Structural and luminescence properties of acetamidinium- and imidazolium-based copper halides

Organic-inorganic hybrid copper halides have emerged as promising candidates for optoelectronic applications due to their structural tunability and luminescence properties. In this work, four copper halides, namely AcaCuI₂, AcaCuBr₂, ImCuI₂, and ImCuBr₂ (Aca = acetamidinium, Im = imidazolium), were synthesized for the first time and characterized structurally, thermally, and optically. Single-crystal X-ray diffraction revealed that AcaCuBr₂, AcaCuI₂, and ImCuBr₂ crystallize with one-dimensional chains consisting of edge-sharing [CuX₄] tetrahedra, whereas ImCuI₂ forms zigzag chains composed of corner-sharing [Cu₃I₇]^4- clusters. Thermogravimetric analysis indicated high thermal stability, particularly for the bromide derivatives, with decomposition temperatures exceeding 200 °C. Optical studies demonstrated that all compounds exhibit broadband emission profiles modulated by structural connectivity: edge-sharing chains exhibit low-temperature self-trapped exciton (STE) emission (460-580 nm), whereas ImCuI₂ enables room-temperature photoluminescence (PL_max = 533 nm) due to its flexible corner-sharing structure. This work provides valuable insights into cation-driven structural engineering for advanced luminescent materials, guiding the future design of efficient and thermally robust halocuprate-based luminescent materials.