Constructing low-dimensional phosphorescent MOFs by site-selective coordination engineering

Low-dimensional (LD) metal-organic framework materials (MOFs) have garnered increased attention due to their inheritance of MOF advantages, such as regular pores and tailorable structures, as well as the unique physicochemical properties of LD materials, including good mechanical properties, flexibility, and enhanced electrical conductivity. In this work, we developed a site-selective coordination engineering (SSCE) strategy to construct novel LD MOFs, including a two-dimensional Zn-binc MOF and a one-dimensional Cd-binc MOF. The former is prepared by coordinating Zn ions with all three heterogeneous coordination sites on 2-(1H-benzimidazol-1-yl)nicotinic acid (Hbinc), whereas the latter is formed by selective coordination between Cd ions and two of these sites. These MOF modules further self-assemble into 3D Zn-binc and 2D Cd-binc supramolecular structures through weak intermolecular hydrogen bonds. The constructed LD MOFs display remarkable roomtemperature phosphorescence (RTP) properties, with long phosphorescence lifetimes of 123 ms for Zn-binc and 188 ms for Cd-binc. These outstanding RTP performances are primarily attributed to the large torsion angles and dense stacking of the Hbinc linkers within the Zn-binc and Cd-binc crystals, which significantly promotes the intersystem crossing process from the singlet to the triplet state and effectively inhibits non-radiative transitions of triplet excitons. This study not only enriches the library of LD MOFs, but also provides an efficient SSCE strategy for constructing new LD MOFs.