Differentiable Detection of Volatile Amines with a Viologen-Derived Metal–Organic Material

The
development of selective sensing materials for amine detection
has received considerable attentions because amines have high toxicity
and exist widely. In this article, we demonstrate for the first time
that a degree of discriminative detection of alkylamines can be achieved
by a metal–organic coordination material. The material is derived
from CdII and 4,4′-bipyridinium-1,1′-bis­(phenylene-3-carboxylate),
shows 1D channels lined with electron-deficient viologen chromophores,
and exhibits different colors upon contact with amine vapors of different
molecular sizes and types (primary, secondary, and tertiary). The
vapochromism is attributable to electron transfer from the amine group
to viologen. The discrimination between amines is because the analyte–receptor
interactions, which either directly mediate or indirectly affect electron
transfer, are influenced by the number of the N–H bonds in
the amine molecule, the size of the amine molecule relative to the
receptor channel and the steric hindrance for the electron donor–acceptor
contacts. The material also shows reversible photo- and hydrochromism
owing to stimuli-induced reversible electron transfer. The compound
can be deposited in paper simply by spraying the mixture solution
of the starting metal salt and the ligand. The paper can be used as
portable test strips for visual and differentiable detection of amines
and as erasable inkless printing medium.