Dual-Emissive γ-[Cu 4 I 8 ] 4- Enables Luminescent Thermochromism in an Organic-Inorganic Hybrid Copper(I) Halide.

A highly luminescent (C13 H28 N2 )2 Cu4 I8 single crystal containing isolated γ-[Cu4 I8 ]4- anionic cluster was synthesized without the use of unsaturated cations. To the best of our knowledge, compounds bearing such like anions are not dual-emitting under UV excitation. However, dual emission does occur in (C13 H28 N2 )2 Cu4 I8 . Moreover, the emission bands were found to be temperature-sensitive, allowing tuning of the emission colors from blue (0.19, 0.20) to green (0.33, 0.47) in the Commission International de L' Eclairage (CIE) chromaticity coordinates. Remarkably, the color could be restored on returning to the initial temperature, confirming an efficient and reversible luminescent thermochromic effect in (C13 H28 N2 )2 Cu4 I8 . The origin of this excellent optical performance is discussed, and the difference in the mechanism with the dual-emissive Cu(I) halide complexes is also elucidated. Overall, our work provides a promising way to achieve efficient luminescent thermochromism. The developed (C13 H28 N2 )2 Cu4 I8 represents one of the viable alternatives for eco-friendly luminescent thermochromic materials.