Photocontrollable Cation Extraction with Crowned Oligo(spirobenzopyran)s

Abstract

Since light is one of the most effective and energy-saving means for changing molecular functions, extensive studies about photoresponsive reagents bearing a photochromic moiety have been reported so far. [1][2][3][4] Spirobenzopyrans, typical photochromic compounds, isomerize from their electrically neutral spirobenzopyran forms to the corresponding zwitterionic merocyanine form, which has a maximum absorption wavelength around 550 nm, by UV-light irradiation, and vice versa by visible-light irradiation and/or heat. [5][6][7][8][9] Since spirobenzopyrans change not only their conformation but also their electrical properties by photoirradiation, the interaction between the photoionized molecule and a cation may be affected considerably.We had already synthesized spirobenzopyran derivatives bearing a crown ether moiety, which we call crowned spirobenzopyrans [crowned mono(spirobenzopyran)].We studied their metal-ion complexing abilities, photochromism, and applications to photocontrollable devices. [10][11][12][13][14][15] Crowned spirobenzopyrans form complexes with metal ions and simultaneously isomerize from their spirobenzopyran form to the corresponding merocyanine form under dark condition, due to the ionic interaction between the phenolate anion of the merocyanine form and a metal ion complexed by their crown ether moiety (Scheme 1). Therefore, the resulting absorptionspectral changes in the visible region are closely related to the strength of the interaction between the phenolate anion of the merocyanine form and a metal ion. In the presence of a hard metal ion such as an alkali or alkaline-earth metal ion, which interacts strongly with the phenolate anion, the absorption spectrum of merocyanine form shows a blue shift, while it shows a red shift in the presence of a soft metal ion such as Hg 2+ and Ag + .We have already observed that, on the metal ion complexation of several diazacrown ether derivatives bearing two spirobenzopyran [crowned bis(spirobenzopyran)] in methanol under photoirradiation conditions, the stability constants of the complexes between these compounds and hard multivalent metal ions such as alkaline-earth and rare-earth metal ions were decreased significantly by visible-light irradiation. We also found that the interaction between the phenolate anion of the merocyanine forms and a metal ion was stronger than that for the metal ion complexation of the corresponding crowned mono(spirobenzopyran)s. [16][17][18][19][20] We have also studied the metal ion extractabilities of crowed mono-and bis(spirobenzopyran)s. Even under dark conditions, these compounds extracted metal ions from an aqueous phase into an organic phase with counteranions. 21,22 The concentration of Li + extracted into the organic phase by (diaza-12-crown-4)-bis(spirobenzopyran) was increased by UV light irradiation, while it was remarkably decreased by visible-light irradiation. The slope for the calibration graph, that is, the sensitivity in the Li + analysis, was increased remarkably by UV light irradiation. We thu...

Photochromism of nitrobenzospiropyran in phosphonium based ionic liquids

“…If we consider the photoisomerization process, the nonpolar BSP molecule when irradiated with UV light isomerizes into a highly polar zwitterionic system MC, and it is known that this system can be used to transport metal ions across organic-aqueous barriers with UV light. [40][41][42] However, it has recently been proposed that ILs are structured at the microand nanoscopic levels, containing polar and non-polar domains. 22,23,43 This hypothesis could explain the reason we observe such low values of K e ; potentially at equilibrium the BSP isomer resides in the non-polar domain of the IL.…”

Analytical and Separation Chemistry by Taking Advantage of Organic Photochromism Combined with Macrocyclic Chemistry

“…38 The photoinduced changes in the metal-ion extractability of crown ether derivatives bearing three or four spirobenzopyran moieties (10 or 11) and their analogues were studied using 1,2-dichloroethane as an organic solvent. 17 Under dark conditions, these compounds extracted Cu 2+ , Ag + , and Pb 2+ with their counteranions from the aqueous phase to the organic phase. The extraction equilibrium constants of the photochromic crown ether derivatives for Cu 2+ and Ag + were successfully determined.…”

Photocontrol of ion-sensor performances in neutral-carrier-type ion sensors based on liquid-crystalline membranes

“…The tunable selectivity by photoirradiation is interesting from the viewpoint of photocontrollable analysis and application. 9,10 In addition, we had reported that the ISEs based on the similar liquid-crystalline membranes without any azobenzene derivative were applied successfully to K + assays in blood sera. 4 Therefore, the ISEs based on the liquid-crystalline membranes containing azobenzene derivative 2 are also useful for K + assays in real biological samples, because the sensitivity and selectivity for K + are comparable to or higher than those for K + -ISEs reported previously.…”