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

Probing of the local environment and calculation of J.O. parameters for Eu3+ CMPO functionalized pillararene complexes by time resolved fluorescence spectroscopy

“…As a result of these factors, the bonding between Eu 3 þ and the oxygen from CMPO pillararenes becomes more effective for the ligand having large spacer length between ligating CMPO moieties and the supramolecular pillararene. Similar observation was also reported for DGA functionalized pillararene [47] while for DGA functionalized calixarenes [49,53] practically no change in the Ω 2 value was reported as a function of spacer length. It was also observed that the overall Ω 2 values for CMPO-pillararene complexes were more than that of DGA-pillararenes.…”

“…Ω 4 which is a measure of long range ordering was found to follow the same trend as Ω 2 for the Eu complexes of CMPO-pillararenes and it was found to be comparable with the Ω 4 values for similar types of supramolecular complexes reported in the literature [47][48][49]53].…”

“…Because of the very weak intensity of 5 D 0 -7 F 6 transition, it cannot be deconvoluted optimizing the error. The above splitting pattern suggested C 6 or C 6v point group symmetry around Eu 3 þ in CMPO-pillararene complex whereas the same for DGA-pillararene complexes were reported to be C 4v [47]. Due to the favorable complexation of four diglycolamide moieties most of their inner sphere Eu complexes were found to exhibit C 4v symmetry [53] while in case of tripodal diglycolamide and upper rime DGA functionalized calixarene the point group symmetries were reported to be C 2v and C 1 /C 2 /C s , respectively [ Table 1] [49].…”

“…Similarly S based ligands, which were softer than the Oxygen based ligands were reported to have appreciably higher Ω 2 values [62][63][64]. The Ω 2 values for DGA functionalized pillararenes and calixarenes were found to be comparable [47,49,53], while that for pyrazine functionalized calixarenes were found to be much lesser [48] suggesting the weaker covalency of metal-oxygen bond for the pyrazine functionalized calixarenes.…”

“…The Eu 3 þ complexes of CMPO functionalized pillararenes were found to be more symmetric compared to the diglycolamide functionalized pillararenes. Among the various supramolecular ligands, the asymmetric factors for the Eu 3 þ complexes followed the trend of ligands as tripodal diglycolamide [44] oDGA functionalized ionic liquid with NTf 2 − anion [45] o CMPO pillararene LI oCMPO pillararene LII oDGA Calixarene LI [46] oDGA functionalized ionic liquid with PF 6 − anion [45] oTODGA [45] oCMPO pillararene LIII oDGA Calixarene LII [46] oDGA pillararene LI [47] oPyrazine functionalized calixarene L4 [48] oboth side DGA calixarene [49] oDGA pillararene LII [46] o Pyrazine functionalized calixarene L6 [48] oDGA pillararene LIII [47] olower rim DGA calixarene [49]. …”