Metal–organic frameworks (MOFs) exhibit a broad range of luminescence characteristics due to the vast array of metal ions and organic linkers available as building blocks. Systematic control over the emissive output of MOFs is highly sought after. Methods for tuning emission profiles are emerging based largely on luminescent metal ions and the encapsulation of emissive guests. Herein, we show how the functionalization of the organic linkers of a series of multicomponent MUF-77 (MUF = Massey University Framework) materials can methodically tune their spectral output. This was quantified by chromaticity diagrams. White-light emission was obtained by combining the photophysical characteristics of the three distinct organic fluorophores present in these materials. Our results also show that both (i) energy transfer interactions between the organic components and (ii) noncovalent interactions with guests can also be harnessed to tune the emission. These results establish multicomponent metal–organic frameworks as fluorescent materials with unique spectral characteristics.

Metal−organic frameworks (MOFs) can respond to light in a number of interesting ways. Photochromism is observed when a structural change to the framework is induced by the absorption of light, which results in a color change. In this work, we show that introducing quinoxaline ligands to MUF-7 and MUF-77 (MUF = Massey University Framework) produces photochromic MOFs that change color from yellow to red upon the absorption of 405 nm light. This photochromism is observed only when the quinoxaline units are incorporated into the framework and not for the standalone ligands in the solid state. Electron paramagnetic resonance (EPR) spectroscopy shows that organic radicals form upon irradiation of the MOFs. The EPR signal intensities and longevity depend on the precise structural details of the ligand and framework. The photogenerated radicals are stable for long periods in the dark but can be switched back to the diamagnetic state by exposure to visible light. Single-crystal X-ray diffraction analysis reveals bond length changes upon irradiation that are consistent with electron transfer. The multicomponent nature of these frameworks allows the photochromism to emerge by allowing through-space electron transfer, precisely positioning the framework building blocks, and tolerating functional group modifications to the ligands.

The guest adsorption phenomena in multicomponent metal−organic frameworks (MOFs) are intricate due to their structural complexities. In this work, we studied two members of the isostructural series of MUF-77 frameworks that consist of long or short alkyl groups. The adsorption of methanol, N,N-dimethylaniline (DMA) and acridine orange (AO) in two structures of MUF-77 has been investigated. 2 H solidstate nuclear magnetic resonance (SSNMR) and two-dimensional 1 H− 13 C NMR spectroscopy were used to probe the dynamics of various compartments of MUF-77. Through the analyses of dynamic behavior by SSNMR and molecular dynamics simulations, we elucidate the spatial distribution of guest molecules are nonuniform around different chemical components, in different pore structures, and across different parts of MOF lattice. In addition, we reveal that the framework flexibility of MUF-77 with short alkyl groups is reduced upon guest adsorption yet the framework flexibility of MUF-77 with long alkyl groups increases upon loading with methanol.