Near‐Full‐Spectrum Emission Control in Copper(I) Iodides via Inorganic Structural Engineering Within a Single‐Cation Host

Abstract Hybrid copper(I) halides have emerged as a new class of optoelectronic materials due to their tunable structure and photophysical properties. However, systematically correlating inorganic polyhedra configurations with emission characteristics remains challenging. Herein, we address this by synthesizing a homologous series of copper(I) iodides templated solely by the [C 13 H 24 N] + cation. Precise control reaction conditions yielded distinct inorganic polyhedral configurations, monomeric [CuI 3 ] 2− ( 1 ), dimeric [Cu 2 I 4 ] 2− ( 2 ), trimeric [Cu 3 I 6 ] 3− ( 3 ), and tetrameric [Cu 4 I 6 ] 2− ( 4 ). We establish a direct correlation where increasing inorganic aggregation systematically reduces the bandgap and dictates the luminescence color across a near‐full visible spectrum, from blue ( 1 ) to cyan ( 2 ), red ( 3 ), and yellow ( 4 ). Detailed spectroscopic and theoretical analyses reveal the self‐trapped excitons emission mechanism dependent on the Cu‐I configuration, in which the closed [Cu 4 I 6 ] 2− configuration is more resistant to excited lattice deformation, thereby resulting in a lowest Stokes shift energy. Furthermore, stimuli‐responsive sequential phase transitions between these well‐defined structures were demonstrated, offering insights into their structural dynamics. This work provides critical fundamental understanding of how inorganic framework engineering within a fixed organic host precisely controls both electronic structure and excited‐state relaxation pathways in hybrid copper(I) halides, paving the way for rational design of materials with tailored optical properties.