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

Abstract

The methods of absorption electronic and NMR spectroscopy were used to study the processes of complexation during the interaction of molecules of unsubstituted indoline spiropyran with aluminum salts. The mechanism of formation and structure of complexes of two types has been established. Negative photochromism of the complex of the merocyanine form of spiropyran with aluminum ions was found. The stability of metal complexes to the action of various agents has been investigated. Keywords: photochromism, spiropyrans, metal complexes, aluminum salts, electron spectroscopy, NMR spectroscopy.

5′-Substituted Indoline Spiropyrans: Synthesis and Applications

“…This interconversion between two states is accompanied by change of color, but additional changes in refractive index, dielectric constant, redox potentials, solubility, viscosity, surface wettability, magnetism, luminescence, or mechanical effects are also possible. One of the unique features of spiropyrans is that the MC form is able to coordinate with metal ions and that the spiroform form (A) does not show such a property [6,8,11,[13][14][15][32][33][34][35][36][37][38][39][40].…”

“…According to these studies (see Table 1) [5,32], the main absorption band of original spiroform (A) of the unsubstituted spiropyran SP1 in ethanol has an λ A max at 295 nm. One of the unique features of spiropyrans is that the MC form is able to coordinate with metal ions and that the spiroform form (A) does not show such a property [6,8,11,[13][14][15][30][31][32][33][34][35][36][37][38][39][40].…”

“…According to these studies (see Table 1) [5,32], the main absorption band of original spiroform (A) of the unsubstituted spiropyran SP1 in ethanol has an λ A max at 295 nm. Under UV irradiation, formation of photoinduced MC form was recorded, which manifests itself in appearance of an absorption band in the visible region of the spectrum (λ B max = 550 nm, ε 550 = 35.0 10 3 M −1 cm −1 ), which immediately spontaneously disappears after turning off the light (k BA db = 0.48 s −1 ) with regeneration of the original SP1 cyclic form.…”

“…At the same time, a novel way was proposed to stabilize the MC form lifetime by complexation with certain cations. We proposed the method of stabilizing the short-lived MC form of unsubstituted indoline spiropyran SP1 by forming stable complexes between the molecules of this compound and aluminum salts [32,53]. Below we present a good illustration of this option to obtain important information about the structure of spiro and MC forms of unsubstituted indoline spiropyran SP1 using 1 Hand 13 C-NMR spectroscopy.…”

“…As a result, diverse photocontrolled systems with artificial ionophore receptors capable of selective complex formation with various ions were proposed and studied. The unique feature of spiropyrans is that the MC form is able to coordinate with metal ions and that the spiroform form (A) does not show such a property [6,8,11,[13][14][15][32][33][34][35][36][37][38][39][40]142]. It was also found that the resulting complexes with various cations, in contrast to the original receptors, have negative or reverse photochromism.…”