Fluorescent Cadmium Bipillared‐Layer Open Frameworks: Synthesis, Structures, Sensing of Nitro Compounds, and Capture of Volatile Iodine

Abstract Fluorescent Cd metal–organic frameworks (MOFs), [Cd 2 (dicarboxylate) 2 (NI‐bpy‐44) 2 ] (dicarboxylate=benzene‐1,4‐dicarboxylate (1,4‐bdc, 1 ), 2‐bromobenzene‐1,4‐dicarboxylate (Br‐1,4‐bdc, 2 ), 2‐nitrobenzene‐1,4‐dicarboxylate (NO 2 ‐1,4‐bdc, 3 ), biphenyl‐4,4′‐dicarboxylate (bpdc, 4 ); NI‐bpy‐44= N ‐(pyridin‐4‐yl)‐4‐(pyridin‐4‐yl)‐1,8‐naphthalimide)), featuring non‐ and twofold interpenetrating pcu ‐type bipillared‐layer open structures with sufficient free voids of 58.4, 51.4, 51.5, and 41.4 %, respectively, have been hydro(solvo)thermally synthesized. MOFs 1 – 4 emitted solid‐state blue or cyan fluorescence emissions at 447±7 nm, which mainly arose from NI‐bpy‐44 and are dependent on the incorporated solvents. After immersing the crystalline samples in different solvents, that is, H 2 O and DMSO ( 1 and 2 ) as well as nitrobenzene and phenol ( 1 – 4 ), they exhibited a remarkable fluorescence quenching effect, whereas o ‐xylene and p ‐xylene ( 4 ) caused significant fluorescence enhancement. The sensing ability of MOFs 1 – 4 toward nitro compounds carried out in the vapor phase showed that nitrobenzene and 2‐nitrophenol displayed detectable fluorescence quenching with 1 , 2 , and 4 whereas 4‐nitrotoluene was an effective fluorescence quencher for 1 and 2 ; this is most likely attributed to their electron‐deficient properties and higher vapor pressures. Moreover, MOFs 1 – 4 are highly reusable for quick capture of volatile iodine, as supported by clear crystal color change and also by immense fluorescence quenching responses owing to the donor–acceptor interaction. Low‐pressure CO 2 adsorption isotherms indicate that activated materials 1′ – 4′ are inefficient at taking up CO 2 .