Development of Flexible Response Systems with High Structural Order Using Platinum(II) Complexes that Exhibit Assembly Induced Luminescence

Abstract

Square-planar platinum(II) complexes have been extensively studied due to not only their strong emission but also their characteristic assembly-induced luminescence behavior based on the Pt···Pt electronic interaction. When the Pt(II) complex units are stacked with short Pt-Pt contacts, a highly efficient emission state, metal-metal-to-ligand charge transfer (MMLCT) state, is generated, and the luminescence of such assembled Pt(II) complexes can be tuned depending on the Pt···Pt interactions. In this work, we focused on neutral Pt(II) complexes bearing a series of N-heterocyclic carbenes and cyanide ions. All the complexes formed stacking structures with short but different Pt···Pt distances. As a result of fine tuning of Pt···Pt interactions, we have succeeded in the fabrication of highly luminescent ³MMLCT emission systems which cover red–blue region. Furthermore, the Pt(II) complex with a bulky tert-butyl substituent exhibited blue/yellow-green vapochromic luminescence based on the single crystal to single crystal (SCSC) transformation. The unique behavior of the stepwise SCSC transformations has been elucidated by in situ measurements of X-ray diffraction.