Polyoxometalate-Viologen Thermochromic Hybrids for Organic Amine Detectors and Memristors with Temperature-Regulating Resistance Switching Characteristics

There are relatively few reports on the combination of viologen and polyoxometalates (POMs). Herein, we successfully synthesized three viologen-POM-based compounds by in situ transformation of ligands under hydrothermal conditions, namely, {M-II(1,4-cby)(2)[H-2(gamma-Mo8O26)]}center dot nH(2)O (1: M = Ni, n = 4; 2: M = Co, n = 6), and [Ni-II(1,3-cby)(H2O)(4)(beta-Mo8O26)0.5]center dot 2H(2)O (3) cby center dot Cl = 1-(3-carboxy-benzyl)-[4,4 & PRIME;]bipyridinyl-1-ium). Isostructural compounds 1 and 2 exhibit two-dimensional (2D) layer structures with POMs as linking nodes, while compound 3 shows a one-dimensional (1D) metal-organic chain with dissociative POM anions. When the temperature increases, compounds 1-3 show good reversible thermochromism properties and also have a fluorescence quenching effect. Moreover, compounds 1-3 can also be used as detectors for organic amines, especially in the atmosphere of ammonia, ethylenediamine, and diethylamine with an obvious discoloration effect. In addition, compound 1 was used as a material for the preparation of memristors with superior properties (distinct temperature-adjusted resistive switching properties). It shows bipolar resistive switching (RS) behavior at different temperatures of 20, 50, and 100 ?. The results show that the 1-based memristor has good thermal stability, which is important for high-temperature environment applications. It also shows that crystalline viologen-POM-based compounds are ideal candidates for making memristors.

Automated summary

This study reports the combination of viologen and polyoxometalates (POMs), and successfully synthesizes three viologen-POM-based compounds. These compounds show thermochromism properties, fluorescence quenching effect, and evident discoloration effect in organic amine detection. Moreover, one of the compounds is used as a material for preparing memristors with superior properties.