Three Robust Blue-Emitting Anionic Metal-Organic Frameworks with High Stability and Good Proton Conductivities

Three anionic luminescent metal-organic frameworks (LMOFs; [M(tcbpe)(CH₃)₂NH₂]·H₂O; M = In³⁺, Eu³⁺, Gd³⁺; tcbpe = 4',4‴,4‴″,4‴‴'-(ethene-1,1,2,2-tetrayl)tetrakis[(1,1'-biphenyl)-4-carboxylic acid]) are synthesized by employing the tetraphenylethene core ligand H₄tcbpe with M³⁺ ions. They stack in the similarly 4-fold-interpenetrated three-dimensional porous structure. All give blue emission when excited at 365 nm, with fluorescence quantum yields of 34.8% (MOF-In), 7.1% (MOF-Eu), and 28.1% (MOF-Gd). Somewhat surprisingly, these three complexes are extremely stable both in various solvents and across a broad pH range: MOF-In is stable between pH = 0 and 14, and MOF-Eu and MOF-Gd are stable between pH = 0 and 13. Additionally, they also show good proton conductivities of 2.29 × 10^-5 S·cm^-1 (MOF-In), 2.02 × 10^-4 S·cm^-1 (MOF-Eu), and 1.24 × 10^-4 S·cm^-1 (MOF-Gd) at high temperature under 98% relative humidity. To the best of our knowledge, this is the first reported LMOF series combining aggregation-induced emission behavior with good proton conductivities.