Vapor-Controlled Full-Color Luminescence in Platinum(II) Complexes Bearing N-Heterocyclic Carbene and a Flexible...

Platinum(II) complexes bearing aromatic ligands have garnered extensive attention as they exhibit highly efficient, stimulus-responsive luminescence originating from the triplet metal-metal-to-ligand charge transfer state when stacked, which enables electronic interactions between platinum ions. However, achieving full-color luminescence changes in a single system through external stimuli remains challenging. In this work, we synthesized a flexible platinum(II) complex bearing an N-heterocyclic carbene ligand with a medium-sized alkyl chain (pentyl group), [Pt(CN)₂(C5im-Mepy)](C5im-MepyH⁺ = 3-pentyl-1-(4-methyl-(2-pyridinyl))-1H-imidazolium, PtC5), thereby developing a material that displays full-color luminescence changes in response to various vapors. The pentyl group adopted diverse conformations within the crystal, enabling the construction of multiple stacking structures within a single complex-a feature unattainable with conventional platinum(II) complexes. Furthermore, reversible structural transformations of PtC5, resulting in distinct luminescence color changes, were induced in the solid state through controlled vapor exposure. Detailed structural and spectroscopic studies elucidated the mechanism underlying the full-color vapochromism-achieved for the first time in this system-, and the influence of the alkyl chain was clarified through a comparison with related complexes. This research provides valuable guidelines for developing advanced luminescent materials with precise and diversely tunable features.