Oligo(p-phenyleneethynylene)-derived porous luminescent nanoscale coordination polymer of Gd^III: bimodal imaging and nitroaromatic sensing

Abstract

Self-assembled highly luminescent nanoscale coordination polymer of {[Gd(OPE)(NO₃)(H₂O)₂]·H₂O} (NCP-1), (oligo-(p-phenyleneethynylene)dicarboxylate) was synthesized by coordination-driven self-assembly of oligo-(p-phenyleneethynylene)dicarboxylic acid and GdIII in polar solvent under refluxing conditions. This nanostructure has been characterized by FESEM, TEM, powder X-ray diffraction, and adsorption study. Interdigitation between 1D coordination polymers through alkyl chains results in a porous supramolecular 3D extended structure. NCP-1 shows permanent microporosity as revealed by type-I CO₂ uptake profile. FESEM and TEM studies of NCP-1 reveal nanorod-like morphology with square-type cross section having dimensions of 50–100 nm diameter and 0.5–0.8 µm length. High-magnification TEM images show long-range structural ordering present in NCP-1 with uniform dark lines having an interspacing distance of 0.9–1.1 nm. Physiological stability and strong luminescence features of NCP-1 have been exploited for bioimaging based on internalization into mammalian cultured cell lines HEK 293T and H1299. Magnetic resonance imaging studies suggest that NCP-1 could act as a potential negative (T2) contrast agent. Furthermore, this porous luminescent NCP-1 shows efficient nitroaromatic sensing as realized by the fluorescence quenching in solution as well as in vapor phase of the analyte like 2,4-dinitrotoluene (2,4-DNT). These results demonstrate that hybridization of a paramagnetic metal center and luminescent linker in a nanoscale porous coordination polymer culminates in a functional hybrid material with potential bimodal imaging and sensing applications.