Acetonitrile-vapor-induced color and luminescence changes in a cyclometalated heteroleptic iridium complex

An iridium complex PIr(qnx) (iridium(III) bis(2-phenylpyridinato-N,C(2))(quinoxaline-2-carboxylate)) is reported for its unique and fast vapochromic and vapoluminescent behaviors. The emission of PIr(qnx) is governed by the whole crystal rather than the individual molecule. PIr(qnx) has been found to exist as both black and red forms in the solid state. The black form can be transformed into the red form upon its exposure to acetonitrile or propiononitrile vapor, whereas no response was observed when it was exposed to other volatile organic compounds. To understand the vapochromic and vapoluminescent behaviors, we determined crystal structures of both forms by X-ray diffraction. In addition, we employed density functional theory in investigating weak intermolecular interactions, such as hydrogen bonding and pi-pi interactions in the two forms.