High-performance fluorescence sensing of lanthanum ions (La(3+)) by a polydentate pyridyl-based quinoxaline derivative.

A polydentate pyridyl derivative, 2,3,6,7,10,11-hexa(2-pyridyl)-dipyrazino [2,3-f:2',3'-h]quinoxaline (HPDQ), exhibits a high-performance fluorescence response to La(3+) with an ∼65 nm redshifted emission wavelength and 38 fold enhanced intensity, in contrast to its weakened emission for other lanthanide ions. The final La(3+) coordination complex in solution has a stoichiometric ratio of 1 : 3 of ligand-to-metal, as testified by the Job's plot and single crystal structure analyses. The red shift of the luminescence emission as well as UV-vis absorption was rationalized in terms of the change of the electron structure as indicated by nuclear magnetic titration, electrochemical experiment and density functional theoretical calculation, while the significant enhancement of emission was attributed to the enhanced π conjugated extent of HPDQ caused by La(3+) coordination.