Bispyrenylalkane Chemosensor for the Naked-eye Detection of Nitro-explosives Chimica Techno Acta LETTER published by Ural Federal University 2021, vol. 8(2), № 20218209 eISSN 2411-1414; chimicatechnoacta.ru DOI: 10.15826/chimtech.2021.8.2.09 1 of 4 Bispyrenylalkane Chemosensor for the Naked-eye Detection of Nitro-explosives I.S. Kovalev a , L.K. Sadieva a,b,* , O.S. Taniya a,b , V.M. Yurk a , A.S. Minin a,b , D.S. Kopchuk a,b , G.V. Zyryanov a,b , V.N. Charushin a,b , O.N. Chupakhin a,b a: Ural Federal University, 19 Mira St., Yekaterinburg 620002, Russia b: Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, 22 S. Kovalevskoi / 20 Akademicheskaya St., Yekaterinburg 620219, Russia * Corresponding author: leilasad@yandex.ru This short communication (letter) belongs to the regular issue. © 2021, The Authors. This article is published in open access form under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract Pyrene-based compounds have a great potential as fluorescent chemosensors for various analytes including common nitro- explosives, such as 2,4,6-trinitrotoluene (TNT). Compounds having two pyrene units in one molecule, such as bispyrenylalkanes, are able to form stable, bright emissive in a visual wavelength region ex- cimers both in non-polar and polar environments. In this work we wish to report that in non-polar solvents the excimer has poor chemosensing properties while in aqueous solutions it provides sig- nificant “turn-off” fluorescence response to TNT in the sub- nanomolar concentrations. Keywords detection of explosives in aqueous media chemical sensors pyrene-based fluorophores fluorescence quenching Received: 15.04.2021 Revised: 20.05.2021 Accepted: 20.05.2021 Available online: 20.05.2021 1. Introduction Due to an increased terrorism threats, the remote detec- tion of TNT and DNT as main components of explosive blends [1] has become an actual task. Visual detection of explosives [2–5] is one of the oldest analytical techniques offering vast possibilities for the on-site, real-time analy- sis with a very fast response time. Among the visual meth- ods, fluorescence [6–9] “turn-off” [10–15] detection is the most convenient due to high sensitivity and fast response time; in the last two decades, various fluorescent sensors for many analytes, including (nitro)explosives, have been reported. Among many fluorescent chemosensors [16], those based on polycyclic aromatic hydrocarbons (PAH- based) have gained wide attention owing to their unique fluorescent properties, such as long-wavelength excimer emission [17] either in a solution [18] or in a solid state. And pyrene-based chemosensors can be ideal candidates to use in PAH-based chemosensors because of the well- known pyrene intense emission with long lifetime values [19–28], tendency to form excimers [29] and high sensi- tivity to electron-deficient molecules (e.g., nitroaromatics) [30,31]. In this manuscript we wish to report our study of the ability of the simple bispyrenylalkane chemosensor to ef- fectively detect a common nitro-explosive, such as 2,4,6-trinitrotoluene (TNT). 2. Experimental Starting materials are commercially available. UV-Vis ab- sorption spectra were measured on the spectrophotometer Shimadzu UV-1600 (Japan). Emission and excitation spec- tra were measured on the Horiba FluoroMax-4 (USA). The emission spectra were normalized automatically using the “Normalize columns” option in the OriginPro 2015 soft- ware (64-bit) b9.2.196. Fluorescence titration experiments were carried out by using the Horiba-Fluoromax-4 spec- trofluorometer (USA). Photos were taken with the Canon D3000 Kit camera. 3. Results and Discussion Chemosensor 1 was prepared as reported earlier [32,33] by using the condensation reaction between the 1-pyrenecarboxaldehyde and acetone with the following reduction of the obtained condensation product (Fig. 1). Next, the photophysical properties of compound 1 in the absence and in the presence of TNT were studied. Pre- viously, the intensive excimer emission of 10 -5 M solutions of compound 1 in methylcyclohexane was reported [32]. http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2021.8.2.09 http://creativecommons.org/licenses/by/4.0/ Chimica Techno Acta 2021, vol. 8(2), № 20218209 LETTER 2 of 4 Fig. 1 Synthetic scheme for sensor 1 However, in our experiments only a feeble response through the excimer fluorescence quenching with poor linearity in the Stern-Volmer plot was observed in cyclo- hexane. Based on the earlier reports [34,35], we suggested that the polarity of a solvent can be the driving force for the geometry changes in the molecule of 1, which are highly soluble in non-polar solvents. In polar solvent media, this lipophilic molecule could act as a surfactant and the hy- drophobic interactions would make molecule 1 to bend over the pentane linker. In this case, the proximity effect between two pyrene moieties will result in excimer emis- sion, while the monomeric emission of 1 will be sup- pressed. In addition, the lipophilic nature of the interior of the cavity formed by molecule 1 would provide a driving force for the transport of TNT molecules from the polar solvent media inside the non-polar micellar chemosensor to cause the dramatic excimer fluorescence quenching. To prove that, the photophysical studies of com- pounds 1 (10 -6 M) in different solvent systems were car- ried out. The selected solvents were arranged in the order of their increasing polarity: cyclohexane, THF (tetrahydro- furan), DMSO (dimethyl sulfoxide), and various solutions of DMSO in water. As it was expected, upon the increasing the polarity of solvents, a gradual decrease in the absolute intensity of the monomer emission was observed (Fig. 2), along with an increase in the intensity of the excimer emission. The highest excimer emission was observed for the 50% aqueous solution of DMSO, and this solvent was selected for our experiments. The visual detection experiments were carried out for the solution of sensor 1 by using common borosilicate glass vials (10 mL), and the picture is presented below (Fig. 3). Thus, depending on the concentration of TNT (10 -4 M solution of in acetonitrile) added to the 10 -6 M so- lution of sensor 1 in DMSO/H2O (1:1), different degree of fluorescence quenching was observed (λex = 365 nm). Fig. 2 Emission spectra (left) and normalized emission spectra (right) of sensor 1 (10 -6 M) in the solvents of different polarity Fig. 3 The visual detection experiment for chemosensor 1 in DMSO/H2O (1:1): pictures of sensor 1 under UV light (λ = 365 nm) after stepwise addition of nitro explosive (TNT) Chimica Techno Acta 2021, vol. 8(2), № 20218209 LETTER 3 of 4 Next, the fluorescence quenching titration was carried out. The fluorescence response of the chemosensor to- wards the nitro-analyte was quantitatively calculated us- ing the Stern-Volmer static quenching model according to Eq. (1): 𝐼0 𝐼 = 1 + 𝐾SV [Q] . (1) The calculated Stern-Volmer constant value for TNT was determined to be as high as Ksv = 4.67·10 5 M -1 for the static quenching model (Fig. 4). At low concentration of TNT quencher the close to linear behavior of Stern-Volmer plots was observed, which suggests the prevalence of only one quenching mechanism, such as static quenching. The calculated limit of detection (LOD) of 143 µg/L (136 ppb) for the sensor 1 was estimated as reported earli- er [36]. 4. Conclusions In summary, we described a tunable bispyrenylalkane chemosensor, which provides a simple, fast and conven- ient way for the detection of common nitroaromatic explo- sive (2,4,6-TNT) in aqueous solutions. Its sensory re- sponse is visible enough to be detected even by the naked eye. The value of the Stern-Volmer constant of the fluores- cence quenching for 2,4,6-trinitrotoluene was found to be high and equal to 4.67·10 5 M -1 . Acknowledgements This work was supported by the Russian Foundation for Basic Research (Project № 19-33-90155). References 1. Yinon J, Zitrin S. The Analysis of Explosives. Elsevier; 1981. 322 p. 2. Kangas MJ, Burks RM, Atwater J, Lukowicz RM, Williams P, Holmes AE. Colorimetric Sensor Arrays for the Detection and Identification of Chemical Weapons and Explosives. Crit Rev Anal Chem. 2017;47(2):138–53. doi:10.1080/10408347.2016.1233805 3. Jenkins TF, Walsh ME. Development of field screening methods for TNT, 2,4-DNT and RDX in soil. Talanta. 1992;39(4):419–28. doi:10.1016/0039-9140(92)80158-A 4. Li Z, Askim JR, Suslick KS. The Optoelectronic Nose: Colorimetric and Fluorometric Sensor Arrays. Chem Rev. 2019;119(1):231–92. doi:10.1021/acs.chemrev.8b00226 5. Wen P, Amin M, Herzog WD, Kunz RR. Key challenges and prospects for optical standoff trace detection of explosives. TrAC - Trends Anal Chem. 2018;100:136–44. doi:10.1016/j.trac.2017.12.014 6. Sun X, Lei Y. Fluorescent carbon dots and their sensing applications. TrAC - Trends Anal Chem. 2017;89:163–80. doi:10.1016/j.trac.2017.02.001 7. Sun X, Wang Y, Lei Y. Fluorescence based explosive detec- tion: From mechanisms to sensory materials. Chem Soc Rev. 2015 Nov 21;44(22):8019–61. doi:10.1039/c5cs00496a 8. Zyryanov GV, Kopchuk DS, Kovalev IS, Nosova EV, Rusinov VL, Chupakhin ON. Chemosensors for detection of nitroaromatic compounds (explosives). Russ Chem Rev. 2014;83(9):783–819. doi:10.1070/RC2014v083n09ABEH004467 Fig. 4 Stern-Volmer plot of emission quenching for sensors 1: points – experimental data, line – linear fit 9. Salinas Y, Martínez-Máñez R, Marcos MD, Sancenón F, Costero AM, Parra M, Gil S. Optical chemosensors and rea- gents to detect explosives. Chem Soc Rev. 2012;41(3):1261– 96. doi:10.1039/c1cs15173h 10. Zyryanov GV, Palacios MA, Anzenbacher P. Simple Molecule- Based Fluorescent Sensors for Vapor Detection of TNT. Org Lett. 2008;10(17):3681–4. doi:10.1021/ol801030u 11. Beyazkilic P, Yildirim A, Bayindir M. Formation of Pyrene Excimers in Mesoporous Ormosil Thin Films for Visual Detec- tion of Nitro-explosives. ACS Appl Mater Interfaces. 2014;6(7):4997–5004. doi:10.1021/am406035v 12. Xiao FN, Wang K, Wang FB, Xia XH. Highly Stable and Lumi- nescent Layered Hybrid Materials for Sensitive Detection of TNT Explosives. Anal Chem. 2015;87(8):4530–7. doi:10.1021/acs.analchem.5b00630 13. Demirel GB, Daglar B, Bayindir M. Extremely fast and highly selective detection of nitroaromatic explosive vapours using fluorescent polymer thin films. Chem Commun. 2013;49(55):6140–2. doi:10.1039/c3cc43202e 14. Andrew TL, Swager TM. A Fluorescence Turn-On Mechanism to Detect High Explosives RDX and PETN. J Am Chem Soc. 2007;129(23):7254–5. doi:10.1021/ja071911c 15. Mosca L, Karimi Behzad S, Anzenbacher P. Small-Molecule Turn-On Fluorescent Probes for RDX. J Am Chem Soc. 2015;137(25):7967–9. doi:10.1021/jacs.5b04643 16. Wu D, Sedgwick AC, Gunnlaugsson T, Akkaya EU, Yoon J, James TD. Fluorescent chemosensors: The past, present and future. Chem Soc Rev. 2017;46(23):7105–23. doi:10.1039/c7cs00240h 17. Ohno K, Satoh H, Iwamoto T. Quantum chemical exploration of dimeric forms of polycyclic aromatic hydrocarbons, naph- thalene, perylene, and coronene. Chem Phys Lett. 2019;716:147–54. doi:10.1016/J.CPLETT.2018.12.034 18. Marsh AV, Cheetham NJ, Little M, Dyson M, White AJP, Beavis P, Warriner CN, Swain AC, Stavrinou PN, Heeney M. Carborane-Induced Excimer Emission of Severely Twisted Bis-o-Carboranyl Chrysene. Angew Chemie Int Ed. 2018;57(33):10640–5. doi:10.1002/anie.201805967 19. Šoustek P, Michl M, Almonasy N, Machalický O, Dvořák M, Lyčka A. The synthesis and fluorescence of N-substituted 1- and 2-aminopyrenes. Dye Pigment. 2008;78(2):139–47. doi:10.1016/j.dyepig.2007.11.003 20. Suzuki Y, Morozumi T, Nakamura H, Shimomura M, Hayashita T, Bartsh RA. New fluorimetric alkali and alkaline earth metal cation sensors based on noncyclic crown ethers by means of intramolecular excimer formation of pyrene. J Phys Chem B. 1998;102(40):7910–7. doi:10.1021/jp981567t https://doi.org/10.1080/10408347.2016.1233805 https://doi.org/10.1016/0039-9140(92)80158-A https://doi.org/10.1021/acs.chemrev.8b00226 https://doi.org/10.1016/j.trac.2017.12.014 https://doi.org/10.1016/j.trac.2017.02.001 https://doi.org/10.1039/c5cs00496a https://doi.org/10.1070/RC2014v083n09ABEH004467 https://doi.org/10.1039/c1cs15173h https://doi.org/10.1021/ol801030u https://doi.org/10.1021/am406035v https://doi.org/10.1021/acs.analchem.5b00630 https://doi.org/10.1039/c3cc43202e https://doi.org/10.1021/ja071911c https://doi.org/10.1021/jacs.5b04643 https://doi.org/10.1039/c7cs00240h https://doi.org/10.1016/J.CPLETT.2018.12.034 https://doi.org/10.1002/anie.201805967 https://doi.org/10.1016/j.dyepig.2007.11.003 https://doi.org/10.1021/jp981567t Chimica Techno Acta 2021, vol. 8(2), № 20218209 LETTER 4 of 4 21. Hrdlovič P, Horinová L, Chmela Š. Spectral properties of ionic derivatives of pyrene and their aggregates with anionic surfactant and polyelectrolyte. Can J Chem. 1995;73(11):1948–54. doi:10.1139/v95-240 22. Daems D, Van den Zegel M, Boens N, De Schryver FC. Fluorescence decay of pyrene in small and large unilamellar L,α-Dipalmitoylphosphatidylcholine vesicles above and below the phase transition temperature. Eur Biophys J. 1985;12(2):97–105. doi:10.1007/BF00260432 23. Kim JJ, Beardslee RA, Phillips DT, Offen HW. Fluorescence lifetimes of pyrene monomer and excimer at high pressures. J Chem Phys. 1969;51:2761–2. doi:10.1063/1.1672406 24. Ruiu A, Vonlanthen M, Rojas-Montoya SM, González-Méndez I, Rivera E. Unusual fluorescence behavior of pyrene-amine containing dendrimers. Molecules. 2019;24(22). doi:10.3390/molecules24224083 25. Lin TI. Excimer fluorescence of pyrene-tropomyosin adducts. Biophys Chem. 1982;15(4):277–88. doi:10.1016/0301-4622(82)80011-2 26. Wang X, Liu L, Zhu S, Peng J, Li L. Preparation of exciplex- based fluorescent organic nanoparticles and their application in cell imaging. RSC Adv. 2017;7(65):40842–8. doi:10.1039/c7ra08142a 27. Kanagalingam S, Spartalis J, Cao TM, Duhamel J. Scaling rela- tions related to the kinetics of excimer formation between pyrene groups attached onto poly(N,N-dimethylacrylamide)s. Macromolecules. 2002;35(22):8571–7. doi:10.1021/ma020784w 28. Bertolotti SG, Previtali CM. Fluorescence of pyrene deriva- tives in the presence of poly(methallyl sulfonate-vinyl ace- tate) copolymers. effect of charge density. J Macromol Sci Part A. 1994;31(4):439–49. doi:10.1080/10601329409351530 29. Förster T, Kasper K. Ein Konzentrationsumschlag der Fluo- reszenz des Pyrens. Zeitschrift für Elektrochemie, Berichte der Bunsengesellschaft für Phys Chemie. 1955;59(10):976– 80. German. doi:10.1524/zpch.1954.1.5_6.275 30. Rehm D, Weller A. Kinetics of Fluorescence Quenching by Electron and H-Atom Transfer. Isr J Chem. 1970;8(2):259–71. doi:10.1002/ijch.197000029 31. Goodpaster JV, McGuffin VL. Fluorescence quenching as an indirect detection method for nitrated explosives. Anal Chem. 2001;73(9):2004–11. doi:10.1021/ac001347n 32. Zachariasse K, Kühnle W. Intramolecular Excimers with α,ω-Diarylalkanes. Zeitschrift für Phys Chemie. 1976;101(1–6):267–76. doi:10.1524/zpch.1976.101.1-6.267 33. Ikeda T, Lee B, Tazuke S, Takenaka A. Time-resolved observa- tion of excitation hopping between two anthryl moieties at- tached to both ends of alkanes: simulation based on confor- mational analysis. J Am Chem Soc. 1990;112(12):4650–6. doi:10.1021/ja00168a004 34. Zhang P, Zhang L, Wang H, Zhang DW, Li ZT. Helical folding of an arylamide polymer in water and organic solvents of varying polarity. Polym Chem. 2015;6(15):2955–61. doi:10.1039/C5PY00096C 35. Ikai T, Shimizu S, Awata S, Kudo T, Yamada T, Maeda K, Kanoh S. Synthesis and chiroptical properties of a π-conjugated polymer containing glucose-linked biphenyl units in the main chain capable of folding into a helical conformation. Polym Chem. 2016;7(48):7522–9. doi:10.1039/C6PY01759B 36. Shrivastava A, Gupta V. Methods for the determination of limit of detection and limit of quantitation of the analytical methods. Chronicles Young Sci. 2011;2(1):21. doi:10.4103/2229-5186.79345 https://doi.org/10.1139/v95-240 https://doi.org/10.1007/BF00260432 https://doi.org/10.1063/1.1672406 https://doi.org/10.3390/molecules24224083 https://doi.org/10.1016/0301-4622(82)80011-2 https://doi.org/10.1039/c7ra08142a https://doi.org/10.1021/ma020784w https://doi.org/10.1080/10601329409351530 https://doi.org/10.1524/zpch.1954.1.5_6.275 https://doi.org/10.1002/ijch.197000029 https://doi.org/10.1021/ac001347n https://doi.org/10.1524/zpch.1976.101.1-6.267 https://doi.org/10.1021/ja00168a004 https://doi.org/10.1039/C5PY00096C https://doi.org/10.1039/C6PY01759B https://doi.org/10.4103/2229-5186.79345