Amphiphilic ferrocenylated alkylpyridinium: the formation of micelles and hydrogels and their disaggregation induced by an external stimulus

Abstract

Ferrocene-containing amphiphiles [py-N-(CH₂)_nOCH₂Fc]Cl (n = 6 (1a), 8 (1b), 10 (1c); py = C₅H₅N, Fc = Fe(C₅H₄)(C₅H₅)) were synthesized. The absorption spectra of 1a–1c in the presence of a small amount of dye (Nile red and pyrene) in aqueous media suggested the formation of micelles which encapsulated the dye molecules. Two critical micelle concentrations were observed at 1.1 mM and 2.3 mM at 20 °C. Compounds 1a and 1c showed a single CMC for each, while the formation of two kinds of micelles, the spherical and rod-like ones, depended on the concentrations. The addition of an oxidant, NaOCl, to the aqueous solution of the micelles of 1b turned ferrocene to ferrocenium and caused the disaggregation of the micelles. The addition of α-cyclodextrin (α-CD) to 2b caused the disaggregation of the micelle and the formation of water-soluble [2]- and [3]pseudorotaxane [{py-N-(CH₂)₈OCH₂Fc}(α-CD)_m]Cl (1b(α-CD)_m) (m = 1, 2), while mixing 1c and α-CD in water formed the rotaxane gel. The addition of NaOCl to the hydrogel of 1c and α-CD changed the gel to sol.