Ligand Influence Versus Electronic Configuration of d-metal Ion in Determining the Fate of NIR Emission from LnIII Ions: A Case Study with CuII, NiII and ZnII Complexes.

Lanthanides (LnIII) are well known for their characteristic emission in the near-infrared region (NIR). However, direct excitation of lanthanides is not feasible as described by Laporte's parity selection rule. Here, we obtain NIR emission from [L–M–Ln] complexes (where, L = an organic ligand, M = a d-block metal ion, and Ln = a lanthanide ion) in which the [L–M] moiety acts as an antenna to absorb the excitation light to transfer to Ln energy levels. Based on fifteen lanthanide complexes that are presented here in which Cu, Ni and Zn complexes with a Schiff base ligand act as an antenna, we have demonstrated for the first time that electronic configuration of the d-block metal ion is very crucial for obtaining NIR emission. With Ln ion and the same ligand, Cu and Ni complexes show completely different emission than that of the corresponding NIR emitting [L–Zn–Ln] complexes.