Coordination-driven nanosized lanthanide 'Molecular Lanterns' as luminescent chemosensors for the selective sensing of magnesium ions

Novel cerium-based 'Molecular Lanterns' Ce-DBDS, Ce-DBBS and Ce-DBOS were achieved via self-assembly from bis-tridentate ligands H4DBDS, H4DBBS and H4DBOS, respectively. Structure analysis of Ce-DBDS shows that six oxygen atoms of the ether bond groups on the ligands form a lantern-like cavity inside the compound. Thus the 'Molecular Lanterns' exhibit crown ether recognition behavior and could be applied in luminescent magnesium chemosensors. The restricted geometry constraints of the internal cavities provide high selectivities of the lantern-like probes towards the Mg2+ ion over other differentsized metal ions such as Al3+, Li+, Ca2+, Na+, Ba2+ and K+. Ce-DBBS which contains three fully substituted benzyl groups exhibited better sensitivity by the cation-p interaction between Mg2+ and the benzyl group, compared to the Ce-DBDS. However, Ce-DBOS can work as an artificial chemosensor for selective fluorescent detection of Al3+ rather than Mg2+, due to its cavity being much smaller than Ce-DBDS and Ce-DBBS.