Blending Ionic and Coordinate Bonds in Hybrid Semiconductor Materials: A General Approach toward Robust and Solution-Processable Covalent/Coordinate Network Structures

Inorganic semiconductor materials are best known for their superior physical properties, as well as their structural rigidity and stability. However, the poor solubility and solution-processability of these covalently bonded network structures has long been a serious drawback that limits their use in many important applications. Here, we present a unique and general approach to synthesize robust, solution-processable, and highly luminescent hybrid materials built on periodic and infinite inorganic modules. Structure analysis confirms that all compounds are composed of one-dimensional anionic chains of copper iodide (Cu_mI_m+2^2–) coordinated to cationic organic ligands via Cu–N bonds. The choice of ligands plays an important role in the coordination mode (μ¹-MC or μ²-DC) and Cu–N bond strength. Greatly suppressed nonradiative decay is achieved for the μ²-DC structures. Record high quantum yields of 85% (λ_ex = 360 nm) and 76% (λ_ex = 450 nm) are obtained for an orange-emitting 1D-Cu₄I₆(L₆). Temperature dependent PL measurements suggest that both phosphorescence and thermally activated delayed fluorescence contribute to the emission of these 1D-AIO compounds, and that the extent of nonradiative decay of the μ²-DC structures is much less than that of the μ¹-DC structures. More significantly, all compounds are remarkably soluble in polar aprotic solvents, distinctly different from previously reported CuI based hybrid materials made of charge-neutral Cu_mX_m (X = Cl, Br, I), which are totally insoluble in all common solvents. The greatly enhanced solubility is a result of incorporation of ionic bonds into extended covalent/coordinate network structures, making it possible to fabricate large scale thin films by solution processes.