New stable colored complex of Al³⁺ with 1',3',3'‐trimethylspiro[2H‐1‐benzopyran‐2,2'‐indoline] (BIPS)

Abstract

Ultraviolet‐visible (UV‐vis) absorption, flash photolysis, and 1H and 13C NMR spectroscopy were used to investigate the mechanism of formation and structure of complexes in the 1',3',3'‐trimethylspiro[2H‐1‐benzopyran‐2,2'‐indoline] (SP, also well known as BIPS) with Al3+ (inorganic salts) in ethanol (EtOH), methanol (MeOH), and in aqueous MeOH solutions. A labile (equilibrium constants ≤ 5000 M−1) complex of SP and Al3+ with broad absorption band in the UV‐vis with λmax = 380 nm appeared promptly in the presence of an excess of Al3+. The slow formation of a stable complex (SC) between Al3+ and two merocyanine (MC) forms of SP with an intensive absorption band at λmax = 430 nm is observed with a yield of 1.0 upon keeping the solutions of these two compounds at constant concentration ratio [Al3+] ≥[SP]/2 in the dark. The rate constants of such SC formation were close to the corresponding rate constant of the transformation of SP into MC in the dark (5.0×10−5‐1×10‐3 s‐1, depending upon the solvent). The photolysis of the SC with visible light (λ > 400 nm) results in the total conversion of the SC into SP. The SC forms promptly after the addition of Al3+ at concentrations of the same order as those of MC. This method allows detection of [Al3+] to concentrations as low as 50 nM. The kinetics and thermodynamic parameters of the SP and MC reactions and of their complex formation with Al3+ are discussed.

Spectral study of the structure and properties of complexes of unsubstituted indoline spiropyran with aluminum ions

“…The rate constant of the complex formation reaction in ethanol in the dark with a tenfold excess of aluminum nitrate is k = 8.56 • 10 −5 s −1 . Preliminary results concerning the kinetics of complex 2 formation and its stoichiometry were published by us in the article [13]. Complex 2 exhibits negative photochromism (Fig.…”

“…Spiropyran SP1 was obtained with yield of 96% by heating at boiling of solution of freshly distilled Fischer's base with salicylaldehyde in anhydrous ethanol in an argon atmosphere according to the known method [12,13]. The structure of the target compound SP1 was proved by a set of modern physicochemical methods of analysis (UV, 1 H and 13 C NMR spectroscopy and mass spectra). LC-MS spectrum (m/z ):…”

“…The NMR spectra of spiropyran SP1 and its complexes with aluminum ions were measured in deuterochloroform and deuteromethanol on Bruker Avance III-500 spectrometer (Germany) with operating frequency of 500 MHz for protons and 126 MHz for carbon nuclei. The complete assignment of the proton and carbon signals was done by a combination of 1D and 2D NMR pulse sequences 1 H− 1 H COSY, 1 H− 13 C HSQC and 1 H− 13…”

“…Photocontrolled photochromic ionophores and artificial receptors, which make it possible to control the process of complex formation with various ligands and the properties of the resulting products, attract the interest of researchers in various fields [1][2][3][4][5][6][7][8]. It was previously shown that substituted derivatives of spiropyran -1 ′ , 3 ′ , 3 ′ -trimethylspiro[2H-1benzopyran-2, 2 ′ -indoline] (BIPS, SP1) undergoing photochromic transformations (Scheme 1) quite easily form complexes when interacting with salts of some d-and felements [3][4][5][6][7][8][9][10][11][12], as well as salts with inorganic acids [13,14].…”

“…In order to develop previously performed studies [13,24] the aim of this article was to study the structure of complexes of photochromic spiropyran SP1 during the interaction of its molecules with aluminum salt using the electronic, 1 H, 13 C and 2D MR spectroscopy.…”