Carbazole-Equipped Metal–Organic Framework for Stability, Photocatalysis, and Fluorescence Detection

Abstract

The useful yet underutilized backfolded design is invoked here for functionalizing porous solids with the versatile carbazole function. Specifically, we attach carbazole groups as backfolded side arms onto the backbone of a linear dicarboxyl linker molecule. The bulky carbazole side arms point away from the carboxyl links and do not disrupt the Zr-carboxyl framework formation; namely, the resultant MOF solid Zr<b>L1</b> features the same net as that of the unfunctionalized dicarboxyl linker, also known as the PCN-111 net or UiO-66 net. The Zr<b>L1</b> structure features only half linker occupancy (about 6 out of the 12 linkers around the Zr₆O₈ cluster being missing) and partially collapses upon activation (acetone exchange and evacuation). Notably, the stability improves after heating in diphenyl oxide at 260 °C (POP-260 treatment; to form Zr<b>L1</b>-260), as indicated by the higher crystallinity and surface area of the activated Zr<b>L1</b>-260 sample. The Zr<b>L1</b>-260 samples achieve 72% yield in photocatalyzing reductive dehalogenation of phenacyl bromide; Zr<b>L1</b> can detect nitro-aromatic compounds via fluorescence quenching, with selectivity and sensitivity toward 4-nitroaniline, featuring a limit of detection of 96 ppb.