Formation of composite microspheres comprising a 2,2′-bipyridyl iron(ii/iii) complex and acrylamide by UV irradiation

Abstract

Formation of the [Fe(bpy)₃]²⁺ complex from FeCl₃ and bpy, and compounding with acrylamide (AA) took place simultaneously upon irradiation with a UV beam at 355 nm in an ethanolic solution of AA. We observed composite microspheres with [Fe(bpy)₃]²⁺ confined in the acrylamide (AA) matrix with a simultaneous color change from yellow to red, due to metal-to-ligand charge transfer (MLCT) of the complex ion. The UV beam induces an ²e←t₁ transition from Cl to Fe(III) in [FeCl₄]⁻, resulting in the reduction of Fe(III) to Fe(II). Photolysis of [Fe(III)Cl₄]⁻ is mediated by ethanol via a transition state comprising [Fe(II)Cl₄]²⁻ with a solvated layer of C₂H₅OH after donating an electron to the [Fe(III)Cl₄]⁻ complex. The reduction, in turn, causes decomposition of [FeCl₄]⁻ to liberate a Cl radical, which changes the state of AA. The pink-colored microspheres are ca. 1 μm in average diameter, water-soluble, well dispersed in ethanol, and are stable even after one year.