Tris(4-imidazole~2,6-dichlorophenyl) methyl radical(TTM-3Im): synthesis and properties

Organic radicals are present in many im-portant chemical and biological processes, and have been increasingly attracting a great deal of attention and interest due to their unique chemical and physical properties. The unique open-shell structures and redox abllity of organic radicals render them as special candidates for application in the field of materials science such as spintronics, magnetic materials, and organic radical battery. Recently, organic radicals have been emerging as unusual luminescent materials and have achieved great success in the application of highly efficient radical-based organi c l i ght-em itt i ng di odes (OLEDs). Organ i c radi cals bear i ng sui table coordi nat i on s ite could also serve as special organic functional ligands, which have been widely employed to constructed radical-metal complexes ranging from one-dimensional coordination chains to two-and three-dimensional metal-radical networks, showing intriguing optical, electrical and magnetic properties. Very recently, some reports have also demonstrated that the coordination of the luminescent radicals with metal ions could affect their emissive properties such as the fluorescence quantum yield and photosta- bllity. Therefore, the design and synthesis of novel luminescent radical ligand and luminescent radicalbased coordination complex are of great interest, and their special chemical and photophysical proper- tesareexpected. However, the luminescent radical coordination complexes and their properties remans unexplored mainly because of the inherent instability of organic radicals that always challenges the skllls of synthet i c chem i sts. In th i s work, a novel lumi nescent rad i cal, namely tr i s(‘- i m i dazole-2,6-di chlorophenyl) methyl (TTM-3Im) radical, consisting of three imidazole has been successfully designed and synthesized. TTM-3Im radical has good stabllity and can be purified by column chromatography, which is fully characterized by means of electrospray onizaton mass spectrometry (ESI-MS), electron paramagnetic resonance (EPR) spectroscopy and X-ray crystallographic analysis. EPR studies show that TTM-3Im is a carbon-centered radical, and it is found that¹³C nuclei are finely coupled. Notably, there is no obvous hyperfine coupiing between carbon radicals and protons, which proves that the radicals are mainly locaiized on the central carbon and expkins the good stabiiity of the radi-cals. TTM-31m also exhibits interesting luminescence properties, the maximum emission wavelength.of TTM-3Im is at 600 nm, showing orange fluorescence at room temperature, and the fluorescence quantum yield is 10. 3%. TTM-3Im bearing three imidazole motifs can serve as a tridentate ligand to construct radical metal organic frameworks (MOFs). As a result, the metal-organic frameworks ma-terial TTM-3Im-CdCl, (MOF-1) has been successfully synthesized by solvent permeation method viathe coordination between TTM-31m and CdCl.. X-ray crystallography analysis revealed the porous MOF-1 featured two-dimensional highly-ordered structure, wherein per Cd ions coordinated with three imidazole and three Cl, respectively. Cd-N bonds and Cd-Cl bands are intertwined to form a continuous hole like structure. More interestingly, a series of eutectic MOFs based on radical precur sor aHTTM-3Im and radical TTM-31m have been synthesized in the same way, and the fluorescence intensity of eutectic MOFs depends on the doping ratio of TTM-3Im radical. Specifically, the resultant eutectic MOFs consisting of a very low concentration (<4%) of TTM-31m radical exhibits the stron gest emission. while the fluorescence experiences severe quenching with the increasing of the radical doping ratio, which is mainly attributed to the aggregation caused quenching. This study represents one of very few examples of the luminescent radical-based MOFs exhibiting solid emissive properties, which will thus not only expand and enrich the content of MOFs but also promote the development of luminescent radicals materials.