynes and azides (CuAAC) [18,19]. Additionally, 1,3-dipolar cycloaddition of organic azides with alkynes as dipolarophiles is the most straightforward way to obtain useful 1,2,3-triazoles [5]. Applications of the Cu-catalyzed (cyclo)addition reactions have already contributed to many areas of modern chemistry, including asymmetric synthesis [20,21,22,23,24], and Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) is a convenient tool for bioconjugation reactions, peptidomimetic chemistry, polymer and materials sciences, and supramolecular chemistry [25,26]. The chemistry of 1,2,3-triazoles has gained much attention since its discovery, and various synthetic protocols have been developed for the synthesis of this moiety [27,28]. In addition, 1,2,3-triazoles are one of the most important connective linkers and functional aromatic heterocycles in modern chemistry [29]. In addition, it is well known that 1,2,3-triazoles, as highly valuable N-heterocyclic compounds, are ubiquitous in many pharmaceuticals and bioactive molecules [30,31].
In this manuscript, we report the synthesis of novel POPOP aza-analogues (Figure 1) via the click reaction between 2-(4-azidophenyl)-5-(aryl)-oxadiazole-1,3,4 and ethynyl-substituted (poly)arenes, as well as an investigation of the photophysical and sensing properties of the obtained products.

2. Results

2.1. Synthesis of Target Fluorophores

As one of the azole fragments, the aza-analog of 1,3-oxazole was used as it is easily derived synthetically [32,33] from 1,3,4-oxadiazol. As mentioned above, 1,3,4-oxadiazole fragment is widely presented in many compounds with various promising biological activities and possesses intriguing photophysical properties. 1,2,3-triazole, an azadeoxa analogue of 1,3-oxazole, was introduced as second azole by using Cu(I)-catalyzed click reaction. Based on these click reactions, we successfully synthesized 4-azidophenyloxadiazoles 2a,b as precursors of the azido components. These 4-azidophenyloxadiazoles were prepared for the first time by means of modified Sandmeyer reaction starting from 4-(5-phenyl-1,3,4-oxadiazol-2-yl)anilines [34] (Scheme 1).
As a second step, we used Cu(I)-promoted azido–alkyne coupling (CuAAC) (Scheme 2) to construct the 1,2,3-triazole ring by using two different approaches. The first approach involved the use of cuprous sulphate derived in situ via the reaction of sodium ascorbate with copper(II) sulphate pentahydrate in aqueous THF (H2O:THF 1:9 v/v) to obtain the target products 3 in 73–96% yields. The second approach involved modified reaction conditions, namely using cuprous bromide in dry DMF. The main reason for using dry DMF is the poor solubility of the starting PAH-ethynyl derivatives in aqueous THF. The target products 3 were obtained in 50–99% yields. It is worth mentioning that the main advantage of the reported copper(I)-catalized azido–alkyne coupling over the classical Huisgen 1,3-dipolar cycloaddition [35] is that the high regioselectivity of the former reaction results in only 1,4-isomer, whereas non-catalyzed 1,3-dipolar cycloaddition gives a mixture of 1,4- and 1,5-isomers [36].
The structures of all the obtained compounds were confirmed by means of 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis (See ESI for details).

2.2. Photophysical and Sensing Properties of the Obtained Compounds

The above-mentioned azaheterocycles 3 could be considered as POPOP aza-analogs. However, initial photophysical studies showed that the photophysical properties of the obtained compounds 3 are not quite similar to those of POPOP, which are, probably, due to the contribution of both peripheral (poly)aromatic substituents and azole moieties. Thus, in the spectra of pyrene-bearing fluorophores 3c and 3g, both absorption and emission are red-shifted in comparison with POPOP, while the emission spectra of other fluorophores are blue-shifted compared to that of POPOP. Among all the fluorophores, a pronounced blue shift is observed for fluorophore 3a. Additionally, the emission spectrum of 3a is the most blue-shifted in comparison to the emission spectra of all other POPOP analogues. Whereas the absorption and emission spectra of POPOP have a weakly expressed vibronic structure, the spectra of all fluorophores 3, including pyrene-containing ones, are blurred. Interestingly, while S0→S1 electronic transition has a higher intensity than S0→S2 transition in POPOP and its analogues 3c and 3e, it is the other way around in the other analogues.
The quantum yield values of the obtained fluorophores vary from 17 to 98%. The introduction of a methoxy group into the aromatic substituent in the 1,3,4-oxazole core results in an increase in the quantum yield. It is especially clearly observed in the values of the quantum yields of pyrenyl-containing analogues 3c (23%) and 3g (84%)—the introduction of a methoxy group results in a dramatical increase in their quantum yields. (Figure 2, Table 1).
In addition, the introduction of a pyrene moiety results in an increase in the fluorescence lifetime values to 4.52 ns (3c) and 4.34 ns (3g), which are similar to the data reported for other pyrene derivatives in the literature [37,38,39]. For the other fluorophores 3, the lifetime values vary from 0.49 to 1.22 ns (Table 1).
The materials and devices for the remote detection of explosives, including fluorescence-based ones, are of high demand from the perspective of a high risk of terrorist attack worldwide [40,41,42]. Additionally, pyrene derivatives, including azole-appended ones, are known to exhibit a well-pronounced fluorescence “turn-off” response toward common nitroatomatic analytes [43,44,45,46,47,48], as well as some nitroaliphatic explosive components [49,50]. In addition, fluorescence- and aggregation-induced emission (AIE)-based small/single-molecule fluorophores, sensors, and probes [51,52,53,54] are of high demand for biovisualization applications [55,56,57,58,59,60,61,62]. Therefore, as a final step, we studied the ability of the present POPOP aza-analogs 3 to detect nitroanalytes. In acetonitrile solutions (10−5 M), except for pyrene derivatives 3c,g, most of the fluorophores showed no response to both nitro-aromatic and nitro-aliphatic explosives. Compound 3g exhibited a well-pronounced fluorescence “turn-off” response toward both traditional nitro-aromatic explosive components, such as TNT (Ksv = 12,036 M−1) and DNT (Ksv = 8427 M−1), and nitro-aliphatic explosive components, such as pentaerythritol tetranitrate (PETN, Ksv =14078 M−1, Figure 3), with a limit of detection (LOD) of 182 ppb for TNT and 183 ppb for PETN (Figure S1, Supplementary material).
The above-mentioned results are comparable to the most recent state-of-the-art studies [63,64,65,66]. The response of 3g toward the above-mentioned nitro-explosives can be explained using a simple static or pseudo-static/false model when a nonradiative molecular complex “sensor—explosive” is formed in a ground state. In the case of compound 3c, a nonlinear behavior is observed in the Stern–Volmer plot (see ESI), which can be explained by using a mixed static and dynamic Stern–Volmer quenching model.
Next, DFT studies [67,68,69,70,71] were carried out to explain the efficient detection of PETN by the compound 3g. Thus, one can assume that the high sensitivity of 3g to PETN lies in the possibility of an efficient photon-induced electron transfer (PET) from the LUMO of 3g to the LUMO of PETN, which leads to the non-radiative decay of the exited state of the sensor. This process becomes possible if the LUMO of the sensor is much higher in energy. For the evaluation of the PETN quenching mechanism, quantum chemical calculations were carried out based on the B3LYP/def2-TZVP//PM6 level of theory with the help of the Gaussian-09 [72].
In the case of the chemosensor/fluorophore 3g, one can suggest a PET-emission quenching mechanism in the presence of PETN (as a quencher) [73,74,75]. Additionally, this suggestion is strongly supported by the fact that the LUMO energy of the sensor 3g (−2.34 eV) is higher compared to the LUMO energy of the PETN quencher (−2.84 eV). Additionally, the calculated energy difference of 0.5 eV is a driving force of the quenching process (Table 2, Figure 4).

3. Materials and Methods

3.1. Synthesis

3.1.1. 2-(4-Azidophenyl)-5-phenyl-1,3,4-oxadiazoles 2ab

General procedure. Corresponding 4-(5-aryl-1,3,4-oxadiazol-2-yl)aniline (1 equiv.) and para-toluenesulphonic acid monohydrate (1.05 equiv.) were dissolved in acetic acid at room temperature. Isopropyl nitrite (1.50 equiv.) added in one portion. After half an hour of stirring the sodium azide (1.50 equiv.) water solution added. After gas evolution ceased (diazonium probe negative), resulting suspension was filtered off and rinsed by water. Cake dried on air.
2a: Yield 240 mg, 92%. 1H NMR in DMSO-d6, δ, ppm: 7.37 (m, 2H); 7.65 (m, 3H), 8.15 (m, 4H). 13C NMR in DMSO-d6, ppm: 119.7 (1C), 120 (1C), 123.1 (1C), 126.4 (1C), 128.2 (1C), 129.1 (1C), 132 (1C), 143 (1C), 163.3 (1C), 164 (1C). EI-MS, m/z (I, %): 263 (11).
2b: Yield 563 mg, 100%. 1H NMR in DMSO-d6, δ, ppm: 3.87 (3H, s, CH3O-C6H4), 7.17 (m, 2H, CH3O-C6H4), 7.36 (m, 2H, CH3O-C6H4), 8.07 (m, 2H, C6H4), 8.13 (m, 2H, C6H4). 13C NMR in DMSO-d6, ppm: 115 (1C), 116 (1C), 116.3 (1C), 121 (1C), 121.2 (1C), 129 (1C),129.2 (1C), 143.4 (1C), 163 (1C), 164 (1C), 164.4 (1C). EI-MS, m/z (I, %): 293 (6).

3.1.2. 2-Phenyl-5-(4-(4-arenyl-1H-1,2,3-triazol-1-yl)phenyl)-1,3,4-oxadiazoles 3ag

Procedure A. In 50 mL ace flask were successively dissolved in water (3 mL) sodium hydroxide (0.40 equiv.), ascorbic acid (0.50 equiv.) and copper (II) sulfate pentahydrate (0.20 equiv.). To the resulting milky suspension added a solution of corresponding etynyl derivative (1 equiv.) and an azido derivative (1.05 equiv.) in THF (6 mL). The flask was argon flushed and stirred under argon at 70 °C for 16 h. Reaction mass was diluted by aqueous 10% NH4OH (10 mL), the precipitated suspension filtered. Cake washed with water and air dried.
Procedure B. In 50 mL ace flask were successively added corresponding 2-(4-azidophenyl)-5-aryl-1,3,4-oxadiazole (1 equiv.), copper (I) bromide (0.20 equiv.) in the presence of triethylamine (2 equiv.), 1-ethynylpyrene (1.05 equiv.) were added to 5 mL of DMF. RM heated for 10 h at 100 °C in an argon atmosphere. After the reaction was completed (TLC monitoring), the reaction mass was diluted by aqueous 10% NH4OH (10 mL). The resulting suspension was filtered. Cake dried on air. Product was purified by flash chromatography if needed.
3a Procedure A. Yield 96%. 1H NMR in DMSO-d6, δ, ppm: 7.39 (m, 1H, Ph), 7.50 (m, 2H, Ph), 7.65 (m, 3H, Ph), 7.97 (m, 2H, Ph), 8.17 (m, 2H, Ph), 8.25 (d, 2H, J3 = 8.53 Hz, Ph), 8.38 (d, 2H, J3 = 8.53 Hz, Ph). 13C NMR in DMSO-d6, ppm: 30.3 (1C), 119.3 (1C), 120.3 (1C), 123.0 (1C), 125.2 (1C), 126.5 (1C), 128.1 (1C), 128.2 (1C), 129 (1C), 129.1 (1C), 130 (1C), 132 (1C), 139 (1C), 147.4 (1C), 163.1 (1C), 164.1 (1C). EI-MS, m/z (I, %): 365 (1).
3b Procedure A. The product was purified by flash chromatography (chloroform-silica gel). Yield 200 mg, 73%. 1H NMR in DMSO-d6, ppm: 7.58–7.72 (5,m, C6H5), 7.58–7.72 (m, 1H, C10H7), 7.91 (m, 1H, C10H7), 8.05 (m, 2H, C10H7), 8.19 (m, 2H, C10H7), 8.30–8.51 (m, 4H, C6H4), 8.58 (m, 1H, C10H7), 9.45 (s, 1H, C2N3H). 13C NMR in DMSO-d6, ppm: 60.1 (1C), 120.5 (1C), 122.1 (1C), 123.1 (1C), 125.2 (1C), 125.3 (1C), 126.1 (1C), 126.6 (1C), 126.6 (1C), 127.1 (1C), 128.2 (1C), 128.3 (1C), 128.8 (1C), 129.2(1C), 128.8 (1C), 131.9 (1C), 133.3 (1C), 138.0 (1C),138.1 (1C), 146.7 (1C), 163.1 (1C), 164.1 (1C). EI-MS, m/z (I, %): 415 (1).
3c Procedure B. Yield 158 mg, 85%. 1H NMR in DMSO-d6, ppm: 7.65(m, 3H, Ph), 8.06–8.50 (m, 14H, Ph + Pyr + C2N3H4), 8.96 (d, 1H, Pyr), 9.58 (s, 1H, C2N3H). 13C NMR in DMSO-d6, ppm: 121.2 (1C), 122.9 (1C), 123.4 (1C), 123.5 (1C), 124.0 (1C), 124.4 (1C), 124.7 (1C), 125.0 (1C),125.3 (1C), 125.5 (1C), 125.8 (1C), 126.7 (1C), 126.8 (1C), 127.0 (1C), 127.4 (1C), 127.5 (1C), 127.9 (1C), 128.1 (1C),128.4 (1C), 128.6 (1C), 129.6 (1C), 130.5 (1C), 131.1 (1C), 132.3 (1C), 139.0 (1C), 147.6 (1C), 163.5 (1C), 164.4 (1C). EI-MS, m/z (I, %): 489 (3).
3d Procedure B. Yield 138 mg, 70%. 1H NMR in DMSO-d6, ppm: 7.57–7.87 (m, 7H, Ph+ C18H11), 8.10–8.46 (m, 7H, Ph + C6H4),8.88 (m, 5H, C18H11), 9.31 (d, 1H, C2N3H), 972 (d, 1H, C2N3H). 13C NMR in DMSO-d6, ppm: 120.1 (1C), 120.2 (1C), 120.5 (1C), 123.3 (1C), 123.5 (1C), 124 (1C), 124.5 (1C), 125 (1C), 126.6 (1C), 128 (1C), 128.1 (1C), 128.4 (1C), 129 (1C), 129.1 (1C), 129.2 (1C), 129.3 (1C), 129.5 (1C), 130 (1C), 130.2 (1C), 131.1 (1C), 132.1 (1C), 139 (1C), 148 (1C), 163.3 (1C), 164.3 (1C). EI-MS, m/z (I, %): 515 (1).
3e Procedure B. Yield 133 mg, 99%. 1H NMR in DMSO-d6, ppm: 3.91 (s, 3H, CH3O-C6H4), 7.13 (m, 2H, CH3O-C6H4), 7.60 (m, 3H, C10H7), 7.88 (m, 1H, C10H7), 7.98 (2H, m, C10H7), 8.09 (2H, m, CH3O-C6H4), 8.35 (m, 4H, C6H4), 8.59 (m, 1H, C10H7), 9.36 (s, 1H, C2N3H). 13C NMR in DMSO-d6, ppm: 55.3 (1C),115 (1C), 115.35 (1C), 120.5 (1C),122.0 (1C), 123.1 (1C), 125.2 (1C), 125.3 (1C),126.0 (1C), 127 (1C), 127.0 (1C), 128.0 (1C), 128.2 (1C), 128.4 (1C), 129 (1C), 130.0 (1C), 134 (1C), 138.4 (1C), 147 (1C), 162.0 (1C), 163 (1C), 164.0 (1C). EI-MS, m/z (I, %): 395 (1).
3f Procedure B. Yield 122 mg, 80%. 1H NMR in DMSO-d6, ppm: 3.91 (s, 3H, CH3O-C6H4), 7.13 (m, 2H, CH3O-C6H4), 7.60 (m, 3H, C10H7), 7.88 (m, 1H, C10H7), 7.98 (m, 2H, C10H7), 8.09 (m, 2H, CH3O-C6H4), 8.35 (m, 4H, C6H4), 8.59 (m, 1H, C10H7), 9.36 (s, 1H, C2N3H). 13C NMR in DMSO-d6, ppm: 55.3 (1C),115 (1C), 115.35 (1C),120.5 (1C),122.0 (1C), 123.1 (1C), 125.2 (1C), 125.3 (1C),126.0 (1C), 127 (1C), 127.0 (1C), 128.0 (1C), 128.2 (1C), 128.4 (1C), 129 (1C), 130.0 (1C), 134 (1C), 138.4 (1C), 147 (1C), 162.0 (1C), 163 (1C), 164.0 (1C). EI-MS, m/z (I, %): [M-N2]+ = 417 (18).
3g Procedure B. Yield 143 mg, 50%. 1H NMR in DMSO-d6, ppm: 3.91 (s, 3H, CH3O-C6H4), 7.14 (m, 2H, CH3O-C6H4), 8.07-8.14 (m, 3H, Ph + Pyr + C2N3H4), 8.16-8.32 (m, 5H, Ph + Pyr + C2N3H4), 8.34-8.46 (m, 4H, C6H4), 8.34-8.46 (m, 2H, CH3O-C6H4),8.96 (d, 1H, Pyr), 9.55 (s, 1H, C2N3H). 13C NMR in DMSO-d6, ppm: 55.5 (1C), 95.3 (1C), 115 (1C), 115.3 (1C), 115.5 (1C), 121 (1C), 123 (1C), 123.4 (1C),124 (1C), 124.2 (1C), 124.5 (1C), 125 (1C), 125.1 (1C), 125.3 (1C), 126 (1C), 126.5 (1C), 127.3 (1C), 128 (1C), 128.3 (1C), 129(1C), 130.3 (1C), 131 (1C),138 (1C),139 (1C),147.4 (1C), 162.2 (1C), 163 (1C), 164.2(1C). EI-MS, m/z (I, %): [M-N2]+ = 491 (12).
For the NMR spectra of the synthesized fluorophores (3ag) please see the Supplementary material (Figures S2–S10).

3.2. Photophysical Investigations

Materials and Equipment

Acetonitrile and methylene chloride were used to prepare a solution of POPOP azaanalogues in order to study the photophysical properties, purity levels “for HPLC, UV, IR, GPC”. Absorption spectra were recorded on a Shimadzu UV-1800 spectrophotometer (Kyoto, Japan). The emission and excitation spectra were recorded on a Horiba-FluoroMax-4 spectrofluorometer (Irvine, CA 92618, USA). Graphical processing of the absorption, emission and excitation spectra was performed using OriginPro 2015 (64-bit) b9.2.196 software. The absolute quantum yields of the photoluminescence of the compounds were obtained using the integrating sphere of the Horiba-Fluoromax-4 instrument (Irvine, CA 92618, USA). Graphical processing of absorption, emission and excitation spectra was carried out using OriginPro 2015 (64-bit) b9.2.196 software; normalization of all electronic spectra was carried out in the Overlay mode automatically using the “Normalize columns” option using the same software. The absolute quantum yields of the photoluminescence of the compounds were obtained using the integrating sphere of the Horiba-Fluoromax-4 instrument (Irvine, CA 92618, USA). The fluorescence lifetime of the compounds was measured on a Horiba FluoroMax-4 instrument (USA) using the TCSPC (Time Correlated Single-Photon Counting) method.
We chose the maxima closest to 350 nm, because this wavelength is the most preferred excitation wavelength when recording the emission spectrum, according to the operating instructions for the Horiba FluoroMax-4 spectrofluorometer (Figure 5).

3.3. Experimental Methods

3.3.1. Fluorometric Titration

Compound 3g was studied as a chemosensor for “turn-off” fluorescence detection of explosives. The chemosensor fluorescence response to nitroanalytes was quantified using the Stern-Volmer static quenching model. The Stern-Volmer fluorescence quenching constants (Ksv) were calculated according to the static quenching equation as the slope of the intensity graph ((I0/I)−1) depending on the concentration of the quencher ([Q]) (Equation (1)):
I 0 I = 1 + K S V Q
Electron-deficient neutral molecules were chosen as quenchers—one of the most common explosives and their decay products 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT), tetranitropentaerythritol (PETN) (2 × 10−4 M). Concentration 3g (10−6 M) (Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 11, Figure 12, Figure 13 and Figure 14).

3.3.2. Limit of Detection Calculation

The limit of detection (LOD) was calculated on the basis of the data of fluorometric titration experiments according to the method published previously [76]. A calibration curve was plotted between the fluorescence intensity and the quencher concentration to obtain a regression curve equation. The LOD was determined using the Equation (2):
L O D = 3 σ ÷ k
where σ is the standard deviation of the fluorophore intensity in the absence of an analyte obtained via STEYX function in Excel and k is the slope of the calibration curve.

3.3.3. Time-Resolved Fluorescence Measurement

We have also measured the time-resolved fluorescence of all the fluorophores 3, which are summarized in Table 3 and Figure 15, Figure 16, Figure 17, Figure 18, Figure 19, Figure 20 and Figure 21.

3.3.4. Excitation Spectra

For all compounds, the excitation spectra were additionally measured in CH2Cl2 [10−5 M] (Figure 22, Figure 23, Figure 24, Figure 25, Figure 26, Figure 27 and Figure 28), at the emission wavelength. The resulting excitation spectra resemble the absorption spectra of the corresponding compounds. A significant decrease in the intensity of short-wavelength excitation bands is observed, which also correlates with the previously reported data [18].

4. Conclusions

In summary, PAH-based POPOP aza-analogues were successfully prepared by means of Cu(I)-catalyzed click reaction between 2-(4-azidophenyl)-5-Ar-1,3,4-oxadiazole and terminal ethynyl-substituted PAHs. Among all the obtained compounds, pyrenyl-substituted fluorophores, such as 3c,g, exhibited the most promising photophysical properties, such as emission up to 441 nm and quantum yield up to 84%, which were closest to the ones reported for POPOP. In most cases, the introduction of an electron-donating methoxy group in the aromatic moiety of these aza-analogues of POPOP improved their photophysical properties. Among the obtained compounds, only pyrene-substituted fluorophore 3g exhibited a well-pronounced fluorescence “turn-off” response toward several common nitroaromatic explosive components, such as DNT and TNT, with 0.8–1.2 × 104 M−1 Stern–Volmer (quenching) constants and an LOD of 182 ppb for TNT. In addition, this compound exhibited an excellent response to the hard-to-detect nitro-aliphatic explosive, PETN, with a 1.4 × 104 M−1 Stern–Volmer constant and an LOD of 183 ppb. Possible quenching via the PET mechanism for 3g was suggested, and this was further supported by means of DFT quantum chemical calculations.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/ijms241210084/s1.

Author Contributions

M.S.M., methodology; I.S.K., conceptualization, validation, formal analysis, investigation, resources, data curation, writing—original draft preparation, visualization; N.V.S., methodology, data curation; L.K.S., methodology, software, formal analysis, data curation; V.A.P., methodology, software, data curation; A.S.N., methodology, software, data curation, S.S., software, validation, resources, writing—original draft preparation, writing—review and editing, funding acquisition; J.E.M., validation, data curation, writing—original draft preparation; G.V.Z., conceptualization, validation, investigation, writing—original draft preparation, writing—review and editing, visualization, supervision, project administration, funding acquisition; V.N.C., conceptualization; B.C.R., conceptualization, project administration, funding acquisition. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Ministry of Science and Higher Education of the Russian Federation (Agreement # 075-15-2022-1118, accessed on 29 June 2022).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The quantum chemical calculations (for A.S.N.) were supported by the RUDN University Strategic Academic Leadership Program.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Adadurov, A.F.; Zhmurin, P.N.; Lebedev, V.N.; Titskaya, V.D. Optimizing concentration of shifter additive for plastic scintillators of different size. Nucl. Instrum. Methods Phys. Res. Sect. A Accel. Spectrometers Detect. Assoc. Equip. 2009, 599, 167–170. [Google Scholar] [CrossRef]
  2. Patterson, M.S.; Greene, R.C. Measurement of Low Energy Beta-Emitters in Aqueous Solution by Liquid Scintillation Counting of Emulsions. Anal. Chem. 1965, 37, 854–857. [Google Scholar] [CrossRef]
  3. Mardelli, M.; Olmsted, J. Calorimetric determination of the 9,10-diphenyl-anthracene fluorescence quantum yield. J. Photochem. 1977, 7, 277–285. [Google Scholar] [CrossRef]
  4. Shank, C.V. Physics of dye lasers. Rev. Mod. Phys. 1975, 47, 649–657. [Google Scholar] [CrossRef]
  5. Basov, N.G.; Logunov, O.A.; Startsev, A.V.; Stoilov, Y.Y.; Zuev, V.S. Vapour phase dye lasers of the visible range. J. Mol. Struct. 1982, 79, 119–123. [Google Scholar] [CrossRef]
  6. Desai, N.; Monapara, J.; Jethawa, A.; Khedkar, V.; Shingate, B. Oxadiazole: A highly versatile scaffold in drug discovery. Arch. Pharm. 2022, 355, 2200123. [Google Scholar] [CrossRef]
  7. Luczynski, M.; Kudelko, A. Synthesis and Biological Activity of 1,3,4-Oxadiazoles Used in Medicine and Agriculture. Appl. Sci. 2022, 12, 3756. [Google Scholar] [CrossRef]
  8. Siwach, A.; Verma, P.K. Therapeutic potential of oxadiazole or furadiazole containing compounds. BMC Chem. 2020, 14, 70. [Google Scholar] [CrossRef]
  9. Li, Z.; Li, W.; Keum, C.; Archer, E.; Zhao, B.; Slawin, A.M.Z.; Huang, W.; Gather, M.C.; Samuel, I.D.W.; Zysman-Colman, E. 1,3,4-Oxadiazole-based Deep Blue Thermally Activated Delayed Fluorescence Emitters for Organic Light Emitting Diodes. J. Phys. Chem. C 2019, 123, 24772–24785. [Google Scholar] [CrossRef]
  10. Mayder, D.M.; Tonge, C.M.; Hudson, Z.M. Thermally activated delayed fluorescence in 1,3,4-oxadiazoles with π-extended donors. J. Org. Chem. 2020, 85, 11094–11103. [Google Scholar] [CrossRef]
  11. Zhou, J.-A.; Tang, X.-L.; Cheng, J.; Ju, J.-H.; Yang, L.-Z.; Liu, W.-S.; Chen, C.-Y.; Bai, D.-C. An 1,3,4-oxadiazole-based OFF-ON fluorescent chemosensor for Zn2+ in aqueous solution and imaging application in living cells. Dalt. Trans. 2012, 41, 10626–10632. [Google Scholar] [CrossRef]
  12. Lakowicz, J.R.; Gryczynski, I.; Malak, H.; Gryczynski, Z. Fluorescence spectral properties of 2,5-diphenyl-1,3,4-oxadiazole with two-color two-photon excitation. J. Phys. Chem. 1996, 100, 19406–19411. [Google Scholar] [CrossRef]
  13. Kolb, H.C.; Finn, M.G.; Sharpless, K.B. Click Chemistry: Diverse Chemical Function from a Few Good Reactions. Angew. Chemie Int. Ed. 2001, 40, 2004–2021. [Google Scholar] [CrossRef]
  14. Sudeep, P.; Vagish, C.B.; Kumar, A.D.; Kumar, K.A. 1,2,3-Triazoles: A Review on Current Trends in Synthetic and Biological Applications. J. Appl. Chem. 2020, 13, 22–40. [Google Scholar] [CrossRef]
  15. Hein, C.D.; Liu, X.M.; Wang, D. Click chemistry, a powerful tool for pharmaceutical sciences. Pharm. Res. 2008, 25, 2216–2230. [Google Scholar] [CrossRef] [Green Version]
  16. Neeraja, P.; Srinivas, S.; Mukkanti, K.; Dubey, P.K.; Pal, S. 1H-1,2,3-Triazolyl-substituted 1,3,4-oxadiazole derivatives containing structural features of ibuprofen/naproxen: Their synthesis and antibacterial evaluation. Bioorg. Med. Chem. Lett. 2016, 26, 5212–5217. [Google Scholar] [CrossRef]
  17. Shang, J.Q.; Fu, H.; Li, Y.; Yang, T.; Gao, C.; Li, Y.M. Copper-catalyzed decarboxylation/cycloaddition cascade of alkynyl carboxylic acids with azide. Tetrahedron 2019, 75, 253–259. [Google Scholar] [CrossRef]
  18. Lauria, A.; Delisi, R.; Mingoia, F.; Terenzi, A.; Martorana, A.; Barone, G.; Almerico, A.M. 1,2,3-Triazole in Heterocyclic Compounds, Endowed With Biological Activity, Through 1,3-Dipolar Cycloadditions. Eur. J. Org. Chem. 2014, 2014, 3289–3306. [Google Scholar] [CrossRef]
  19. Farooq, T.; Haug, B.E.; Sydnes, L.K.; Törnroos, K.W. 1,3-Dipolar cycloaddition of benzyl azide to two highly functionalized alkynes. Mon. Fur Chemie. 2012, 143, 505–512. [Google Scholar] [CrossRef] [Green Version]
  20. Wang, Y.-F.; Wang, C.-J.; Feng, Q.-Z.; Zhai, J.-J.; Qi, S.-S.; Zhong, A.-G.; Chu, M.M.; Xu, D.-Q. Copper-catalyzed asymmetric 1,6-conjugate addition of in situ generated para-quinone methides with β-ketoesters. Chem. Commun. 2022, 58, 6653–6656. [Google Scholar] [CrossRef]
  21. Wang, Y.; Yin, J.J.; Li, Y.; Yuan, X.; Xiong, T.; Zhang, Q. Copper-Catalyzed Asymmetric Conjugate Addition of Alkene-Derived Nucleophiles to Alkenyl-Substituted Heteroarenes. ACS Catal. 2022, 12, 9611–9620. [Google Scholar] [CrossRef]
  22. Pan, Z.-Z.; Pan, D.; Li, J.-H.; Xue, X.-S.; Yin, L. Copper(I)-Catalyzed Asymmetric Conjugate Addition of 1,4-Dienes to β-Substituted Alkenyl Azaarenes. J. Am. Chem. Soc. 2023, 145, 1749–1758. [Google Scholar] [CrossRef]
  23. Wang, Z.-H.; Liu, J.-H.; Zhang, Y.-P.; Zhao, J.-Q.; You, Y.; Zhou, M.-Q.; Han, W.-Y.; Yuan, W.-C. Cu-Catalyzed Asymmetric 1,3-Dipolar Cycloaddition of N-2,2,2-Trifluoroethylisatin Ketimines Enables the Desymmetrization of N-Arylmaleimides: Access to Enantioenriched F3C-Containing Octahydropyrrolo[3,4-c]pyrrole. Org. Lett. 2022, 24, 4052–4057. [Google Scholar] [CrossRef]
  24. Zhang, D.-Y.; Shao, L.; Xu, J.; Hu, X.-P. Copper-Catalyzed Asymmetric Formal [3 + 2] Cycloaddition of Propargylic Acetates with Hydrazines: Enantioselective Synthesis of Optically Active 2-Pyrazolines. ACS Catal. 2015, 5, 5026–5030. [Google Scholar] [CrossRef]
  25. Zeng, L.; Li, J.; Cui, S. Rhodium-Catalyzed Atroposelective Click Cycloaddition of Azides and Alkynes. Angew. Chem. Int. Ed. 2022, 134, e202205037. [Google Scholar] [CrossRef]
  26. Luvino, D.; Amalric, C.; Smietana, M.; Vasseur, J.J. Sequential Seyferth-Gilbert/CuAAC reactions: Application to the one-pot synthesis of triazoles from aldehydes. Synlett 2007, 2007, 3037–3041. [Google Scholar] [CrossRef]
  27. Lauko, J.; Kouwer, P.H.J.; Rowan, A.E. 1H-1,2,3-Triazole: From Structure to Function and Catalysis. J. Heterocycl. Chem. 2017, 54, 1677–1699. [Google Scholar] [CrossRef]
  28. Thomas, J.; John, J.; Parekh, N.; Dehaen, W. A Metal-Free Three-Component Reaction for the Regioselective Synthesis of 1,4,5-Trisubstituted 1,2,3-Triazoles. Angew. Chem. 2014, 126, 10319–10323. [Google Scholar] [CrossRef]
  29. Totobenazara, J.; Burke, A.J. New click-chemistry methods for 1,2,3-triazoles synthesis: Recent advances and applications. Tetrahedron Lett. 2015, 56, 2853–2859. [Google Scholar] [CrossRef]
  30. Dubey, N.; Sharma, P.; Kumar, A. Clay-Supported Cu(II) Catalyst: An Efficient, Heterogeneous, and Recyclable Catalyst for Synthesis of 1,4-Disubstituted 1,2,3-Triazoles from Alloxan-Derived Terminal Alkyne and Substituted Azides Using Click Chemistry. Synth. Commun. 2015, 45, 2608–2626. [Google Scholar] [CrossRef]
  31. Kushwaha, D.; Dwivedi, P.; Kuanar, S.K.; Tiwari, V.K. Click Reaction in Carbohydrate Chemistry: Recent Developments and Future Perspective. Curr. Org. Synth. 2013, 10, 90–135. [Google Scholar] [CrossRef]
  32. Kang, M.; Ying, Q. Synthesis and Fluorescence Properties of Bisbranched 1,3,4-Oxadiazole Derivatives. Chin. J. Org. Chem. 2009, 29, 71–77. Available online: http://sioc-journal.cn/Jwk_yjhx/EN/abstract/article_326517.shtml (accessed on 15 March 2023).
  33. Li, A.F.; Ruan, Y.B.; Jiang, Q.Q.; He, W.B.; Jiang, Y.B. Molecular logic gates and switches based on 1,3,4-oxadiazoles triggered by metal ions. Chem. Eur. J. 2010, 16, 5794–5802. [Google Scholar] [CrossRef] [Green Version]
  34. Kutonova, K.V.; Trusova, M.E.; Postnikov, P.; Filimonov, V.D.; Parello, J. A simple and effective synthesis of aryl azides via arenediazonium tosylates. Synthesis 2013, 45, 2706–2710. [Google Scholar] [CrossRef] [Green Version]
  35. Huisgen, R. 1.3-Dipolare Cycloadditionen Ruckschau und Ausblick. Angew. Chem. 1963, 75, 604–637. [Google Scholar] [CrossRef]
  36. Liang, L.; Astruc, D. The copper(I)-catalysed alkyne-azide cycloaddition (CuAAC) “click” reaction and its applications. An overview. Coord. Chem. Rev. 2011, 255, 2933–2945. [Google Scholar] [CrossRef]
  37. De Silva, T.P.D.; Youm, S.G.; Fronczek, F.R.; Sahasrabudhe, G.; Nesterov, E.E.; Warner, I.M. Pyrene-benzimidazole derivatives as novel blue emitters for OLEDs. Molecules 2021, 26, 6523. [Google Scholar] [CrossRef] [PubMed]
  38. Türel, T.; Mahadevan, G.; Valiyaveettil, S. Modular Synthesis and Structure–Property Correlation of Pyrene—Rylene Dyes for Cellular Imaging. Eur. J. Org. Chem. 2020, 2020, 3303–3311. [Google Scholar] [CrossRef]
  39. Sadieva, L.K.; Kovalev, I.S.; Taniya, O.S.; Platonov, V.A.; Novikov, A.S.; Berseneva, V.S.; Santra, S.; Zyryanov, G.V.; Ranu, B.C.; Charushin, V.N. Bola-type PEG-linked polyaromatic hydrocarbon-based chemosensors for the ‘turn-off’ excimer fluorescence detection of nitro-analytes/explosives in aqueous solutions. Dyes Pig. 2023, 210, 111014. [Google Scholar] [CrossRef]
  40. Thomas III, S.W.; Joly, G.D.; Swager, T.M. Chemical Sensors Based on Amplifying Fluorescent Conjugated Polymers. Chem. Rev. 2007, 107, 1339–1386. [Google Scholar] [CrossRef]
  41. Shaw, P.E.; Burn, P.L. Real-time fluorescence quenching-based detection of nitro-containing explosive vapours: What are the key processes? Phys. Chem. Chem. Phys. 2017, 19, 29714–29730. [Google Scholar] [CrossRef] [PubMed]
  42. Curnrning, C.; Fisher, M.; Sikes, J. Amplifying fluorescent polymer arrays for chemical detection of explosives. In Electronic Noses & Sensors for the Detection of Explosives. NATO Science Series II: Mathematics, Physics and Chemistry; Gardner, J.W., Yinon, J., Eds.; Springer: Dordrecht, The Netherlands, 2004; Volume 159. [Google Scholar] [CrossRef]
  43. Salinas, Y.; Agostini, A.; Pérez-Esteve, É.; Martínez-Máñez, R.; Sancenón, F.; Marcos, M.D.; Soto, J.; Costero, A.M.; Gil, S.; Parra, M.; et al. Fluorogenic detection of Tetryl and TNT explosives using nanoscopic-capped mesoporous hybrid materials. J. Mater. Chem. A 2013, 1, 3561–3564. [Google Scholar] [CrossRef]
  44. Turhan, H.; Tukenmez, E.; Karagoz, B.; Bicak, N. Highly fluorescent sensing of nitroaromatic explosives in aqueous media using pyrene-linked PBEMA microspheres. Talanta 2018, 179, 107–114. [Google Scholar] [CrossRef] [PubMed]
  45. Bal, M.; Köse, A.; Özpaça, Ö.; Köse, M. Pyrene, Anthracene, and Naphthalene-Based Azomethines for Fluorimetric Sensing of Nitroaromatic Compounds. J. Fluoresc. 2023; ahead of print. [Google Scholar] [CrossRef]
  46. Zyryanov, G.V.; Kopchuk, D.S.; Kovalev, I.S.; Nosova, E.V.; Rusinov, V.L.; Chupakhin, O.N. Chemosensors for detection of nitroaromatic compounds (explosives). Russ. Chem. Rev. 2014, 83, 783–819. [Google Scholar] [CrossRef]
  47. Verbitskiy, E.V.; Baranova, A.A.; Lugovik, K.I.; Shafikov, M.Z.; Khokhlov, K.O.; Cheprakova, E.M.; Rusinov, G.L.; Chupakhin, O.N.; Charushin, V.N. Detection of nitroaromatic explosives by new D–π–A sensing fluorophores on the basis of the pyrimidine scaffold. Anal. Bioanal. Chem. 2016, 408, 4093–4101. [Google Scholar] [CrossRef] [PubMed]
  48. Kovalev, I.S.; Sadieva, L.K.; Taniya, O.S.; Yurk, V.M.; Minin, A.S.; Santra, S.; Zyryanov, G.V.; Charushin, V.N.; Chupakhin, O.N.; Tsurkan, M.V. Computer vision vs. spectrofluorometer-assisted detection of common nitro-explosive components with bola-type PAH-based chemosensors. RSC Adv. 2021, 11, 25850–25857. [Google Scholar] [CrossRef]
  49. Khasanov, A.F.; Kopchuk, D.S.; Kovalev, I.S.; Taniya, O.S.; Giri, K.; Slepukhin, P.A.; Santra, S.; Rahman, M.; Majee, A.; Charushin, V.N.; et al. Extended cavity pyrene-based iptycenes for the turn-off fluorescence detection of RDX and common nitroaromatic explosives. New J. Chem. 2017, 41, 2309–2320. [Google Scholar] [CrossRef]
  50. Kovalev, I.S.; Taniya, O.S.; Sadieva, L.K.; Volkova, N.N.; Minin, A.S.; Grzhegorzhevskii, K.V.; Gorbunov, E.B.; Zyryanov, G.V.; Chupakhin, O.N.; Charushin, V.N.; et al. Bola-type PAH-based Fluorophores/Chemosensors: Synthesis via an Unusual Clemmensen Reduction and Photophysical Studies. J. Photochem. Photobiol. A Chem. 2021, 420, 113466. [Google Scholar] [CrossRef]
  51. Sun, H.; Chen, S.; Zhong, A.; Sun, R.; Jin, J.; Yang, J.; Liu, D.; Niu, J.; Lu, S. Tuning Photophysical Properties via Positional Isomerization of the Pyridine Ring in Donor–Acceptor-Structured Aggregation-Induced Emission Luminogens Based on Phenylmethylene Pyridineacetonitrile Derivatives. Molecules 2023, 28, 3282. [Google Scholar] [CrossRef]
  52. Fu, Y.; Finney, N.S. Small-molecule fluorescent probes and their design. RSC Adv. 2018, 8, 29051–29061. [Google Scholar] [CrossRef] [Green Version]
  53. Jensen, E.C. Use of Fluorescent Probes: Their Effect on Cell Biology and Limitations. Anat. Rec. Adv. Integr. Anat. Evol. Biol. 2012, 295, 2031–2036. [Google Scholar] [CrossRef] [PubMed]
  54. Georgiev, N.I.; Bakov, V.V.; Anichina, K.K.; Bojinov, V.B. Fluorescent Probes as a Tool in Diagnostic and Drug Delivery Systems. Pharmaceuticals 2023, 16, 381. [Google Scholar] [CrossRef] [PubMed]
  55. Ma, H.; Yang, M.; Zhang, C.; Ma, Y.; Qin, Y.; Lei, Z.; Chang, L.; Lei, L.; Wang, T.; Yang, Y. Aggregation-induced emission (AIE)-active fluorescent probes with multiple binding sites toward ATP sensing and live cell imaging. J. Mater. Chem. B 2017, 5, 8525–8531. [Google Scholar] [CrossRef]
  56. Yang, Q.; Wen, Y.; Zhong, A.; Xu, J.; Shao, S. An HBT-based fluorescent probe for nitroreductase determination and its application in Escherichia coli cell imaging. New J. Chem. 2020, 44, 16265–16268. [Google Scholar] [CrossRef]
  57. Zhao, D.; Han, H.-H.; Zhu, L.; Xu, F.-Z.; Ma, X.-Y.; Li, J.; James, T.D.; Zang, Y.; He, X.-P.; Wang, C. Long-Wavelength AIE-Based Fluorescent Probes for Mitochondria-Targeted Imaging and Photodynamic Therapy of Hepatoma Cells. ACS Appl. Bio Mater. 2021, 4, 7016–7024. [Google Scholar] [CrossRef]
  58. Du, X.; Wang, J.; Qin, A.; Tang, B. Application of AIE-active probes in fluorescence sensing. Chin. Sci. Bull. 2020, 65, 1428–1447. [Google Scholar] [CrossRef]
  59. Ma, J.; Gu, Y.; Ma, D.; Lu, W.; Qiu, J. Insights into AIE materials: A focus on biomedical applications of fluorescence. Front. Chem. 2022, 10, 985578. [Google Scholar] [CrossRef]
  60. Terai, T.; Nagano, T. Fluorescent probes for bioimaging applications. Curr. Opin. Chem. Biol. 2008, 12, 515–521. [Google Scholar] [CrossRef]
  61. Li, Y.; Chen, Q.; Pan, X.; Lu, W.; Zhang, J. Development and Challenge of Fluorescent Probes for Bioimaging Applications: From Visualization to Diagnosis. Top. Curr. Chem. (Z) 2022, 380, 22. [Google Scholar] [CrossRef]
  62. Gao, L.; Wang, W.; Wang, X.; Yang, F.; Xie, L.; Shen, J.; Brimble, M.A.; Xiao, Q.; Yao, S.Q. Fluorescent probes for bioimaging of potential biomarkers in Parkinson’s disease. Chem. Soc. Rev. 2021, 50, 1219–1250. [Google Scholar] [CrossRef]
  63. Liu, A.; Liu, H.; Peng, X.; Jia, J.; Fu, Y.; He, Q.; Cao, H.; Cheng, J. Direct and ultrasensitive fluorescence detection of PETN vapor based on a fuorene-dimer probe via a synergic backbone and side-chain tuning. Anal. Methods 2018, 10, 2567–2574. [Google Scholar] [CrossRef]
  64. Ganiga, M.; Cyriac, J. Detection of PETN and RDX using a FRET-based fluorescence sensor system. Anal. Methods 2015, 7, 5412–5418. [Google Scholar] [CrossRef]
  65. Wang, C.; Huang, H.; Bunes, B.R.; Wu, N.; Xu, M.; Yang, X.; Yu, L.; Zang, L. Trace Detection of RDX, HMX and PETN Explosives Using a Fluorescence Spot Sensor. Sci. Rep. 2016, 6, 25015. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  66. Andrew, T.L.; Swager, T.M. A Fluorescence Turn-On Mechanism to Detect High Explosives RDX and PETN. J. Am. Chem. Soc. 2007, 129, 7254–7255. [Google Scholar] [CrossRef] [PubMed]
  67. Vovusha, H.; Sanyal, B. DFT and TD-DFT studies on the electronic and optical properties of explosive molecules adsorbed on boron nitride and graphene nano flakes. RSC Adv. 2015, 5, 4599–4608. [Google Scholar] [CrossRef]
  68. Cawkwell, M.J.; Zecevic, M.; Luscher, D.J.; Ramos, K.J. Dependence of the Elastic Stiffness Tensors of PETN, α-RDX, γ-RDX, ϵ-RDX, ϵ-CL-20, DAAF, FOX-7, and β-HMX on Hydrostatic Compression. Propellants Explos. Pyrotech. 2022, 47, e202100281. [Google Scholar] [CrossRef]
  69. Gruzdkov, Y.A.; Dreger, Z.A.; Gupta, Y.M. Experimental and Theoretical Study of Pentaerythritol Tetranitrate Conformers. J. Phys. Chem. A 2004, 108, 6216–6221. [Google Scholar] [CrossRef]
  70. Liu, S.; Ess, D.H.; Schauer, C.K. Density Functional Reactivity Theory Characterizes Charge Separation Propensity in Proton-Coupled Electron Transfer Reactions. J. Phys. Chem. A 2011, 115, 4738–4742. [Google Scholar] [CrossRef]
  71. Zhao, D.; Liu, S.; Rong, C.; Zhong, A.; Liu, S. Toward Understanding the Isomeric Stability of Fullerenes with Density Functional Theory and the Information-Theoretic Approach. ACS Omega 2018, 3, 17986–17990. [Google Scholar] [CrossRef] [Green Version]
  72. Frisch, M.J.; Trucks, G.W.; Schlegel, J.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Schlegel, H.B.; Scalmani, G.; Barone, V.; Mennucci, B.; et al. Gaussian 09, Revision C.01; Gaussian, Inc.: Wallingford, CT, USA, 2010. [Google Scholar]
  73. Doose, S.; Neuweiler, H.; Sauer, M. Fluorescence Quenching by Photoinduced Electron Transfer: A Reporter for Conformational Dynamics of Macromolecules. ChemPhysChem 2009, 10, 1389–1398. [Google Scholar] [CrossRef]
  74. Akbar, R.; Baral, M.; Kanungo, B.K. Photoluminescence and Coordination Behaviour of Lanthanide Complexes of Tris (Aminomethyl)Ethane-5-Oxine in Aqueous Solution. J. Fluoresc. 2017, 27, 89–103. [Google Scholar] [CrossRef] [PubMed]
  75. Thongyod, W.; Buranachai, C.; Pengpan, T.; Punwong, C. Fluorescence quenching by photoinduced electron transfer between 7-methoxycoumarin and guanine base facilitated by hydrogen bonds: An in silico study. Phys. Chem. Chem. Phys. 2019, 21, 16258–16269. [Google Scholar] [CrossRef] [PubMed]
  76. Shrivastava, A.; Gupta, V.B. Methods for the determination of limit of detection and limit of quantitation of the analytical methods. Chron. Young Sci. 2011, 2, 21. [Google Scholar] [CrossRef]
Figure 1. POPOP and its aza-analog core. POPOP = 1,4-Bis(5-phenyl-2-oxazolyl)benzene.
Figure 1. POPOP and its aza-analog core. POPOP = 1,4-Bis(5-phenyl-2-oxazolyl)benzene.
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Scheme 1. Synthesis of the azido components 2a,b. PTSA = p-Toluenesulfonic acid.
Scheme 1. Synthesis of the azido components 2a,b. PTSA = p-Toluenesulfonic acid.
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Scheme 2. Synthesis of the POPOP analogues 3.
Scheme 2. Synthesis of the POPOP analogues 3.
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Figure 2. Absorption (A) and emission (B) spectra of POPOP and its aza-analogues 3 in CH2Cl2 (10−5 M). POPOP = 1,4-Bis(5-phenyl-2-oxazolyl)benzene.
Figure 2. Absorption (A) and emission (B) spectra of POPOP and its aza-analogues 3 in CH2Cl2 (10−5 M). POPOP = 1,4-Bis(5-phenyl-2-oxazolyl)benzene.
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Figure 3. Stern–Volmer plot (A) and overlayed graph (B) of the chemosensor 3g fluorescence quenching by PETN. PETN = Pentaerythritol tetranitrate.
Figure 3. Stern–Volmer plot (A) and overlayed graph (B) of the chemosensor 3g fluorescence quenching by PETN. PETN = Pentaerythritol tetranitrate.
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Figure 4. Energy diagram of the PET quenching process. PET = photon-induced electron transfer; PETN = Pentaerythritol tetranitrate.
Figure 4. Energy diagram of the PET quenching process. PET = photon-induced electron transfer; PETN = Pentaerythritol tetranitrate.
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Figure 5. Normalized emission spectra of aza analogues POPOP. POPOP = 1,4-Bis(5-phenyl-2-oxazolyl)benzene.
Figure 5. Normalized emission spectra of aza analogues POPOP. POPOP = 1,4-Bis(5-phenyl-2-oxazolyl)benzene.
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Figure 6. Fluorescence quenching of chemosensor 3g by TNT. TNT = 2,4,6-Trinitrotoluene.
Figure 6. Fluorescence quenching of chemosensor 3g by TNT. TNT = 2,4,6-Trinitrotoluene.
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Figure 7. Fluorescence quenching of chemosensor 3g by DNT. DNT = 2,4-Dinitrotoluene.
Figure 7. Fluorescence quenching of chemosensor 3g by DNT. DNT = 2,4-Dinitrotoluene.
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Figure 8. Fluorescence quenching of chemosensor 3g by PETN. PETN = Pentaerythritol tetranitrate.
Figure 8. Fluorescence quenching of chemosensor 3g by PETN. PETN = Pentaerythritol tetranitrate.
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Figure 9. Overlayed graph of the chemosensor 3g quenching by DNT (UV-Vis). DNT = 2,4-Dinitrotoluene.
Figure 9. Overlayed graph of the chemosensor 3g quenching by DNT (UV-Vis). DNT = 2,4-Dinitrotoluene.
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Figure 10. Overlayed graph of the chemosensor 3g quenching by DNT (Emission). DNT = 2,4-Dinitrotoluene.
Figure 10. Overlayed graph of the chemosensor 3g quenching by DNT (Emission). DNT = 2,4-Dinitrotoluene.
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Figure 11. Overlayed graph of the chemosensor 3g quenching by TNT (UV-Vis). TNT = 2,4,6-Trinitrotoluene.
Figure 11. Overlayed graph of the chemosensor 3g quenching by TNT (UV-Vis). TNT = 2,4,6-Trinitrotoluene.
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Figure 12. Overlayed graph of the chemosensor 3g quenching by TNT (Emission). TNT = 2,4,6-Trinitrotoluene.
Figure 12. Overlayed graph of the chemosensor 3g quenching by TNT (Emission). TNT = 2,4,6-Trinitrotoluene.
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Figure 13. Overlayed graph of the chemosensor 3g quenching by PETN (UV-Vis). PETN = Pentaerythritol tetranitrate.
Figure 13. Overlayed graph of the chemosensor 3g quenching by PETN (UV-Vis). PETN = Pentaerythritol tetranitrate.
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Figure 14. Overlayed graph of the chemosensor 3g quenching by PETN (Emission). PETN = Pentaerythritol tetranitrate.
Figure 14. Overlayed graph of the chemosensor 3g quenching by PETN (Emission). PETN = Pentaerythritol tetranitrate.
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Figure 15. Normalized emission and absorption spectra 3a.
Figure 15. Normalized emission and absorption spectra 3a.
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Figure 16. Normalized emission and absorption spectra 3b.
Figure 16. Normalized emission and absorption spectra 3b.
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Figure 17. Normalized emission and absorption spectra 3c.
Figure 17. Normalized emission and absorption spectra 3c.
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Figure 18. Normalized emission and absorption spectra 3d.
Figure 18. Normalized emission and absorption spectra 3d.
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Figure 19. Normalized emission and absorption spectra 3e.
Figure 19. Normalized emission and absorption spectra 3e.
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Figure 20. Normalized emission and absorption spectra 3f.
Figure 20. Normalized emission and absorption spectra 3f.
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Figure 21. Normalized emission and absorption spectra 3g.
Figure 21. Normalized emission and absorption spectra 3g.
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Figure 22. Excitation spectrum 3a.
Figure 22. Excitation spectrum 3a.
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Figure 23. Excitation spectrum 3b.
Figure 23. Excitation spectrum 3b.
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Figure 24. Excitation spectrum 3c.
Figure 24. Excitation spectrum 3c.
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Figure 25. Excitation spectrum 3d.
Figure 25. Excitation spectrum 3d.
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Figure 26. Excitation spectrum 3e.
Figure 26. Excitation spectrum 3e.
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Figure 27. Excitation spectrum 3f.
Figure 27. Excitation spectrum 3f.
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Figure 28. Excitation spectrum 3g.
Figure 28. Excitation spectrum 3g.
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Table 1. Data showing the photophysical properties of fluorophores (3) and POPOP (10−5 M) in CH2Cl2 solvent.
Table 1. Data showing the photophysical properties of fluorophores (3) and POPOP (10−5 M) in CH2Cl2 solvent.
EntryComp.λabs max a, nm (εM, M−1 cm−1)λem max b, nmStokes Shift, nmτ, ns cΦf, (%) d
1POPOP346 (99,000)
361 (111,400)
384 (68,000)
416
443
97 97.5 e
23a248 (43,300)
309 (61,800)
356
370
47 17
33b248 (22,500)
259 (21,600)
307 (14,500)
3981500.6648
43c245 (17,800)
282 (35,600)
348 (26,300)
4411594.5223
53d271 (56,200)
317 (35,900)
3821111.2230
63e259 (31,500)
315 (75,200)
373580.7298.13 f
73f228 (93,400)
247 (43,400)
258 (39,900)
315 (33,200)
3881600.4971
83g228 (39,100)
245 (43,200)
282 (32,400)
319 (26,900)
346 (29,900)
393 (sh)
417
1724.3484
a Absorption spectra were measured at r.t. in CH2Cl2 in the range from 200 to 450 nm; b emission spectra were measured at r.t. in CH2Cl2; c weighted average decay time τav = Σ (τi × αi) in CH2Cl2 (LED 310 nm); d absolute quantum yields were measured as reported earlier using the Integrating Sphere on a Horiba-Fluoromax-4 at r.t. in CH2Cl2; e calorimetric value in cyclohexane [3]; and f calorimetric value in THF.
Table 2. HOMO–LUMO energy levels for 3g and PETN (in eV).
Table 2. HOMO–LUMO energy levels for 3g and PETN (in eV).
StructureHOMO EnergyLUMO Energy
3g−5.71−2.34
PETN−9.14−2.84
Table 3. Fluorescence lifetime of probes 3ag (C = 2 × 10−6 M) in CH2Cl2.
Table 3. Fluorescence lifetime of probes 3ag (C = 2 × 10−6 M) in CH2Cl2.
EntryCompoundτ1, ns aα1 bτ2, ns aα2 bτav c, ns aχ2 d
13a0.971.0000--0.971.08
23b0.540.89421.640.10580.661.22
33c1.550.11144.890.88864.521.15
43d0.890.90924.560.09081.221.23
53e0.721.0000--0.721.15
63f0.420.94581.680.05420.491.18
73g1.080.06724.580.93284.341.12
a Decay time, b Fractional contribution, c Weighted average decay time τav = Σ (τi × αi), d Quality of fitting.
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Mohammed, M.S.; Kovalev, I.S.; Slovesnova, N.V.; Sadieva, L.K.; Platonov, V.A.; Novikov, A.S.; Santra, S.; Morozova, J.E.; Zyryanov, G.V.; Charushin, V.N.; et al. Polyaromatic Hydrocarbon (PAH)-Based Aza-POPOPs: Synthesis, Photophysical Studies, and Nitroanalyte Sensing Abilities. Int. J. Mol. Sci. 2023, 24, 10084. https://doi.org/10.3390/ijms241210084

AMA Style

Mohammed MS, Kovalev IS, Slovesnova NV, Sadieva LK, Platonov VA, Novikov AS, Santra S, Morozova JE, Zyryanov GV, Charushin VN, et al. Polyaromatic Hydrocarbon (PAH)-Based Aza-POPOPs: Synthesis, Photophysical Studies, and Nitroanalyte Sensing Abilities. International Journal of Molecular Sciences. 2023; 24(12):10084. https://doi.org/10.3390/ijms241210084

Chicago/Turabian Style

Mohammed, Mohammed S., Igor S. Kovalev, Natalya V. Slovesnova, Leila K. Sadieva, Vadim A. Platonov, Alexander S. Novikov, Sougata Santra, Julia E. Morozova, Grigory V. Zyryanov, Valery N. Charushin, and et al. 2023. "Polyaromatic Hydrocarbon (PAH)-Based Aza-POPOPs: Synthesis, Photophysical Studies, and Nitroanalyte Sensing Abilities" International Journal of Molecular Sciences 24, no. 12: 10084. https://doi.org/10.3390/ijms241210084

APA Style

Mohammed, M. S., Kovalev, I. S., Slovesnova, N. V., Sadieva, L. K., Platonov, V. A., Novikov, A. S., Santra, S., Morozova, J. E., Zyryanov, G. V., Charushin, V. N., & Ranu, B. C. (2023). Polyaromatic Hydrocarbon (PAH)-Based Aza-POPOPs: Synthesis, Photophysical Studies, and Nitroanalyte Sensing Abilities. International Journal of Molecular Sciences, 24(12), 10084. https://doi.org/10.3390/ijms241210084

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