Luminescence investigation on Eu-pillar[5]arene-based diglycolamide (DGA) complexes: Nature of the complex, Judd-Ofelt calculations and effect of ligand structure

An attempt was made to understand the insight of complexation of Eu3+ ion with three different structurally modified pillar[5]arene-based diglycolamides (P5DGA) and a comparison was also made with their molecular identity, TODGA. 7F0-5D2, 5G2,3,4, 5L6 transitions were observed in the absorption profiles while 5D0-7F0,1,2,3,4 transitions for emission spectra. Number of water molecules present in the primary coordination sphere of Eu3+ and the number of species were calculated from the life time measurement of the complexes under investigation. From the splitting pattern of the luminescence spectra of Eu3+ complex the point group symmetry around Eu3+ was found to be C4v. Judd-Offelt parameters (Ωλ, λ=2,4) were calculated for the complexes and correlated with the covalency of metal ligand bonds and long range ordering, respectively. It was demonstrated that preorganization of ligating moieties on the platform of pillararenes favoured the covalency of the metal-ligand bond in diglycolamides. Different photo physical properties such as radiative and non radiative life time, magnetic and electric dipole transition probabilities, branching ratio values for different transitions, quantum efficiency were evaluated for all the Eu3+-diglycolamide complexes.