Three viologen-derived Zn-organic materials: photochromism, photomodulated fluorescence, and inkless and erasable prints

Abstract

Three zinc–viologen compounds, namely, {[Zn(Mebpy)(Hbtc)Cl]·2H₂O}_n (1), {[Zn₃(Cebpy)₂(Hbtc) (H₂btc)₂ (OH)₂]·4H₂O}_n (2), and {[Zn₄(Cebpy)₂(IPA)₃(OH)₂]·2H₂O}_n (3) (Mebpy = N-methyl-4,4′-bipyridinium, Cebpy = N-carboxyethyl-4,4′-bipyridinium, H₃btc = 1,3,5-benzenetricarboxylic acid, and H₂IPA = isophthalic acid) have been constructed from aromatic carboxylic acid and viologen-derived ligands. In compound 1, the Hbtc²⁻ ligands bridge Zn²⁺ cations to form a 1D fence-like chain with the Mebpy⁺ ligand suspended on the chains. Compound 2 possesses a 2D (4, 4) double-layered grid structure based on linear trinuclear Zn₃O₂ cluster units. The structure of compound 3 can be described as a 3D open-framework based on tetranuclear Zn₄O₂ cluster units and helical chains with helical channels. All three compounds display photochromic properties from pale yellow to dark blue after being irradiated by a xenon lamp with different photoresponsive rates. Compounds 2 and 3 can be deposited in paper simply by coating them with a solution of ethanol. The papers can be used as inkless and erasable print media. In addition, the photo-modulated luminescence of these compounds was also investigated.