Luminescence Vapochromism of a Cu(I)/Na Phosphane Iodide Assembly Based on a Secondary‐Sphere Sodium Response

ABSTRACT Photoluminescent compounds showing distinct and selective optical response to external perturbation are essential components for sensing applications. Herein, we present a copper(I) iodide–sodium luminescent complex assembled with a hybrid phosphane‐phosphinate ligand. The photoemission of the tetrametallic {Cu 2 I 2 Na 2 } aggregate is consistent with the thermally activated delayed fluorescence that originates from the [CuI(phosphane)] motifs but strongly depends on the coordination environment of sodium ions completed by O‐donor solvent molecules, Na–π(phenyl) interactions, and/or Na–I bonds. The reversible removal and vapor‐phase addition of methanol, ethanol, water, and dimethoxyethane as Na‐bound ligands alter the solid‐state luminescence from blue (461 nm) to yellow (570 nm) with quantum yields reaching 0.73. Importantly, different photoemission responses to methanol (522 nm) and ethanol (492 nm) are complemented by preferred binding of methanol and its detection in up to 1:10 methanol:ethanol mixtures. Variations of luminescence among the studied solvates are attributed to the alterations of secondary sphere interactions involving sodium ions and illustrate a new approach to stimuli‐responsive metal complexes constructed from soft‐hard donor ligands.