Cation-Dependent Dimensionality in Hybrid Copper(I) Iodides: Leading to Tunable, Hydrochromic Emissions for WLEDs and Information Storage.

Hybrid copper(I) halides show notable structural diversity and tunable optoelectronic properties. However, achieving precise dimensionality control and hydrochromic behavior remains challenging. By varying the methyl substitution position of methylbenzylamine (MBA), two hybrid copper(I) iodides, (2-MBA)CuI2 (1) and [(4-MBA)CuI2]·0.5H2O (2), with different dimensionality and polarity were prepared. Compound 1 crystallizes in a centrosymmetric space group, featuring a one-dimensional (1D) structure and red emission. In contrast, compound 2 adopts an acentric space group with a two-dimensional (2D) network, exhibiting pronounced second-harmonic generation (SHG) and green emission. Theoretical calculations and variable-temperature photoluminescence (PL) analysis revealed that the emission of compound 1 originates from one self-trapped exciton (STE) state, whereas that of compound 2 involves two distinct STE states. Using compound 1 as a red-emitting phosphor, a white-light-emitting diode (WLED) with a color rendering index (CRI) of 87 was fabricated. Moreover, compound 2 exhibits reversible hydrochromic behavior, with emission switching between quenched and recovered states upon dehydration and rehydration, enabling information recording and erasing. This work provides a practical strategy for dimensionality control in hybrid copper(I) halides and introduces a new hydrochromic system, advancing stimulus-responsive materials.