Highly Efficient Sensitized Red Emission from Europium (III) in Ir−Eu Bimetallic Complexes by ³MLCT Energy Transfer

Abstract

Two novel iridium-europium bimetallic complexes, {[(dfppy)2Ir(mu-phen5f)]3EuCl}Cl2 and (dfppy)2Ir(mu-phen5f)Eu(TFAcA)3 [dfppy represents 2-(4',6'-difluorophenyl)-pyridinato-N,C(2'), phen5f stands for 4,4,5,5,5-pentafluoro-1-(1',10'-phenanthrolin-2'-yl)-pentane-1,3-dionate and TFAcA represents trifluoroacetylacetonate], were successfully synthesized. The novel ligand Hphen5f with four coordination sites was designed as a bridge to link the Ir (III) center and the Eu (III) center. The X-ray diffraction data shows that the nonbonding distances for Eu...Ir are 6.028, 5.907, and 6.100 A in the bimetallic complex {[(dfppy)2Ir(mu-phen5f)]3EuCl}Cl2. Photophysical studies implied that the high efficient red luminescence from the Eu (III) ion was sensitized by the (3)MLCT (metal-to-ligand charge transfer) energy based on an Ir (III) complex-ligand in a d-f bimetallic assembly. The excitation window for the new bimetallic complex {[(dfppy)2Ir(mu-phen5f)]3EuCl}Cl2 extends up to 530 nm (1 x 10(-3) M in EtOH), indicating that this bimetallic complex can emit red light under the irradiation of sunlight.

Functional IrIII Complexes and Their Applications

“…[13] The ligand was designed to bridge the Ir III and Eu III centers. The X-ray diffraction data showed that the nonbonding distances for Eu-Ir were 6.028, 5.907, and 6.100 Å , respectively.…”

“…[35] Chen et al further developed Ir III -Ln III systems by producing complexes 7, [14] which are based on a previously reported Ir III -Eu III assembly. [13] When the cyclometalated ligand from the Ir III moiety was changed from 2,4-difluorophenylpyridine (dfppy) to 2-phenylpyridine (ppy), the triplet energy level of the Ir III complex was lowered, making it more suitable for the sensitization of NIR-emitting Ln III (Ln ¼ Nd, Yb, Er) ions. [36] Upon irradiation of the MLCT absorption of [Ir(ppy) 2 (phen5f)] at excitation wavelengths from 380-490 nm, the spectra of the three Ir 2 Ln arrays in both the solid state and in CH 3 CN showed characteristic emissions from Ln III (Fig.…”

“…This leads to a diverse range of emission colors from Ir III complexes. [4][5][6] Thus, Ir III complexes have been widely studied for many applications including organic light-emitting diodes (OLEDs), [7][8][9][10][11] light-emitting electrochemical cells (LECs), [12] luminescence sensitizers, [13,14] biological labeling, [15,16] and chemosensors. [16][17][18][19][20][21] In pursuit of a highly emissive Ir III complex, many heteroleptic complexes of the type [Ir(C^N) 2 MLCT transitions.…”

Acridone‐Benzimidazole Ring‐Fused Ligands: A New Class of Sensitizers of Lanthanide Luminescence via Low‐Energy Excitation

“…Up to now, d-block chromophores are the most intensely investigated sensitizing groups taking advantage of their intense metal-to-ligand charge transfer absorption bands generally spanning the visible range. [12][13][14][15][16][17] The main disadvantages of such sensitizing systems are (i) the high prices of most of the adequate d-metals (mainly Cr III , Ir III , Os II , Pt II , Pd II , Re I , and Ru II ) and (ii) the large spatial distance r separating the donor and acceptor moieties, i.e. the absorbing d-block and the emissive lanthanide ion, that often reduces the efficiency of the energy transfer.…”

Europium-Enoxacin Complex as Fluorescence Probe for the Determination of Folic Acid in Pharmaceutical and Biological Samples

“…This is because of intra-molecular energy transfer from the triplet state of excited organic ligand, ENX to the resonance energy level of the Eu 3+ at room temperature. 31,32 The rate of energy transfer depends upon the extent of overlap of the emission spectra of the donor with the excitation spectra of the accepter as well as the distance between them. Energy transfer easily occurs between Eu 3+ and ENX because of the strong spectral overlap between the emission spectra of donor (ENX) and the excitation spectra of accepter (Eu…”