Ultrasensitive photochromic and Raman dual response to ethylenediamine gas through polyoxometalate–viologen crystalline hybrid

Abstract

The sensitive and selective detection of ethylenediamine (EDA) has great significance due to its threat to environment and human health. Herein, a rationally designed polyoxometalate–viologen complex (1) has been demonstrated, in which the viologen molecules are hydrogen bonded to Dawson-type polyoxoanions. When complex 1 is in the atmosphere of EDA, the chromic intensity or Raman signals present proportional response to EDA concentrations. In particular, a very low detection limit of 0.1 ppb can be obtained for 1 based on its Raman signal output, which is the most sensitive complex than the reported EDA sensors. Also, high selectivity is observed for 1 when other amine molecules coexist as interfering compounds. According to the structural analysis and comparative experimental results, the highly sensitive and selective chromic or Raman response can be ascribed to the existence of viologen in the crystal lattice, which can not only accept electrons from EDA but also effectively accelerate the electron transfer to polyoxometalate. This work affords a novel concept for the design of highly sensitive and dual response polyoxometalate-based sensors by virtue of viologen-boosting electron transfer.