Novel Photo- and Ionochromic Benzothiazole-Substituted Spirobipyrans
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Novel Photo- and Ionochromic Benzothiazole-Substituted Spirobipyrans E. V. Solov’evaa, N. A. Voloshina, A. V. Chernysheva,*, Yu. S. Reutovaa, and A. V. Metelitsaa Presented by Academician V.I. Minkin May 13, 2020 Received May 13, 2020; revised September 5, 2020; accepted September 22, 2020
Abstract—Novel photochromic spirobipyrans containing benzothiazole group in the 2H-chromene moiety have been synthesized. The spirobipyrans combine with Co2+, Ni2+, Zn2+, and Cu2+ ions to give intensely colored complexes of merocyanine form with long-wavelength absorption bands at λ > 600 nm. Keywords: spiropyrans, chemosensors, photochromism, complex formation DOI: 10.1134/S0012500820090050
Among photochromic compounds, spiropyrans are intensively studied due to wide possibilities of structural modification [1] and opportunity to design polyfunctional molecular systems on their basis [2]. The presence of chelating substituents in the ortho position to the pyran oxygen atom of spiropyrans favors the formation of complexes with metal ions [3–5], while the photochromic properties of resultant complexes opens a way to use spiropyrans as photocontrolled sensors of ions and molecules [6–8]. The majority of coordination-active spiropyrans studied to date refer to indoline series, while these complexes display absorption in visible range up to 600 nm. Furthermore, it is necessary for biological application to prepare photoactivated sensors of metal ions whose analytical signal is in the range λ > 600 nm, which considerably decreases losses from absorption by tissues [9]. Therefore, it seems promising to synthesize and study coordination-active spiropyrans with hetarene fragment distinct from indoline. One of classes of such compounds is spirobipyrans of symmetrical and asymmetrical structure. In spite of thermochromic and photochromic properties of spirobipyrans are well studied [10, 11], there are only few examples of their complexation with metal ions. A series of symmetrical 3,3'-dimethyl-2,2'-spirobi(2H-1-benzopyrans) with iminodicarboxylic acid residues in the 8 and 8' position was described. According to the data of NMR spectroscopy, spirobipyrans formed complexes aResearch Institute of Physical and Organic Chemistry, Southern Federal University, Rostov-on-Don, 344104 Russia *e-mail: [email protected]
in colorless cyclic form with Ca2+, Mg2+, Sr2+ ions and did not change color on complexation. It should be also noted the lack of photochromic properties at ambient temperature for both initial ligands and their complexes [12, 13]. Therefore, the aim of this work is to synthesize and study new asymmetric spirobipyrans containing a coordination-active fragment. New asymmetric spirobipyrans (SBP) containing benzothiazole group in the naphthopyran fragment were obtained by the condensation of benzopyrylium salts 1–3 with benzothiazolesubstituted hydroxynaphthoic aldehyde 4 in acetic acid, isolation of resultant salts of o-hydroxynaphthylvinyl derivatives 5–7, and treatment of the latter with ammonia to form SBP 8–10 (Scheme
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