A novel spectroscopic technique for studying metal-organic frameworks based on Mie scattering

Metal-organic frameworks (MOFs) are promising candidates for a wide range of applications, and spectroscopic techniques are important tools for analyzing their structures and properties. Here, we propose a novel and general scattering spectroscopic approach to study various MOFs such as zeolitic imidazolate frameworks (ZIF-67 and ZIF-8), HKUST-1, Co-based MOF (Co-MOF), and Ni-based MOF (Ni-MOF) based on their inherent Mie scattering properties. We show that by using a dark-field microscope, the inherent scattering colors and spectra can be obtained, which are mainly from the high-order magnetic and electric resonant modes. The scattering capacities are dependent on the chemical structures for producing polarized charges and internal circular displacement currents. Additionally, all the MOFs are capable of responding to solvent guests due to their high porosity, and the scattering peaks are in a linear correlation with solvent refractive indices, displaying scattering solvatochromic behaviors. Our results open up a powerful and universal avenue for visually studying the host-guest interactions in MOFs.