Solvent engineering for achieving six copper-based halides from a single organic cation: full-colour luminescence and multimode-stimulus response

Abstract

Organic–inorganic metal halides (OIMHs) with tunable structures and optical properties hold promising application prospects in the intelligent luminescence material field. However, luminescence regulation of most OIMH materials is predominantly realized through changing organic or metal cations. It is exceptionally challenging for a single organic and metal cation to obtain multiple (especially more than three) OIMH crystals with different structures and luminescence properties, though it can meet the growing demand for advanced anti-counterfeiting and information encryption applications. Herein, by employing the conformationally flexible trans-1,4-diaminocyclohexane as the organic ligand, six hybrid copper halides are successfully synthesized through solvent engineering which feature distinct inorganic structures including zero-dimensional [Cu₂I₆]⁴⁻ (B), [Cu₂I₄(CH₃CN)₂]²⁻ (C), [Cu₃I₇]⁴⁻ (G), one-dimensional [Cu₃I₆]³⁻ (Y), [Cu₂I₄]²⁻ (N) and two-dimensional Cu₄I₄ (R). These compounds exhibit diverse structural characteristics, including zero-dimensional dimers, one-dimensional chains, and two-dimensional layered architectures. These OIMH crystals display distinct luminescence colours, with their emission spectra covering the entire visible region. Notably, the six hybrid halides not only demonstrate sensitive and reversible responses to various external stimuli (such as heat, solvent and force), but also undergo interconversion under specific conditions, thereby achieving controllable full-colour multimode-stimulus response through intrinsic photophysical properties rather than material multiplicity. These exceptional properties of the Cu-based OIMHs enable their successful application in multi-level anti-counterfeiting and programmable anti-leakage information encryption.