Highly Stable Tetrahydrothiophene 1-Oxide Caged Copper Bromide and Chloride Clusters with Deep-Red to Near-IR Emission.

All-inorganic copper(I)-based metal halides have emerged as promising candidates for the replacement of lead perovskites because of their outstanding optical properties. However, the limited structure tunability prohibits their further exploration of properties including red photoluminescence (PL). Here, we report a series of red-emissive lead-free hybrid organic-inorganic copper halides A6(C4H8OS)12[Cu8X13][Cu4X4(OH)(H2O)] (ACX-THTO, A = K, Rb, and Cs; X = Cl, Br; THTO = C4H8OS) with the highest photoluminescence quantum yield (PLQY) of 42%. These compounds possess similar crystal structures, and their emission can be tuned in the spectral range of 676-732 nm by controlling their compositions. Additionally, by removing and adding THTO, the reversible transformation between CsCu2Br3 featuring one-dimensional (1D) chains and Cs6(C4H8OS)12[Cu8Br13][Cu4Br4(OH)(H2O)] (CCB-THTO) with zero-dimensional (0D) clusters can be realized. We also demonstrate that the incorporation of THTO in the crystal structures instead of dimethyl sulfoxide (DMSO) can significantly enhance the stability and PL of compounds with the same inorganic components.