Structural transformation in isomeric 0D copper(i) iodide hybrids and their utilization as water-stable luminophores for furaltadone detection†

The family of copper-based metal halides has drawn increasing attention owing to their structural flexibility and optical tunability. However, the controllable synthesis of isomers to further regulate luminescence reasonably and thoroughly understand the structure–luminescence–performance relationship remains a challenge. In this work, a pair of isomers of the hybrid copper iodide 4-BrBTP(Cu₂I₄)_0.5 (1-α and 1-β, 4-BrBTP = (4-bromobenzyl)triphenylphosphonium bromide) were synthesized using the same precursors but varying the solvents and molar ratios. The Br⋯π and Br⋯I interactions of the bromobenzyl group may be considered as the driving forces for the growth of these two isomers. 1-α exhibits orange emission centered at 601 nm, while 1-β shows yellow emission centered at 552 nm at room temperature. Particularly, 1-α could be transformed into 1-β by soaking in methanol, accompanied by photoluminescence switching from orange to yellow. The experiments reveal that the orange light of 1-α stems from self-trapped exciton (STE) emission, whereas the yellow emission of 1-β is attributed to metal-to-ligand charge transfer or halide-to-ligand charge transfer (MLCT/HLCT) and cluster-centered (CC) excited states. Taking advantage of their water stability, the performance of the two isomers was evaluated in detecting the antibiotic furaltadone hydrochloride (FTD) in water. The results showed that 1-α has a detection limit that is an order of magnitude lower than that of 1-β. Furthermore, the spectral overlap between the FTD and two isomers combined with the theoretical calculations of energy levels was conducted to clarify the potential sensing mechanisms. This work achieved luminescence regulation between copper iodide isomers, laying the foundation for the development of 0D organic–inorganic hybrid metal halide (OIMH) luminescent sensors and promoting their potential application in detecting antibiotics in real samples.