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 (PLmax = 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.