Three Viologen Compounds Containing Keggin and Mo-Capped Weakley Polyoxometalates: Photo-/Thermo-/Electro-Chromic Studies
Qinghai Lu, Jun Ying, Aixiang Tian, Mengle Yang
Abstract
Multiresponsive color-changing materials have important applications in daily life. In this work, three photochromic, thermochromic, and electrochromic compounds were synthesized by introducing two kinds of polyoxometalates into the viologen system, namely, {[Ni(dibipy)(4,4′-bipyH)(H 2 O) 3 ]·[Ni 4 (H 2 O) 2 Ge 2 Mo 18 O 68 (MoO 2 ) 2 ] 0.5 }·10H 2 O ( 1 ), {[Ni II (nibipy) 2 (4,4′-bipy)(H 2 O) 2 ]·(SiMo 12 O 40 )}·2H 2 O ( 2 ), and [(Hnibipy) 2 ·(SiMo 12 O 40 )]·2.5H 2 O ( 3 ) (dibipy·Cl = 1-(3,5-dimethyl-isoxazol-4-ylmethyl)-[4,4’]bipyridinyl-1-ium chloride, nibipy·Cl = 1-(4-Nitro-benzyl)-[4,4’]bipyridinyl-1-ium chloride and 4,4′-bipy = 4,4′-bipyridine). Compound 1 contains the Mo-capped weakley anion [Ni 4 (H 2 O) 2 (Ge 2 Mo 18 O 68 (MoO 2 ) 2 ] 8–, which is very rare in polyoxometalates. Both 1 and 2 own mixed organic ligands to modify anions, such as viologen and 4,4′-bipy. Compounds 1 and 3 exhibit fast responsive photochromic effects, while compound 2 has rapid recovery of thermochromic properties. Sandwich-type rigid devices based on compounds 1 – 3 also exhibit electrochromic properties. In addition, hydrogels and poly(methyl methacrylate)-based mixed matrix membrane systems were introduced to achieve portable visual UV detectors. The applications of these compounds in metal ion detection and anticounterfeiting were also studied.