Metal-Organic Framework with Color-Switching and Strongly Polarized Emission

Hybrid fluorescent metal-organic frameworks (MOFs) use long-range intermolecular structural motifs in which the properties of the scaffold molecular system can be designed for specific applications. In this work, we constructed a MOF-chromophore system with a strongly polarized fluorescence and a large emission wavelength shift. To achieve this, we first devised a fluorophore with a linear conjugated backbone, bulky and noninteracting side chains, and easily accessible nitrogen atoms on its pyridine end groups. The linear nature of the conjugated backbone can lead to a strongly polarized luminescence, the side groups assist structural stability and minimize intermolecular interactions, and the sterically accessible pyridines provide a large fluorescence color-changing ability. These features were demonstrated by synthesizing a planar Zn-based MOF in which the linear backbone of the chromophore molecules was highly aligned. The MOFs demonstrated a strong polarization effect and a color-shifting ability from green-yellow to orange. The results show that hybrid metal-organic materials can be designed to generate a strong command of the material luminescence, in terms of both emission color and polarization.