New Insights into Structure and Luminescence of Eu^III and Sm^III Complexes of the 3,4,3-LI(1,2-HOPO) Ligand

Abstract

We report the preparation and new insight into photophysical properties of luminescent hydroxypyridonate complexes [MIIIL]− (M = Eu or Sm) of the versatile 3,4,3-LI(1,2-HOPO) ligand (L). We report the crystal structure of this ligand with EuIII as well as insights into the coordination behavior and geometry in solution by using magnetic circular dichroism. In addition TD-DFT calculations were used to examine the excited states of the two different chromophores present in the 3,4,3-LI(1,2-HOPO) ligand. We find that the EuIII and SmIII complexes of this ligand undergo a transformation after in situ preparation to yield complexes with higher quantum yield (QY) over time. It is proposed that the lower QY in the in situ complexes is not only due to water quenching but could also be due to a lower degree of f-orbital overlap (in a kinetic isomer) as indicated by magnetic circular dichroism measurements.

Luminescent Eu(III) coordination polymer cross-linked with Zn(II) complexes

“…Finally, Eu 3+ coordination polymer [Eu(hfa) 3 (dppy) 2 ZnCl 2 ] n (Eu-Zn) was prepared by the complexation of Eu(hfa) 3 Their τ obs , k r , k nr , and Φ Ln values are summarized in Table 1. The emission quantum yields are calculated using τ rad constant based on the emission spectra.…”

“…The polymeric structure of Eu-Zn promotes enhancement of luminescent properties related to large k r and 8 small k nr . The emission quantum yield of the Eu-Zn coordination polymer is larger than that of Eu(hfa) 3 12 c) Non-radiate rate constants k nr = 1 / τ obs -1 / τ rad .…”

“…The photophysical properties were estimated using the emission spectra, the emission lifetimes, and the emission quantum yields. The emission quantum yields are larger then that of precursor Eu(hfa) 3 (H 2 O) 2 . The emission quantum yield of Eu-Zn was found to be 59%.…”

“…The 4f-4f transitions of lanthanide complexes lead to narrow emission bands (FWHM < 10 nm) and long emission lifetime (τ > 1 μs), resulting in formation of remarkable luminescent materials such as display devices and bio-imaging applications [1,2]. The strong and characteristic luminescence of lanthanide complexes including Eu 3+ , Tb 3+ , Sm 3+ , Yb 3+ and Pr 3+ ions have been reported [3][4][5].…”

“…The large ED is directly linked to the asymmetric geometric structure of Eu-Zn and enhanced radiative rate constant (k r ).The emission lifetimes observed from the 5 D 0 excited level (τ obs ) were determined from the slope of the logarithmic decay profile(Figure 3b and 3c). The time-resolved emission profiles of En-Zn and Eu(hfa)3 (H 2 O) 3 show single-exponential decays with millisecond scale lifetimes. The emission lifetimes for Eu-Zn and Eu(hfa) 3 (H 2 O) 3 were determined to be 0.85 and 0.55 ms.…”