Substituted Phenanthrolines as Antennae in Luminescent Eu^III Complexes

Abstract

Eight novel europium(III)‐based coordination compounds with 1,10‐phenanthroline (phen) ligands with a chloro, methoxy, ethoxy, cyano, carboxylic acid, methyl carboxylate, ethyl carboxylate, and amino substituent on the 2‐position have been prepared in yields ranging from 43 to 89 %. Additionally, one lanthanum(III) coordination compound of 2‐amino‐1,10‐phenanthroline has been isolated. All compounds have the general formula [Ln(L)2(NO3)3], except for the compound with the carboxylate ligand, which has the formula [Eu(O2Cphen)3]. Three of the EuIII complexes as well as the LaIII compound crystal structures have been determined, all of which show similar N4O6 coordination spheres for the LnIII ion. Seven compounds exhibit bright luminescence that is characteristic of EuIII upon irradiation with near‐UV radiation, thus indicating efficient ligand‐to‐metal energy transfer. The complex with 2‐amino‐1,10‐phenanthroline is nonluminescent. The solid‐state photoluminescent quantum yields range from 10 to 79 %, and the luminescence lifetimes vary from 0.43 to 1.57 ms. Analysis of the spectral intensities with the Judd–Ofelt theory shows a significant contribution of nonradiative processes that quench the luminescence of the 5D0 level on EuIII.

A Quantitative Description of the σ‐Donor and π‐Acceptor Properties of Substituted Phenanthrolines

“…[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] In the present study, we applied ETS-NOCV to a series of [Mo(CO) 4 -(phen*)] complexes (phen* = substituted 1,10-phenanthroline) with the purpose of describing and quantifying the σ-donor and π-acceptor properties of phen* depending on their substitution. Among others, 1,10-phenanthrolines form a ubiquitous, significant class of ligands [32] that find application as fluorescent receptors, [33] antennae in luminescent metal complexes, [34] and in the synthesis of highly emitting phosphorescent compounds, [35] to name but a few. In particular, [M(CO) 4 (phen*)] compounds (M = Cr, Mo, W) have been the subject of extensive reports dealing with their electrochemical behavior, [36] photophysical properties, [37] photochemical reactivity, [38] and use as catalysts.…”

Ring Opening of Donor–Acceptor Cyclopropanes with the Azide Ion: A Tool for Construction of N‐Heterocycles

“…The emission spectra are independent of the excitation wavelength, which is consistent with the presence of a single Eu 3+ local site (Figure S5 in the Supporting Information). Although the 5 D 0 → 7 F 2 is a typical forced electric dipole (ED) transition that depends on the Eu 3+ local symmetry, the 5 D 0 → 7 F 1 transition is a parity‐allowed magnetic dipole (MD) transition, which is almost independent of the host material 14. The fact that the 5 D 0 → 7 F 2 transition is much stronger than the 5 D 0 → 7 F 1 transition shows that the Eu 3+ ions reside in a coordination environment lacking an inversion center, in accord with the single‐crystal structure.…”

“…The fact that the 5 D 0 → 7 F 2 transition is much stronger than the 5 D 0 → 7 F 1 transition shows that the Eu 3+ ions reside in a coordination environment lacking an inversion center, in accord with the single‐crystal structure. It is well known that the intensity ratio R , I ( 5 D 0 → 7 F 2 )/ I ( 5 D 0 → 7 F 1 ), of ED versus MD transitions is a measure of the Eu 3+ site symmetry 14. When R is high, the Eu 3+ ions occupy a site of low symmetry, without an inversion center.…”

Synthesis and spectroscopy of anionic tridentate benzimidazole-pyridine carboxylate and tetrazolate chromophore ligands

“…We developed these tridentate ligands to make neutral homoleptic tris-complexes of the lanthanides. The lanthanide ion in this type of complexes is expected to be nine-coordinate [7][8][9][10][11][12]23]. We also report on the synthesis of non-symmetric pyridines P2-P4 that are 2,6-or 2,4,6-substituted with hydroxymethyl, carboxaldehyde, and carbonitrile groups (Scheme 3).…”

“…Polydentate carboxylate [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and tetrazolate [21][22][23][24] ligands are strong chelators for lanthanide ions and efficient sensitizers of their luminescence. Here, we report on synthesis and spectroscopy of anionic tridentate carboxylate and tetrazolate benzimidazole-pyridine ligands HL1-HL7 that are functionalized with chromophore and solubilizing groups (Schemes 1 and 2).…”