NEW 2,5-BIS(2-ETHYLHEXYL)- PYRROLO[3,4-c]PYRROLE-1,4(2H,5H)-DIONE-2,2’-BIPYRIDINE-BASED CO-POLYMER, SYNTHESIS, PHOTOPHYSICAL PROPERTIES AND RESPONSE TO METAL CATIONS Chimica Techno Acta LETTER published by Ural Federal University 2021, vol. 8(4), № 20218417 eISSN 2411-1414; chimicatechnoacta.ru DOI: 10.15826/chimtech.2021.8.4.17 1 of 4 New 2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)- dione-2,2’-bipyridine-based co-polymer, synthesis, photophysical properties and response to metal cations Alexey P. Krinochkin ab*, Мaria I. Savchuk ab, Еkaterina S. Starnovskaya аb, Igor L. Nikonov ab , Artem V. Baklykov ab, Ekaterina A. Kudryashova a, Svetlana S. Rybakova a, Evgeny D. Ladin a, Dmitry S. Kopchuk ab , Zhuo Wang c,Оleg N. Chupakhin ab a: Ural Federal University, 620002 Mira st., 19, Yekaterinburg, Russia b: I.Ya. Postovsky Institute of Organic Synthesis of the Ural Branch of the RAS, 620990 Kovalevskoy/Akademicheskaya st., 22/20, Yekaterinburg, Russia c: Beijing University of Chemical Technology, 100029 Beijing, China * Corresponding author: yapet89@mail.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 A new co-polymer based on fragments of 2-(2- pyridyl)monoazatriphenylene and 2,5-bis (2-ethylhexyl)-3,6- di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione was pre- pared by using the Sonogashira reaction. The photophysical proper- ties of the polymer were studied. The presence of a strong batho- chromic shift of the absorption and emission maxima in comparison with the previously described monomer units is shown. The polymer exhibits an intense “turn-off” response toward Cu2+ cations. Keywords Sonogashira coupling polymer monoazatriphenylene 3,6-di(thiophen-2- yl)pyrrolo[3,4-c]pyrrole- 1,4(2H,5H)-dione fluorescence Cu2+ “turn-off” response Received: 16.12.2021 Revised: 19.12.2021 Accepted: 23.12.2021 Available online: 24.12.2021 1. Introduction Acetylene-based polymers find a variety of applications as functional materials for sensorics and molecular electronics [1]. In particular, conjugated polymers containing 2,2'-bipyridine moieties [2] as monomer units are of inter- est in terms of optical response to metal cations [3]. Thus, the selective determination of Cu2+ [4] and Hg2+ [5] cations has been described with the help of such polymers. On the other hand, bis-pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-diones (DPPs) were widely used as components of donor–acceptor alternating co-polymers, which were reported as promising hole-transport materials [6,7], as materials for molecular electronics and photovoltaics [8,9], components of laser dyes [10], dyes for two-photon fluorescence microscopy [11], chemosensors for Cu2+ [12] and Hg2+ [13] cations, and many other applications [14]. One of the most important application of DPP-based materials was in their use as rea- gents for photothermal therapy of cancer [15], including photoacoustic imaging-guided photothermal therapy [16]. In this work, we wish to report the synthesis of a polymer containing fragments of 2-(2-pyridyl)monoazatriphenylene and 2,5-bis(2-ethylhexyl)-3,6-bis(thiophen-2-yl)pyrrolo[3,4- c]pyrrole-1,4(2H,5H)-dione. 2. Experimental 1H NMR spectra were recorded on a Bruker Avance-400 spectrometer (400 MHz), the internal standard was SiMe4. Elemental analysis was performed on a Perkin Elmer PE 2400 II CHN analyzer. UV–visible absorption spectra were recorded on a Perkin Elmer Lambda 45. Luminescence spectra were obtained using a HORIBA Scientific Fluoro- Max-4 spectrofluorometer. GPC measurements were per- formed using a chromatograph Agilent 1200 with an aero- sol light scattering detector (ELSD) (Agilent technologies, http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2021.8.4.17 https://orcid.org/0000-0002-2493-0056 https://orcid.org/0000-0002-0397-4033 http://creativecommons.org/licenses/by/4.0/ Chimica Techno Acta 2021, vol. 8(4), № 20218417 LETTER 2 of 4 USA). The starting monomers 1 [17] and 2 [18] were ob- tained as described in the literature. The chemical polymerization process was carried out in accordance with the modified method [19]. The com- pounds 1 (33 mg, 0.048 mmol) and 2 (19.1 mg, 0.048 mmol) were dissolved in the mixture of diisoprop- ylamine/toluene (2:3, 4.0 ml). Then CuI (5.8 mg, 0.030 mmol), Pd(tpp)2Cl2 (3.4 mg, 0.0048 mmol) and PPh3 (2.5 mg, 0.01 mmol) were added. The reaction mix- ture was stirred in an autoclave under argon atmosphere at 65 °C for 3 days. Then the solvents were evaporated under reduced pressure. Water (10 ml) was added to the residue and the product was extracted with methylene chloride (3×10 ml). The organic phase was washed with an aqueous solution of NH4Cl and then dried over anhy- drous Na2SO4. The solvent was evaporated under reduced pressure. The polymer was obtained as a purple powder. Yield 32 mg (70%). NMR 1Н (CDCl3, δ, ppm): 0.77–0.96 (m, 14H, 2-ethylhexyl), 1.14–1.40 (m, 28H, 2- ethylhexyl), 1.49–1.63 (m, 9H, 2-ethylhexyl), 7.44–7.49 (ddd, 2H, 3J 7.6 Hz, 7.6 Hz, 4J 2.6 Hz, CHarom), 7.52–7.58 (m, 1H, CHarom), 7.64–7.67 (m, 1H, CHarom), 7.67–7.70 (m, 1H, CHarom). IR (ν, cm–1): 1660 (C=O). 3. Results and discussion The synthesis of monomers 1 [17] and 2 [18] was carried out according to the described methods. Thus, compound 1 was obtained on the basis of commercially available pre- cursor 3 as a result of successive N-alkylation and bromin- ation of thiophene rings (Scheme 1). In the case of pyri- dylmonoazatriphenylene 2, the starting compound is the previously described 3,11-dibromo-6-(pyridin-2-yl)-8,9- dihydro-7H-dibenzo[f,h]cyclopenta[c]quinoline 4 [20]. The monomer was obtained as a result of the Sonogashira reaction at two bromine atoms, followed by removal of the trimethylsilyl protection. The polymerization process was carried out in accordance with a modified technique under the conditions of the Sonogashira reaction [19]. The data of the 1H NMR spectrum of the obtained polymer do not contradict its proposed structure. In the IR spectra, the presence of a vibration band corresponding to carbonyl groups in the region of 1660 cm–1 can be noted. Next, we studied the photophysical characteristics of the obtained polymer 5. In the solution of acetonitrile this polymer demonstrates absorption maxima around 550 nm (Table 1). Analysis of the literature data showed that, in the case of polymer 5, there is a bathochromic shift of the absorption maximum relative to the monomer units. Thus, for unsubstituted pyridylmonoazatriphenylene 6 [20], the longest wavelength absorption maximum corresponds to 357 nm, and in the case of 2,5-bis(2-ethylhexyl)-3,6- di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-(2H,5H)-dione 7 [21] this parameter was 541 nm. A similar bathochromic shift is observed for the emission maxima of polymer 5 relative to compounds 6 and 7. For example, there is a shift from 541 nm to 55 nm. The absorption and emission spectra of the polymer are shown in Fig. 1. Next, we studied the fluorescent response of the new polymer 5 with respect to cations of a number of metals. Thus, it was found that the addition of Cu2+ cation to the solution of polymer 5 in acetonitrile results in almost complete quenching of its fluorescence, which is due to the influence of both monomer units on the supramolecular properties of the whole polymer. Fig. 2 depicts GPC chromatography for the resulting polymer 5. According to the obtained data, the resulting product 5 is a mixture of oligomers/short polymers, among which there are structures with molecular weights of up to 3–4 kDa. Thus, the method reported herein for the preparation of the polymer 5 requires further develop- ment in order to increase its average molecular weight. Table 1 The photophysical characteristics for polymer 5 and com- pounds 6 and 7 in MeCN at room temperature Compound Absorption maxima, nm Emission maxima, nm [20] 263, 313, 339, 357 364, 381, 403 (sh) [21] 341, 353, 508, 541 560, 600 Polymer 5 550 571, 616 Fig. 1 Absorption and emission spectra of polymer 5 in acetonitrile at room temperature Chimica Techno Acta 2021, vol. 8(4), № 20218417 LETTER 3 of 4 Scheme 1 Synthesis of polymer 5. Reagents and conditions: i) CuI, PPh3, Pd(tpp)2Cl2/diisopropylamine, 65 °C, 3 days Fig. 2 GPC chromatogram for polymer 5 Chimica Techno Acta 2021, vol. 8(4), № 20218417 LETTER 4 of 4 4. Conclusions In conclusion, a co-polymer containing 2-(2- pyridyl)monoazatriphenylene and 2,5-bis(2-ethylhexyl)- 3,6-bis(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)- dione fragments as monomer units was prepared. 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