The potential of pyridine-2,6-dicarboxylic acid based organolanthanide complexes for efficient near-infrared emission

Abstract

We present detailed spectroscopic data obtained from Nd pyridine-2,6-dicarboxylic acid based complexes in which the 4-position of the pyridine ring has been substituted with OH and Cl. In each case the ligands formed stable complexes with the Nd ion without the requirement for any additional 'neutral' ligand to satisfy the 8-9 coordination requirement of the lanthanide ion. Photoluminescence is observed from both the ligand (centered ∼700 nm) and the Nd ion (at ∼900 nm, 1064 nm, and 1320 nm due to the F → I, F → I, and F → I transitions respectively) following excitation in the low energy tail of the ligand π → π* absorption. The intensity of the ligand emission and sensitized Nd emission was found to be dependent on the substituted 4-position of the pyridine ring. The origin of the observed phenomena are discussed in relation to the energy transfer process from ligand to Nd ion and the non-radiative relaxation of the sensitized Nd ion. These results suggest that further modification of the ligand through complete halogenation and/or addition of other functional groups may provide an attractive route to obtaining an efficient near-infrared emitting organolanthanide complex