Chromogenic properties of spiropyrans caused by metals in the form of ions and as a part of uncharged bis(chelate)s

Abstract

: Ionochromic properties of spiropyrans caused by interaction of merocyanine isomers with metal ions are widely known. However, chromogenic transformations induced by metals as uncharged bis(chelate)s remain less explored. For the first time we have quantitatively studied complexation of spiropyran ligands with such coordination centers. The merocyanine of spironaphthopyran form stable 1:1 complexes with neutral, coordinatively unsaturated bis(β-diketonates), whose structures were established by X-ray diffraction. Increasing of electron-withdrawing properties of substituents in the β-diketonate fragment enhances the stability of complexes in the range acac<tfac<ttfac<hfac. In solution, complexes with bis(chelate)s of diamagnetic ions, as well as cobalt, demonstrate negative photochromism due to reversible photodissociation. These findings provide a foundation for the molecular design of heteroligand complexes that incorporate, in addition to the photochromic merocyanine, ligands with other functional properties (fluorescence, redox activity, etc.) enabling the development of polyfunctional molecular systems.